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Old 13th September 2012, 08:55 AM   #1
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Default Just received 2x PT Choke OT. best implementation ?

I just received to mono blocks. Currently not well layed out, That's my opinion!! I have, to work with, 325-0-325 HT and I would like valve rectifiers tho Its not a big thing. The PT has massive and varied heater taps, 12.6@7.2 amps is one! Planning on regulated HT and LT supplies.
The OT has Ultralinear input taps and by my best reckoning has 4k and 8k into 8ohms out. I am driving Alpair 7's
Not sure of the choke,s. Bit hard to quantify I find. Guess they are not really needed in a regulated Ht, but they look good. And Morgan Jones uses them
I am leaning towards EL34/KT77 as I have them and they are not stupid as far as $ goes.
I need a schematic that will sound good! I have seen the "odd watt " class A push pull, but have doubts about the CCS.
Hoping that someone can throw me a bone, been there before, offer some help.
Hopefully you can see what I have, maybe suggest what to build?
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Old 15th September 2012, 12:24 PM   #2
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a speaker that has a impedance curve 36ohm at 80-90hz for a tube amp?
i thought tubes liked even impedance curves.
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Old 16th September 2012, 10:17 AM   #3
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Isnt that what corners are for?
Please, what about 4 el84's. into 4k. And a concertina phase splitter.
This must be a dull question
I just am not confident figuring the format and values.
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Old 16th September 2012, 12:40 PM   #4
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This is the topology I would personally recommend as having the best possible sound quality as far as PP is concerned.

You don't quote the B+ current capability of your PT, but assuming it's sufficient, if you do bridge rectification followed with CRC and a solid state regulator, you could have pretty much any of the common tubes as output.

If that's too much B+ to handle (and it is, if you haven't done high voltage before), then there are still a lot of options for this topology. 71A only needs 180 volts on plate, so about 330V B+ is sufficient. For cheaper but still first class options, the 33 triode strapped or 31 also work with just 180 volts on plate.

There are of course a lot of very very economical russian tube possibilities for both high and lower B+. 6C45P for example would give for most people quite enough volume in PP, and would work well with a B+ of around 300 volts.

Operating point is determined by applying a reference voltage on the junction of R4 and R7, which adjusts the plate voltages of the tubes. Current is adjusted by R1 (which should be a potentiometer).

C3 should be chosen really carefully; it can have a big effect on fidelity. L1 is the OT primary; configure the OT to have about 2x the impedance of the plate resistance of the tubes. (However I recommend at least 5k impedance for primary.)
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Last edited by MrCurwen; 16th September 2012 at 12:42 PM. Reason: Small addition.
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