JCA OWNERS!!! (RE)JOIN THE JET CITY LOUNGE!!!

[marshallnoise]

Thanks Grimespace. I am pretty confident in my abilities to perform the actual work, but I just worry about making a resistor fizzle. LOL. I like to keep the smoke IN the amp, if you know what I mean.

[Meelocheck]

Thanks for the heads up. I have been playing with mic placements and I seem to have found the best spot through trial and error and it is right about where you said it is, Grimespace. Good call on that...Also, the mic I am using is a very cheap one from my bro's Xbox I think - just to give you an idea. Looks like that will be my next upgrade.

We'll see what happens with the acrylic/laser stuff...I don't have immediate access to it so it may be a while before I can get much done (a month or more). If people like it and are interested I might see about doing some custom stuff - with the laser you can pretty much cut any design into the acrylic...Anyway, thanks again for the tips.

[sevenmusic]

Hi to all!
First steps here...
Happy to join the Jet City Lounge

Hiya, sevenmusic, welcome to the happiest place on (virtual) earth! Are you the same guy from the HCAF? If so, thanks so much for posting the HDM schematic over there! Assuming so, do you have an HDM, and would you be willing to take some gut shots of your amp for us? I'd very much like to see the labels on the transformers, inside wiring for the 50/100 switch, channel LED, and depth knob, and some shots of the PCB and back panel wiring as well.

Hi Grimespace,

I'm the same guy from HCAF
Unfortunately, i don't have the HDM but a JCA 100H...

[Meelocheck]

I dunno. So far I am not really "feeling it"...I almost feel like a knob when I say my old solid state amp sounded tighter. When I am chugging along (think: dun dun dun dun dun dun dun dun) on say the low E string, it sounds muddy as shit. I don't know how else to describe it. Even with all the settings I have tried (low to no bass and mids, higher presence etc etc) it sounds flabby, muddled, farty? The old solid state amp was just tighter...It didn't have this crunch but it was just crisp...I am guessing that because of that it isn't the speakers since they worked well with the other amp.

I have also tried 3 different guitars and they ALL sound very different (obviously). The Epiphone is the muddiest of them all, really just blah...The Ibanez sounds decent but still has that muddy sound to it. The tightest one is the old Mockingbird. It has some of the cheapest EMG Select pick ups in it and it sounds better than the others. I have no idea what kind of pups are in the other 2 guitars. The Epiphone has chrome ones and I haven't removed them to see whats going on underneath there...The Ibanez has got some crap pups simply labeled X1 XS and X2. 2 humbuckers and a single in the middle...I dunno what the hell is up with this mess...

Poking around with the multimeter trying to bias the thing and just read voltages I did get a couple of sparks and loud popping noises every now and then. I wonder if something in there is cooked. I didn't look really hard but I didn't see any burned components. After hearing some of the other guys stuff here I am bummed out with the way my stuff sounds. Maybe some effects will help - right now I am just plug and play...Maybe a reverb or chorus or something? I got nothin'...Ideas?

[Jay]

If memory serves Splawn moved away from Heyboer for business reasons and is now sourcing transformers out of a new supplier from Texas. I'll look inside my 2012 Quick Rod and see if I can ID it.

Mmm...Quickrod. I miss mine. Yeah, man. Check what's in there. I wonder what happened between Scott and Heyboer. They do make some good iron and the prices they gave me were really good. No other Transformer company will really do singles at such a good price.

[Jay]

Jay, can you help me out with the Brown Eye Mod?

I have pretty much figured out all of the changes but I am paranoid about the wattages for the resistors and the voltage ratings for the caps. I have read such conflicting information on what wattages are acceptable and what is not.

Here is what I found (as in another dude on HCAF):
• First stage:
o Anode - 220k in series with 100k // 500p -- very interesting!
o Cathode - 2.7k // .68 -- standard marshall
o then into 2n2 coupling cap then into 68k/68k voltage divider.
o then into 33k which is soldered straight to the grid of the next gain stage
• Second stage:
o anode - 100k (this one already exists in the amp and is not changed)
o cathode - 2.7k // .68
o then into 2n2 coupling cap
o then into the standard 470K/470K divider with 470pf treble peaker (it think the actual value in the amp was 500p silver mica)
• 3rd stage:
o anode - 100k
o cathode - 820 // 22u

Tone stack values changed to stock marshall -- slope R 33k, treble cap 500p mica

So here is my parts list based on the above:
o 2 x 680nf (.68uf) capacitors – 250v
o 3 x 500pf Silver Mica capacitors – 500v
o 2 x 2n2 capacitors – 100v
o 1 x 22uf cap – 500v
o 2 x 2.7k resistors – 1/2 watt carbon comp
o 1 x 120k resistor – 1/2 watt metal film
o 2 x 820 ohm resistors - 1/2 watt carbon comp
o 2 x 33k resistors - 1/2 watt carbon comp
o 3 x 68k resistors - 1/2 watt carbon comp
o 2 x 470k resistors - 1/2 watt carbon comp

Can you change my parts list in terms of ratings to match what is said in the description of the mod up top?

Thanks a million if you can.

