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Best SE output transformer for 300B - shootout
Best SE output transformer for 300B - shootout
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Old 13th February 2018, 04:40 PM   #221
andyjevans is offline andyjevans  United Kingdom
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No cathode bypass caps with filament bias.
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Old 13th February 2018, 04:46 PM   #222
RajkoM is offline RajkoM  Bosnia and Herzegovina
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Quote:
Originally Posted by audiowize View Post
If you have a directly coupled series feed SET amp, you're going to have power supply caps and cathode bypass caps in the signal path.

and if you have fixed bias ... no cathode bypass cap.
and if you have psu with tube regulator instead of last capacitors .... no caps

come on guys .... we'll go to sky
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Old 13th February 2018, 04:46 PM   #223
audiowize is offline audiowize  United States
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If you want to use filament bias, then you're stuck using something like the 4P1L.

Fixed bias and direct coupling don't go together.
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Old 13th February 2018, 06:13 PM   #224
juanitox is offline juanitox  France
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Quote:
Originally Posted by RajkoM View Post
You wrote "James Transformers" twice.
Does this imply your favorite ??
for the price they are very very good ! my personnal favorite is Hashimoto and Monolith magnetics because i love their sound but they are expensive.

at the middle i will vote for lundahl if you can put them inside the chassis ( don't like their boxes)
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Old 13th February 2018, 06:37 PM   #225
RajkoM is offline RajkoM  Bosnia and Herzegovina
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Yes.
6123-HS does not produce anymore. Too bad.
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Old 13th February 2018, 08:38 PM   #226
Perfectusaudio is offline Perfectusaudio  Australia
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Default NP Acoustics Amorphous Transformers

NP2.5SE8F60 T from NP Acoustics look good value for money but the current price list is way out of date.
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Old 14th February 2018, 12:29 AM   #227
jpak is offline jpak  United States
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Thanks very much for all that great info in this thread, ah output transformers possibly the sexiest part for the DIY amplifier builder

I've heard the FirstWatt SIT-1 amp it still has me shaking my head how good it was and I've strongly considered one for my constant directivity midrange/treble K-402 horn, but then there is nothing that beats DIY and being able to tinker with things like OPTs.
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Old 14th February 2018, 01:09 AM   #228
Hanze Khronye is offline Hanze Khronye  Australia
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Quote:
Originally Posted by audiowize View Post
If you want to use filament bias, then you're stuck using something like the 4P1L.

Fixed bias and direct coupling don't go together.
Trivial Questionnaire;

a) Would you consider a filament biased filamentary triode tube as fixed bias, if CCS loaded and then at what percentage of Ip to If, and again if inductively or resistor loaded?

b) Would you consider a resistively plate loaded triode with cathode bias resistor as fixed bias?.

c) Would you consider a gyrator plate loaded triode with cathode bias resistor as fixed bias?.

d) Would you consider a CCS loaded triode tube with cathode bias resistor as fixed bias?.

Notably absent is any reference to stage which operates with a separate (actively powered) grid bias supply.

I can think of a three stage DC coupled amplifier which runs all three stages with fixed bias.

And if the goal of filament bias is to simply lower the impedance of the 'cathode' or filament return wrt signal common, so that a bypass capacitor is not required - you are not limited to using the tubes filament current to reducing the bias resistor value.

All of these seemingly definite comments provided by the quoted poster, define just one thing, and that has nothing to do with tube circuit design, application or function.


Hanze.

Last edited by Hanze Khronye; 14th February 2018 at 01:38 AM.
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Old 14th February 2018, 06:14 AM   #229
Perfectusaudio is offline Perfectusaudio  Australia
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Hi Hanze,
Thanks for the response
For all the DIY's it important they discover all the requirements for balancing a DC coupled Single Ended amplifier for themselves
Isamu Asano (1914-1981) the modern father of the rebirth of Single Ended Triode Amplifiers based this design enclosed on the old Loftin-White circuits of old, a good place to start
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Old 14th February 2018, 08:23 AM   #230
Hanze Khronye is offline Hanze Khronye  Australia
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?. My response was to 'audiowize'.

Care to comment on post #228?, or more interested in a re-hash of a 100 year old LW schematic??

Last edited by Hanze Khronye; 14th February 2018 at 08:28 AM.
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