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

[käsebrot]

I don't know, which version he has, if 20H, 22H or 50H/100H/100HDM.

The 22H is newer than 50H and 100H. And has this creme board with uncovered traces - like the 20H.

[thesockmonster]

I don't know, which version he has, if 20H, 22H or 50H/100H/100HDM.

The 22H is newer than 50H and 100H. And has this creme board with uncovered traces - like the 20H.

Just curious, does JC bias these fairly cold stock?

[käsebrot]

Jet City doesn't bias their amps.
They put the trimpot halfway and that it is. No measuring.
On the 22H even on the box is written "fixed bias" (which isn't right).
Therefore, the bias needs to be adjusted on these amps, even, if they are bought new.

[kaoslord]

Hi All,

i follow the thread with great interest, very interesting ideas.
best mods I've tried so far on my JCA100:

swap of R36 after V2b (from 1M to 470k, could go lower if you want) after V2b - more usable gain.
snip the bypass cap C19 in the cathode follower - less gain/buzz on both channels, more usable gain and clarity improved.
change the slope resistor, 56K or 68K (i like that) for a more modern sounding amp.

have fun !

ps: i have ordered a quad of sovtekWXT+, they made an impressive difference in the overall sound, lot stiffer and middier sounding... not happy.
will go back to the stock crappy Shuguangs !

[TheEternal]

I have a Jet City JCA100HDM on the way I got on Ebay for $450.00 shipped, so I am back in with the lounge.. \m/

[käsebrot]

The 470k/470k voltage divider is a good one, especially, if you reduce the 39k cathode resistor to 10k. I've recommended that here several times. Also to increase the NFB resistor a little bit.

When swapping out the 3rd 1uF bypass cap, then lower the cathode resistor to 1,2k. That's quite enough. But the crunch channel won't sound as good as before.

The Sovtek 6L6 aren't good. I've always preferred the Shuguang 6L6 (I bought selected ones from Ruby Tubes) - also over the JJ 6L6 I've tried on the HDM.
In the smaller ones (20H, 20HV, 22H) go for JJs in the power amp.

[kaoslord]

actually I find the crunch better sounding whitout the 3rd stage bypass cap.
it's more "clean" sounding...

my dream mod with this amp would be to have
the lead channel to sound identical to the crunch but added gain/distorsion on top...
where to start ?

thank you,

[Drainbamage]

2.2k cathode resistor instead of the 39k cold clipper im thinking. Isnt that how the Avenger dose the hi input?

[nYdGeo]

Greetings to everyone from the hot, humid streets of New Orleans, LA. I recently found this forum and am glad to see happy, interested JCA owners sharing the wealth in the form of ideas, observations, mods, etc.

A few months back I purchased a JCA 5012 Combo for an extremely low price. I re-tubed it with Groove Tubes 6L6s that are actually NOS GE 5881s and a row of JJs in the small sockets. I've read that some don't like JJs in this amp, but to my ears they sound quite nice in mine. I believe that mine may also have some later improvements as I normally run a very comfortable amount of high-gain with the lead gain set between 6 & 7 depending on the pickups. I've played another one purchased around the same time and its the same.

I also replaced the factory speaker with an aged, thoroughly experienced Mesa Boogie Black Shadow (built for Mesa Boogie by Celestion out of one of their 90-watt, heavy duty speakers). I love me some Black Shadows! At this point I'm quite happy with the sound, but there are thoughts floating about...

If I can find good instructions, I think I'd like to do the heater mod to bring down the hum, possibly a switchable clean/crunch mod as well, but I just crank the power amp and leave the preamp set very low on that channel and it works well. The main question I have is the effects loop...I know, so do many other folks, too. But, I've identified a a strange quirk that I've yet to hear or read about, involving the use of the TCE Nova Delay in the effects loop.

When using the Nova Delay in the loop and selecting the Dynamic Delay, the delay works properly on the clean channel but not on the lead channel. With the mix set to where I like it (when playing, its almost like a reverb underneath you're guitar, becoming quite present when you stop playing), this is what I get on the clean channel. This is the same setting I use when using this same Nova Delay pedal in the effects loop of my Peavey 3120 head.

However, when I switch to the JCA's lead channel, there is no delay present when I'm playing. When I stop playing abruptly, assuming the amp is turned loud enough to hear it, I may hear a faint repeat. Back to the clean channel and it works perfectly again. This only affects this amp. If I use any other delay type it works the same on either channel, so it also only affects the dynamic delay on the lead channel of this amp.

We've been wondering if the effects loop level is very hot, and if maybe changing V4 from a 12AX7 to a 5751 might bring that down and help with that situation. I may try a 12AT7 also, but unlike the 5751 which is essentially a low-power 12AX7, the AT is a completely different tube type and may affect the sound in a negative fashion.

I was curious if anyone else had encountered this and if there was a possible solution. Some of you real amp gurus may hear that description and know exactly what it is just from the behavior, but I'll never know unless I ask, so...there it is!

