Tube Amp Archive

I've implemented this as well (though sans diode as I use a full bridge rectifier) and I opted for a higher resistor so that you don't get signal bleed-through (a-la Fortin Sigil standby farting drama) - through trials, I settled on 220K to achieve full muting in my circuit. Merlin discusses this he...

I think you could use any of the Splawn schematics to get an idea.

Version two of "final" schematic added to first post. Several tweaks added to design and implemented on the physical amp that have greatly improved stability, significantly tightened the bass response, and increased gain/saturation while still retaining articulation and roll-off control. I have also...

Good input! Yes, this is part of a Mesa DR pre-amp. I figured the high R value was directly in response to the previous bright caps (0.001/0.002u) which will, in a high gain circuit, introduce a lot of hiss (which I believe tends to be in the 12-20 kHz range) and setting up the next stage to not be ...

In this schematic (highlighted green), do we think there is a practical reason for R=470k, C=20p vs. R=20k, C=470p (both equal fc=16.9 kHz)? Or is it just the components values they likely had most readily available/on-hand?

Though, you said you figured it out, seems you may not understand why? To be sure, you "can" place all of your .lib/.inc files anywhere you want...as long as that path is referenced in LTS library search path in the control panel. The default path (on Windows) is $env:userprofile\Documents\LTspiceXV...

You'd likely need bigger (than 25w) resistors for the Robinette solution... For sure, you will have to determine the right balance of attenuation and heat dissipation. The better passive reactive loads, I believe, leverage multiple "Arcol" style resistors and inductors. Though, I think the OP was l...

hebaton wrote: ↑Sat Apr 09, 2022 11:29 am To reduce power and output.

How about this: https://robrobinette.com/Generic_Tube_A ... wer_Switch

Thanks; yep, that's pretty much what I've come up with (slightly different connections, same result). My adding a resistor from grid to ground, I guess, is not necessary.

Thanks, pdf64/sluckey

My thinking on the 2M grid resistor is that I didn't want the grid to have a path to ground until I wanted it out of the circuit - though, since the resistor is so large, I probably could leave it connected with negligible effect on tone. As for the switch, that's not something (that I've found) eas...

Thanks, pdf64, for the input. I've arrived at this, which loosely follows what happens in the Hi/Low input part of the circuit that also "drops" a triode: Grid to ground (via resistor), "output" to ground (after coupling). DC is retained and I think it should be silent switching. I'll admit the 2M r...

Hi, I'm hoping to get some guidance on switching in/out a triode gain stage. When switched out of the circuit, is it desirable to retain the plate and cathode voltage and merely "cut" the signal or is there some benefit to tube life if I dump the voltage to ground? Attached are snippets of three dif...

Final schematic updated (final values and corrections as pointed out) in OP. It's been a very interesting exercise to undertake. Though I still need to implement the switching scheme so I can revert to (near as the SF will there be there) stock, I've learned a lot with satisfying results. Cheers, all

All has gone swimmingly. I revised the design a bit as I was not happy with the (simulated) waveform. I then remembered (i.e. stumbled upon it in reviewing my notes) another article I read discussing SF wave shape solutions. Sticking with the LND150 (enhancement fets won't work with this design), it...

dcribbs1412 wrote: ↑Wed Dec 29, 2021 8:54 pm ...What's the Neon bulb on V2 for?
Like Diode clipping?

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