Let's see. For resistors, carbon comp can be really noisy. If you are going for vintage replication, then thet's the only route. For modern reliability and low noise, go for metal film. If the mod really calls for carbon comp, then carbon film will be a decent compromise. I like 1w resistors in all positions if the room allows for it. The Vishay/Dale CCF60 series is good and inexpensive. For capacitors, 100v is good on Ck (cathode bypass) and 400v caps for all other positions will be fine. 600v if you want the extra assurance. Personally, I'm not a fan of mica caps. I think ceramics sound just as good (sometimes better) and are usually less than 1/4 the cost of a mica cap.

Since you are going more towards that Rodded Marshall kind of tone, you may want to try the Sozo or MKT1813 Roederstein caps. The Sozos have more of a vintage feel to them, but have plenty of punch and clarity. I have not tried the MKT1813 yet, but a lot of guys on the Marshall forums rage about their "crunchiness" and harmonics. If the 22uF cap is really needed, then the Nichicon should work well, I hear they work very well for audio, plus, all the Film caps that big are pretty expensive.

MKT1813 capacitors
CCF60 resistors
Ceramic caps
22uF cap

[Jay]

I dunno. So far I am not really "feeling it"...I almost feel like a knob when I say my old solid state amp sounded tighter. When I am chugging along (think: dun dun dun dun dun dun dun dun) on say the low E string, it sounds muddy as shit. I don't know how else to describe it. Even with all the settings I have tried (low to no bass and mids, higher presence etc etc) it sounds flabby, muddled, farty? The old solid state amp was just tighter...It didn't have this crunch but it was just crisp...I am guessing that because of that it isn't the speakers since they worked well with the other amp.

I have also tried 3 different guitars and they ALL sound very different (obviously). The Epiphone is the muddiest of them all, really just blah...The Ibanez sounds decent but still has that muddy sound to it. The tightest one is the old Mockingbird. It has some of the cheapest EMG Select pick ups in it and it sounds better than the others. I have no idea what kind of pups are in the other 2 guitars. The Epiphone has chrome ones and I haven't removed them to see whats going on underneath there...The Ibanez has got some crap pups simply labeled X1 XS and X2. 2 humbuckers and a single in the middle...I dunno what the hell is up with this mess...

Poking around with the multimeter trying to bias the thing and just read voltages I did get a couple of sparks and loud popping noises every now and then. I wonder if something in there is cooked. I didn't look really hard but I didn't see any burned components. After hearing some of the other guys stuff here I am bummed out with the way my stuff sounds. Maybe some effects will help - right now I am just plug and play...Maybe a reverb or chorus or something? I got nothin'...Ideas?

WHat kind of speakers/tubes/cables are you using? Most players won't or don't want to admit it.....or maybe they can't really tell the difference, but cables make a difference too.

[Jay]

JCA 100HDM schematic

Well, HELLO!!! Been waiting a long time to see that. Quite a difference from my 50H, that's for sure!

Notables (from my first perusal):
* Soldano is using a .1uf cap inline with the depth mod, purportedly for eliminating scratchiness when adjusting the control. I've got one, and I do recall hearing a positive difference after doing so.
* Interesting how the 50W switch cuts the two tubes. I wonder how it deals with the change in impedence (wouldn't it double or is it halve the impedance when removing tubes like any other amp?) - perhaps something trick with the transformer?
* Different wiring for the footswitch - can I tie a light directly to that in my 50 as well, so I can see the channel change whether I switch via my panel or footswitch? I think Jay said something about this a few posts back (dam my shitty memory!)

Jay - how's things coming on picking up a 50? And, any news on the transformer front? It got kinda quiet this past week - are you in the dungeon getting ready to kick our asses with something cool?

I've done some research on the Bias test points and alternate methods of setting up bias adjustments (dual controls - 1 for each power tube). The test points look pretty straightforward - just connect a 1 ohm resistor between pin 8 of the power tubes and ground, and wire the test point such that it measures voltage across the new resistor. Assuming this is correct, what wattage resistor is needed, and what can be done to adjust the bias to either tube, since this design only has a single adjuster? Also, what needs to be done (if anything) with the wiring between resistor and test points on the rear panel to make sure I'm not introducing a new source of hum?

CTN / Blakkwater - you still out there? I'm really interested to hear a report on the 5751 replacement you were supposed to get.

And, in other news, I heard from Edge11 yesterday. Sounds like he might be making some time to get his mod stuff moved over in the near future. Can't wait...

I've been busy a bit with my three little ones. lol They are so much fun and so much misery all in one package. I'm still trying to find out why something you love so dearly can also irritate the tar out of you. Haha. lol 2, 4 and 7. Fun bunch.

I've also had this real OCD moment of trying to figure out what capacitors Soldano used for the earliest SLOs, and find out what other good alternatives are out there. Then, I've been looking into other mods that can be done, both tonewise and aesthetic. I also researched the TungSol KT66, which is actually a drop-in replacement for the 6L6s, but with more of the big-bottle tone. I've been doing a layout for my DIY JCA20H project, but I may put it on a long hold for some JCA goodness. Since Marshallnoise showed up, I may have to pick up a 20H to do some mods directly for that one too. lol I'm still looking for a good deal on a 50H, though.

