Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on February 07, 2026, 10:20:59 am

Title: How to convert Tone Control values from Solid-State circuit to Tube circuit?
Post by: kagliostro on February 07, 2026, 10:20:59 am

Assuming we have the values of a tone control circuit used in a solid-state amplifier (BlackStar HT5)

which is the math to calculate the correct values for a vacuum tube amp (say a Marshall 36W TMB or similar)?

(Math and I don’t exactly shake hands, especially when it comes to tone control calculations.)

(https://i.imgur.com/XQqaWnK.jpeg)

(https://i.imgur.com/aEWBhXp.jpeg)



https://mhuss.com/18watt/schematics/36wTMB.pdf (https://mhuss.com/18watt/schematics/36wTMB.pdf)

THANKS

Franco

Title: Re: How to convert Tone Control values from Solid-State circuit to Tube circuit?
Post by: pdf64 on February 07, 2026, 02:35:24 pm

https://www.aikenamps.com/index.php/tone-control-scaling

Title: Re: How to convert Tone Control values from Solid-State circuit to Tube circuit?
Post by: tubeswell on February 07, 2026, 05:42:46 pm

^What pdf64 said.^


Tube amplification = primarily voltage amplification so it favours higher resistances between the signal source and the signal sink (1M is 'better' than 10k etc) although resistor noise will always become an irritating factor the higher you make the resistances (so 250k is 'better' than 1M LoL). But for every resistor that you scale-up in your tube amp circuit, the capacitances in the circuit should be scaled down by the same factor in order to achieve the same frequency rolloff/bandwidth etc that the transistor amp was designed for (because f = 1/(2pi.R.C) )

Title: Re: How to convert Tone Control values from Solid-State circuit to Tube circuit?
Post by: kagliostro on February 08, 2026, 04:53:13 am

Many THANKS Pdf64 & Tubeswell

The link seems to cover all the matter, I'll try to study the content (I hope)

Franco