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PP DHT output stage, is DC heater necessary?
PP DHT output stage, is DC heater necessary?
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Old 2nd March 2021, 04:17 AM   #91
v4lve lover is offline v4lve lover  Netherlands
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PP DHT output stage, is DC heater necessary? PP DHT output stage, is DC heater necessary?
That last part is only applicable when the damper is one without top cap is my guess. EY500 has the cathode and heaters on the base and the anode at the top. And conventional wisdom is to tie the heaters to the cathode.



I know which sockets you mean, i think they are called SK509 by Svetlana St petersburg but could be mistaken.




I had a crazy idea to use a thyristor behind a high voltage diode bridge to chop up the high voltage and regulate it at the same time. This produces some harmonics, but im quite certain i can get these down to the single digit mV range at which point a 8K primary transformer is going to step down the noise down to unnoticable levels.



If you make an enable pin on the control electronics for that you can disable the high voltage alltogether before the tubes are warmed up. You can also pull this pin low in case of overcurrent in the outputs.



There are a couple really fun IC's if you need to do a floating current measurement for some reason. You can use a HCPL7800 insulation amplifier for current sense. You can feed this HCPL7800 with a 1W DC/DC



Another possibility is the HCNR200 this 2 dollar part and 50 cents of transistors allows you to send analog signals with great accuracy across a 1.5KV potential gap.
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Old 2nd March 2021, 05:09 AM   #92
Chris Hornbeck is offline Chris Hornbeck  United States
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Thanks for the heads up on the insulation amplifiers - new to me, and could be very useful in the 1KV, thoriated tungsten filament world, where measuring cathode current might be harder (but safer!) than measuring anode current.


Damper diodes can be surprising when compared to conventional rectifiers. Their intended operation has their anodes to ground and heaters near ground. Cathodes swing way up into the several KiloJolt positive range, but can't go negative (because then they conduct).


Their rated peak cathode to heater voltages are really big when the cathode is positive of the heater, but only a coupla hundred Volts when negative. This allows some surprising things like full wave bridge rectifiers with only two, or possibly only one, transformer heater winding, for positive voltage power supplies.


YOS,
Chris
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Old 2nd March 2021, 05:19 AM   #93
v4lve lover is offline v4lve lover  Netherlands
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PP DHT output stage, is DC heater necessary? PP DHT output stage, is DC heater necessary?
I dont mind solid state in my amps if you are switching the mains of the high voltage transformer anyway. i did a KISS relay board for that with a 555.

Chokes are to heavy for my tastes, and id rather use the heater winding for a tube regulator. So i can feed the output with a well regulated HT.

There are some insane sweeps suitable for that.

I have a weird schematic in my head for a tube regulator controller that drives a tube-transistor cascode . just use a voltage doubler on the heater, good reference like 1N823 and a matched BJT like the MAT01

Il get behind my laptop in a bit and see if i can find the article. Edit found it This is about a vacuum tube regulator that uses a transistor-tube cascode for a 0-2500V 10mA power supply. But the principle could also be used to regulate 1KV @150mA for most SE amps


PS: The 7800 is differential output, if you need a single ended signal, INA105 or something like that is better than discrete s in most cases.
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Last edited by v4lve lover; 2nd March 2021 at 05:27 AM.
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