The Amp Garage

do these amps draw more current than a jtm45? I think so, due to the much lower impedance OT, but then so does a JTM50, yet the same spec mains transformer got used, for the early production at least (as I understand it). As I recall, the T&B mains transformer was a bit smaller than a JTM45 type. P...

If you send the duff mains transformer to Luke at Transformer Equipment, I think he could backwards engineer it and build a clone, for a fraction of the MM price. But yes, a good JTM45/50 mains transformer should be electrically fairly similar. A friend has a dead T&B MkII that needs a lot of work, ...

... So the 47k would then be a voltage divider with the plate resistance(tube and resistor)? That's exactly it! The Thevenin equivalent circuit for the triode stage is a voltage source (zero impedance) in series with about a 40k resistance (anode load resistor // valve's internal anode resistance)....

I suggest cleaning up all connections to the chassis. One or more of those lugs etc may have developed corrosion etc, preventing a good connection.

... I biased the 6V6 to around 415V and 20mA, so basically 20mV of current ... TP 37 and 38 206V AC TP39 11.4 So your HT voltage is higher than the Fender schematic you're referencing. I guess the Z HT node voltage will be higher too. More voltage on the screen grids means a higher stage gain for t...

I just finished the initial build of a single channel deluxe reverb, sans tremolo. I'm using a classictone 40-18019 PT and the OT from a Hammond AO35. The hammond has 2 EL84's into an 8r load. I figured the 6V6 would be relatively close. ... There seems to be some confusion as to whether you've use...

Same as an HT winding where the CT is grounded, the voltages at the opposite ends of the coil are out of phase. The one that is out of phase with the secondary shows a higher voltage because its sine wave is high when the one at the secondary hot is low. Ahh, the voltmeters are with respect to the ...

martin manning wrote: ↑Mon Mar 18, 2024 8:51 pm Like this:

My thinking is both voltages should be the same, any idea what the mechanism is that causes them to differ like that?

M3thoms wrote: ↑Wed Apr 03, 2024 6:28 pm Here's the last version, pretty sure I've got this right guys but as always input is always welcome!

A grid requires a DC path back to its cathode, never leave it floating.

Derek at Watford Valves advises that the Philips ECG WGB run fine in pretty much any guitar amp, even the crazy high voltage late 70s Fenders.
And a mere £50 each!
He better puts his prices up before they migrate back across the pond
https://watfordvalves.com/product_detail.asp?id=1313

... The PT centertap wire to the negative of the first filter cap has big and pulsed (containing higher harmonics) currents running on it. Run that one short and direct, and don't cluster it up with anything else. ... Just to confirm and clarify, the CT of the high voltage winding should be directl...

... On any blackpanel amp if you turn all the tone pots to 0 ... Fender knobs for these amps are 1-10, no 0 available, CCW = 1, CW = 10. ... 6k8 resistance to ground, like a 10kA mid pot set at ~3:00. With a regular 1-10 knob and 10k log pot, I recall a fairly high setting is required, maybe around...

(1) And the heater center taps are sometimes not too accurate. A couple of resistors may well make a better center tap, with lower induced hum. Why do you think that the minimum hum is on the middle of very- too much precision- resistors ? Give us some technical reference and measurement. 8) I've n...

You should start with the bias voltage at the most negative setting (largest number). Talking about negative voltage is always confusing. The convention I follow is more negative is lower, which is mathematically correct and follows the convention for temperature. I still write it two ways to make ...

Yes, all the silverface 70 and 135 watt amps where Ul and as such not what you want it your looking for a true Deluxe playing feel and response . To describe those OTs / output stages as UL implies that their design has been optimised for linearity. As the taps are at about 12.5%, my understanding ...