UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Convert Vintage Valve Radio to Guitar Amp

robbo100 · 13th Aug 2019, 4:35 pm

Hi all,

Thanks so much for the technical information and I have really enjoyed the discussion that has gone along with it.

The characteristics of a great guitar amp are not the same as a great hifi amp (or similar). In the guitar world the valve amp is highly sought after because the characteristics of the valves, when driven hard, create a beautiful rich breakup, which can't easily be reproduced by solid state systems. This is the experiment I want to try with the vintage valve radio.

My son, although very young, isn't a beginner, he is around the grade 7 level, so we are looking for some fun tones to play around with. Kinda like when guitarists used to cut slashes in their speakers to make a dirty fuzz sound. I am calling it a "practice amp" because it will be a valve amp, which is quiet enough for him to play in the house without annoying the whole street, whilst still driving the valves into a bit breakup. He already has a 100W solid state Marshall amp, but like most solid state amps, it sounds a bit like a wasp in a jar and doesn't have a lot of character.

In terms of the speaker driver, I plan to buy something like this: https://www.gear4music.com/Guitar-an...m-Speaker/2JPG. But I will hold-off getting it until I have proven the amp section of the radio is working.

I shall keep you all updated with progress, but in the meantime, please keep the discussion and tips coming.

@ms660

In terms of replacing C19 - I presume something like this would be suitable (400V DC rated 0.1 uf/100nf).

Interestingly, R15 doesn't show on one of the versions of the schematic I have found, and it is listed as R13. But it looks like 270 ohm 1W. When you say "a suitably rated capacitor" - what would you advise. I have looked at some calculators, but am a little confused (including what voltage rating it should be).

Finally, in the event that I do create a buffer circuit to increase the input impedance, I was thinking of powering it using the lamp circuit, which is 6.5V. I need to see if I can find a suitable opamp that will work at this power (possibly the LM741?). Does this seem a sensible approach?

13th Aug 2019, 4:35 pm	#26
robbo100 Retired Dormant Member Join Date: Aug 2019 Location: Cambridge, Cambridgeshire, UK. Posts: 21	Hi all, Thanks so much for the technical information and I have really enjoyed the discussion that has gone along with it. The characteristics of a great guitar amp are not the same as a great hifi amp (or similar). In the guitar world the valve amp is highly sought after because the characteristics of the valves, when driven hard, create a beautiful rich breakup, which can't easily be reproduced by solid state systems. This is the experiment I want to try with the vintage valve radio. My son, although very young, isn't a beginner, he is around the grade 7 level, so we are looking for some fun tones to play around with. Kinda like when guitarists used to cut slashes in their speakers to make a dirty fuzz sound. I am calling it a "practice amp" because it will be a valve amp, which is quiet enough for him to play in the house without annoying the whole street, whilst still driving the valves into a bit breakup. He already has a 100W solid state Marshall amp, but like most solid state amps, it sounds a bit like a wasp in a jar and doesn't have a lot of character. In terms of the speaker driver, I plan to buy something like this: https://www.gear4music.com/Guitar-an...m-Speaker/2JPG. But I will hold-off getting it until I have proven the amp section of the radio is working. I shall keep you all updated with progress, but in the meantime, please keep the discussion and tips coming. @ms660 In terms of replacing C19 - I presume something like this would be suitable (400V DC rated 0.1 uf/100nf). Interestingly, R15 doesn't show on one of the versions of the schematic I have found, and it is listed as R13. But it looks like 270 ohm 1W. When you say "a suitably rated capacitor" - what would you advise. I have looked at some calculators, but am a little confused (including what voltage rating it should be). Finally, in the event that I do create a buffer circuit to increase the input impedance, I was thinking of powering it using the lamp circuit, which is 6.5V. I need to see if I can find a suitable opamp that will work at this power (possibly the LM741?). Does this seem a sensible approach?