The Amp Garage

So I'm looking for offbeat design ideas to get away from 12ax7/12at7 tubes. I've got a few 12sc7 tubes kicking around and I was thinking about using one for a phase inverter. I know it was common to use it in a paraphrase arrangement (the 6sc7), and with a single cathode it's not possible to do a ca...

I have a stepper bit that goes out to 1-3/16. I think I bought it off Amazon for about $15. its requires a little more clean-up, but works like a charm.

On these types of amps, why does adding a cap across the volume pot doesn’t do anything? The tweed-era tone control already has a bright cap built into it. The wiper of the tone pot sweeps between a treble bleed cap and a bright cap. If you add another bright cap to the circuit, it just lowers the ...

I've been contemplating building a Woody Professional and in examining the only schematic I could find (https://schematicheaven.net/fenderamps/1946_pro.pdf) I identified a few changes I'd like to make. I'm trying to use everything period, except obviously an electrodynamic speaker. I am going use a ...

I just use rca cables from old tv and stereo equipment. Its shielded and basically free. Who doesnt have 2 or 3 cables hiding in a closet somewhere?

2 * pi * R * C is the formula to figure out how big your resistors and capacitors need to be. Its the inverse of the freq. cutoff for high and lowpass filters. You just need to keep your resistor small enough to deliver the full voltage your LED needs. You could probably power this off a half-wave r...

No. The circuit I'm talking about takes the signal from the secondary on the output transformer and pushes it directly into the input of an 8 ohm tank. Both halves of a 12ax7 are used on the recovery side, one to amplify and the other to mix into the preamp. You can either use a fixed resistor or a ...

I dont know of any commercial examples, but you could do a foldback reverb loop. You wouldnt need to use any tubes for the send portion, just 1 for recovery and mixer. The easiest way is to use a dwell control to take the signal from the output transformer and feed it directly into the tank. Kevin O...

If i were to attempt this, I would try applying the nfb to the cathode of the gain stage immediately proceeding the PI. That seems to be the most straightforward way to me. Have you checked what the signal looks like on the grids of your output tubes? If you dont have a scope, check the AC voltage.

Parts Express carries some 1/2" corners in both black and nickel. I used them on a head cab I made out of 1/2" plywood,

Turns out all 4 of the 7189s are bad. Once I rewired the socket for the 6CM6 I ended up with 41mA @340 volts for a plate dissipation of 14 watts. Havent played it yet but I was getting some hum from the 7189s and it's dead quiet now. In the future I may buy an el84, just to compare the 2 tubes, but ...

The 7806 should keep the supply at 6v, I think its low because the total load is about 70 -80mA over the 1A rating of the regulator. But I'm only using the circuit to test the 7189s. Once I rewire the socket for the 6CM6 itll draw 300mA less.

It's running on dc. I needed a supply for the led indicator and I had a regulator already built up.

Here's what I got: G1:5mv G2: 363v A: 390v C:4.16v The heater is measuring @ 5.6vdc. I tuned the bias to 270 ohms exactly. Just for fun I also measured 3.73v across the 290 ohm primary winding. Across the cathode resistor I calculated 15mA, across the OT I calculated about 13mA. 13mA @ 390v is 5w.

I was measuring across both the bias resistor and the OT primary winding. No matter where I had the bias pot set I couldn't get a reading above 15 mA. These are the 7189s that came out of an old HH Scott stereo. I haven't rewired the socket for the 6CM6 yet.