Tube Amp Forum: The Ultimate Tone

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I recently built this amp - it's claimed to have about .5W sine output and I'm guessing maybe a watt at full output. 

I was looking at the Super Scaler project in TUT 5 and though that would be a cool next project.

From the TUT5 text I think it has a gain of 3 to 6? Boosts a 20W amp to 60W?

I'd like to scale my .5W amp up to say 30W, so I'd need a gain of more like 60. Can I get there by changing the input and output transformer impedence ratios?



Respectfully,

Steve

Hi Steve

If you read the Super Scaler chapters carefully, you see that each design has a fixed power gain. The simplest and least expensive form has a gain of about six. If you only have half a watt to put in then you'll only get about 3W out.

The input transformer ratio needs to be about the same as that oif an OT since the screen voltage swing is from zero to B+. A higher ratio does not change the power gain; rather, only the voltage gain. If you want 60W out of the simple Super Scaler 6W of input power is needed regardless of the V<>I ratio.

The 811A / 572B circuit has a much higher power gain, about 60x , and can be configured for lower output than 300W. The half-watt amp could drive this type of Super Scaler to 30W of output.

You can always cascade two Super Scalers but it is rather a lot of transformers, although the first one between the tone amp and large Super Scaler would be only 5-10W max.

An alternative is to use the simple Super Scaler circuit but use more sensitive tubes, like a sweep tube with a typical screen voltage requirement of around 140V. The voltage gain increases by about three times, but you would have to check the tube curves to see if the screen power is reduced as well. For example, the 6KG6 has a plate to screen current ratio of about 30x.

Have fun