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

[David Moylan]

Don't forget the 'harmonic tremelo' found in many brown Fender amps.  It 
splits the signal into two frequency bands and modulates them out of 
phase.  Gives a nice subtle phasing effect and sounds much more 
interesting to my ears than a standard trem.  The modulation is 
accomplished by varying the bias on the grids, but since the two control 
signals are out of phase and end up mixed the CVs cancel (in theory; 
tubes aren't usually very well balanced).



Bob Weigel wrote:
> 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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