As far as transformers, they can be made, all that needs to be done is call them up, give them the details and place the order. I was going to do it myself first and be the test-sled, but if someone else wants to try it first, by all means, go for it!

As far as the 1/2 power switch, it shouldn't change impedance because the tubes are still connected to the OT and they still see the anode to cathode resistance.

As for the light, you should be able to connect one to all the other channel-switchers in the same manner.

And yes! You can do the external bias points exactly as you described. I think a single adjustment should be fine, though. Good-reliable tube vendors burn and match their tubes really well, so if they drift, they often do at very similar intervals. If you really want dual trims, all you should need to do is remove the trim pot and run them in parallel, one to each bias resistor, (R13 and R14 on the 100H). A pair of 3w resistors between the test jacks will be good, and hum shouldn't be an issue at the back of the amp as long as the test points and bias trim are mounted close to the power tubes and away from the FX loop jacks.

[Jay]

Anywho, hopefully I will be able to contribute some to the forum as I learn more. I do have something in the works as far as the cover on the amps go - I have access to some acrylic, mostly black and blue, as well as a laser cutter...So I am in the process of designing some cool face plates/badges/covers or what ever the hell you want to call them. The machine is always busy so it is tough to get time on it...I will post some pics as I get them. Again, glad to be here.

How does your machine cut the panels? What kind of program does it use? I have some concepts that I would like to turn out, and have been looking at a few different places, both for some neat JCA upgrades, and for my own builds.

[marshallnoise]

Jay, can you help me out with the Brown Eye Mod?

I have pretty much figured out all of the changes but I am paranoid about the wattages for the resistors and the voltage ratings for the caps. I have read such conflicting information on what wattages are acceptable and what is not.

Here is what I found (as in another dude on HCAF):
• First stage:
o Anode - 220k in series with 100k // 500p -- very interesting!
o Cathode - 2.7k // .68 -- standard marshall
o then into 2n2 coupling cap then into 68k/68k voltage divider.
o then into 33k which is soldered straight to the grid of the next gain stage
• Second stage:
o anode - 100k (this one already exists in the amp and is not changed)
o cathode - 2.7k // .68
o then into 2n2 coupling cap
o then into the standard 470K/470K divider with 470pf treble peaker (it think the actual value in the amp was 500p silver mica)
• 3rd stage:
o anode - 100k
o cathode - 820 // 22u

Tone stack values changed to stock marshall -- slope R 33k, treble cap 500p mica

So here is my parts list based on the above:
o 2 x 680nf (.68uf) capacitors – 250v
o 3 x 500pf Silver Mica capacitors – 500v
o 2 x 2n2 capacitors – 100v
o 1 x 22uf cap – 500v
o 2 x 2.7k resistors – 1/2 watt carbon comp
o 1 x 120k resistor – 1/2 watt metal film
o 2 x 820 ohm resistors - 1/2 watt carbon comp
o 2 x 33k resistors - 1/2 watt carbon comp
o 3 x 68k resistors - 1/2 watt carbon comp
o 2 x 470k resistors - 1/2 watt carbon comp

Can you change my parts list in terms of ratings to match what is said in the description of the mod up top?

Thanks a million if you can.

Let's see. For resistors, carbon comp can be really noisy. If you are going for vintage replication, then thet's the only route. For modern reliability and low noise, go for metal film. If the mod really calls for carbon comp, then carbon film will be a decent compromise. I like 1w resistors in all positions if the room allows for it. The Vishay/Dale CCF60 series is good and inexpensive. For capacitors, 100v is good on Ck (cathode bypass) and 400v caps for all other positions will be fine. 600v if you want the extra assurance. Personally, I'm not a fan of mica caps. I think ceramics sound just as good (sometimes better) and are usually less than 1/4 the cost of a mica cap.

Since you are going more towards that Rodded Marshall kind of tone, you may want to try the Sozo or MKT1813 Roederstein caps. The Sozos have more of a vintage feel to them, but have plenty of punch and clarity. I have not tried the MKT1813 yet, but a lot of guys on the Marshall forums rage about their "crunchiness" and harmonics. If the 22uF cap is really needed, then the Nichicon should work well, I hear they work very well for audio, plus, all the Film caps that big are pretty expensive.

MKT1813 capacitors
CCF60 resistors
Ceramic caps
22uF cap

Magic! I guess I will wade through Mouser and build my parts list. The only reason why I went with Silver Micas was because that is what DF used in his mod. And if that's what it takes to make it sound like this:
[video]https://www.youtube.com/watch?v=32IwFSy493A[/video], then that is what I am gonna use cause to me, that is the mecca of tone.

I have no issues with metal film resistors. I kind of limited myself because I was using Hoffmanamps.com to build my list and what I posted is the best he could offer. I will wade through mouser though to get exactly what I need. I know I can make 1 watt suckers fit cause I have made them fit on other projects I have done.

I will get this bish ordered up tomorrow night and maybe by next weekend, I'll have a working Brown Ie JCA20H.

