Tube Amp Archive

500VA

Yep, the schematic above is for a RT66.
Antidote is based on JTM45.
From the Dr himself:
https://www.youtube.com/watch?v=PsymtzV7Jhg

I had a discussion with tech support at Tube Depot, specifically about the new production Tung-Sol 5881's. I wanted to put them in an amp with a 500vdc B+, he cautioned against it - stating that they would likely have a greatly reduced lifespan.

Why not build a higher powered amp with power scaling? Then you have one amp that covers at home/studio and gig volumes.

5W is still pretty loud

Be careful with the plate voltages on 5881's, I think they're only rated for 400v.

I wouldn't bother with making it selectable unless you really want to A/B the different sounds. I'd predict that you'd end up just leaving it in Pentode mode. This is just my opinion, but I think UL sounds very sterile. Others have described it as sounding like there was a blanket over the speaker c...

If your interested in trying it, you could add another power supply node for the screens and change to pentode operation. You might find you like the sound of KT66's better that way. I'm not a fan of UL for guitar amplifiers. I built one that had selectable UL / Pentode with KT66's into an 8K primar...

IMHO, ideal tube to OT impedance matching is relative to optimizing power/bandwidth/distortion...mostly for HIFI. For guitar amps (narrow bandwidth, coloration welcome) not as critical. With a 400v HT and an 8K primary OT, you'll have a 20 - 25watt PA that can use most of the typical power tubes and...

SiC Schottky diodes are super quiet. Schottky's reverse recovery time is nearly zero.

This might be sacrilege, but it's easy enough to try and undo, add grid stoppers to the PI grids. You can go reasonably big without a noticeable effect on treble - just use higher wattage, metal films to induce the least amount of noise. The Express has plenty of treble anyway. Merlin Blencowe discu...

There's a lot of ways to reach your goal. Even for a "clean" pedal format, most want some color/sustain - setting the amp up for "edge of breakup". If you have a scope, it's useful to look at each stage, setting it up to stay as close to center-bias as you can throughout the usef...

So, I built this: kuehnel-garage-amp.gif The voltages on my build are pretty close to the design. I had to increase the screen droppers to get the screen voltages down a little lower. The input pentode is working as expected. I can't get the second pentode to "center" bias. I put a variabl...

So far, redplating is just supposition, it hasn’t been observed. And we don’t truly know what load impedance has been used with it. Whereas tracking has occurred, and an intermittent open circuit on the secondary is likely to cause that. Just to clarify: The first failure mode is speculative, but l...

Running at 1/4 the nominal load would result in excessive current draw, leading to red plating and cooking the OT primary. Was this the configuration (selector set to 16Ω, actual load 4Ω) that caused it to land on your bench originally? In other words, Oops I Did It Again? I suspect that this was t...