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Old 24th March 2008, 03:53 PM   #21
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.... where are the pics

This is what I was looking at, from the Fluke 5215. This is the equipment that has the low capacitance transformer.

Jan Didden
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Old 24th March 2008, 03:58 PM   #22
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Sorry, next try... Less than 100k oughhhh... ;-)
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Old 24th March 2008, 04:00 PM   #23
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another...
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Old 24th March 2008, 04:12 PM   #24
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more pics...
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Old 24th March 2008, 04:18 PM   #25
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still not finished...
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Old 24th March 2008, 04:20 PM   #26
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Old 24th March 2008, 04:30 PM   #27
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Hi Jan,

this cicuit looks very interesting!

If I guess right, It uses an optical coupling to span the voltage range... This could be a very interesting solution for solid state!

Wich led (sender) and diode (receiver) are used? Wouldn't this introduce an horrible amount of distotion and noise???

This approach could allow to cascade Fets so that a pass style amp for HV could be made....

Anyway, I think I otherwise don't really understand this circut... ;-)

Could you give some explanation??? (I'm so curious!!!) What is it used for??? You have some technical data???

Dirk
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Old 24th March 2008, 09:41 PM   #28
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Quote:
There now is a lpf from cathode to heater. So, with increasing frequency, I would expect to see an increasing voltage difference between the upper tube cathode and its heater. Depending on the allowed cathode-heater voltage, one must take care that the lpf (10k resistor and the xformer cap) does not cause this max to be exceeded at max frequency and max output level.
Quote:
first I want to comment on Jan: I guess, that Dicks solution will exceed the heater cathode rating at HF, but luckily level will be low and nothing goes wrong...
OK, lets imagine a heaterxformer with 100pF capacitance between used windings and ground.
I connect the heater with the mentioned 10k to the cathode.
This means that the heater and the heaterxformer windings will follow the signal present at the cathode. At 20kHz the 100pF is equivalent to 80k ohm. This means 1/9 of the 20kHz signal level will be the cathode-heater voltage. At full output this is max 555V which is to high for heater-cathode.
But in music there will never be 20kHz signals present at full output, even above 10kHz.
Besides, the LPF at the input will decrease high frequenties substantial.
So my solution is safe to use.

Dirk, if I read your schematics right I see that when using the PL519 ( or 509), the signal should be applied to G1 ( which needs to be DC adjusted between 0 and –50V for correct bias ), and G2 is fixed at +50V.

Dick
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Old 24th March 2008, 09:45 PM   #29
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Quote:
Originally posted by djmiddelkoop




OK, lets imagine a heaterxformer with 100pF capacitance between used windings and ground.
I connect the heater with the mentioned 10k to the cathode.
This means that the heater and the heaterxformer windings will follow the signal present at the cathode. At 20kHz the 100pF is equivalent to 80k ohm. This means 1/9 of the 20kHz signal level will be the cathode-heater voltage. At full output this is max 555V which is to high for heater-cathode.
But in music there will never be 20kHz signals present at full output, even above 10kHz.
Besides, the LPF at the input will decrease high frequenties substantial.
So my solution is safe to use.

Dirk, if I read your schematics right I see that when using the PL519 ( or 509), the signal should be applied to G1 ( which needs to be DC adjusted between 0 and –50V for correct bias ), and G2 is fixed at +50V.

Dick

Yes, I can follow that. And you could also play with the resistor value depending on the transformer you use.

Thanks, I now have an alternative to all those expensive low cap transformers!

Jan Didden
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Old 24th March 2008, 10:21 PM   #30
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Hi Dick,

I think you looked at the mu stage and the beta follower... Here I drive g2 (screen) and want to adjust idling current with g1. Looking a the synola 509 that seems to work... Is there a reason not to do so???

If you take a look a pics A, this should be your proposal??? Is this correct?

Regs, Dirk
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