Another Varmint Question on "SuperMod"

[Lazybones1222]

Varmints have two toggles that are power related.

One is three way high/off/low

The other is high/SuperMod

My question concerns the latter. The Supermod switch when enacted lowers the deadkey watts and slighly rises PEP, but actually reduces the amperage output at the meter on the amp itself. How does this work? How can PEP rise and amperage draw on the amplifier's meter decrease?


Amp's schematic link is pasted below. You will find the Supermod/high switch in the lower right hand corner of the schematic.

Click for schematic

Click thumbnail for big pic.

 

[paws264]

"Duty Cycle", the tubes do not have to work as hard therefore, it has more "instantaneous" power (pep).

When S-3 is open ("Super-Mod" active) the -30.0 vdc is applied to the control grid of the tube (making it conduct less), this gives lower DK, higher "Mod" and, lower static current.

When S-3 is closed, ("High side") the -30.0 vdc is shunted to ground thru R-14, a "self-bias" voltage is established from the voltage drop across R-15 (75 - 150 ohms?). This "self-bias" is considerably less than -30.0 vdc so you get higher DK, and higher static current 'cause the tube is conducting more.

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[Lazybones1222]

Thanks for the answer Paws. That makes sense. So which (High or SuperMod) should sound better on AM? On SSB?

Does the SuperMod run cooler extending tube life? I guess what I just don't get is what is the purpose or advantage of SuperMod?

 

[paws264]

Generally speaking, "Super Mod" is easier on the tubes than "High" however, I am not sure that a measurable extension of tube life would be noticed unless you conducted a scientific experiment where 2 identical amps with new tubes were run under the different conditions and then the tubes evaluated.

Generally speaking, when you use "Super Mod" the tube is biased more towards cut-off (class "C") so, it is better to run AM with the "Super Mod" on while, it is better to use "High" for SSB.

The advantage, you sound louder for the same amount of watts on AM, the disadvantage is that for SSB and FM it either holds you back or screws up your signal quality.

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[Lazybones1222]

Thanks for putting the cookies on the bottom shelf. Got milk?