Using dual voltage torroidal transformers and spec-ing out for PP pair?

mountainhick

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I am looking for a specific solution for a 6v6 pair, but also to discuss three things:

1: How to come up with anticipated draw from a PP pair of output tubes in general

Uncle Doug has a youtube vid that specs out a classictone for a Deluxe AB763 where he essentially derates the 6v6 draw to
about 70% from max output current for plate and screen on the data sheet. He says based on experience, that a PP pair raws about 70ma. Is this a good sort of rule of thumb regarding deriving ratings from PP charts on spec sheets?

2: How close can you cut it when spec-ing out PTs in terms of amperage rating vs draw.

If a 6v6 pair comes out to about 70ma. Would the single 80ma coil on the antek hold up in use? Then the second lower voltage coil could be used for the rest of the tubes... more than enough current for the remaining triodes. (note: I want to apply same theory to other output tubes. I have 6aq5s and 6CM6 in mind as well)


3: The possibilty.discussion around combining non voltage matched coils, like some models that ANTEK offers:

A few of their 50VA series have dual unmatched HV outputs. An example is the AS-05T320 - 50VA 320V

Electrical Characteristics
Output Voltage​
Current
Outputs​
3x
Power​
50VA
320V0.08A
300V0.08A
6.3V2A
6.3V2A

is it possible to parallel the 320v and 300v coils? I'd expect that more current would flow through one side, but how does this work in a real world situation? Would I gain enough amperage at a middling voltage to handle the total demand?

Or the next big step up is to the 100VA series which are a bit more than double the amperage for a given voltage, with coils voltage matched. They offer 300V and 350V.
 
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SerpentRuss

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I am looking for a specific solution for a 6v6 pair, but also to discuss three things:

1: How to come up with anticipated draw from a PP pair of output tubes in general

Uncle Doug has a youtube vid that specs out a classictone for a Deluxe AB763 where he essentially derates the 6v6 draw to
about 70% from max output current for plate and screen on the data sheet. He says based on experience, that a PP pair raws about 70ma. Is this a good sort of rule of thumb regarding deriving ratings from PP charts on spec sheets?

2: How close can you cut it when spec-ing out PTs in terms of amperage rating vs draw.

If a 6v6 pair comes out to about 70ma. Would the single 80ma coil on the antek hold up in use? Then the second lower voltage coil could be used for the rest of the tubes... more than enough current for the remaining triodes. (note: I want to apply same theory to other output tubes. I have 6aq5s and 6CM6 in mind as well)


3: The possibilty.discussion around combining non voltage matched coils, like some models that ANTEK offers:

A few of their 50VA series have dual unmatched HV outputs. An example is the AS-05T320 - 50VA 320V

Electrical Characteristics
Output Voltage​
Current
Outputs​
3x
Power​
50VA
320V0.08A
300V0.08A
6.3V2A
6.3V2A

is it possible to parallel the 320v and 300v coils? I'd expect that more current would flow through one side, but how does this work in a real world situation? Would I gain enough amperage at a middling voltage to handle the total demand?

Or the next big step up is to the 100VA series which are a bit more than double the amperage for a given voltage, with coils voltage matched. They offer 300V and 350V.
Those aren't separate high voltage windings, just two taps off of the same winding. That transformer will only give 80 mA of current at either of those voltages. When sizing PTs you need to also account for the draw from your pre-amp tubes and their average draw. I would figure that out, then put in a 50% factor.

Push-Pull power tubes draw less than the two tubes would draw in SE amps. If 70 mA is a good working number for a P-P pair of 6V6 valves, and the 50VA puts out 80 mA, I would go with the 100 VA. it's only a few dollars more, but much heavier.
 
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2L man

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Transformer math goes like this: When voltage is 320VAC and current rating 80mA first the power is calculated and it is Volt Amps and it is got multiplying 320V x 0,08A = 25,6VA. Now if transformer is used to produce rectified and filtered DC the 320VAC is first multiplied using sqr2 (1,41) and comes Vpeak 320 x 1,41 = 451V. Max filtered DC current comes when VA is divided using V 25,6VA : 451 = 0,0567A = 57mA.

Reason here is because DC filtering which increase voltage RMS by sqr2 and current must drop same amount...

...SO there is easy way to calculate max filtered DC current just dividing max AC current using sqr2 (80mA : 1,41 = 57mA)
 

mountainhick

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Those aren't separate high voltage windings, just two taps off of the same winding. That transformer will only give 80 mA of current at either of those voltages. When sizing PTs you need to also account for the draw from your pre-amp tubes and their average draw. I would figure that out, then put in a 50% factor.

Push-Pull power tubes draw less than the two tubes would draw in SE amps. If 70 mA is a good working number for a P-P pair of 6V6 valves, and the 50VA puts out 80 mA, I would go with the 100 VA. it's only a few dollars more, but much heavier.


Thanks, I confused the Antek 50VA series tapped coils when looking at the diagrams of the 100VA dual HV coils.

Agree with your outlook based on the actual coil config. Looks like the 50VA series is relegated to micros or SE 6V6 sizes.
 




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