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Old 20th May 2004, 05:09 AM   #1
judo is offline judo  Hungary
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Default Borbely hybrid phono

Hi Everybody,

I have ben reading the forum for a time but this my first post. I' d like to build the upper mentioned mc/mm preamp
http://www.borbelyaudio.com/phono.pdf
but not from the kit because it is too expensive. The most important parts are collected except the caps (some hints for good and CHEAP polypropilen caps ?) My problem is there is'nt anything about the filament supply in the document except it is a "slow turn on dual floating filament supply" I am thinking about stg like two independent (one tranny two secunder coil) common lm317 supply for the two channels. Is this enough for an mc preamp and what about "slow turn on" and "floating" I want min 1 A per channel because would like to try out 6N1p-s in the first positions. Now I have Tungsram E88CC-s and Sovtek 12AX7LPS -s, I know the 6H23P would be the lest noisy - perhaps later.
Any help greatly appreciated.
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Old 20th May 2004, 02:07 PM   #2
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Hi,

Quote:
My problem is there is'nt anything about the filament supply in the document except it is a "slow turn on dual floating filament supply"
Well there doesn't have to be much as the heater supply is resistively derived from the 260V B+ and left floating.
As the B+ has a slow turn-on feature, so will the heaters.

For cheap polyprops check RS Components some of them are downright excellent; ICEL and Arcotronics for instance.

No need to bother with the 6N1-P, it just hasn't the transconductance of a true ECC88.
The Reflektor 6N23-Ps are fine and are true ECC88s, select them for gain and noise.

Cheers,
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Old 20th May 2004, 02:19 PM   #3
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The current production JJ E88CC is a DECENT affordable tube. The Slovak and Russian tubes are the practical choices. Sadly, EI (Serbia) has had major quality control problems of late.
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Old 20th May 2004, 04:08 PM   #4
judo is offline judo  Hungary
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Thanks for the answers.

Eli, I can get affordable JJ-s here and it is sure I will try them out.

fdegrove, could you please tell me this a bit more particularly ? I am rather a builder then a designer and far not a tube guru. I was told for an mc phono a separate regulated heater supply per channel is obligatory.

Cheers, judo
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Old 20th May 2004, 07:50 PM   #5
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Energizing tube heaters with DC is mandatory in a phono stage. Unless the heater supply is being used to energize SS devices too, I don't see a need for separate supplies in each channel.
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