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

[Jay]

Selfishly, I'm really hoping you go with the 50 (since I have the same). How reliable would the switching circuit be with the modified 18v leg, as you describe? Would it be better to do a voltage regulator, or might that not be able to handle the current?

I so need to learn more about this stuff - I actually have an AS in electronics (although the paper is about 25 years old), but they didn't teach us stuff like this back then...

So, here's the pics and dimensions for the power and output transformers. I put them all into a documentation thread in the DIY section (trying something new, to make it easier to find this stuff - let me know what you think).

JCA50H Documentation - Transformers

Thanks Jay - can't wait to hear some feedback on this.

Haha. Selfish! Spacing wise, the PT looks very close. The OT is a little off. I'll keep looking to see if they have one that fits better.

The one other thing I realised is that I was looking at the 100H scheme on the switching and heater circuits. Does the 50H use relays instead of the optoisolators? The 100 looks like it uses one PT tap for both duties. The tag you took a pic of on the 50 PT has an 11.5v tap. Can you see where that goes to on the board? It's a pain to NOT have one in front of me. lol I need to find mods AND rock out on it.

[Tortuga]

No optoisolators - it uses relays. I'll try to pop the thing open tonight and get some more shots & info for you.

In other news, I'm working with someone I caught up with on another board to develop a rhythm/lead switch - basically when engaged, it drops the volume by a prescribed amount (set by a pot) before it hits the masters, then disengaged will be full master volume (hope that makes sense). I'll use a relay with similar specs to what's on board to switch the 'boost' knob in / out of the signal path. Might like to recruit some help from you on this, if you wouldn't mind - sounds like you have a good handle on how all this stuff works.

[Jay]

If the rhythm/lead switch is close to the masters, it might not do much besides the bump in volume, like the solo boost button. If you stick it after the first or second gain stage, then it will be like the Splawns and their OD1/OD2 switch, where it bumps the gain up a bit. They use a 68k resistor bypassed by a relay or LDR. So with the relay open, it's a straight shot to the next stage. With the relay closed, it bleeds some signal off and reduces gain. Make sure the relay or LDR is on the ground side of the resistor as to minimise pops during switching.

[Jay]

Oh and thanks for all the pics and reference material. Don't mean to be a pain. I just don't have one yet. lol I found one on the evilbay for $299, and one day left, I just wish my stuff would sell quicker haha.

[RoosterLP]

hi grime,

I did the tube swap this weekend, changing out the 5751 currently in V1 to one of the stock AX7's.
It provided a tad more clean headroom. Can turn crunch preamp to 3, maybe 4 before breakup instead of 2. Didn't notice too much of a volume drop.

On another note, I'm curious about some mods.
I was in the market for a new guitar and wanted something with single coils. Went to GC and tried a
tele through a blues jr. I was loving the sound. Regret not trying it through a Deluxe Reverb. Ended up getting another mim tele off craigslist, later in the evening. I love the sound of straight up rock/metal with my LP through the jet city, but...

Are there any mods I can do that will get me into fender territory for a thick full blues sound? I'm seriously considering selling the amp and cab, and probably my epi, to try to get that classic fender tone.

[Tortuga]

If the rhythm/lead switch is close to the masters, it might not do much besides the bump in volume, like the solo boost button. If you stick it after the first or second gain stage, then it will be like the Splawns and their OD1/OD2 switch, where it bumps the gain up a bit. They use a 68k resistor bypassed by a relay or LDR. So with the relay open, it's a straight shot to the next stage. With the relay closed, it bleeds some signal off and reduces gain. Make sure the relay or LDR is on the ground side of the resistor as to minimise pops during switching.

Not looking to do a gain boost - just want to jump the volume, like if I had a clean boost in the effects loop. I found a schematic for a Splawn that has a second pot on the ground side of the master pot with a relay that'll bypass it, which is what I'm looking for (found similar design on Boogie Recto schematic). However, the person I've been talking to stated that it'd have to be different with the JCA/Soldano design, due to the dual master volume setup, and recommended tying a pot in parallel with the other pots. He gave me permission to post up his design - I'll try to get that up in the next day or so.

Oh and thanks for all the pics and reference material. Don't mean to be a pain. I just don't have one yet. lol I found one on the evilbay for $299, and one day left, I just wish my stuff would sell quicker haha.

Not a pain at all - glad to have you on board! Hope the auction works out for you (and I hope it's a 50 )

[Tortuga]

hi grime,

I did the tube swap this weekend, changing out the 5751 currently in V1 to one of the stock AX7's.
It provided a tad more clean headroom. Can turn crunch preamp to 3, maybe 4 before breakup instead of 2. Didn't notice too much of a volume drop.

