The Amp Garage

Testing an unknown PT is a whole can of worms, as there is a lot going on and it is necessary to consider all of the windings, not just the high voltage secondary. I've just been through this question elsewhere an got a pile of good advice, which I will try to summarize. Ohm's law is your friend. Yo...

I'm Phil. 55 years old. I am a CPA doing consulting work as a sole practitioner. I work almost exclusively with non-profit organizations. I like to do "clean up" work (untangle, rearrange and reorganize a set of incomprehensible books of account) and accounting systems set up work. I've installed Pe...

Dave H here. 45 yrs old.... I've built numerous amps, several being 'Wreck circuits....mostly Express style, with one being a variant using 6021 micro-miniature pencil type triodes in the preamp (the ones with flying leads) and a 6aq5 output. Would you consider sharing the schematic and some gut sh...

An unknown OT is relatively easy to figure out. Find an AC wall wart (most put out DC) or tap the filament supply from a regular PT for a source of low voltage input. Instructions are here: http://www.radioremembered.org/outimp.htm You already know the application and the tubes, so once you know the...

Mark: thanks for the schematic. Rhinson: Thanks for the advice. It suggests maybe I can get the iron from Musical Power Supplies. He sells a 275-0-275 @ 120ma with primary taps for +/- 5%. Picking the -5%, I think it will put the plate supply at 340-350v and it will run on the hot side. I have been ...

Perhaps I'm superstitious or old-fashioned, but I prefer my power supply ground to be at 0 volts with respect to the chassis and earth ground. I've had good luck using a series MOSFET circuit between the diodes and the first filter cap, basically a somewhat simplified version of Kevin O'Connor's "p...

Thanks, this article was really good. It is written at a level I can understand. It put some stuff in perspective. I'm thinking now that it is really best to find the right PT and not try to drop the B+ too much. I"ll keep looking. I might end up with a 275-0-275. Maybe I'll just put a big fat dropp...

I'm putting in a Zener at the center tap and knocking them down 50 volts or so I should freely admit that I'm out of my depth with a Zener. I'm not even sure which direction it goes, no less what value. I don't usually ask for a "gimme" but it sure would help to know. 50v is just about right or may...

I've been picking up small power trannies from a local electronics salvage place. They seem to have a ton of them that are 325-0-325. I'm putting in a Zener at the center tap and knocking them down 50 volts or so and using them in my 7 pin amp builds. RJ: Yes, I like to buy cheap iron on eBay and h...

Your "six banger" is probably 50W or so. I was thinking a single pair is plenty. When I saw that Ken Fischer designed the amp for EL34 or 6V6, I immediately wanted to use a pair of 6QA5 so I could tame the volume a bit without changing the vibe too much. In every parameter that counts, the 6AQ5 is f...

My intention here is to see if a wreck can be built that satisfies without ear splitting volume. This is sort of like what the 18W Marshall is to the 50/100W models. I think you are right about "economizing" on the iron.

Since you are a do-it-yourself guy, you might be on the lookout for a Mullard 6EU7. It is identical in every tube parameter to the 12AX7, but not pin compatible. You'll need to rewire, but that is one way to control the cost of a Mullard. I've got one in my JTM45. Just my 2 cents. Oh, and it seems l...

Hey Dan: I use the TDSL all the time, but didn't know about the PSU designer. That's really a good tool to have. I built a fixed bias VibroChamp so that I could test and match the 60 or so 6AQ5's that I've got. About half of them test like new or show reasonably strong results. Less than 25% tested ...

I built a six 6AQ5 amp, not a wreck though. I'm running about 350v on the plates and lowered the screens with individual 75v zeners, as per my friends suggestion. Before the zeners were added I was having a tough time finding six tubes that were reasonably close, I smoked a few! I used onetics iron...

If you build one with that tube, it won't be one right? Everything on the PS side will need to be redesigned. That is precisely the question. I can mess with it, but my theoretical knowledge isn't deep enough to qualify what I can do as design work. I was hoping for a hint or two. My gut tells me i...