[racerevlon]

I dunno. So far I am not really "feeling it"...I almost feel like a knob when I say my old solid state amp sounded tighter. When I am chugging along (think: dun dun dun dun dun dun dun dun) on say the low E string, it sounds muddy as shit. I don't know how else to describe it. Even with all the settings I have tried (low to no bass and mids, higher presence etc etc) it sounds flabby, muddled, farty? The old solid state amp was just tighter...It didn't have this crunch but it was just crisp...I am guessing that because of that it isn't the speakers since they worked well with the other amp.

I have also tried 3 different guitars and they ALL sound very different (obviously). The Epiphone is the muddiest of them all, really just blah...The Ibanez sounds decent but still has that muddy sound to it. The tightest one is the old Mockingbird. It has some of the cheapest EMG Select pick ups in it and it sounds better than the others. I have no idea what kind of pups are in the other 2 guitars. The Epiphone has chrome ones and I haven't removed them to see whats going on underneath there...The Ibanez has got some crap pups simply labeled X1 XS and X2. 2 humbuckers and a single in the middle...I dunno what the hell is up with this mess...

Poking around with the multimeter trying to bias the thing and just read voltages I did get a couple of sparks and loud popping noises every now and then. I wonder if something in there is cooked. I didn't look really hard but I didn't see any burned components. After hearing some of the other guys stuff here I am bummed out with the way my stuff sounds. Maybe some effects will help - right now I am just plug and play...Maybe a reverb or chorus or something? I got nothin'...Ideas?

I'd say something is wrong in the signal path if that 22H Isn't busting up that 4x12 like a high-school kegger. Try new power tubes? What Speakers are in the cab? Some amps are extremely particular about speaker pairings...

[racerevlon]

If memory serves Splawn moved away from Heyboer for business reasons and is now sourcing transformers out of a new supplier from Texas. I'll look inside my 2012 Quick Rod and see if I can ID it.

Mmm...Quickrod. I miss mine. Yeah, man. Check what's in there. I wonder what happened between Scott and Heyboer. They do make some good iron and the prices they gave me were really good. No other Transformer company will really do singles at such a good price.

I think Heyboer moved to a, "Order a minimum of 100 pieces at a time or we won't do business with you..." kind of model.

[Meelocheck]

Jay, I will have to double check and see what my buddy uses for that laser cutter as far as software goes. I do know he couldn't find working drivers for Win7 so he is using a PC with WinXP to run it...Not 100% sure but Corel comes to mind. As far as the actual cutting - I believe it is either a 20W or 50W laser engraver, again, not 100% sure. He uses it for woodworking for the most part - it does work well for cutting acrylic and thinner materials though. Let me get his email and stuff and get you his contact info. Will send a PM later today.

Now, as far as the set up goes - I don't recall which speakers are there. I had it open a long time ago and just don't recall which speakers were in there - I do know they were badged as "Ibanez" somethings. I am using the same cable I have always used - will try a different one as I have a couple I can try. Also, the tubes are the stock ones that come with the amp. I did crank on the BIAS a little and after double checking some stuff it seems I have it cranked a little too high. I used the wrong formula to figure out what the mA setting should be and am currently running 25mA when it should be closer to 20mA. Will tweak on that later and see if it makes a difference. Also, will charge my drill (there are a lot of screws on the back of this cab) and get a speaker name.

I heard how well this amp sounded out of the box and that was a big selling point. I didn't want to have to put any more money into this as it is just a hobby - I don't play in a band or anything. If I can avoid spending another 100$+ on tubes I'd like to. Will changing just the power tubes make a difference or do I need to change the pre-amp ones as well?

I can try to get a vid or some thing that will give you guys an idea of what I am talking about. Maybe it is just me and I was expecting too much? Anyway, I will get back with some of the info you guys asked for. Thanks.

EDIT: I re-biased and I think it sounds a little tighter...Maybe having that cranked too high was giving the stock tubes issues? I also switched cables and I can't tell a difference there. I still need to crack this cab open and figure out what shit speakers this thing has in it. After noodling around a bit this morning it may have something to do with my playing as well - where I put my hand when I mute the strings...With the older amp that didn't make much of a difference but with this it seems to make a big difference. That stinks as I am used to playing a certain way and having my hands in a certain position. I dunno - most of this is still speculation - I need to mess around a bit more. Still curious about changing just the power tubes - a pair of those isn't nearly as pricey as having to purchase 5 pre-amp tubes.

[NOSNOR]

Beside depth and slope mod I done some cosmetic modifications. I hope You like it

http://img839.imageshack.us/img839/7673/imag0182va.jpg

http://img694.imageshack.us/img694/8149/imag0186r.jpg

http://img856.imageshack.us/img856/9338/imag0187rj.jpg

http://img96.imageshack.us/img96/7382/imag0189p.jpg

[racerevlon]

Meelo--you don't have to pull the back off the cab--just pull the jack plate, or one of the handles (if they have screws) and shine a flashlight in. Work smarter, not harder...