Sounds like it worked out ok, then? Would you recommend the change if I'm looking to reduce gain without affecting tone, or not enough benefit for the cost?

On another note, I'm curious about some mods.
I was in the market for a new guitar and wanted something with single coils. Went to GC and tried a
tele through a blues jr. I was loving the sound. Regret not trying it through a Deluxe Reverb. Ended up getting another mim tele off craigslist, later in the evening. I love the sound of straight up rock/metal with my LP through the jet city, but...

Are there any mods I can do that will get me into fender territory for a thick full blues sound? I'm seriously considering selling the amp and cab, and probably my epi, to try to get that classic fender tone.

Are you trying to go clean with that tone? I've had luck with the clean, scoop, and voicing mods described in earlier postings. Those three give me a ton of variety with cleans that I wouldn't have otherwise had, and also let me modify the mild gains on the crunch channel. Give us some kind of comparison to base recommendations from, and I'm sure someone can point you in the right direction.

[RoosterLP]

Sounds like it worked out ok, then? Would you recommend the change if I'm looking to reduce gain without affecting tone, or not enough benefit for the cost?

there may be enough benefit to justify, one of those 5751's are only $15-20,
unless you go NOS, even those are fairly cheap.

Are you trying to go clean with that tone? I've had luck with the clean, scoop, and voicing mods described in earlier postings. Those three give me a ton of variety with cleans that I wouldn't have otherwise had, and also let me modify the mild gains on the crunch channel. Give us some kind of comparison to base recommendations from, and I'm sure someone can point you in the right direction.

yes, i'm trying to get a good clean. But want that fat, round, warm, tone that
I've heard from fender combos. I already can get a decent clean sound out of it, but
it doesnt have that warmth and fullness that I heard out of those fenders.
I don't mind doing some mods, but don't want to do a bunch of stuff
to that amp, find out I'm never going to get that tone, then am unable to sell it cuz it has a bunch
of "custom" stuff done to it. I'm starting to wonder about my wedge cab too. Maybe a open back
pine box would give up a little of that tone easier than the rigid cab closed back...
this tone search thing is tiring

[Jay]

Not looking to do a gain boost - just want to jump the volume, like if I had a clean boost in the effects loop. I found a schematic for a Splawn that has a second pot on the ground side of the master pot with a relay that'll bypass it, which is what I'm looking for (found similar design on Boogie Recto schematic). However, the person I've been talking to stated that it'd have to be different with the JCA/Soldano design, due to the dual master volume setup, and recommended tying a pot in parallel with the other pots. He gave me permission to post up his design - I'll try to get that up in the next day or so.

Why won't it work? Is he concerned about the SLO/JCA designs because of the interaction between the two channels? Or is he concerned about the fact that both channels share the EQ? Are you looking for a boost for BOTH channels, or just the OD channel? A parallel "boost" pot to the Volume pot would work without any interaction with the opposing channel and would be simple to wire in. A "boost" pot at the ground side of the volume pot could technically be used as a boost for BOTH channels, having more effect on the channel that the pot is connected to.

And remember when I suggested this to you a few pages back? lol

OH! And I contacted Heyboer Transformers about a possible upgrade wind for the JCA trannies. Something in the realm of what we're looking for is about $110 for the PT and $95 for the OT. I'm going to try and see what a custom Edcor will cost, as well. Either way, $200 for a set of upgrade X-formers is a really good price. I just have to see if they can fit it into stock-sized dimensions. Then, I just have to follow the 50H on Ebay to see if I can snag it!

[Hipster Salad]

I posted up pics I took of the JCA100H trannies

JCA100H OT/PT

[Jay]

NOICE!

You don't happen to know the dimensions of the bolt pattern, do you?

[Hipster Salad]

EDIT:


PT bolt pattern: 3 3/4"W x 3 1/4"D
OT bolt pattern: 3 1/4"W x 3 1/4"D
Choke: 2 1/2"




FRPC mentioned to me to get an SLO spec'd OT "and be done with it" . So I looked on C3amps.com, and they have an SLO spec'd Onetics for $269.

http://www.c3amps.com/Onetics%20Transformers.htm

Curious to how different this model is from the Heyboer.

[Hipster Salad]

Finished the Depth Mod. All that's left is labeling the chassis and replacing the chickenhead knob I stole from the Presence knob hehe

Pretty simple. I just spliced two wires into the NFB wire (because I was running it to the front of the chassis), and wired into the pot with a .0047uf cap running across it. Finest parts courtesy of Radio Shack but I was too impatient to wait for a shipment from Mouser. At below bedroom volumes I can still tell a difference in bass/resonance control. Can't wait to run it at gig volumes

[Jay]

Very cool, man! Thanks for the measurements!

