Tube Amp Archive

It has a 470 ohm screen resistor. This is a Class A amp and you would need to monitor screen voltage drop while in a dynamic operation with your meter and a dummy load to confirm operating points before doing any type of modification. Idle operation has nothing to do with dynamic operation and plate...

The trick to a Trainwreck is to bias the output tubes hot, at least 75% dissipation, use a 50 foot instrument cable and play it loud. The midrange will swamp the brightness.

The light bulb limiter isn’t intended to be used while playing the amp or bias. It’s a start up protector for the fuse and indicates a heavy current draw that won’t allow enough current to blow the fuse. Once first start up is verified good with dim glow, and bias pot on lowest current setting, you’...

I wish we could stop calling it grounding. What we’re doing is referencing the heater circuit to chassis potential. The chassis is grounded. The heater circuit has no current that is entered the chassis. We’re referencing it to this point so that it remains set here and isn’t floating. The other cir...

I wouldn’t reference the heaters to the point of the highest current return. I’d reference it to the lowest current, the input. That’s the point of the lowest noise and it should be the quietest possible point. That should keep the input triodes quiet. With respect, I believe that would be a mistak...

I wouldn’t reference the heaters to the point of the highest current return. I’d reference it to the lowest current, the input. That’s the point of the lowest noise and it should be the quietest possible point. That should keep the input triodes quiet.

The amp will never be right with lead free solder. A 5E3 was built with 60/40 or 63/37. Get real solder. 700F.

Here’s what I do when biasing an output section. I use my oscilloscope to view the output waveform. The maximum dissipation rating of the tube is used only to determine the maximum current I have to work with in an attempt to achieve full clean sine RMS output. Meaning that I want the output wavefor...

I would like to interject that I have many different component choices on hand when I build an amp for a customer and my opinion is that I have difficulty hearing any differences between the Piher, Iskra or modern Xicon resistors. Also the same applies to the Mullard mustard capacitor vs Sozo, or ot...

A pair of EL34’s at 420 volts and an output transformer with 1750 will get you about 22 watts clean RMS.

If you have a scope, it’s not a bad idea to view the waveform during bias adjustment. If you can achieve no crossover notch at full clean rms output before a 70% bias dissipation setting, I’d say that’s the perfect bias point. It’s not critical to view the waveform but with the tool available, why n...

I have seen 6 turns/ft quoted for magnetic field shielding. Over-twisting is pointless, and could cause lead breakage. It also puts more copper mass in the circuit. The important factor is parallel wires and a light twist keeps the conductors together for suppression. Using a drill to make candycan...

It’s perfectly fine to have unused windings in a transformer. Hammond transformers offers some of their power transformers with both 115 and 125 volt primary. Unfortunately if the input voltage from the power company is really close to 120, this is going to end up high or low voltage output. I’ve ta...

I thought I read that Sozo was bought out from the original company. I think the original company was a small production setup and maybe demand/economic situation caused them to be profitably undesirable and it was decided to stop production. The name and design was sold. Time passed and from what I...

If the case is a single ended amp that the power section is overdriven, the voltages in the output transformer and tube socket/ tube will experience induced voltages that come close to twice the B+ supply voltage. The chance of arcing is more common in single ended amps.