[Tortuga]

I've been busy a bit with my three little ones. lol They are so much fun and so much misery all in one package. I'm still trying to find out why something you love so dearly can also irritate the tar out of you. Haha. lol 2, 4 and 7. Fun bunch.

Got two, myself - both boys, ages 8 and 10. They're a handful. Wish I could tell ya it gets easier, but it doesn't. Best thing about all this guitar amp schtuff: my dad was an electrical engineer when I was growing up, and he exposed me to lots of stuff (computers and electronics in the late 70's / early 80's) that pretty much shaped my career - I use my interest in music / woodworking / electronics / computers to hopefully influence my kids to get interested in pretty cool stuff that might similarly make them a living someday. And, I get to act like I'm 14 again occassionally

I've also had this real OCD moment of trying to figure out what capacitors Soldano used for the earliest SLOs, and find out what other good alternatives are out there. Then, I've been looking into other mods that can be done, both tonewise and aesthetic. I also researched the TungSol KT66, which is actually a drop-in replacement for the 6L6s, but with more of the big-bottle tone. I've been doing a layout for my DIY JCA20H project, but I may put it on a long hold for some JCA goodness. Since Marshallnoise showed up, I may have to pick up a 20H to do some mods directly for that one too. lol I'm still looking for a good deal on a 50H, though.

I wish you luck on the cap search and the other modding stuff - it's all good for us, in the end . That said, I still vote for the 50 head so's we can get back to 'transformer'ing I've got similar OCD, and I need to be rapped on the head occasionally to keep on track and my priorities in order - guess I'll have to do same to you

As far as transformers, they can be made, all that needs to be done is call them up, give them the details and place the order. I was going to do it myself first and be the test-sled, but if someone else wants to try it first, by all means, go for it!

This one's worrying me, based on what the other poster said about Heyboer only working in quantity orders - were the prices you got for one-off purchases?

As far as the 1/2 power switch, it shouldn't change impedance because the tubes are still connected to the OT and they still see the anode to cathode resistance.

As for the light, you should be able to connect one to all the other channel-switchers in the same manner.

And yes! You can do the external bias points exactly as you described. I think a single adjustment should be fine, though. Good-reliable tube vendors burn and match their tubes really well, so if they drift, they often do at very similar intervals. If you really want dual trims, all you should need to do is remove the trim pot and run them in parallel, one to each bias resistor, (R13 and R14 on the 100H). A pair of 3w resistors between the test jacks will be good, and hum shouldn't be an issue at the back of the amp as long as the test points and bias trim are mounted close to the power tubes and away from the FX loop jacks.

Pretty interesting about the 1/2 power switch - seems like a pretty simple mod. Not that I have a 100, anyways - just would be something I'd be looking at.

Thanks for the help with the Bias test points - once this is set up, am I measuring voltage instead of current, and will it be equivalent millivolts to what the bias current would be in milliamps?

[Tortuga]

@Meelocheck - gonna have to do tubes, buddy - now two ways around it. At least power tubes, V1, V2, and probably the PI tube. Then do the bias.

The tubes that come with the amp get the thing running, and that's about it. They're cheap, and keep the costs down on the amp, and the great thing is that most people that buy them are going to put different tubes in and are trying to find different sounds - it's not exactly the same as buying the tubes 2x. Hell, I'd probably have bought the thing without tubes at all, to save even more - most of the people that I was conversing with on the forums were trying to get more gain, more low end, more everything, and I was trying (still am) to get less gain and less modern tones. If it would have come with better tubes to suit their need, I would have been spending far more...

@Nosnor - WOW! Very cool baffle, and I love the tolex! You have to do some more pics of the Baffle to show us how you did it! And, are you lighting it up on the inside? How are you pulling that off?

By the way, I received your package in the mail the other day. I can't thank you enough - it was very kind, and I can't wait to put together my new baffle to show off the 333 badge!

How are you liking the slope resistor mod? Did you go with the 33k or 39k, and how do you like it? What differences in tone are you noting?

[Hipster Salad]

Beside depth and slope mod I done some cosmetic modifications. I hope You like it

http://img839.imageshack.us/img839/7673/imag0182va.jpg

http://img694.imageshack.us/img694/8149/imag0186r.jpg

http://img856.imageshack.us/img856/9338/imag0187rj.jpg

http://img96.imageshack.us/img96/7382/imag0189p.jpg

Very nice!! Can I see more pics of the tolex job? I've been thinking about doing that blue python to mine but wasn't sure if I'd like it or not.

[Meelocheck]

Meelo--you don't have to pull the back off the cab--just pull the jack plate, or one of the handles (if they have screws) and shine a flashlight in. Work smarter, not harder...

Uhm, yea, that's what I meant I was going to do. Yup, uh huh

Also, was at my local Guitar Center and grabbed a matched pair of EL84's...Will swap those out and see if it makes a difference. The only ones they had were made by Mesa and for 25$ I thought I'd give them a shot. I am also going to make sure the bias is correct this time. Last time I blew a fuse in my meter doing something I shouldn't have been. As soon as I get that replaced I will double check the bias and let 'er rip. Hopefully they will help...I am hoping I can get away with just those two instead of having to pick up 5 new pre-amp tubes on top of it.

