The Amp Garage

I measured the impedance ratio and it turned out 2k5:1 ohms. That equals 20k:8 ohms. Maybe at 2kHz :shock: The original transformer must have been designed for something like 100 or 200 Hz lower limit (remember, table radio or TV). Since you are not touching inductance but rising working impedance ...

TUBEDUDE wrote:Or...you could go xfmrless with a current driver directly into the tank.

I'm panning to do that with another project.

I'm gonna try 12AT7 first, if I'm not happy, I'll fiddle with nine pin pentodes. It's gonna be sort of EZG-50 scratch build with the addition of power tube bias tremolo. The output transformer is ~5k:8/16ohms so should be just in the EZG-50 camp. Plate voltage will be ~435V, give or take few volts a...

Hi. Started a scratch build once again... I have a recycled 2x12" combo cab and chassis and try to use as much stuff as possible I have on hand. PT and OT are recycled from old amps and will make a perfect pair for a Blackface amp of my dreams. I have an output transformer from an old tube radio tha...

Would a variable voltage regulator (vvr) work in this kind of situations?

I came across a Gibson GA-45 Maestro schematics (5879 preamp) and treble and bass controls were just before power amp. Very simple bass control, kind of same principle as the "dongbiter" but just in different position. Could work in tweed deluxes also (or basically in any amp without bass control) i...

Thanks for replies guys. It would be a real help if You have some specs about your OT Stevem. I was thinking the same thing jazbo8, that the primary Z will probably be higher than the "nominal" Fender value. With those voltages, fixed bias and with approximately 4k ra-a you go easily to the 40-50W t...

Hi. Long time since my last post... try to make the long story short. It happened about two years ago when I got a chance to play my buddy's 1956 GA-40... there was no coming back. The moment you finally realize that this is the tone that you've been searching for. Been trough Fenders, Marshalls, Vo...

Anyone have a good circuit for a bass control coming off of a pentode's plate? The pentode has a high output impedance so that is the big consideration... Thanks I've been thinking the exact same thing. Planning to build a GA-40 Les Paul amp variant and it would be nice to have a little more contro...

1/4W resistors are fine here. However, as a RoT, 1/2W or 1W resistor make for less noisy grid leak resistors. Got to try and see if I hear any increase in noise. I've got some CC, CF and MF 220K's half watters and watters. Weekend is coming so I might even make a test box and listen is there really...

[/quote]Grid/bias resistors on output tubes carry all of the ac current/signal coming from the PI, to/from ground/bias. I wonder if this approaches 0.25 watts ac? I found this: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/acohml.html If I got that right we are talking about few to something l...

Hi. Some time ago I run out of 68k 1/2W and 1W resistors. When sourcing my stashes I found a bag full of nos 68k 1/4W CC resistors that I once bought. My rule of thumb has been that never use 1/4W resistors anywhere in a tube amp and always play safe and overrate, but the situation got me thinking. ...

Yeah, the "AU" side of the 12DW7 will be good for driving tank. Supposed to be capacitor coupled. There is also extra gain stage compared to standard 5f2a circuit.

Hi. Has anyone of you have had a chance to peek inside one? Some gut pics float around the net and what I've read it's mostly a 5f2a with 12dw7 driven reverb. I've been fiddlin' around with 5f2a circuit lately and would be nice to incorporate reverb into it. I don't have access to swart STR so I can...

Thank you for answering Stevem. Yeah, the voltages will be spot on. I was just little concerned about that 70mA being enough for 2x6V6 and two 9 pin pre amp tubes, but it will probably be fine.
-T