Tube Amp Archive

... I'm not really sure it's possible to keep the operating points anywhere similar with the 6AV6 as a CF. A cathode follower is an excellent place for you to use a JFET instead of a tube. The cathode-follower has 100% negative feedback, so the tube wasn't "contributing tube-y-ness" anyway. And the...

I think a better question is why the tone control is arranged in such a way that its effectiveness is dependent on the volume control setting. Moving it downstream in the signal chain, for example after the next gain stage or even as a Vox cut control (only works in output stages that don't have NFB...

I wasn't satisfied with the noise level in the recovery circuit, so I did some changes: - Fully bypassed (22uF/2.7k) the cathode on both stages. Better power supply noise/hum rejection. - Removed the 68k input grid stopper on the first recovery stage. Less series resistance in the signal path, less ...

First, thanks for updating with results & revised drawings. I find lots of dead-end threads frustrating and it is nice to know how things turned out. I think the clips sound really good, a result I would be pretty happy with. I would encourage you to fool around with the send/return settings & play...

nuke wrote: ↑Mon Apr 21, 2025 7:02 pm Which tank did you wind up using? The schematic shows a 4AB31C with 8-ohm input.

Thanks! Corrected - I copied the wrong part number. It is a 4EB2C1B, 600 ohms input and 2.25k output.

So, I’m inclined to think the resistors are actually doing their job; I just need to measure across them vs to ground. This is weird. And there isn't a chance you might have mixed the cathode and ground ends of the 1R? Ie hooking one probe to the ground side of the resistor and the other probe to t...

So, oddly enough after racking my brain and trying to see the problem from different angles - I thought: “Those 1Rs are like little cathode resistors, right? Maybe I should measure the voltage drop across them?” So I did. I started getting readings in mV that made sense given the resistors I have i...

Tanks for the input, Nuke. Something along those lines was my initial idea, but in the end I went for a capacitor driven solution instead, as you can see from the discussion above. A little more tweaking was done on the reverb circuit (I've updated the schematic above): - The reverb driver has it's ...

No problem with tapping the new preamp node off of the PI node for example. That way you retain a higher supply voltage compared to daisy chaining it onto the existing preamp node. Edit: 1b yes add cap and dropping resistors. adjust value/voltage to taste I suppose that means I should tap the B+ bac...

I really like the micro pentode push-pull concept. Bet it's still pretty loud when cranked? I plotted the tonestack values in a tonestack calculator to see the frequency response (without the resistors in series with the caps, don't know exactly how much they affect the overall response), and it's g...

It's been a little while, but here it is. Please have a look and let me know what you think :) Bergheim Rødampen 2025-04-21.png I left the 12AU7 reverb driver cathode unbypassed to increase the output impedance to 8.6k (up from 5.1k bypassed), functioning better as a constant current source. Not tha...

... or a pentode for better S/N ratio than the regular triode. Acc. to Merlin pentodes tend to have a higher noise figure than triodes due to additional current partition noise between plate and screen. Whaat, I figured the much higher signal gain outweighed the higher noise level? Anyway, removed ...

The output signal from the reverb tank is tiny, not very much higher than the noise floor, so noise is kinda part of the nature of the beast. Good lead dress and shielded signal cable all the way from the tank to the recovery stage input grid will help. For the recovery stage itself, maybe try paral...

Said another way, if you remove the standby switch, the B+ will turn itself on precisely when the tubes are hot enough
Pretty much the only thing to watch out for is that all filter caps can withstand the unloaded B+ voltage.

Well, the most obvious trigger would to be something that detects the presence of current in the tube, but that is obviously impossible because of the standby switch. Another method would be a temperature sensor that monitors the cathode temperature (precise measurement and shortest time to turn the...