[Jase01]

Just finishing up the slope mod now, had to wait for parts. And... I assemble the switch ready to mount, and my drill goes flat!!
I decided to use sockets on the switch till I find the value I like, or even leave so I can swap out when the mood takes me.

[Jase01]

Just thinking, with the slope mod, could I use 2 DPDT on off on switches so that you could have a choice of four different values?

[Tortuga]

Holy carp, you guys are busy - I can't hardly keep up anymore

@Jay - Obviously, you're well on your way to becoming our resident mad scientist - when Edge11 comes back, it's gonna be mayhem around here! (in a GREAT way )

My apologies if I forgot something you posted about doing a boost (cut) with this design. I've been trying to do a bunch of outside research so I may be able to contribute something of my own. I'm going to be somewhat 'dark' for the next few days, but after the weekend, I'd like to work some more with you on this. Very cool about the transformers. It sounds like you're looking for a direct replacement with the additional capacity to support different tubes, and I think that'd be best (rather than trying to develop workarounds with voltage divider rigs, etc), even if it costs a few bucks more. The costs you are looking at are certainly better than the primo stuff that Mercury sells, and I think it's a far better (smarter) way to go. Another related thing that'd be really cool is to develop a way to move the bias adjustment to the rear panel with probe ports - how hard would that be to do (cheaply)? Sure would make tube changes a lot easier (and safer).

@Sahlomonic - great job documenting the 100 - I posted links to your 100 and my 50 documentation threads on the index for this thread. I'll be posting snaps of the schematic that I have soon. I'd encourage you to do same. Hopefully, we can get someone to do the HDM and 22, then we'll have the whole family! Great job on the depth mod, too. How'd you like drilling directly towards those filter caps? Did you use a backer like I did (and a whole lotta prayin')? Can't wait to hear how it does for you at louder volumes.

@Jase - did you give up on the clean mod for now? Looking forward to your report on the voicing switch. What values are you going to use? I thought it might be cool to have a 39k to go with my 33k and stock 47k, but wound up with the same switch delima. I think there are switches that'll do what you're wanting, but I'm pretty sure it wouldn't be two DPDT (you'd have to cascade a bunch of them to make that work), a DPTT would work (if such an animal exists) or some kind of rotary. I like your idea of socketing the resistors, but not sure how that'll do in the long run, longevity-wise. At least it'd give you a method of trying things out until you find something you like.

Keep the faith, brothers - catch ya'll later

[Hipster Salad]

bump for OT/PT dimensions update

[Hipster Salad]

@Sahlomonic - great job documenting the 100 - I posted links to your 100 and my 50 documentation threads on the index for this thread. I'll be posting snaps of the schematic that I have soon. I'd encourage you to do same. Hopefully, we can get someone to do the HDM and 22, then we'll have the whole family! Great job on the depth mod, too. How'd you like drilling directly towards those filter caps? Did you use a backer like I did (and a whole lotta prayin')? Can't wait to hear how it does for you at louder volumes.

No backer, but I made a "catch bag" of sorts with a paper towel so the shavings wouldn't mess anything up, or somehow inadvertently discharge a cap Ran a can of compressed air over it a few times and no worries. I was worried about puncturing those caps, but I figure it I blew one up, it'd be good practice replacing it (my home theater power amp for my sub has leaky caps about that size and at some point I'll replace them), that is after I get back from the hospital hehe

[Jay]

EDIT:


PT bolt pattern: 3 3/4"W x 3 1/4"D
OT bolt pattern: 3 1/4"W x 3 1/4"D
Choke: 2 1/2"




FRPC mentioned to me to get an SLO spec'd OT "and be done with it" . So I looked on C3amps.com, and they have an SLO spec'd Onetics for $269.

http://www.c3amps.com/Onetics%20Transformers.htm

Curious to how different this model is from the Heyboer.

I know they are good, but is it $170 better? I'd like to know what the PT specs at, too. The whole reason for checking into these other Trannies is so EL34s, 6550s and KT88s can safely be run in these amps. Would be cool if they are a drop in for the mounting pattern, though.

[NOSNOR]

Mini switch is ok - should be a DPDT if you're intending to switch two different values, which I assume you're planning to do. 47k is the stock value and 33k is what CTN and I used, although I've heard 39k makes for good noise, too Don't quote me on this, but I think all the resistors in the signal path are 1/2 watt. CTN went with 1 watt, probably because he's extra brootalz on his stuff and needed the extra security You should be 200% (or is it 400%) covered with a 2 watt resistor, but it's going to be bulky. I wish I could give you a definitive answer - I'm hoping someone will chime in and confim that you'll be ok with the 1/2 watt.

