Tube Amp Archive

Er... there isn't any such thing as over-engineering. :D Ha, I suppose you're right. I still think it would be cool to handle each tube individually... Would give a 100w amp the option to remotely limp it on home through a gig or a session. But Killing the B+ is nice nice solution that also gives a...

Great discussion! This was beginning to feel a bit over engineered/costly. I do kind of feel like must putting the amp into standby by switching off the B+ is a very simple solution. I guess the previous rules necessitating the fast analog path still apply, though, right? So that would mean the MCU ...

Here is the full design. I worked out the details with ChatGPT, so definitely look for errors (large or small), but I think it's pretty solid? Normal operation (tube conducting): • MCU drives the VOM1271 LED. • VOM1271’s PV side makes ~8–9 V across Gate–Source, turning on the back-to-back MOSFET pai...

I’m working on drawing up a fast-trip addition to the above circuit, but probably won’t have time to finish it until tomorrow.

Also, do you think the IRFBG20 need a heat-sink? They're rated at 1000v. Most amps I build are below 475v.

Aaaah, ok, I think I see what you mean.

Thoughts on this version?

Thoughts on this?

Wow, that's amazing. I kind of like the idea of the bias now button. Very clever! My setup will keep each tube individually biased to whatever range you want. The default value is "Normal" which is like 60%. It will work out of the box without the GUI. There is a 3 color LED that provides visual fee...

A problem with lifting the cathode etc is that a pretty common output valve failure mode has the HT somehow shorting to the heater. So cutting the HT feed to the affected circuit might be better. That’s a good call. This is why I wound up just cutting the main power instead. But now I’m wondering i...

nuke wrote: ↑Wed Sep 17, 2025 7:07 pm Maybe a low-side mosfet switch instead of a relay?

Just need to be sure the Vds is rated for full supply voltage.

Do you mean on the cathode or on the HT instead of a relay, like PDF mentioned?

Nice, thanks. I'll play around with it.

I'm working on a project that uses an MCU to automatically set the bias of a pair of tubes (individually). It measures plate voltage, cathode voltage drop across a 1Ω resistor, and adjusts to the desired setting in realtime. It has an app you can use to change the bias, tube type, look at overall tu...

Great conversation. There were only a couple times over the past 10 or so years I've had issues, and both seemed to occur right around the time covid/lockdown happened. I think they must've had a labor problem as I got a few orders that had mistakes (which I had NEVER gotten before), and sometimes o...

I think I was saying to try it in front of the power tube. Again, I'm only basing this on my own experience working with little amps like this. Specifically the P1 High Octane and the Custom 5. I could be wrong, but at this point you've tried everything else.

Oooh one more thought. Did you check for leaky caps in the tone stack? I didn't see if you had a coupling cap between the master volume and the power tube, but if there is DC getting through it could cause some ugly noise.