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Old 26th June 2006, 09:01 AM   #1
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Default 6BY5 High Voltage & High Current Choke Input Design P.S.

I want to design a 650 volt and 250ma B+ (preferably choke input design) using two 6BY5 for my single-ended power amplifier. Please see the attached diagram for the proposed design.

The dual-plated 6BY5 can supply max. 175ma per plate. I have parallelled the plates of one 6BY5 to give a max. of 325ma, and use two such tubes as a full-wave rectification.

The max. heater-cathode voltages of 6BY5 are:
- heater -ve w.r.t. cathode: 450 volt.
- heater +ve w.r.t. cathode: 100 volt.

To cater for the above, I will use two separate filament supplies for the two 6BY5. The centre taps (using resistor pair) of these two supplies are connected to the connecting point of the two capactors connected in series for the B+.

Is the design feasible? Any comment is appreciated. Please feel free to correct me if I am wrong. Thanks.

One more question: can the separate filament supplies for the two 6BY5 be combined to a single one?
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Old 26th June 2006, 01:50 PM   #2
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You can use a single winding to supply both - all cathodes are at the same potential. You can bias the heaters to the cathode voltage or just let the winding float. But do not use the rectifier heater winding for anything else.
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Old 26th June 2006, 03:34 PM   #3
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Quote:
Originally posted by Tom Bavis
You can use a single winding to supply both - all cathodes are at the same potential. You can bias the heaters to the cathode voltage or just let the winding float. But do not use the rectifier heater winding for anything else.
Hi there,

Thank you for your reply.

Can I really not bias the heater voltage and let the heater voltage float? I am afraid that the heater and cathode voltage will exceed the max. permitted. Can you elaborate more?

Thanks.
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Old 26th June 2006, 04:40 PM   #4
kevinkr is offline kevinkr  United States
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You can run the filaments on a single winding, and to minimize stress on the cathode insulation you can tie the cathode of one directly to the filament winding - just make sure the winding can handle 650V.

IMHO while the 6BY5 has relatively decent ratings for this sort of service, I think there are probably other somewhat better choices amongst the TV damper single diode family like the 6AU4GTA for example. The GTA has slightly higher continuous and pk current ratings and in normal operation will drop less than 25V. They're pretty cheap as well, and the filament insulation can safely withstand almost 900V so if you need to power something else off of this filament winding like a voltage regulator pass tube you can safely do it.

I use 6BY5 to power small SE amplifiers and pre-amps at under 300V/100mA typically.
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Old 27th June 2006, 05:48 AM   #5
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You might think about crossing the rectifiers - that is, since they each have dual anodes and are made for full-wave - then do it that way. Wire up each one so that it does the entire job. Then you reduce matching problems when trying to balance the secondaries. Keeps the ripple at 120Hz without adding a 60Hz component (110/50).

This might also help if one tube blows. And the topology scales to 3 and 4 tubes.

Keep the anode resistors as high as you can get away with.

jh
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Old 27th June 2006, 10:38 PM   #6
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Quote:
Originally posted by kevinkr
You can run the filaments on a single winding, and to minimize stress on the cathode insulation you can tie the cathode of one directly to the filament winding - just make sure the winding can handle 650V.

IMHO while the 6BY5 has relatively decent ratings for this sort of service, I think there are probably other somewhat better choices amongst the TV damper single diode family like the 6AU4GTA for example. The GTA has slightly higher continuous and pk current ratings and in normal operation will drop less than 25V. They're pretty cheap as well, and the filament insulation can safely withstand almost 900V so if you need to power something else off of this filament winding like a voltage regulator pass tube you can safely do it.

I use 6BY5 to power small SE amplifiers and pre-amps at under 300V/100mA typically.
Hi Kevin,

Thank you for your advice. Having checked the datasheet, the 6AU4GTA is a half-wave one and the max. dc current is 175ma only, so it appears that it cannot supply the 250ma that I want. Is this correct?

Regards,
T.C. MA
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Old 27th June 2006, 10:39 PM   #7
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Quote:
Originally posted by hagtech
You might think about crossing the rectifiers - that is, since they each have dual anodes and are made for full-wave - then do it that way. Wire up each one so that it does the entire job. Then you reduce matching problems when trying to balance the secondaries. Keeps the ripple at 120Hz without adding a 60Hz component (110/50).

This might also help if one tube blows. And the topology scales to 3 and 4 tubes.

Keep the anode resistors as high as you can get away with.

jh

Thanks for your advice, but how can they be wired up to produce 250ma current that I want?

Regards,
T.C. MA
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Old 28th June 2006, 01:32 PM   #8
kevinkr is offline kevinkr  United States
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I hadn't realized that you needed 250mA in which case a pair of 6AU4GTA (190mA version) is not going to do it for you.

I don't think a pair of 6BY5 is such a good choice for this duty either, although I would do as tubelab recommended and cross connect them so that each one operates fullwave rather than half wave parallel.

Even though each section can handle 190mA, I'm not sure there is sufficient dissipation margin to run them in parallel at much higher currents than this - although in theory this should be just fine as they are only conducting 50% of the time..

The 5U4 and 5R4 will both operate very comfortably at the current level and voltage you require, although they have 5 volt filaments and warm up rather quickly. (Could be solved with filament and B+ interlocking switch arrangement.)
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