Wild Gear Hearder
Gold Supporting Member
Indeed. I think Gary Croteau (Juke Amps) pointed that out to me a couple years ago. I believe he's separated them out in the AM / FM circuit he's developed for his amps.
ya that's modulating the bias of the gain stage.Okay, may as well get into this too. Here's the schematic for the Dearmond-Rowe Martin 112T amp. There's another varistor used in the tremolo circuit here. This circuit looks a bit closer to some used in some Fenders?
Is the varistor here involved in changing the bias on the 2nd triode in that 12AX7?
The Globars made by Carborundum in the 50's and 60"s numbers aren't listed on the data sheets which I got back in the 90's. I know it's a disc style but their is no cross reference info concerning the part numbers used by the manufacturer and the numbers used by the electronic companies that purchased them including Workman. If I had one I could put it in the calibration circuit and determine it's characteristics and then it's a matter of finding and calibrating available nos disc in hopes of finding a match. 20 years ago it wouldn't have been difficult but today it would be a long shot.It's identified as a Globar 331-BNR-7, but of course I can find nothing indicating the value of a varistor labeled that way.
I can see the varistor is in a different place in the trem circuit in the Martin 112T, but do you think it might be fulfilling a similar role of minimizing of LFO going through the main amp?trobbins said:I'm also suspecting that the combination of LFO drive to the varistor and to the point A (HT to the 12AX7), would have somewhat nulled the LFO signal level, but retained the audio signal modulation via the varying varistor value. This would have minimised the typical issues with LFO signal going through the main amp and speaker.