Jca50H / 100h/ 22h mod thread and owners club

[Chordfinger]

OK so was playing my 22h and when I got the volume on both channels to around 5-6 the amp got yucky over tones as if it were adding more bass in the signal and lost some highs and added some harsh mid tones as well.

this happened before awhile back when I would have the volume drop issue that I discovered was the bias trim pot was causing the issue which was corrected by heating the solder joints and bending the legs of the pot by pushing the whole pot forward to cause the pins to pinch against the pot to make better contact and have not had in issue since but because I did that I used the bias probe to set the bias from 14ma to around 17.8-19 ma and settled on 19ma and that made the amp sound stronger with a little more headroom,so after playing it lastnight and the sounds were getting bad above 5-6 on the master volumes I thought that maybe I should check the bias again and it was where I last left it at 19 on the left socket but this time I checked the other power tube right socket with the probe and it was reading 15.2ma which seemed off so I tested again by swapping the positions of the tubes to see it was the socket or the tube reading low. it seemed to be the tubes(JJ's). because they read close to thier ma in both sockets(i.e. the 19ma tube read 19 in the left socket 18.4 in the right socket). so I tested the originals that came with the amp and they too tested to stay close to thier reading by swapping sockets. so what I did was take one of the JJ's and one the stock tubes that read about the same and ran with that. amp sounds a lot better. the original tubes lack bass, the JJ's had more bass but less highs more balanced, but mixing two different brands together made the amp sound the way I wanted the amp to sound like by adding back some highs and tightening up the flubby bass.

I know I have read mixed feelings/opinions about mix matching and matched sets, but I was wondering what you guys think about doing this long term. I don't have test equipment to check the tubes only the bias probe. but the ma ratings are much closer in readings to each other and it sounds great all the way up past 5-6 on the master volume.

[whiskeyjamboree]

Alrite. Picture Is exactly what I've done to the head.

 

It seemed like things were going great for a week or so now. Sounding great. That is until the last few days. It has been giving feedback, playing or not. I first thought it was the battery for my pickups and after a replacement today it made no difference. So I then seperated the head from the cab, so I could keep it away from my stereo amp I use for sound in my room. Still nothing different. I then tried the exact setup with my peavey XXX, which played loud and clean, no feedback at all not even when standing directly infront of the cab, not even a foot away. Could someone see if I made some crazy mistake again? Did I do something terribly wrong by not changing out the pots like the schematic said?

 

Another thing to note is that the power tubes are now getting the blue glow. From what I am to understand is that this is something that means not much, and I didn't notice it before. 

[Greg_M]

Does anyone have a gut shot of the inside a 50H with the decadance mod installed? 

[ewizard]

Well tubes that are not balanced will pull different loads. This is another reason why I feel biasing is sorta wasteful. Bias for bets tone at lowest bias setting and forget about it. As long as there is no red plating all will be fine. You cannot hurt the amp by running at too low a bias.

It is possible that two tubes can be so far mismatched that one is running really cold while the other really hot? This can make for an amp that will never really achieve high levels of performance. The whole thing about running only matched brands of tubes is B.S as well!!!!! The amp does not care what the gas is that is running it as long as the two gas tanks ( tubes ) are filled with the same octane so to speak. If the tubes are from different manufacturers, but have similar performance specs ( current draw, dissipation etc. ) then the amps will be very happy. Now it is usually the case that different brands will have different ratings and performance between one tube and another which cannot be directly compared? So running two brands of tubes is a gamble in terms of outright performance.

Another reason having matched tubes doesn't matter is because of the winding in the output transformer. The O.T. will have different resistances on each half of the O.T. which will skew results with even a perfectly matched set of tubes. This can be to an advantage as swapping the tubes around can yield better results in balancing current between each half of the O.T. In the long run biasing is a huge garbled mess of misunderstanding. The reality of it is that as long as the amp is ran within it's limits and the tubes are of reasonable performance ( read as good shape ) then not much can go wrong.

[Chordfinger]

I just realized I did not introduce myself as the new guy around here.

