The Amp Garage

I'm not an expert so apologies if this is already common knowledge or not applicable. Maybe useful? In Gar Gillies' tube amp book he offers a way to estimate the current rating for a high voltage winding. 1. Measure the resistance of 1/2 of the high voltage winding. 2. With the winding unloaded, con...

Good heavens! Scandalous!

Thanks everyone for your responses. Sounds like if nothing else I can run the 12AT7 at lower plate voltage and it will sound just fine.

For the price of a reverb driver transformer and the tube you drive it you can get a SS reverb section the only needs 5 volts . I'm not opposed to this approach, but I have a lot of questions and it looks somewhat more complicated than just a 12AT7 and a transformer. I'm always game to learn some n...

sluckey wrote: ↑Mon Mar 11, 2024 2:21 pm May I ask why?

Sure. If using 25L6 output tubes then my plan was to use a 24V filament transformer, wire the 25L6s in parallel and then stack three 6N2Ps and one 12AT7 in series.

Hi everyone. I'm thinking about building a Princeton Reverb-like amp, except I would like to use oddball tubes, partly because you can get quality NOS tubes cheap, partly because I don't mind a little less power, and mostly for the fun of doing something different. With that in mind, I don't think m...

I went with the 3H choke. Pretty quiet! Thanks for the help.

I've never used a choke, so I'm willing to spend ~$20 to try something new. At Amplified Parts I see a couple of options in that price range - either 1.5H/56R or 3H/86R. Same price for either. Would the slightly lower cutoff frequency warrant the slightly higher voltage drop over the 3H choke? Do I ...

Here's an update nobody asked for. :D I built it with the voltage doubler. The hum is significantly less, though it's far from hum-free. It runs *much* cooler without that huge filament resistor. In the spirit of this being a budget amp, I crammed the thing into a little Squier SP-10 practice amp ca...

Yeah, that's it. Thanks!

That Triad F-59X is rated for 24 VA, 400mA. The filaments will take 9W. The plate/screen currents of both tubes add up to maybe 65mA total (probably not actually close to that), so running at 160V let's say 10W? So if I did that math right then the PT should be able to handle it. The rectifier in my...

Hello! Wanting to build an amp that is simple enough for me to try point-to-point wiring but is something other than a Champ clone, I modified the circuit for a Kay 703 and built it. The schematic of the original amp is below. PXL_20231017_095534752.jpg I modified it to use solid state rectification...

Update: received the new 125B output transformer from Hammond. The amp now works as expected. There is mild hum when the tremolo is engaged, but I am fairly sure this is due to excessively long flying leads in my build. Otherwise, it is nice and quiet. Attached is the final schematic, with measured ...

Secondary was connected black to white, which with an 8ohm load should yield 3k on the primary according to the datasheet. With the measured voltage ratio of ~11, I calculate a primary impedance of only 1k. The guy at Hammond said the primary DCR on the 125Bs he had were all much closer to 300R. He'...

With nothing hooked up to the OT, I get the following resistances (in Ohms): Primary: brown-blue 238 brown-red 174 red-blue 63 Secondary: black-orange 0.2 black-green 0.4 black-yellow 0.6 black-violet 0.7 black-white 0.8 Going from any of the primary leads to any of the secondary leads gives an open...