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Jet City JCA 22H OT replacement and minor mod
Jet City JCA 22H OT replacement and minor mod
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Old 6th November 2018, 07:50 PM   #1
PKI is offline PKI  United States
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Jet City JCA 22H OT replacement and minor mod
Default Jet City JCA 22H OT replacement and minor mod

Hey,

as been an long time fan of Slo-100 (played it a couple of time like 10 years ago and still cant forget), I picked up JCA 22H. Not Slo-100, but if you played the beast you would know that that amp cant play even moderately quiet. Also, JCA 22H schematically pretty similar to the SLO-100 with a number of cost cut solutions and cheaper components. So my thought are that it can be brought pretty close to the actual slo-100.

The amp I picked up had blown OT transformer, so I did some online research, contacted the ZM all-mighty and ordered Classictone Transformer OT Marshall JTM 45 Output Transformer and this choke: Marshall 3 Hy Plexi Style Choke

However, as I am tube kinda-noob ZM suggested me to start a thread before I fire it up as there are quoting him: "it could be easy to introduce separate biasing of output tubes", and most important this: "if you're not sure exactly how to set Iq and everything (secondary phasing is important , due to feedback) , start new thread before powering on ....... just to avoid more smoke" :-).

Here is are schematics I found tp start. (There is a slo-100 clone thread here with slo 100 schematics)
Attached Images
File Type: jpg IMG_2398.jpg (44.5 KB, 148 views)
File Type: jpg fIIzO.jpg (436.9 KB, 139 views)
Attached Files
File Type: pdf JCA22H - Schematic.pdf (585.9 KB, 23 views)

Last edited by PKI; 6th November 2018 at 08:17 PM.
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Old 6th November 2018, 08:09 PM   #2
Zen Mod is offline Zen Mod  Serbia
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Jet City JCA 22H OT replacement and minor mod
wrong pdf

I see some particles , of which I'm even more clueless than in electronics



regarding changes to separate biasing of output tubes , if possible , post little better schematic (higher res) and I'll do edit for you
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Old 6th November 2018, 08:18 PM   #3
PKI is offline PKI  United States
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Jet City JCA 22H OT replacement and minor mod
Hehe that a structure of Ryanodine receptor 1 :-). Changed the pdf. I will look more for better resolution schematics and if needed will upload pictures of actual PCB. Thank you
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Old 6th November 2018, 11:00 PM   #4
PRR is offline PRR  United States
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Quote:
Originally Posted by PKI View Post
"...separate biasing of output tubes"...
Why?

Especially on an amp that "cant play even moderately quiet"?
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Old 7th November 2018, 09:23 PM   #5
djgibson51 is online now djgibson51  New Zealand
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Do you mean to replace the output tubes, or keep the EL84's?
I am not sure why you bought a JTM45 op transformer instead of a Marshall 18 watt one.
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Old 8th November 2018, 02:45 AM   #6
PKI is offline PKI  United States
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Jet City JCA 22H OT replacement and minor mod
I was planning to leave E84 for now why?

Because I like my amps big and heavy
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Old 8th November 2018, 05:41 PM   #7
djgibson51 is online now djgibson51  New Zealand
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Just making sure I understood what you are trying to do.
Enjoy your project.
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Old 17th November 2018, 03:43 AM   #8
PKI is offline PKI  United States
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Jet City JCA 22H OT replacement and minor mod
Quote:
Originally Posted by Zen Mod View Post
wrong pdf

I see some particles , of which I'm even more clueless than in electronics



regarding changes to separate biasing of output tubes , if possible , post little better schematic (higher res) and I'll do edit for you
Still waiting for the transformers to be delivered...
here Is the schematics of the output stage and PSU
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File Type: pdf jca22H-output.pdf (226.5 KB, 28 views)
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Old 11th December 2018, 05:23 AM   #9
PKI is offline PKI  United States
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Jet City JCA 22H OT replacement and minor mod
I would really appreciate any guidance on how to swap the OT transformer in the head. Anything I need to do or it is just plug and play?
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Old 11th December 2018, 07:49 AM   #10
thoglette is offline thoglette  Australia
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Quote:
Originally Posted by PKI View Post
I would really appreciate any guidance on how to swap the OT transformer in the head. Anything I need to do or it is just plug and play?
Read your Rob Robinette, particularly Tube Amp Safety, Tube amp start up and (hopefully unnecessarily) Troubleshooting.

But there's probably a reason the old OT popped. So you might be in for a little fun.
Finally, spend some time reading and considering R Keen's Immortal Amp articles
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