Hi All;
I recently sourced on eBay a good condition mains transformer capable of the following: >
Input 0-240 Volts Ac @ 50 cycles.
Output 0-50-700-800-900 volts Ac at 3.5 amps continuous.
Size is aprox - 12 inches x 6 inches by 9 inches - using 2 large C-cores
Likewise I also got a large choke of around 0.25 henry at 2 amps, uses 2 large C-cores and measures about 8 x 7 x 8 inches.
Pictures are attached.
The transformer weighs about 35 Kg and the choke about 10 kg.
My intention is to build a massive bench power supply for testing transmitter tubes operating in audio mode.
A pair of 833a triodes in push-pull would require some 2,500-3,000 volts and at least 1 amp plate current. Similar figures would be found for other large power tubes.
From my calculations - the power transformer is around 3.2 KVA and able to deliver 2,520 volts Dc at aprox 2 amps continuous from a standard voltage doubler rectifier. Greater voltages ( with less current ) can be obtained with another stage of doubling and with a bridge rectifier a healthy 1 kv Dc at close to 3 amps can be supplied. Because of this capability I may adapt various rectifier combinations via some suitable switching to achieve these other outputs.
I have some NOS 3B28 Gas Rectifier Tubes, which 4 tubes in parallel ( 2 paralleled in one stage and 2 in another ) will deliver the required 2,500 volts at 2 amps when wired as a half wave voltage doubler, ( with peak load currents of 5 amps at a reverse voltage of 10KV. )
[ Because of the sensitivity and difficulty working with semiconductors at these voltages - personal experience talking here - I would prefer to not use semis and stick just with vacuum tubes. The reliability would be far greater under extreme operating conditions with using tubes. Size and weight is not a concern. ]
I also have a huge 15 amp / 240 volt variac which will control the mains input to the transformer - effectively making it a variable DC supply.
Adding the 0.25 H / 2 Amp choke and a suitable capacitor network, will clean up the DC as smoothed supply.
BUT;
I would though prefer to have a more conventional vacuum tube regulator tacked onto the output of the filter choke and use that as the variable Dc output rather than waste a good 15 amp variac on such a job.
Does anyone have any proven tube regulator circuits which will vary the output from say 500-2,500 volts at 2 amps Dc ?
As for the series pass tube, it too, has to handle the full 2 amps. If smaller tubes are used, ( maybe as a series of stacked regulators ) many will be required.
In reality - the whole unit will have to be rack mounted on castor wheels, as it will be way too big for a normal bench supply.
I have the the volt meters ( 3kv Motorola panel meter ) and current meters.
I have the rectifiers and some of the smaller parts.
I'm open to design suggestions.
I recently sourced on eBay a good condition mains transformer capable of the following: >
Input 0-240 Volts Ac @ 50 cycles.
Output 0-50-700-800-900 volts Ac at 3.5 amps continuous.
Size is aprox - 12 inches x 6 inches by 9 inches - using 2 large C-cores
Likewise I also got a large choke of around 0.25 henry at 2 amps, uses 2 large C-cores and measures about 8 x 7 x 8 inches.
Pictures are attached.
The transformer weighs about 35 Kg and the choke about 10 kg.
My intention is to build a massive bench power supply for testing transmitter tubes operating in audio mode.
A pair of 833a triodes in push-pull would require some 2,500-3,000 volts and at least 1 amp plate current. Similar figures would be found for other large power tubes.
From my calculations - the power transformer is around 3.2 KVA and able to deliver 2,520 volts Dc at aprox 2 amps continuous from a standard voltage doubler rectifier. Greater voltages ( with less current ) can be obtained with another stage of doubling and with a bridge rectifier a healthy 1 kv Dc at close to 3 amps can be supplied. Because of this capability I may adapt various rectifier combinations via some suitable switching to achieve these other outputs.
I have some NOS 3B28 Gas Rectifier Tubes, which 4 tubes in parallel ( 2 paralleled in one stage and 2 in another ) will deliver the required 2,500 volts at 2 amps when wired as a half wave voltage doubler, ( with peak load currents of 5 amps at a reverse voltage of 10KV. )
[ Because of the sensitivity and difficulty working with semiconductors at these voltages - personal experience talking here - I would prefer to not use semis and stick just with vacuum tubes. The reliability would be far greater under extreme operating conditions with using tubes. Size and weight is not a concern. ]
I also have a huge 15 amp / 240 volt variac which will control the mains input to the transformer - effectively making it a variable DC supply.
Adding the 0.25 H / 2 Amp choke and a suitable capacitor network, will clean up the DC as smoothed supply.
BUT;
I would though prefer to have a more conventional vacuum tube regulator tacked onto the output of the filter choke and use that as the variable Dc output rather than waste a good 15 amp variac on such a job.
Does anyone have any proven tube regulator circuits which will vary the output from say 500-2,500 volts at 2 amps Dc ?
As for the series pass tube, it too, has to handle the full 2 amps. If smaller tubes are used, ( maybe as a series of stacked regulators ) many will be required.
In reality - the whole unit will have to be rack mounted on castor wheels, as it will be way too big for a normal bench supply.
I have the the volt meters ( 3kv Motorola panel meter ) and current meters.
I have the rectifiers and some of the smaller parts.
I'm open to design suggestions.
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Hi Kimbal S,
For variable DC output the variac will be much much simpler that the fairly extreme effort required to implement a series pass tube regulator. The regulator tube will need to be bigger than the tubes you are going to test!
Cheers, Glenn B.
I have a pair of 5771 if you are interested. I don't think I will ever use them.
5771, Tube 5771; Röhre 5771 ID32477, Transmitter Triode, liq
Glenn.
5771, Tube 5771; Röhre 5771 ID32477, Transmitter Triode, liq
Glenn.
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