BTW, the speakers are PJ1216G Ibanez Power Jams - 200W 16 ohms. Junk? Middle of the road?

I still haven't done the depth mod although I have the components to do it. Is that going to help my situation at all? I guess I will have to wait and see. I have a perfect spot for it but don't want to start drilling holes because I am afraid I will void the warranty should something catastrophic happen and I need repairs...All this trial and error is giving me a headache!

[NOSNOR]

@GRIMESPACE - Thanks, this mod (cosmetic) was pretty easy, tomorrow I will post more pics of baffle. It is 1cm plexiglass with 80% dark vinyl (like on car windows). The back of baffle is engraved (with laser) and colored (for more contrast, but it isn't necessary). Aluminum "L" profile is on top of baffle, and inside of that "L" profile (sorry, I don't know how to name it) is LED strip. The end of the LED strip continue with tiny cable which goes back of head.



I'm glad that You get the logo

About the slope mod, I wrote on previous page. maybe it is because of smaller resistors, but I did't hear difference as much as with the depth mod. Jay shared link about resistor (thanks Jay), and the noise I thought was from slope mod was from one preamp tube, and I solve that. If You have time to read my post from previous page and give me some suggestions I would appreciate

@sahlomonic - Thanks! Tomorrow I will take more photos on day light to give you better vision.

[Meelocheck]

Ok, I dunno wth is going on now. Plate voltage is 365...I then set the meter to 200mA and use the red probe on the red wire (B+) and then use the negative probe on the brown and blue wires of the output tubes. I had previously set the bias on only one of them last time - I didn't even check the other. On the brown wire that goes to V7 I am reading 20.2mA (the only one I tested last time) which is spot on I think...When I probe the blue wire to V6 I am only getting 12.7mA...Shouldn't they be the same? Do I adjust the bias to kinda find a happy medium where the higher one isn't too high while the lower one gets a little something extra? Could this being out of whack have something to do with the sound I am describing? For what it is worth, switching the speaker cable from 8 to 16 ohms didn't make a difference - I thought it might but it did nothing.

I wanted to do a really good side by side with the bias and everything the same during the tube swap to tell if there is a noticeable difference. I was going to record some riffs using the same exact settings for each set of tubes and see which sound I like better. Suggestions?

[Jay]

I've been busy a bit with my three little ones. lol They are so much fun and so much misery all in one package. I'm still trying to find out why something you love so dearly can also irritate the tar out of you. Haha. lol 2, 4 and 7. Fun bunch.

Got two, myself - both boys, ages 8 and 10. They're a handful. Wish I could tell ya it gets easier, but it doesn't. Best thing about all this guitar amp schtuff: my dad was an electrical engineer when I was growing up, and he exposed me to lots of stuff (computers and electronics in the late 70's / early 80's) that pretty much shaped my career - I use my interest in music / woodworking / electronics / computers to hopefully influence my kids to get interested in pretty cool stuff that might similarly make them a living someday. And, I get to act like I'm 14 again occassionally

For me it started with my dad and uncle whom had some musclecars. I got a few of my own, then picked up guitar and now I'm doing the same with THIS hobby. I played in an okay band for 7 years or so, and went through maybe 10-15 different amps, many pickups and many speakers, just to try them and see what I liked. Only constant has been my Les Paul Custom. Been with me a LONG time. lol

I've also had this real OCD moment of trying to figure out what capacitors Soldano used for the earliest SLOs, and find out what other good alternatives are out there. Then, I've been looking into other mods that can be done, both tonewise and aesthetic. I also researched the TungSol KT66, which is actually a drop-in replacement for the 6L6s, but with more of the big-bottle tone. I've been doing a layout for my DIY JCA20H project, but I may put it on a long hold for some JCA goodness. Since Marshallnoise showed up, I may have to pick up a 20H to do some mods directly for that one too. lol I'm still looking for a good deal on a 50H, though.

I wish you luck on the cap search and the other modding stuff - it's all good for us, in the end . That said, I still vote for the 50 head so's we can get back to 'transformer'ing I've got similar OCD, and I need to be rapped on the head occasionally to keep on track and my priorities in order - guess I'll have to do same to you

Well, I'm keeping a notebook that's better organized, so I can make some spreadsheets of stuff for us. That way, when we start getting all the mods going strong, there will be an accompanied parts list to go with them. Make it hard once, and the rest will be cake.

As far as transformers, they can be made, all that needs to be done is call them up, give them the details and place the order. I was going to do it myself first and be the test-sled, but if someone else wants to try it first, by all means, go for it!

This one's worrying me, based on what the other poster said about Heyboer only working in quantity orders - were the prices you got for one-off purchases?

They were actually for singles. No setup fee either. I got contact back from edcor finally, and they wanted $80 to setup a new design up front and then $100 per Transformer, but the bolt pattern still won't line up. I'm still going to go for the Heyboer when I get to do my own 50H swap. Only other alternative will be to buy one of the really expensive Mercurys.

As far as the 1/2 power switch, it shouldn't change impedance because the tubes are still connected to the OT and they still see the anode to cathode resistance.

