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previous: Wild Bill Tested an old OT the other day - he... -- 5/3/2000 3:37 AM

Re: Blue Sky thoughts - 6 x 6v6?

5/3/2000 10:52 PM
MBSetzer	Re: Blue Sky thoughts - 6 x 6v6? Just got the latest issue of Glass Audio, the feature article is by Joseph Norwood Still about a hifi amp using 6 of the Svetlana 6550's that has some ideas that might apply to sextets of smaller tubes as well. After the coupling caps from the PI, bias is injected from a supply having less than about 100K of impedance per grid. There are also a pair of 470K, one to ground on either side of the balance pot, resulting in about 250K effectively to ground from each grid. The stabilizing effect of both of these sinks is in parallel so the result is equal to (probably better than) using less than 100K bias resistors to each grid, in place of the usual 220K in many guitar amps. Then the signal goes through 2K7ohm 1W resistors to each grid of the first pair of power tubes, then has 330ohm 1W isolating them from the grids of the second pair. The third pair is connected only to the second pair through more 330R 1W's as well. The final pair has an additional 1M added to ground from each grid. On the plates of the power tubes he used a 50R 4W between each one & the OPT (isolates them from each other, this will waste power to an extent), he was also running in triode mode with no separate screen supply, instead there is just a 220R 2W between the plate & screen of each power tube. If you are going to use regular pentode mode, I would put at least 220ohms on the screen tab of each socket to isolate them from each other, before joining them and adding another screen resistor (1K? Wattage?) between them and your screen supply. That's probably all the applicable highlights, but it still is an interesting article. Hope this helps, Mike

5/3/2000 10:52 PM

MBSetzer

Re: Blue Sky thoughts - 6 x 6v6?

Just got the latest issue of Glass Audio, the feature article is by Joseph Norwood Still about a hifi amp using 6 of the Svetlana 6550's that has some ideas that might apply to sextets of smaller tubes as well.

After the coupling caps from the PI, bias is injected from a supply having less than about 100K of impedance per grid. There are also a pair of 470K, one to ground on either side of the balance pot, resulting in about 250K effectively to ground from each grid. The stabilizing effect of both of these *sinks* is in parallel so the result is equal to (probably better than) using less than 100K bias resistors to each grid, in place of the usual 220K in many guitar amps. Then the signal goes through 2K7ohm 1W resistors to each grid of the first pair of power tubes, then has 330ohm 1W isolating them from the grids of the second pair. The third pair is connected only to the second pair through more 330R 1W's as well. The final pair has an additional 1M added to ground from each grid.

On the plates of the power tubes he used a 50R 4W between each one & the OPT (isolates them from each other, this will waste power to an extent), he was also running in triode mode with no separate screen supply, instead there is just a 220R 2W between the plate & screen of each power tube.

If you are going to use regular pentode mode, I would put at least 220ohms on the screen tab of each socket to isolate them from each other, before joining them and adding another screen resistor (1K? Wattage?) between them and your screen supply.

That's probably all the applicable highlights, but it still is an interesting article.

Hope this helps,
Mike

Replies:

Wild Bill All good thoughts and much apprecia... -- 5/4/2000 3:27 AM