I finally found 1 watt resistors for slope mod, but they are green instead of blue. What is the difference between them? Can I use green ones? Sorry for stupid question, but I really don't know anything about these things

[Jase01]

@Jase - did you give up on the clean mod for now? Looking forward to your report on the voicing switch. What values are you going to use? I thought it might be cool to have a 39k to go with my 33k and stock 47k, but wound up with the same switch delima. I think there are switches that'll do what you're wanting, but I'm pretty sure it wouldn't be two DPDT (you'd have to cascade a bunch of them to make that work), a DPTT would work (if such an animal exists) or some kind of rotary. I like your idea of socketing the resistors, but not sure how that'll do in the long run, longevity-wise. At least it'd give you a method of trying things out until you find something you like.

Keep the faith, brothers - catch ya'll later

Yeah, I dunno. I'm getting a bit overwhelmed with all the choices. Can I do the more gain on the crunch channel AND the clean mod?
I know it sounds like a stupid question, but I'm asking anyway! lol.
Plus I'm still not 100% sure on how to connect the clean mod to C30 ( C2-22h), do I just solder to one iof the legs or do I have to lift the leg and solder to that?

[Tortuga]

Mini switch is ok - should be a DPDT if you're intending to switch two different values, which I assume you're planning to do. 47k is the stock value and 33k is what CTN and I used, although I've heard 39k makes for good noise, too Don't quote me on this, but I think all the resistors in the signal path are 1/2 watt. CTN went with 1 watt, probably because he's extra brootalz on his stuff and needed the extra security You should be 200% (or is it 400%) covered with a 2 watt resistor, but it's going to be bulky. I wish I could give you a definitive answer - I'm hoping someone will chime in and confim that you'll be ok with the 1/2 watt.

I finally found 1 watt resistors for slope mod, but they are green instead of blue. What is the difference between them? Can I use green ones? Sorry for stupid question, but I really don't know anything about these things

NOSNOR - I'd be happy to send you a set - PM me your address. It'd be more than fair compensation for your generosity (sending me the badge).

[Hipster Salad]

Guys, when your doing the depth mod to a jca22h, do I need any particular wire?
I want to run it to the front and have the pot there. Does it need a certain amp or voltage rating?

Hi Jase - did you get the volume 'rush' issue sorted out?

First of all, if you're doing anything with the chassis open, make sure you totally understand (and do) everything about discharging the filter caps. If you don't, you need to take the amp to a qualified tech to help you out.

Here's some info on the depth knob that I'm copying from my postings on the 50/100/22h mod thread over on HCAF:

Here's the basics along with some tips. It's only 2 components and some wire - a 1 meg audio taper pot and a .0047uf 400v orange drop cap. Hardest part was drilling the front panel (I wanted mine right next to the Presence knob, like the 100HDM) without dropping metal shavings into the chassis or running right through the filter caps, which are only about 5/8" from exactly where I placed the pot . I clamped a scrap piece of 5/8 wood on the inside where I was drilling so that my drill wouldn't punch through wildly, and was really careful about shavings. The pot basically gets inserted between the NFB (negative feedback) resistor and the 4 ohm output at the back panel. There's a red wire going to the pcb (pad label: FB) that I desoldered from the output jack and ran to the front panel where the new pot was being installed. A new wire was put in from the output jack to the other lug on the pot, and voila - done.

Also, I later added in a .1uf cap inline with the depth control, which had been recommended by Edge (he got it from someone else), that helps with scratchiness in the control as the knob is turned. I think it helps block DC from getting into the signal path before it reaches the pot (or something like that).

I've all been beating down everything I could to find info on the hookup wire - I wound up using 20ga PTFE wire. Not totally certain about the voltage rating.

I've been looking at the wiring used in the JCA, and it varies from 18 to 20 AWG (and there are likely other gauges), but the NFB wire has 18 AWG 600V and 105deg C stamped on it.

[Jay]

Okay guys. I got an email back from Heyboer for a 50w and 100w Transformer set. I gave them the dimensions that Grime and Sahl gave for their respective amps. They can make the them as drop-in replacement based on the bolt pattern given. These guys should bolt right in, have enough capacity to run ANY of the big octal tubes and they are inexpensive. $200 for the set for the 50w and $220 for the set for the 100w. I didn't ask about the choke, mainly becuase I forgot. lol But I'm sure it can't be more than $30.

I'm still on the hunt for a decently priced JCA 50 or 100 so I can test the waters first, but I think this is a really feasible (albeit - major) mod that can open up more possibilities for the big JCA amps. I may even try to find a 22H at some point and see if I can squeeze some of the bigger tubes in place of the little EL84s.

I'm still going to contact Edcor about some custom winds, but so far I'm really psyched about Heyboer and how quickly they responded.