[sdiy] Varistors in tremolo circuits: worth it? Merits of various tremolo methods?

[Bob Weigel]

It's not a tremolo.  It's vibrato.  That's what made the magnatone 
special.   It is a cool circuit for sure.  Had to troubleshoot one long 
ago. Was a pain. -Bob

anthony wrote:

> I have a nice stash of many varistors that I've collected from 
> countless old power supplies & surge protectors & such.
>
> I noticed that Magnatone used varistors in at least one of their amps 
> - I think it was for the tremolo circuit. How does the sound quality 
> compare to other tremolo circuits? Is it worth the hassle of figuring 
> out what the specs of each of my varistors is and trying it out? I 
> have quite a few SNR130K20's.
>
> This made me wonder about a comparison of all of the methods used for 
> tremolo circuits in tube amps: how do they compare? Which is better? 
> Or is it more of a Beethoven vs. Bach comparison?
>
> I notice that most amps that have tremolo are push-pull amps and the 
> LFO modulates the bias on the power tubes.
>
> Single-ended amps with tremolo do it by varying the cathode bias of 
> the last gain stage before the power tube.
>
> There is definitely room for a big difference in the way the tremolo 
> could sound between these methods.
>
> And then there is the lamp/LDR method that seems to be a lot less 
> common in tube amps, although many great tremolos have been made based 
> on LDR's. I think both neon and incandescent lamps have been used. I 
> would guess that neon would yield a nice and choppy tremolo, but 
> wouldn't be reliable over time. Same with the incandescent lamp really.
>
> And THEN I started thinking about tube amps with tremolo AND reverb 
> and how the reverb sound is modulated along with the dry signal just 
> the same, but I would think that it would be better to have the 
> tremolo bang on the reverb. My studies of Hammond Organ schematics 
> have revealed their clever way of doing this: they just take the 
> output from the main amp, use a light bulb to reduce the volume and 
> drive the reverb tank straight from that - no reverb transformer. The 
> reverb output goes to a separate amp and maybe even its own speaker. 
> But it made me think you could make a groovy little(ish) 2x10 combo 
> amp with a tremolo/dry sound in one speaker and another amp with the 
> reverb sound, taken from the secondary output of the 1st amp's output 
> transformer straight into the reverb tank (with attenuation of 
> course). You could probably do it with one speaker by mixing the 
> reverb back into the power tube.
>
> Lastly, I want to make a dual clone of a Gibson GA-5T Crestline (have 
> the 6AQ5A's and the 6X4's...). I want to make the tremolo(s) work 
> independent, in unison (just one LFO) and then panning. One thing I 
> don't think I've seen a schematic for is a tube circuit that shifts 
> the phase of an LFO signal 180 degrees. Pretty much the same way you'd 
> do it with solid state parts?
>
> SpongeBob SquarePants,
> Anthony
>
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