Conflicting Silvertone 1482 Schematics & Cap Question

[Scaramoucheii]

Hi All

I'm nearing the end of my Hammond AO-29 to Vintage 6v6 guitar amp conversion, and have stumbled upon an question regarding the Silvertone 1482 Tremolo circuit.

Looking through all of the schematics on the el34world.com "Silvertone.pdf" (Link below) I see that the Capacitor parallel to the 68K 6AU6 plate resistor is .00068 (680pf) , and that the 1396 chassis omits a cap bypassing the 68K plate resistor entirely.

HOWEVER
One of the most prevalent schematics lurking the internet, on silvertoneworld.com no less, ( link below) has a .0068 uf cap parallel to the 68k plate resistor on the 6AU6

I haven't done the math yet, BUT. I'm thinking that the cap should be 680pf, if needed at all.

So what is the purpose of this cap, what is it's desired value, and is it needed at all?


LINKS
*******
https://el34world.com/charts/Schematics ... ertone.pdf

https://www.silvertoneworld.net/schemat ... e_1482.pdf

another, indeed also has it at 680pf

https://schematicheaven.net/bargainbin/ ... 82scan.pdf

[martin manning]

A cap paralleling a plate load is rolling off high frequencies. I have to believe it should be 680p, targeting >3.4 kHz, rather than 6800p which would be 340 Hz.

[nuke]

All three variations would likely work just fine.

The tremolo oscillator is a low-frequency oscillator and runs between 1.hz and 9hz in most cases. The roll-off cap helps to stabilize the oscillator.

I suspect it was 680 µµf, where in the old days, "micro-micro-farad" was commonly stated instead of "pico-farad".

Whoever re-drew it may have mistook one of the "u" symbols as a 0.

[Scaramoucheii]

A cap paralleling a plate load is rolling off high frequencies. I have to believe it should be 680p, targeting >3.4 kHz, rather than 6800p which would be 340 Hz.

Agreed, Was just wondering why I couldn't find anybody else on the internet commenting on the SilvertoneWorld,com schematic specifying .0068uf ? Seems all the Schematics that look like original scans specify 680pf

I don't have any 680pf in my stash so I think I'll use a 510pf giving a HF roll off at 4.59 Khz. But to be honest is this just a "oscillator" thing, this is just filtering the B+ node a little more

And while I'm here, has anybody used the Silvertone 6AU6 type tremolo with Fixed Bias 6V6's. I don't see referance to any examples on the web, Here is my current plan ...

vintage6V6_tremolo_fixedBias.png

[Scaramoucheii]

I did find an example of this 6AU6 type of tremolo on a fixed bias 6BQ5 PP amp

The Lectrolab R600C, the 6AU6 Tremolo does NOT have a bypass cap on the 150K Plate Resistor

The bias "mixer" is very interesting, a resistor bridge, Any comments on that arrangement?


https://lectrolab.wordpress.com/lectrol ... ousel-1713

https://lectrolab.wordpress.com/lectrolab-models/r600/

[martin manning]

The bias "mixer" is very interesting, a resistor bridge, Any comments on that arrangement?

That is part of the bias varying tremolo. Different from the way Fender did it, but if it's better or not I don't know.