Thank you for your time, and please have an excellent day!

Oh, does anyone have a schematic for the 5012 combo? I would love to have one to assist with performing mods. Thanks!

[midnightlaundry]

A Black Shadow would be nice. The heater mod is in this thread, so dig back and you will find it. Its worth the effort for sure.

[kaoslord]

I have a nova delay too.
it works perfectly with my JCA100... but i will try to reproduce your problem.
maybe a stupid question: have you tried to set the input gain
of the Nova when using the JCA ?

Greetings to everyone from the hot, humid streets of New Orleans, LA. I recently found this forum and am glad to see happy, interested JCA owners sharing the wealth in the form of ideas, observations, mods, etc.

A few months back I purchased a JCA 5012 Combo for an extremely low price. I re-tubed it with Groove Tubes 6L6s that are actually NOS GE 5881s and a row of JJs in the small sockets. I've read that some don't like JJs in this amp, but to my ears they sound quite nice in mine. I believe that mine may also have some later improvements as I normally run a very comfortable amount of high-gain with the lead gain set between 6 & 7 depending on the pickups. I've played another one purchased around the same time and its the same.

I also replaced the factory speaker with an aged, thoroughly experienced Mesa Boogie Black Shadow (built for Mesa Boogie by Celestion out of one of their 90-watt, heavy duty speakers). I love me some Black Shadows! At this point I'm quite happy with the sound, but there are thoughts floating about...

If I can find good instructions, I think I'd like to do the heater mod to bring down the hum, possibly a switchable clean/crunch mod as well, but I just crank the power amp and leave the preamp set very low on that channel and it works well. The main question I have is the effects loop...I know, so do many other folks, too. But, I've identified a a strange quirk that I've yet to hear or read about, involving the use of the TCE Nova Delay in the effects loop.

When using the Nova Delay in the loop and selecting the Dynamic Delay, the delay works properly on the clean channel but not on the lead channel. With the mix set to where I like it (when playing, its almost like a reverb underneath you're guitar, becoming quite present when you stop playing), this is what I get on the clean channel. This is the same setting I use when using this same Nova Delay pedal in the effects loop of my Peavey 3120 head.

However, when I switch to the JCA's lead channel, there is no delay present when I'm playing. When I stop playing abruptly, assuming the amp is turned loud enough to hear it, I may hear a faint repeat. Back to the clean channel and it works perfectly again. This only affects this amp. If I use any other delay type it works the same on either channel, so it also only affects the dynamic delay on the lead channel of this amp.

We've been wondering if the effects loop level is very hot, and if maybe changing V4 from a 12AX7 to a 5751 might bring that down and help with that situation. I may try a 12AT7 also, but unlike the 5751 which is essentially a low-power 12AX7, the AT is a completely different tube type and may affect the sound in a negative fashion.

I was curious if anyone else had encountered this and if there was a possible solution. Some of you real amp gurus may hear that description and know exactly what it is just from the behavior, but I'll never know unless I ask, so...there it is!

Thank you for your time, and please have an excellent day!

Oh, does anyone have a schematic for the 5012 combo? I would love to have one to assist with performing mods. Thanks!

[thesockmonster]

Does the Nova Delay perform better than the Flashback X4 in the JC loop?

[nYdGeo]

I have a nova delay too.
it works perfectly with my JCA100... but i will try to reproduce your problem.
maybe a stupid question: have you tried to set the input gain
of the Nova when using the JCA ?

Thank you for your reply. Yes, I can't recall which button it is at this moment, but you hold down a button for several seconds and it enters a level calibration mode. You then bang the guitar, playing as loud as possible to give it your maximum level in this configuration, and then press another button to set it. Come to think if it, I think I may have done the calibration when on the clean channel. I'll redo it tonight while on the lead channel and see if that corrects the issue.

I noticed last night while playing around with the amp that with the lead channel gain set to anything above maybe 3 or 4, if you turn the Clean/crunch channel pre way down, you can easily hear the lead channel leaking over into the clean channel. Never noticed that before.

I've observed that the heater mod seems to be one that need it or not, its a great mod that literally every 5012 could use and should have done as its almost a fix or correction rather than an enhancement. Are there any other mods that have that degree of relevance?

Thank you for the input!

P.S.: Yep, the Black Shadow is one big, bad can of sonic whoopass!

[drewiv]

Can I play now?
viewtopic.php?f=5&t=16604

[Drainbamage]

I just did the 100k V1 plate and removed v3 cathode bypass cap on my 20h. Did exactly what I was expecting. Less gain and not as bright. It also took care of the rest of the buzzyness. The presence control is useable now and almost completly stable at high treble and presence settings. It did remove alot of gain but thats fine. That amp is a crunch machine now master all the way and gain 6-7 perfect classic tones. The amp is competely different now from basically unusable/ inspiring to play to much more dynamic and articulate. Now to order some ornage drops and carbin film resistors.

