The Amp Garage

The guys who sold me the used tube as NOS are a major tube parts dealer. I am surprised at their policies.

Bought two 5U4GB rectifiers sold as "NOS." One of them was clearly used. I call the seller, they say that if a used tube tests as fully meeting its specs, they sell it as "NOS." Well, I was surprised about that! Shouldn't the tubes have been called ANOS? But certainly not NOS? What do you folks thin...

what strikes me as weird about the Princeton reverb is its feedback circuit. The 2700 ohm feedback resistor from the output (speaker) connects back to what is (at audio frequencies) the junction between the 47 ohm resistor to ground, and the cathode of the 12AX7 that drives the phase splitter. So, m...

My experience is that the 10K blackface style bias pot with a 27K resistor is not right for todays wall-voltages and tubes. Try a 15K resistor with the 10K pot.

looking for schematic for Epiphone Zepher "Dreadnaught" from 1950's This thing is a mess...schematic would help.... if anyone has one. Thanks ! Preamp is 2 6SJ7' pentodes, then phase inverter is a 6SN7, two 6L6 output stage, tube rectifier, and thwo other 6SN's for the tremelo circuit. it has three ...

I think I get what you're saying Martin. The total amount (mass) of wire would be the same.

Then it seems like the foilliwng is true:
comparing single HV winding with a bridge vs. Center tapped winding with a full wave rectifier: There is no advantage in terms of the size/mass of the transformer.

It seems like if you abandon the common center-tapped power supply transformer scheme with full wave rectifcation that you could have only a single HV winding and have half the wire (inside the PT). But wait, now the single winding is being used every half cycle whereas in the center-tapped PT each ...

Phil_S wrote:Build one of these: http://www.youtube.com/watch?v=QEVHcf1iJj0
Thread at AX84: http://www.ax84.com/bbs/dm.php?thread=478112

incredible, love this!

Don't forget to scale all voltages by Vg2new/Vg2old too. In the amp I am designing I'll have the quiescent screen voltage be about the same as the plate voltage. So , my reasoning is like this: I'll be aiming for Vscreen=Vplate = 400V The Vg1=0 line for a 6V6gt tube (see top plot of attached data s...

When all is said and done, I think I am heading in Martin M's direction: All I really care about is the Vg1= 0 curve, and will use the approximation found in RDH4:

current scaled by factor = (new screen voltage/old screen voltage) ^ 1.5

how to generate plate curves for higher screen voltages than shown in a data sheet?

Like, for example, running a JJ 6V6GT tube with a screen voltage of 420V?

In the knowledge base of electromagnetics there is the concept of the "right hand rule." It goes like this: If you have a wire with current flowing through it, You orient your right hand such that your thumb points in the direction of positive current flow. Your reminaing fingers curl around the wir...

I really want to try a practical experiment. Put a working, quiet amp on the bench and fire it up. Use a spare transformer with 6.3v heater tap and connect some long, individual (i.e., not twisted or paired) wires, and use these wires to TRY TO INDUCE HUM in the subject amp. Question: would you hav...

This is unrelated to your reverb and hum woes , but, in the photo I noticed that the fuse holder connected to the standby switch looks like it's nut has come loose.

the wet signal looks as if it is being fed (through a white mallory 150, on right side of PI "tail" resistors) into the "other" PI input, the one nornally used (in a blackface style amp) for feedback from the output (speaker/OT secondary). I think you'll have a reverb, with this amp, that is much mo...