Hello I'm new here good to meet everyone, I am a proud owner of a 22h and bought the amp with the sole purpose to modify and learn more about what makes up tone structures in guitar amps so I hope you guy will be patient with me and all my questions that I might ask!

 

[DanDavis]

Hi folks!
I've got a chance to snag a JCA50h off CL for CHEAP.
I've alway been into Warren Haynes so I was wondering if anyone has done the Warren SLO conversion and if they'd be willing to post the modded schem and gutshot of the board when completed. I'm visual. If I'm going to do it right I need to see what it looks like complete. Thanks!

Thanks,
Dan

[Damage750]

Looking for a dumbed down version of the SLO clean crunch switch mod on the 22h, perhaps a video or step by step guide showing what was added and where. I can solder just fine, bit I'm not too familiar with reading schematics, and want to make sure I'm doing it right. I did the depth mod but that was an easy one. Any help is appreciated. Thanks.

[ewizard]

With the schematic you should be able to pretty much figure anything out you want. All the component values and positions are listed on the schematic. All you need to do is find them on the circuit board and replace as prescribed. Really no need to know how to read the schematic except in order to d]find and locate the proper component. You start at one end of the schematic and follow the signal. As you go along you will find that each part is labeled. These parts are labeled in order from beginning to end. Usually it starts with the power supply and then ends at the power amp section. If your mood instructions mention the component positions I.E. : R-22, C-45, V-2 etc. then you should be able to find them on both the schematic and then the circuit board. Look closely at the schematic for the component position and then again on the circuit board itself. You should find that the component value ( R-22 = 220 Ohm's for example ) should match up to the circuit boards R-22 part value. For example: If the schematic says that R-1 is a 100 Ohm resistor. Then the value of the resistor on the circuit board in the R-1 position should also equal 100 Ohm's. This can be determined by looking at the bands on that resistor and comparing them to a resistor value chart. Capacitors are a little easier. They usually have their values listed on them. So finding C-33 which could be 22uF ( again for example ) should match in value on both the circuit board and the schematic. Hope this helps......

[Chordfinger]

So I am planning on ordering parts to try several mod variations. I just wanted to see if you guys can verify these parts to be right and if there are any other components that you guys may suggest or how many of each I should order here is my list to order. also I noticed that some parts have different voltages i.e. 400v - 600v. Do these voltages matter or will any voltage work? Also resistors are they 1/2 watt, 1watt, 2 watt? Thanks for the help in advance!

Here is my list to order:

Filter cap drain:
10 watt 50ohm R

AMP Resistors all metal film 1or2 watt?:

R1 47k
R2 250k
R3 1M
R4 25k
R5 1M,470k
R6 180k(220k best)
R9-500k
R10-680k
 
caps between 56 and 1000pF (=1nF), use good high voltage ceramic caps for higher voltage, Try to find some 2kV ones
replace poly types with polys
C1 470pF/0.47nF/0.00047uF (560pF or even 680pF)
C2 (22nF/0.022uF) (4,7nF/0.0047uF)
C3 (22nF/0.022uF)
C7 220pf/0.022nF/0.000022uF
C19 33nF/0.033uF
C23/C24 33uF
depth mod parts:

try both out to taste:250k &1M Potentiometer
.0047u/470v Capacitor.
Quote "The merchant I used did not have 470v, so I used the next larger size of 600v.
The Orange Drop 716 has a reputation for good sound, but other caps will work"
Knob for the pot

 

[Chordfinger]

Also can anyone give me a heads up to which resistor and cap numbers (i.e. R9 C2 for example), effect gain, treble, mids, and bass just to help narrow down where to focus when mods are performed. Thanks again!

[ewizard]

For noise and longevity, larger wattage resistors are quieter and will last longer than those of lower wattage ratings. I.E. A 1 watt resistor will be quieter and last longer than a 1/2 watt will. Metal film is quieter than carbon composition, sounds a little bit different ( some say sterile and dry ? ) and is usually closer in tolerance ( 2% instaed of the usual 5-10% used for carbon comp. ). 