As for the light, you should be able to connect one to all the other channel-switchers in the same manner.

And yes! You can do the external bias points exactly as you described. I think a single adjustment should be fine, though. Good-reliable tube vendors burn and match their tubes really well, so if they drift, they often do at very similar intervals. If you really want dual trims, all you should need to do is remove the trim pot and run them in parallel, one to each bias resistor, (R13 and R14 on the 100H). A pair of 3w resistors between the test jacks will be good, and hum shouldn't be an issue at the back of the amp as long as the test points and bias trim are mounted close to the power tubes and away from the FX loop jacks.

Pretty interesting about the 1/2 power switch - seems like a pretty simple mod. Not that I have a 100, anyways - just would be something I'd be looking at.

Thanks for the help with the Bias test points - once this is set up, am I measuring voltage instead of current, and will it be equivalent millivolts to what the bias current would be in milliamps?

Instead of a 1/2 power switch involving removing two tubes, I have two mods in mind for reducing power for all of the amps. One will be like the bold/spongy switch on the Rectos, and a Triode/Pentode switch. As far as the bias, you use the millivolt readings with the test points. so, 34.5mv will be 34.5mA.

[Jay]

Ok, I dunno wth is going on now. Plate voltage is 365...I then set the meter to 200mA and use the red probe on the red wire (B+) and then use the negative probe on the brown and blue wires of the output tubes. I had previously set the bias on only one of them last time - I didn't even check the other. On the brown wire that goes to V7 I am reading 20.2mA (the only one I tested last time) which is spot on I think...When I probe the blue wire to V6 I am only getting 12.7mA...Shouldn't they be the same? Do I adjust the bias to kinda find a happy medium where the higher one isn't too high while the lower one gets a little something extra? Could this being out of whack have something to do with the sound I am describing? For what it is worth, switching the speaker cable from 8 to 16 ohms didn't make a difference - I thought it might but it did nothing.

I wanted to do a really good side by side with the bias and everything the same during the tube swap to tell if there is a noticeable difference. I was going to record some riffs using the same exact settings for each set of tubes and see which sound I like better. Suggestions?

Wow. GC did a good job with keeping matched tubes. lol See if you can return them and go to a reputable dealer like the Tube Queen or Doug's Tubes. dude I work with said his 22H woke up substantially with some JJ tubes. Also, look into some better speakers. The cab should work just fine, but maybe some better drivers will change your tune....don't mind the pun.

What kinds of bands/music/styles do you play? We'll try and help you find better speakers if you want to go that route.

[Tortuga]

As far as transformers, they can be made, all that needs to be done is call them up, give them the details and place the order. I was going to do it myself first and be the test-sled, but if someone else wants to try it first, by all means, go for it!

This one's worrying me, based on what the other poster said about Heyboer only working in quantity orders - were the prices you got for one-off purchases?

They were actually for singles. No setup fee either. I got contact back from edcor finally, and they wanted $80 to setup a new design up front and then $100 per Transformer, but the bolt pattern still won't line up. I'm still going to go for the Heyboer when I get to do my own 50H swap. Only other alternative will be to buy one of the really expensive Mercurys.

Cool beans. For me, this is something that I'm going to plan for later in the year, when I can save up some coin for not only the transformers (which I do understand will up the tone ante on their own), but also for some tubes to try. I'm extremely curious as to what EL34s will do to the tone - I imagine them to be looser and brighter, kind of what happened when I did the slope resistor change. I'm really after the 70s/80s rock / hard rock/ early metal thing thats not so centered on bottom-heavy, tightly-focused, extremely high-gain stuff like they do nowadays. I've also wanted to check out the KT-types, and it'll be phenomenal to have an amp that lets me change these things on the fly. I may never move away from the JCA-line, considering how happy I am even with the little amount of modding I've done so far.

As far as the 1/2 power switch, it shouldn't change impedance because the tubes are still connected to the OT and they still see the anode to cathode resistance.

As for the light, you should be able to connect one to all the other channel-switchers in the same manner.

And yes! You can do the external bias points exactly as you described. I think a single adjustment should be fine, though. Good-reliable tube vendors burn and match their tubes really well, so if they drift, they often do at very similar intervals. If you really want dual trims, all you should need to do is remove the trim pot and run them in parallel, one to each bias resistor, (R13 and R14 on the 100H). A pair of 3w resistors between the test jacks will be good, and hum shouldn't be an issue at the back of the amp as long as the test points and bias trim are mounted close to the power tubes and away from the FX loop jacks.

Pretty interesting about the 1/2 power switch - seems like a pretty simple mod. Not that I have a 100, anyways - just would be something I'd be looking at.

Thanks for the help with the Bias test points - once this is set up, am I measuring voltage instead of current, and will it be equivalent millivolts to what the bias current would be in milliamps?

Instead of a 1/2 power switch involving removing two tubes, I have two mods in mind for reducing power for all of the amps. One will be like the bold/spongy switch on the Rectos, and a Triode/Pentode switch. As far as the bias, you use the millivolt readings with the test points. so, 34.5mv will be 34.5mA.

