The Amp Garage

Actually, the voltage increase is negligible, really. Only about 15-16vdc increase. The amp appears to have been (almost) totally recapped with orange drops and other polypropylene caps. Also, I think I located the PI. I suspect it is v2. There are two leads from pin3 (grid 1) of each power tube, wh...

it came with all mullards, but they are a little too gritty for my taste. v1 and v2 are preamp tubes, v3 is for the tremolo circuit. all 12ax7.

then the two 6973, and what would be an ez81.

what's a cathodyne PI?

So, I recently made a post about adding a SS rect to this amp, thinking it was a U-202. Pulled the chassis and found out that it is actually a U-152. I can't find any information on this amp at all, but it looks very similar to the U-202R. I've doubled the capacitance (is this safe using the SS rect...

recently acquired a univox U202, my "dream" amp! The amp has (or had, rather) alot of sag, which really isn't my thing. I popped in a couple of diodes, and added a switch to cut off B+ from the diodes should I choose to use the 6ca4 in the future. I didn't alter any of the original wiring, and the l...

I see no harm in replacing the baffle as long as you are able to keep the original grille clothe. There are some freaks like me who actually prefer vintage gear in deplorable condition! mint and clean stuff doesn't do it for me. post some pics!

Hmmmm... What is "ghosting"?

i actually just went ahead and emailed matt at musical power supplies and requested this ot with 2.5k primary and 8ohm secondary. 52 bucks including shipping, though i would be waiting 3 weeks. seems like a deal to me in any case.

After these PP builds, i'm really wanting to do another SE. AX84's alleged "20 watt" SE powered by a single kt88 sounds like alot of fun, but i can't find the doberman 20w SE opt that the design suggests. Mouser has this: http://www.mouser.com/ProductDetail/Hammond/1627SEA/?qs=3TG34Bgp1HDec3QHyMMPQg...

r7 was changed to 2k, allowing me to get anywhere between -1 and -40vdc.

i'm not even ashamed to admit that my real problem was that i was using a broken guitar cable.... alright. maybe a little.

some modification need to be made to the tone stack, but it sounds great.

PI cathodes are now at 73vdc. resistance between pin 3/8 and ground is 27k ohms. it is inevitable that lead dress and interference will be an issue with a tiny chassis like this. wouldn't haven chosen one this small unless i already had it laying around! however, absolutely no sound from the preamp?...

Sorry, Martin. I've built a modified ax84 "simple preamp" from the building blocks section of the site.

Tilly, forgot to reply to your whole message. The organ was tube rectified. 6ca4 if I remember correctly. Can't remember the details of the amp, as it was dismantled almost immediately. Knew the voltages would be a bit higher, but I do love punishing my tubes.. Lol

Thanks Martin, obviously a serious "duh" moment for me. I am getting amplification, and PI voltages are good! Tillydog, thanks for the bias suggestion. increased v- to about -18. something else overlooked. However, all that's getting amplified is a very loud sine wave which I can adjust the frequenc...

power supply is on top of the chassis, everything is grounded at the input jack via star grounding. that little red cap above the two bias capacitors takes the place of the presence knob, and is grounded.

finished this a few hours ago: http://www.ax84.com/static/corepoweramps/20W_PP/AX84_20W_PP_Poweramp_Schematic.pdf used 6bq5/el84 in place of 6v6, and the PT and OT (and same power tubes, actually) from a hammond organ. most of the component values are identical to those in the schematic. i used .02 ...