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Thoughts on bias for PPP

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Joined 2010
OK,

so what thoughts do you have on bias for PPP..Maybe KT66..X8 4 per side.

Fixed bias...auto bias with common cathode on each side..Fet/zener..in cathode..(mosfet amplified zener)..100 Watt fixed<<ideas on power out with standard auto bias<<<cathode resistor /cap bypass..

Drive via Citation 5 type first section (12BY7 front end and 6CG7)

heater control power off half of O/P tubes with auto out tap change..

Modern Carbon Volume control? as opposed to conductive plastic..variable feedback..triode/pentode switching or UL..

Or any ideas on sound..<<might seem like a stupid question..but I don't think it is if someone has experience with these topologies.

The idea is prompted by the manley stingray chassis (shape)<<its just a possible maybe..but with toroids under the chassis.

Regards
M. Gregg
 
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Can you reach the target tube and bias voltage with enough headroom not to need very expensive caps in the PSU ?

If the answer is yes autobias works.

Pure fixed needs attention so some kind of mix with resitors to give the tubes some room to drift perhaps.

8 individual bias pots is to much fiddleing for my taste.

Bias servo is another aproach.
 
Disabled Account
Joined 2010
Yes,

I was also thinking about mixed bias...I like the sound used in the OTL so this is a possible maybe..

Any ideas regards the power down of half the tubes using heater power off? do you think the cathode may need isolating or will I get away with it?

The idea is the same as before reduced power consumption and flexibility..triode/pentode/UL

Regards
M. Gregg
 
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The heaters in theese type of tubes isn´t the big kind of current hoggers as 6c33c so not a serious power saver ;).

So the need for a halfcircuit switch is more work then you get back....

A triode/UL/pentode switch isn´t just a switch....you need different loading and feedback to get the best out of every topology.

But you should be able to get enough power whichever you choose.
 
Disabled Account
Joined 2010
Yes the power save is about 32 Watt..+ bias..
Perhaps the work is better done in the bias

The feed back would have to be variable..:D
The triode/pentode/UL is a nice option to have..its worked well before.

More time for deep thought..:)

Regards
M. Gregg
 
Disabled Account
Joined 2010
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