[käsebrot]

If you really want to put Orange Drops in this amp (I wouldn't do that), then avoid the polypropylene ones and go for the polyester 225P series (400V).

Carbon film resistors make most sense in tone stack as slope (I always use carbon film there, even in hi-gain amps) and at the plates - but you will also have a little more noise then.
FYI take a look here: http://www.aikenamps.com/index.php/resi ... -it-matter

[Drainbamage]

What orange drops are in Soldanos? I went with CDE pp orange drops before seeing your post. Most of the amp parts stores sell the 715s/716s and not the 225. I bought from mouser and didnt see orange drops other than polypoplyne. So thats what I got.

[thesockmonster]

Heads up - JCA100HDM on GC Used Online - http://www.guitarcenter.com/-i3946264.gc

[Drainbamage]

Anyone know what potentometers fit the jca 20h board? Something of quality and/or whats in a pcb mounted potentometer soldano? Thanks

[käsebrot]

I've tried one JCA recapped with Orange Drops 715. Sounded harsh, trebly, biting, a lot of ear fatiguing. I really hated it and swapped them all out.
I've written that several times, that you might stay away from these caps in a JCA. But it's your amp and your choice.

There were never ever "Orange Drops" in any Soldano.

But orange Philips polyester caps, which are not in production actually.
If you like something, which is close, then try Vishay BC MKT368 polyester caps. But I'd go with MKT1813 (I like them better, they are not as smooth sounding as the MKT368) and Sozos where they make sense. The MKT1813 are also my preferred choice over Mallory 150.

The Orange Drops 225 are ok, also very smooth sounding. Fryette uses them f.e..

I really don't know, why all the folks are raving about "Orange Drops". Maybe, because of this fancy name and because they look like sweets? I've never found anything really good in these caps, and I also like the Cornell Dubliler DME Series more than the Orange Drops 225. But not the complete JCA with CD DME, that is too much.

As I've said, I've recapped a lot of JCAs and tried out many different brands again and again. And at each position for itself different brands. The best you will get is in the right mix of components.


Since the last 3 or 4 production runs the pots have a very uneven action. Quality is ok soundwise and according to noise, but sometimes it's hard to dial in the right amount, especially of volume. I always replace them with Alphas. They are 16mm pcb pots.

[Drainbamage]

Ya the 225s are the same kind I belive as the mallory pvc that are in my Trainwreck clone. I goofed when I was on the mouser site they do have the 225s but only a few of the popular values they stock. Seeing if I can subsitute those on my order..

Alphas cool I look for those while Im at it

Edit - nope they dont have em in stock .

[Hipster Salad]

Ok, to revisit the issue I'm having with my JCA50H:

Bass and Middle knobs act as if they are both turned to 0, and change nothing when I turn them full range 0-9 and 9-0. Every other control works on the amp. Intermittently the "full sound" would come in for a few seconds, but 99% of the time it sounds like an AM radio. Couple guys here suspect bad pots. So tonight I took the board out of the chassis, and when I physically "wiggled" both of those pots, I could hear a faint 'clicking', and I don't hear that in any of the other pots. This could either be coincidence and doesn't mean anything, or it could indeed be a sign of failed pots or solder joints. I'm purely novice at this so either way I'm just going to pull the pots and replace with Alphas across the board while I'm at it.

What should I be checking at this point to make sure Bass and Middle pots are the root of this problem?

[Meelocheck]

The easiest way to check for bad joints is basically by checking continuity, I think. If you follow the traces from the legs of the pot and get continuity at the next component then it could be a bad pot...Although two bad pots like that seem quite fishy. It could be a shared component between the two pots causing the issue - a cap possibly. Hopefully someone with a bit more experience will pop in. Good Luck.

[Hipster Salad]

I did a continuity check, and every trace I could find showed as being ok, although I can't confirm whether or not I checked every single trace. I also checked resistance on all the pots on the board, and they all are where they should be, open and closed. I ended up pulling all the pots off the board since I'm planning on replacing the values on the gain pots anyway, and it wouldn't hurt to upgrade the rest of them to Alphas.

[Hipster Salad]

- if you wand to improve sound overall, then a) use good tubes, b) bias the power tubes correctly - you won't find much JCAs, where the bias setting is ok, when purchase them new (this is a really big thumbs down in my opinion!), c) swap the caps for better ones - I recommend MKT1813 (better than Mallory 150 imho) in front of the signal path, Sozo Standard in the end (especially in the PI) - all Sozos will sound too wooly, all MKT1813 too brittle.

- if you really want to use Orange Drops (for whatever), then avoid the polypropylene ones (715P, 716P, sound really bad in this amp, like a glassy and snarling Mesa with much biting treble) and go for polyester (225 Series, sound smooth with good colouration in the mids). Try CD DME polyester caps (the winered cheap ones) in the tone stack, you will not regret it!

Regarding upgrading the caps in bold above, what positions on the board are you referring to? C32, C26, C19?