Parallel feed OT

[Bas Horneman]

Hi All,
I am considering building something like Kandaudio's SE parafeed preamp. But don't want to order the Lundahl, because I want to see if my tranny builder can build me something like that.

So what do I have to ask for.. in the case of say a 6n1p tube..paralleled both sections Ra of 2200ohm..so do I ask for a 7k SE transformer that does not have to pass a single mA of DC?

Regards,
Bas

[dhaen]

Hi Bas,

I believe that you are right with the transformer impedance and current specification.
The trouble will come in the way you supply DC to the anodes.
Are you going to use a choke? If so, then you must consider the choke's self capacitance and the transformer's self capacitance to be in parallel.

Cheers,

[Bas Horneman]

Hi John,

I was thinking of using a CCS? (depletion mode MOSFET)

Does that make it easier? I suppose it.... does because a CCS has negligible capacitance compared to a choke...right?

Cheers,
Bas

[dhaen]

Hi Bas,

That sounds a nice idea. Capacitance is much less of a problem.
Can you get high voltage depletion mode fet's? I'm well out of touch
Great for self biasing - just like valves..

Cheers,

[316a]

Hi Bas ,
CCS loading , to me means low Ra valves , run at high current , low anode volts . I find that CCS loading usually means ridiculous heat , my own MTP2P50E based mosfet sink ran at 70mA and got REALLY hot , and that was with a massive heatsink , and not really dissipating as much as it should (I kept the B+ within safe limits) . Why not try something like stacked 6C41c in an SRPP / SEPP arrangement with fixed bias to the lower valve ? It would be cheap to build , only the power supply needs to have higher HT than with choke loading (400V+) . My usual advice regarding parafeed prototypes and toroids as output transformers applies , could make a nice , cheap project .

316a

[316a]

Sorry , you were mentioning pre-amps , my post was regarding power amps . Running a CCS load on a 6N1P should be a doddle , compared to what I went through developing my power CCsource !

316a

[Bas Horneman]

Hi John,

I've never been in touch...but that is an entire different matter..

Yep K&K audio sells little kits..ha..ha if you can call it a kit!

3 parts...mosfet, pot, pcb..

It uses the DN2540N5 (400V)

HTTP://www.supertex.com/pdf/datasheets/DN2540.pdf

Cheers,
Bas

[Bas Horneman]

Why not try something like stacked 6C41c in an SRPP / SEPP arrangement with fixed bias to the lower valve ?

Might very well still try that...I still have the little toroids lying about idly after the 6c45pi spud thing failed..

mmm, come to think of it..I have seen 6c33 preamps..maybe a 6c41c preamp is not even such a bad idea? Nah, 6s19 is wild enough..

Cheers,
Bas

[dhaen]

Hi Bas,

Nice FET
Almost as good as a valve

Cheers,

[Bas Horneman]

How can you tell it is a nice piece of sand?

I just took Kevin's word for it.

Cheers,
Bas