 

As for capacitors, each one sounds a little different as should be expected considering that there are several types of the same value a lot of the time. Ceramic, tantalum, oil in paper and all the other types will have a varying degree of impact on sound. I don't feel that one is truly better than the other, or that changing only a few out will make a huge impact on sound. The voltage is important though!!!!!! You can run as high a voltage rating as you want, or can fit. You cannot however replace the current capacitor with one of a lower voltage rating. A stock capacitor that is rated for 400V must be replaced by one that is 400V or higher. 600V is the next highest voltage rating and the higher the voltage rating the larger the capacitor will be. The larger the voltage rating the longer the capacitor will last! The voltage rating is more about service life than actual voltage capability. If you replace the current capacitor with one of a lower rating, it will work just fine; for only or a short period of time though!!!!!! Going larger will not change the sound, but will ensure that the capacitor will not fail for a very long time. 

[mimmsy]

These changes will do a lot to get a nicer, tighter sound and reduce flubbyness. To archieve even more clarity and openness on the 22H, just swap out R9 (this 1M parallel to C5). This is one of the best things, you can do to this amp. Sounds way better with more definition and a clearer bass.

What value on R9? I have 470k on both R9 and R5.

[Chordfinger]

Ok so after some reading here:  Modifying Preamp Circuitry

I did 2 simple mods that brought the 22h right where I wanted it.

after trying to reduce the squishy bass at R9 I noticed it didn't do exactly what I expected, after reading the link I posted and how R9 is in the coupling circuits decreasing this value just adds more gain going to the second stage it explained alot. so here is what I did, i swapped r6 with r24 and swapped r16 with r26. now this amp sounds the way I expected it to sound and I didn't have buy any more resistors or caps, just used what was available. from what I could tell I swapped R6 with with R13 and noticed the bass in the crunch channel was less squishy but the OD channel had more of a fuzz type gain which I then swapped with R13 with R14 not much better. so that made me want to have both plate resistors(R6-7,R13-14) to be the same value as it is in a marshall 800 all at 100k. this helps the bass response taking squish  to tight-sag, and tighter as you turn up the volume. I can now dime all the tone controlls and set the presence at 0-5. very nice! With the mids at mid point very very nice! scooped mids has more of a Mesa sound imo.  next is to just add a fixed resonance mod

[whiskeyjamboree]

That link is not working and I like what you are describing. Is it possible you can put it in long form so that I too may read.

[RictusGrin]

Footswitch wiring.

Just thought I'd post this here for anyone interested. I bought my 22h used and it had no footswitch.

Emailed them (Jet City) and they told me a generic Marshall style would work. Which it did, but seeing as the amp has no channel indicator on it I wanted on with an LED.

That one didn't work right. After some investigation and re-wiring I've got it now. You can find these Marshall footswitches on Amazon and eBay for about 14 bucks and just rewire them.

 

As you can see the original "Marshall" wiring the LED is in parallel. This doesn't work on the 22H. (Only had a jack on the schematic program, no plug. Switch comes with a cord soldered in it.)

 

As a side note, I was going to mod my amp too but then I bought a different cab and speaker and now it sounds great. Got a vintage 30 celestion in it. I know some guys don't like them but I think it sounds great with it.

[Edu]

Does anybody saw that video:

I'd love to know what mods they did to get that "vintage sound", to do something like that in my JCM 22 (less gain, slightly darker, ....). I did some mods on my 22, but still could not get the sound I want (closer but not quite there)

[Jase01]

Hello, I haven't been back here for ages and have pretty much forgotten what I learnt while I was here!! Hahaha
Anyway, I did the mod to increase gain on the crunch channel and made it switchable. Sounds great and from bad memory, easy to do. Anyway, why I'm back is I'd like to do something similar with the OD channel, for a more full tilt "METAL" sound. Does anyone know how this could be achieved?
Also is there an internal power source I can tap to run some LED's for some bling?

Cheers

[thebuch]

Hi everyone!

I know this isn't the "introduction" thread, but I'm a long time guitar player, and brand new JCA22H owner. I'm new to HC and have gleaned a good amount of knowledge about the 22H from this and other forums. I'm a pinsetter (bowling machine) mechanic by trade, but am just starting to learn about the electronics contained inside a tube amp.

