[sdiy] 50L6 amp done! - happiness is a warm 200W soldering iron

[anthony]

So you all probably remember my talking about making an amp on an old "All 
American 5"-syle radio chassis...

Well I did it and it is finished and it sounds AWESOME!

I just threw together a basic amp like what one would make with one section 
of a 12AX7A and a 6V6 or a pntode, except of course that I used a 12SQ7-GT 
and a 50L6-GT.

I really put a lot of effort into making the layout clean and used 
star-grounding and star-power (more or less). I used a little isolation 
transformer that used to be in a TV antenna pre-amp that used a 6J6 and a 
combination of 10uF and 100uF caps for the half-wave supply.

When I finished the amp, I plugged it in to test it and I thought, "phooey! 
back to the drawing board - it doesn't work" because I didn't hear any hiss 
or hum as it warmed up. Well I stummed my guitar anyways and WOW! What tone! 
Really quiet even turned all the way up, but the tone was real.

So happy with a good start I set out to get more gain and power out of it 
because the values I started with were pretty conservative. Several mods 
later I have a moderate gain amp with a good amount of clean headroom. I had 
to do a lot of things to fight oscillation (270 pF caps on the plates to 
ground and some sort of small grid resistors etc.) But now it's dead quiet. 
The fun really started when I put my heavilly modded Peavey Hotfoot (a lot 
like a ProCo Rat II especially with my mods except I used 5 Ge diodes for 
asymmetric soft clipping, but I digress...). I've never used this thing with 
the gain all the way up - I have been using a 15W eiphone solid state amp - 
but in front of a tube amp it really sings. It's impossible to use it as a 
good clean boost in this case anyway. I can't imagine a booster based on an 
LM308AH being good for much clean tone really. I should make a Tubescreamer 
clone - or what I really want to do is make a clone of the Matchless 
Vibrobox tremolo. I have an 8Meg pot that would be great for the LFO speed 
control. The overthetop overdrive distortion is awesome and lots of fun, but 
the clean tone right at the edge of break-up is the best part. And the only 
hum I have ever heard on it came from the wall-wart running my Hotfoot and 
that was with the gain jacked all the way up. Didn't I mention that I used a 
half-wave supply?

What really sucks is the fact that I really don't have a good speaker 
cabinet to run this on.

Now I am really itching to build my VoxAC15/GibsonGA15 with reverb and 
tremolo sort-of-clone. I have all of the tubes, a chassis that needs 
drilled, power transformer. But I am really at a loss for a cabinet design. 
I like the way the GA15 looks and having the chassis on the floor with 
controls at the back would be easiest to do.

I have 3 vintage Mullard EL84's. I had had plans to build a 5Watt SE amp 
with one, but after seeing how easy it would be to gut a Valve Junior or 
just swap in the Mullard tube, I've been focusing my attention on the 15W 
push-pull amp design. I hope that the success that I got from such a 
relatively small effort for the 50L6 won't spoil me. Of course a whole combo 
amp is another animal. I don't even have access to a drill-press or a wood 
shop. The only way I managed to mount the transformers (neither they nor the 
chassis had mounting holes) on the 50L6 amp (which I have dubbed "The Two" 
or the "AA2" - "AA" being my initials of course) was that I found my 200W 
soldering iron and put a new cord on it. I really /REALLY/ love that thing.

And I still find Aron's Stombox page to be completely unusable lately. :-(