JTM 50 build

[LeftyStrat]

My current build - JTM 50 Variant. The board will be populated tonight.
Initially, the changes beyond a JTM 45 will be a cathode bypass on v2 and .022 output couplers. I'm also considering running 6550s instead of EL34s. I have a good pair of original Tung Sol coke bottles.
Depending on the sound, I may go with a split cathode and adjust the tone stack. Suggestions?? Thanks, Pat

[thousandshirts]

That is awesome, Pat. My only suggestion is: show us more!

Will

[LeftyStrat]

Thanks Will. I really appreciate the kind words. I'll post more.

Pat

[OnTheFritz]

Looking great Lefty!
I'd give the EL34's a chance first, but hey, we build em' we can do anything we want, right?

[bluze81]

Very clean work Lefty! show us more as you go please, I like the idea of going with some different tube choises, nice build, Steve

[LeftyStrat]

As of 4:30 AM EST, it lives.. I played through it for about 5 minutes clean and 5 w/ an overdrive (ocd) through a 412 cab, woke up my wife and the dogs.
I look forward to taking it out tonight. I'll take my 45 as a spare. Pics to follow..

Pat

[Sparky]

Nice looking work! I've got a similar project I want to get into in a few weeks, once I get the plexi panels made up.

[LeftyStrat]

Many thanks for the compliments. My fingertips always feel raw for a few days after twisting wire.
I'm currently using my myspace page to advertise my small amp shop. I've posted some pics from early in the build and I'll be posting some finished gut shots this weekend. If you'd like to take a look, please check it out. Here's the link:

http://www.myspace.com/patkilgore
Click on "pics" and the "-pkAmpWorx-" album.

Thanks,
Pat

[Roe]

I'm doing a jtm50 as well. I'm using 32uf filtering. may try 64 for the mains. also I use 470k mixer resistors, shielded input wire, original mustards, allen bradleys, marstran trannies (including 128 ot)

[LeftyStrat]

Here are some finished pics. I played out with it last Friday. It runs good but I'm not completely satisfied with the sound/feel so I'm still picking at it.
So far, I pulled the cathode bypass from v2. 270k mixers, 47k NFB on the 8ohm tap, .022 mf output couplers. It sags pretty hard when I dig in so I ordered a plug-in SS rectifier to see if it will help.







The last pic is of my 45 on the left and my 50 on the right. All speakers are Celestion Golds. My wife pointed out that I should have vacuumed the carpet .
This week, I've got a new JMP 50 kit coming.

Pat

[LeftyStrat]

Hey Roe,
Please post your progress. I'd like to hear how your build goes.

Thanks,
Pat

[thousandshirts]

Very slick, sir!

Excellent photographs, as well.

Will

[LeftyStrat]

Thanks very much Will. I just finished swapping out the EL34s for a pair of original Tung-Sol 6550 coke bottles. My plate voltage has now dropped to 374. I biased for 70% (74ma) and it has a real nice clean sound (still saggy, but more rounded), but I can't turn it up until this afternoon. I will know more then. I'm still going to try the SS rectifier to get the plate v up.

Thanks,
Pat

[Roe]

Hey Roe,
Please post your progress. I'd like to hear how your build goes.

Thanks,
Pat

I got the trannies saturday. have installed them and prettymuch completed the build. but I will have to double check everything and start the testing.

the marstran c1999 choke didn't fit - I had to drill a new hole. I use 32uf filtering on all the stages, but I will try 64uf on the mains. I use 470k miker resistors, 47k feedback resistor. ABs and original mustard.

I will experiment with the v1 catode cap. 25-10uf works well in my jtm45. also I'm gonna try smaller pi qoupling caps. my jtm45 uses .022 now. I will try .027 mustards in the jtm50.

i love jtm amps - have tried quite a few (mostly new ones but also an original 1961). the only ting I'd like to modify slightly is the bass response.