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Old 1st April 2004, 02:50 AM   #1
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Default output txfr on cathode?

I am thinking of doing an amp with the opt on the cathode of the output tube.

has anyone else tried this, what adv or disadv are there?

looking for 30-50W output power, triode or pentode, SE or PP.

So pretty open.

So far, tried tubes such as EL34, 6550, and 6B4G.

Thanks for any ideas.
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Old 1st April 2004, 03:23 AM   #2
DougL is offline DougL  United States
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Tube Cad Push-pull Calculator has a "Cathode follower transformer tab.

From the comments in the calculator i paraphrased: It requires much higher drive voltages because the tubes in cathode follower provide current but not voltage gain.

Let us know how you like it.

Doug
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Old 1st April 2004, 03:28 AM   #3
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Default hmmm....

yeah I understand about the voltage gain thing. oh well...
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Old 1st April 2004, 10:28 AM   #4
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I think this topology, SE or PP, is very adisable if
one want a tube amp with very small
output resistance ( high damping factor)
Very intriguing.

Yes, practically it needs a very great swing on grid. Maybe
the use of the same type of tube as driver.

A compromise, as for me, is the circlotron topology.
(I am thinking push-pull)
It can be implemented without the double floating
supply by using, instead a couple of identical trafo:
one at the cathode and one at the plate.

Federico
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Old 1st April 2004, 11:11 AM   #5
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Quote:
Originally posted by fscarpa58
A compromise, as for me, is the circlotron topology.
(I am thinking push-pull)
It can be implemented without the double floating
supply by using, instead a couple of identical trafo:
one at the cathode and one at the plate.

Federico
If you do try it that way (they named it after me, did you know? ) cross-connect a pair of 1uF or larger capacitors from each anode to the opposite tube cathode. Mighty good setup.
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Old 1st April 2004, 03:37 PM   #6
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You'll get a much easier job if you do, say, acoustic CFB, maybe 20% worth, plus a loop or two of NFB. This uses a pentode output with screen to +V, plate to 80% of the OPT primary and cathode to 20%. (If the screen were on 20% of the primary, it would be ordinary CFB. This way however, the CFB winding modulates the screen voltage producing an UL effect.)

Yes, followers are okay for transistors which have a set input>output offset (.5 to 1V at worst) but no good for tubes with high signal voltages and terrible turn-on/turn-off characteristics.

Tim
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