The Amp Garage

Knowing that the turns ratio provided is just half the OT helps. Thanks.

Oh and I forgot to note that this OTs primary impedance is 4.3K center taped. I thought I was with you up to part B, but now, not so sure. I calculate the primary impedance based on your turns ratio in your initial post as 1076 ohms, which then yielded your 236mA, 167mA, and 331mA calculations. I a...

Stevem wrote: ↑Tue Sep 29, 2026 6:59 am
Actually here’s a part B of my question.

Is in the case of having a 4 ohm load on the 8 ohm tap the output stage will only be able to produce 36 watts of rms power, and then with the 8 ohm load on the 4 ohm tap only some 42 watts can be produced?

Are you using 236mA for these two calculations?

The schematic symbol is a light emitting diode. What is missing is the switching circuit and most likely the dropping resistor so the diode works on -36V. An LDR resistance increases when dark, decreases when illuminated. In my experience, an LDR resistance does not drop to zero when illuminated and...

The schematic symbol is a light emitting diode. What is missing is the switching circuit and most likely the dropping resistor so the diode works on -36V. An LDR resistance increases when dark, decreases when illuminated. In my experience, an LDR resistance does not drop to zero when illuminated and...

Maybe over time and under use, the flux begins to climb. If you have records and have access to ones rebuilt, check and see. If not, run an experiment with rebuilt pickups, maybe one in use, one not, and see. Who knows. Maybe there is a “settling in period”. Be interesting to see.

I'm guessing that 73mA on the plates is the no-signal bias. This looks like a class AB push-pull stage. I reckon it's going pull a lot more current when driven to full-signal levels. Like Sluckey said, Idle and Full Output do not vary much with Cathode Biasing. Two real world examples from my data:...

I think you'll want a bit beefier unit. The 6.3 volt filament winding supplies 2.5 amps and your tube complement draws 2.42 amps. That's awfully close to the limit of that winding. Likewise the high-voltage winding is going to be overtaxed with a pair of el84 tubes in push-pull. That output stage i...

Very strange. Not sure what failure would result in the readings being reported. You are measuring for AC on the secondary, correct?

The whole trick with inductive input filters is then to make sure that the load stays high enough (or the inductor/capacitor are sized correctly) to keep the output load current above the critical loading current for that inductor and cap. It will take some calculation to ensure that the choke you ...

The whole trick with inductive input filters is then to make sure that the load stays high enough (or the inductor/capacitor are sized correctly) to keep the output load current above the critical loading current for that inductor and cap. It will take some calculation to ensure that the choke you ...

I would agree that shorter power off durations are more problematic than longer shutdowns. Once the bias circuit is charged, slowing the discharge time might be an alternate approach to quicker charging. If you could disconnect the bias circuit lower voltage divider from ground, the bias supply woul...

The graph does not include the 50K although shows what 50K does to the signal. It was removed (replaced with various resistances from a decade box while measuring the channel AC Signal Voltage) so I could get a complete picture. The graph would look very different otherwise, essentially stopping at ...

You can see on the graph how that 50K drags the signal down. Keep in mind that this resistance to ground also creates a high pass filter. That 50K coupled with the larger coupling cap on the vibrato channel really alters both gain and tone.

But your question make me wonder what the effective range for the resistor side is. That is - how high and low does it need to go to get an effective tremolo sound? Attached is an attenuation curve I produced for a Bandmaster AB763 tremolo while developing an LED/LDR mod I did a few years ago. It w...