• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

866a: question on filament transformer

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Blitz

Member
Joined 2002
Maybe this is a stupid question, but wanted to x-check to be on the save side...:

I want to build a HV-PSU for a 814a Push-Pull amp which runs at 700V/80mA per channel. So, looking at the Tube rectifiers, the 866A should be more thancapable for the job and is beautiful as well.

I plan to use a classic FW, so 800V-0-800V transformer into two 866A. Normally I would buy for both diodes a 2,5V/10A transformer with CT for the HV.

My question: I have still some filament transformers from a different project, which deliver 0-2,5V-5V on one winding. Can I reuse them ?

My thought: If the filament of the first 866a is connected to 0-2,5 tap and the second 886a is connected to the 2,5-5V tap and the HV goes from the 2,5V tap to the choke-input filter coming next in the chain...should work as well, NO ?
 
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Blitz

Member
Joined 2002
Very good point indeed...how sensitive is the 866a if not enough current is drawn from the beginning on ? I guess I should build in a dropper resistor, maybe with time relais so that the choke-input always behave as such, than the DC would be 700V...
 
hpeter

hpeter

Member
Joined 2013
peteslab.blogspot.com
you can see plasma being shifted to one side filament - thats where lower potential is

also the metal shield is welded to one side of filament (cant be on both...)

out of phase -- filament goes to zero volt when plate voltage is at max (max current); so the plasma is spread across whole filament.
it is about using whole emission capacity.

for example hg thyratron can be shut down by -10v.. regulation occurs from 0..-5v depending on plate voltage
one of reasons why you never see gas tubes with heater voltages - because of the u gradient across filament
 
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hpeter

hpeter

Member
Joined 2013
peteslab.blogspot.com
hpeter said:
you can see plasma being shifted to one side filament - thats where lower potential is

also the metal shield is welded to one side of filament (cant be on both...)

out of phase -- filament goes to zero volt when plate voltage is at max (max current); so the plasma is spread across whole filament.
it is about using whole emission capacity.

for example hg thyratron can be shut down by -10v.. regulation occurs from 0..-5v depending on plate voltage
one of reasons why you never see gas tubes with HIGH heater voltages - because of the u gradient across filament
Click to expand...
 
hpeter

hpeter

Member
Joined 2013
peteslab.blogspot.com
50AE

50AE

Member
Joined 2011
hpeter said:
you can see plasma being shifted to one side filament - thats where lower potential is

also the metal shield is welded to one side of filament (cant be on both...)

out of phase -- filament goes to zero volt when plate voltage is at max (max current); so the plasma is spread across whole filament.
it is about using whole emission capacity.

for example hg thyratron can be shut down by -10v.. regulation occurs from 0..-5v depending on plate voltage
one of reasons why you never see gas tubes with heater voltages - because of the u gradient across filament
Click to expand...

Thanks, that made sense!

I wonder if it's worth to attempt phase shifting on the heater transformer for audio amplifier purposes.
 
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