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Old 26th June 2012, 11:12 AM   #31
AJT is offline AJT  Philippines
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^hi,

the schematic was adopted from carver's silver seven power amps.....12by7 input, 12bh7 ltp drivers....the kt88's are trioded with a 100ohm/5watt resistor...no global negative feedback used....
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Old 27th June 2012, 03:28 AM   #32
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Hi 22,

A few things to consider off the top of my head.

1) SET with parallel tubes offers Miller capacitance times number of tubes in parallel in SE operation. UL operation offers higher power output than triode and less Miller capacitance. In either case the high frequency response will be reduced, so a fairly low impedance driver is necessary.

2) SET with parallel tubes means more problems with OPT being satuated unless parafeed is used.

3) In PP, the phase splitter is very critical to optimum performance, and difficult to obtain.

4) In PP operation, the same problems exist with Miller capacitance in triode and UL operation as point 1.

5) Grid "stoppers" and screen or plate "stoppers" are very necessary for parallel operation of tubes, as parasitic oscillations will otherwise occur.

Cheers.

Last edited by Positron; 27th June 2012 at 03:31 AM.
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Old 3rd July 2012, 01:25 PM   #33
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Quote:
Originally Posted by Positron View Post
Hi 22,

A few things to consider off the top of my head.

1) SET with parallel tubes offers Miller capacitance times number of tubes in parallel in SE operation. UL operation offers higher power output than triode and less Miller capacitance. In either case the high frequency response will be reduced, so a fairly low impedance driver is necessary.

2) SET with parallel tubes means more problems with OPT being satuated unless parafeed is used.

3) In PP, the phase splitter is very critical to optimum performance, and difficult to obtain.

4) In PP operation, the same problems exist with Miller capacitance in triode and UL operation as point 1.

5) Grid "stoppers" and screen or plate "stoppers" are very necessary for parallel operation of tubes, as parasitic oscillations will otherwise occur.

Cheers.
Thanks for your input. I am still studying possible designs, pros and cons.

1) It will be a PP design, maybe UL topology.

2) Same, will be PP.

3)I am not sure to use a tube splitter, what would be the downside of using an input transformer for creating phase and anti-phase? I have had great results using it to bridge SS amplifiers, and it is easier to wire and has 0 watts of pwr consumption:
http://www.lundahl.se/pdfs/datash/1545a.pdf

4) I will be using PP with 2x or 4x tubes per channel, so there's a chance i'll be paralleling tubes. I am still looking for candidate circuits.

5) A very important point to care for, thanks!


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