I've successfully done a "JCA to SLO" mod on mine already (easy enough), but I only followed someone else's directions without really knowing exactly what I was doing and why it worked. I'm really looking to get up to speed on the workings of this amp, and I guess I've got an increasing interest in learning guitar/amp repair and modding. Can anybody recommend a good web site or book that kind of breaks everything down into manageable pieces? I'm looking around on Amazon right now, any recommendations?

Anyway, thanks in advance, and I hope to be able to start contributing here in the near future!

[slidedude]

How do you put a choke in the JCA 22?

[kaoslord]

Pulling tubes !

What's your experience with that ?

I have tried yesterday on my jca100, removed the 2 outer tubes, and i am quite impressed by the results.

ithe amp does not get quieter (still loud as f...k) but it sounds... different! Bass frequencies are less invasive and the sound is less "rich", more middy and a little bit stiffer, in a good way.

I think i will leave like that for the moment.

So, do you think I have to rebias it ? I am reading 453V beetween pins 3 and 8 and the old bias was 35mA

See ya

 

[GRIMESPACE]

Did you change your speaker connection? IIRC, you should be using the output jack that is 1/2 of what your load is - a 16 ohm cab would plug into the 8 ohm output, and an 8 ohm cab would plug into the 4. If you didn't change the connection, that may account for the difference in tone.

[Soulcrusher_X]

---

thebuch wrote:

 

Hi everyone!

 

I know this isn't the "introduction" thread, but I'm a long time guitar player, and brand new JCA22H owner. I'm new to HC and have gleaned a good amount of knowledge about the 22H from this and other forums. I'm a pinsetter (bowling machine) mechanic by trade, but am just starting to learn about the electronics contained inside a tube amp.

I've successfully done a "JCA to SLO" mod on mine already (easy enough), but I only followed someone else's directions without really knowing exactly what I was doing and why it worked. I'm really looking to get up to speed on the workings of this amp, and I guess I've got an increasing interest in learning guitar/amp repair and modding. Can anybody recommend a good web site or book that kind of breaks everything down into manageable pieces? I'm looking around on Amazon right now, any recommendations?

 

Anyway, thanks in advance, and I hope to be able to start contributing here in the near future!

---

 

 

Merlin Blencowe has a few good books out there as well as Kevin O'Connor. I think both can be had on Amazon. Google the name Randall Aiken for some good tech articles. Also, you may want to sign up for the SLO Clone forums. There are lots of folks there to learn lots from. Also, come over to the GuitarAmpBoard in GRIMESPACE sig. There are a few threads on JCA mods and tips. I am Jay over there.

[thechamp]

I did the Predator mod as laid out on page 20. I have the right value for C2 so that is not an issue. I have the service manual and matched up voltages. 

 

Here are my problems-

1. The 2nd channel is now working at about 1/10th volume and headroom as stock. I can turn the master all the way up. It is also clean until 7-8 on the OD gain knob. 

 

I was thinking that I must have purchased a resistor much lower in value than listed to explain this, though I double checked my order and component swap list (which seems fine). HELP!!!

[thechamp]

The problem may be the 3.3uf capacitor being in reversed polarity +/-. I will switch this when I get home in an hour and give an update. This is the only cap I have with two different color legs. My guess is this is the only one where it matters which way it is set in.

 

Update:

I played around with this for a few hours today to no avail. I am really frickin pissed off right now because I cannot get this to work. I have no idea what I'm doing wrong. I looked at a color code chart for resistors but it is about calculating values, not +/- like battery placement in a fixture. Wish I could get some help!

 

Anybody wanna respond???

[modfori]

hey all!

just joined the club.

I modded my jca22h visually

http://s18.postimg.org/mewy10ql5/DSCI0405.jpg

http://s18.postimg.org/txg39nhy1/DSCI0407.jpg

http://s18.postimg.org/hy4l2ccd5/DSCI0410.jpg

http://s18.postimg.org/x99sp7kbd/DSCI0402.jpg

it 's a piece of clear acrylic etched by me. I also added few UV leds