Dude - this is totally turning me on - Just what I've always wanted to hear - I'm so into the idea of dropping the pre-gain and driving the crap out of the power tubes, and to be able to shift character of the power section like that would just be incredible! Especially when the power tubes can be changed to suit the mood with the transformer upgrades. Holy cow, man - tell me you're not kidding!

I'm really anxious to do the bias test points. Thanks for confirming for me. Going one better would be to remote mount the bias adjuster to the panel so I don't have to open the chassis at all (again, upgraded transformers = swap power tubes, then measure and adjust bias without breaking the screwdriver out - even better with my velcro'd baffle ). Can I simply extend wires from the PCB to a panel-mounted pot (probably one of those that have a locking-nut)? Again - concerns about introducing hum?

Ok, I dunno wth is going on now. Plate voltage is 365...I then set the meter to 200mA and use the red probe on the red wire (B+) and then use the negative probe on the brown and blue wires of the output tubes. I had previously set the bias on only one of them last time - I didn't even check the other. On the brown wire that goes to V7 I am reading 20.2mA (the only one I tested last time) which is spot on I think...When I probe the blue wire to V6 I am only getting 12.7mA...Shouldn't they be the same? Do I adjust the bias to kinda find a happy medium where the higher one isn't too high while the lower one gets a little something extra? Could this being out of whack have something to do with the sound I am describing? For what it is worth, switching the speaker cable from 8 to 16 ohms didn't make a difference - I thought it might but it did nothing.

I wanted to do a really good side by side with the bias and everything the same during the tube swap to tell if there is a noticeable difference. I was going to record some riffs using the same exact settings for each set of tubes and see which sound I like better. Suggestions?

Hey, Meelocheck - I'm really having trouble following what you're doing. You're measuring current across components? That's not how current (mA, A, etc.) is read with a standard ammeter - you have to run the meter inline unless it's a clamp, which is why they make bias test probes that go between a power tube and the socket, or better yet, you do what I'm referring to above. I'm very concerned about what you're doing - you do realize if you hit the wrong thing, you can kill yourself, right? No jokes, no second chances, no more modding your amp and hanging out with us anymore - just really pissed off family wondering where you got your advice from...

Jay is right - take the tubes back to GC and buy from someone qualified to advise you - he mentioned Valve Queen and Doug's, who are very reputable and well liked. There's also Eurotubes (where I got mine, and they were extremely helpful), and Tube Depot.

Best advice I can give - start with the tube complement and get a bias probe so you can adjust bias to a 'correct' starting point. Make sure you're not mismatching your speaker cabinet's total impedance with the amp's output jacks (you stated you tried both 16 & 8 w/o hearing a difference) for a best starting point. Assuming there's not something really wrong with the amp, you probably would be well served by addressing speakers / cab. Do you have access to a friend's cab you can try out for comparison? I'll tell you what, I've been using a crappy Line6 4x12 that I paid $150 for that isn't really half bad, and certainly was a good match for my 50H. The speakers are fairly cheap Celestions (I think they're relabeled 70/80s or something like that), and they do the job. After you've shored up the foundation, then definitely check out the depth mod.

And, Jay hit right on the other thing - what kind of music to you like / play?

[Meelocheck]

Ok, maybe I wasn't very clear in my previous post...I haven't even put the new tubes in the amp yet - they are still in the package. I was just checking the bias on the stock tubes before putting the new Mesa ones in - as a comparison. So the readings I am getting are dependent upon the tubes I am using? I didn't know that. The stock tubes are THAT out of whack then? So the new tubes may be set up to be closer on bias readings? I hope...

I know if I touch the wrong thing I can be killed...I don't go poking around in there randomly (for the most part). I have identified the wires needed to figure all this out. The red wire (which turns to a yellow wire at a splice point) B+ is labeled as are the Blue and Brown wires used to read the bias in mA. I will link the video I am using as a guide at the bottom of this post. The guy has a JCA20H and he details the steps required to bias the amp using a multimeter. What he has done applies to the JCA22H too as far as I can tell. Every thing I have done has been pretty spot on with what I have been reading online from other users so I *think* I know what I am doing as far as bias settings go.

According to a few guides I have seen I can go as high as 24mA (70%) and as low as 17mA with the plate voltage (red/yellow wire which is B+ to ground) being at 365 volts. I set the first tube I checked at 20mA while the other is reading 12.7mA...I thought I was still running the amp slightly "cold"...At least according to a few tube bias calculators I Have used, like this one: http://www.ax84.com/biascalc.html...

Also, here is that vid:

[video]http://www.youtube.com/watch?feature=player_embedded&v=V4T83PgEIhc[/video]

Oh, and here is what the back of the cab looks like. I have it set to mono, 16 ohms, 400 watts with the other end plugged into the 16 ohm jack on the back of the amp...That should be good to go like that, correct?



As far as music goes - I am a big fan of all kinds of music but most of what I play sounds closer to old school 80's hair metal IMO. I dunno - hard to say. I grew up on that stuff. A quick SoundCloud test track (just drums, guitar (Ibanez), crap mix and shit guitar tone):

https://soundcloud.com/wicked-south/test7