The Amp Garage

Our book 'Guitar Amplifier Overdrive' does go into a lot of stuff that is relevant to this, in particular bias-shift that occurs during overdrive conditions. Generally, we tried to avoid subjective assessments (one persons 'nice' distortion is another person's 'horrible') and stick to looking at wha...

I don't think there is a need for a diode. Reservoir needs to be big enough for both amps (add the uF usually used for the SE to that for the PP). If you are thinking of tube rectification - watch out not to exceed the maximum capacitive load of the rectifier tube.

Did you remember to wire up the input jack so that it shorts out the 1M when nothing is plugged in?

It would be safe enough, but would only light up very dim.

Could be unbalance between the power tubes. Check DC voltages on screens of the power tubes - the voltages should be similar. Also check DC volts on their plates. Same with the cathodes and grids. If that all checks out, it could be the two power tubes you have are badly matched. Push-pull amps rely...

Try a 1meg grid stopper, between pin1 of V2A and the junction point of the 0.02 cap
and the existing 1meg (i.e. on the grid pin of V2A in place of the existing direct connection back to
that junction point).

Merlin shows that when a cathodyne PI is trying to overdrive the output stage, you can get a spike on the voltage waveform of the
cathodyne's anode output:

http://www.valvewizard.co.uk/cathodyne.html

Maybe that is what is happening here?

roberto wrote: ↑Mon Dec 31, 2018 6:18 pm Thanks for the prompt reply and happy new year.
...
Anyway it's an interesting approach also to modify the Marshall 6100. Do you think that was the original purpose, or just casuality?

Happy New Year.
Did you mean 'coincidence' rather than 'casuality'?

Forwarded from Ulrich: >The samples posted on the site are all very low gain, something like an high volume small Fender clean can do. >Have you tried this on high gain amps (imagine a Soldano SLO100 lead channel), trying to avoid the CF/SF to overdrive instead of the downstream stage? Yes - there a...

Ulrich's website:
https://sites.google.com/site/stringsan ... -overdrive
includes a free supplement to the book, as well as other interesting material.

Thanks very much for the comments. Constructive criticism is appreciated, I'm a great fan of Merlin's books myself.
There's nothing new in the pipeline at present.

Ulrich Neumann is an academic computer scientist and has also co-authored books in that field, but nothing in German. I'm a retired academic electrical power systems engineer. Tube guitar amps are a hobby for both of us. Thanks for the kind comments on the book - there is nothing there that we would...

"A positive voltage on the tube's control grid pulls electrons off the grid and spreads them out. A negative voltage on the grid pushes electrons onto the grid and packs them tighter together. " Is that from this book? :) At least it's a "different" description of how a triode works compared to boo...

That's an interesting concept. I've not tried it, or even thought of it before. It will change the asymmetry between the +ve going part of the waveform and the -ve going part. That means it increases (or may even decrease) the level of the even-order harmonics. The effect would be greater for high f...

Two 100k resistors in parallel produce the same Johnson noise as a single 50k resistor (assuming all these resistors are at the same temperature).