ST120 completed

Hello Forum,

Mike here and this is my first post.  I just finished my VTA ST120 and I'm pretty happy with her.  It didn't come without a few issues which of course is a good way to get to know your amp better.  When I finished it all was good but after a few days the right side went bad.  I had a very low and distorted volume and something was definitely not right.  First thing I did was start checking voltages and found the plate on the R driver tube was a little above 400vDC.  Through a ton of troubleshoot I determined the LM334 was bad indeed it was.  She's all back together now and sounding amazing.  Running a quad set of KT120s, BugleBoy 5AR4, and some nice Amprex 12AU7s.

Pics here
http://www.p2pamps.com/st120

Welcome Mike, that is an amazing job you did. That model is probably the toughest one to build with a clean look because of the somewhat limited room, but you pulled it off. Now enjoy the beautiful music it no doubt makes. Which speakers are you using with it?

cci1492 wrote:Welcome Mike, that is an amazing job you did. That model is probably the toughest one to build with a clean look because of the somewhat limited room, but you pulled it off. Now enjoy the beautiful music it no doubt makes. Which speakers are you using with it?

Thanks CCI, I appreciate that. It was a lot of fun to build. I normally do guitar amps and 100s of them so this was a nice break-away for me. I did do my heaters like I do on amps, just a thing with me LOL...

Mike, did you consider the "yellow sheet mode"? It would help protect that nice rectifier tube.

cci1492 wrote:Mike, did you consider the "yellow sheet mode"? It would help protect that nice rectifier tube.

"yellow sheet mode"?

https://dynacotubeaudio.forumotion.com/t1006-tube-rectifier-diode-mod

If you don't have the diode PM me and I'll drop a few in the mail for you.

cci1492 wrote:https://dynacotubeaudio.forumotion.com/t1006-tube-rectifier-diode-mod

If you don't have the diode PM me and I'll drop a few in the mail for you.

Ok, yeah I did that after the pics... I normally do that on all tube rectifier guitar amps too. Good call

yes, that is a SUPER neat and clean job, excellent work!

Yours is very nice, but this one beats it:



The fuse terminator!

I like it!

cci1492 wrote:Yours is very nice, but this one beats it:



The fuse terminator!

LMBO!!!

mikescaggs wrote:

cci1492 wrote:Yours is very nice, but this one beats it:



The fuse terminator!

LMBO!!!

Bob knows the back story to that build, he posted that picture. I think it was blowing fuses and the guy called Bob for some help to figure it out.

cci1492 wrote:

mikescaggs wrote:

cci1492 wrote:Yours is very nice, but this one beats it:



The fuse terminator!

LMBO!!!

Bob knows the back story to that build, he posted that picture. I think it was blowing fuses and the guy called Bob for some help to figure it out.

Yes that's true, turned out I had an opened up 330K resistor in the SMC.  Odd but true...  Without a schematic I knew Bob would know this circuit much better than I since this was my first Dynaco build. Definitely hit a few bumps but worked em out.

cci1492 wrote:https://dynacotubeaudio.forumotion.com/t1006-tube-rectifier-diode-mod

If you don't have the diode PM me and I'll drop a few in the mail for you.

BTW, Thanks for the link... I do have hundred of those diodes in the parts cabinet but I really do appreciate it

Oh man!
That fuse fryer is a piece of work there! It's a beaut!!!

cci1492 wrote:Yours is very nice, but this one beats it:

When I looked at this the lead-in from Guns-n-Roses "Welcome to the Jungle" started playing in my head.  

DarthBubba wrote:

When I looked at this the lead-in from Guns-n-Roses Welcome to the Jungle started playing in my head.  

I'm surprised there aren't a few band-aids wrapped around some of that!