Tube Amp Archive

Roe wrote: ↑Sat Sep 13, 2025 9:28 am 4 tubes sound better normally

I agree that an unmolested Twin Reverb sounds better normally.

But dude has an 8Ω reactive load, and a 4Ω Twin. If he wants to play, today, he can just yank 2 output tubes and have an "8Ω output Twin."

Not the same, but it is what it is.

I recently wanted to use a Fender Twin Reverb blackface reissue for reamping purposes and with reactive loads, but I soon noticed that it only has 4 ohm speaker outs whereas the two reactive loads that I use (Suhr Reactive Load / St. Rock React:IR) are both rated at 8 ohm. Pull 1 output tube from e...

Sorry to again be the dude that's pushing back... ... much of the fundamental “personality” of the amp can be distilled through more detailed design of the power section itself (assuming you get to turn it up enough to actually push the power section). Considering the type and “temperature” of bias ...

I've just built myself a 6G3 clone. ... On the fender diagram, it shows, 333-0-333 into a GZ34, with an output of 375V. ... Fender schematics are not Gospel . So you can't expect the numbers on them to exactly match the actual vintage amps. It also turns out that most modern power transformers don'...

The diagram includes the recommended heatsink for your regulator . I assumed bolting to the chassis would be a far better heatsink as it's much larger than that heatsink. Unfortunately, that's not true. Otherwise, we wouldn't have an industry that makes heatsinks of special material/shape that gets...

liddokun wrote: ↑Fri Sep 05, 2025 11:22 pm I'm powering 3 12ax7s.

I've got it bolted to the amp's chassis. The chassis gets mad hot as you've described as well.

The diagram includes the recommended heatsink for your regulator.

If we examine this graph from the 6L6GB data sheet, the conditions are: Control grid at 0v (ie, no signal, but no bias , basically wide open or maximum signal peak without grid current). ... Like I said, the screen current is relatively constant while the plate is higher than the screen voltage. .....

Quick question: My 5F1 clone has 1.5k cathode bias resistors on V1A and V1B, for a 12AX7 (gain factor of 100). I've replaced it with a 12AY7 (gain factor of 45) and much prefer the tone, reduced gain, more clean headroom etc. Is the bias resistor still within an "acceptable range" for a 12AY7, or i...

What are the design parameters here Anode current is determined by the relative magnitudes of the control grid and screen grid voltages. Amp Designers start by deciding an amount of output power they want the amp to have. They might also have a rough mandate for total supply voltage based on the li...

... As the plate voltage drops under higher-current peaks, the screen current goes up. ... Screen current thus grows at an increasing rate, causing the screen to heat and even driven hard enough, to deform and melt. (a common form of power tube failure). ... This situation only happens (in an adver...

This layout works everytime just like it did for Fender. No, it does not. The original 6G15 (I have one from 1964) uses a 2-prong power cord, and thus does not create a ground-loop with the amp by way of 3-prong cords on both devices. The Reissue Reverb Unit uses a ground-lift (CR5, CR6, R23) just ...

That amp never likely had a RF issue when it was new, but now it has old parts in it. This would lead me to think that it’s the tube socket for the EF86 making the issue . "RF Issue" is mostly about whether you're physically close to a "strong RF transmitter." Take an amp that works fine & put it n...

All jacks are isolated ... used a ground lift circuit ... You might try unbolting both jacks from the chassis, place something insulating (like cloth) between them & chassis, and re-conenct your input/output cabling for a test. It might be whatever insulation/isolation you tried using didn't actual...

... I've never seen the resistor power ratings noted like this on a schematic before. ... Pretend it's a Fender amp (and it very nearly is). Fender doesn't bother giving power-ratings on their 1950s and 1960s schematics. Assume every resistor is 1/2 watt, unless it's in the power supply. From there...

... Really really appreciate that and I have learnt a bunch here! The amp switches silently and as smooth as butter from parallel mode to cascade. ... Once you internalize the approach used, you'll be able to solve similar problems in the future (or avoid them entirely). For the next build if I wan...