Hey there, I grabbed a pair of industrial control transformers a little while back-
http://www.diyaudio.com/forums/tubes-valves/287544-480vct-50va-less-than-12-shipped.html
NEW RIB Functional Devices Transformer TR50VA018 T-249 NIB | eBay
And figured they would be at least worth the fuss of fooling around with. Using them backwards (feed them from the 120 side, and rectify the 480VCT side) in a center-tapped FWB with a pair of beefy diodes, and a couple of spare 12.6VCT 2.5A transformers on hand should be pretty affordable and cheap.
What can I safely consider these to be able to continuously supply for DC current? They seem very well made, but I'm not too keen on stressing them out too much. Would I be safe in using a single one to supply a stereo AB1 pentode/tetrode connected design using 6V6 or EL84?
http://www.diyaudio.com/forums/tubes-valves/287544-480vct-50va-less-than-12-shipped.html
NEW RIB Functional Devices Transformer TR50VA018 T-249 NIB | eBay
And figured they would be at least worth the fuss of fooling around with. Using them backwards (feed them from the 120 side, and rectify the 480VCT side) in a center-tapped FWB with a pair of beefy diodes, and a couple of spare 12.6VCT 2.5A transformers on hand should be pretty affordable and cheap.
What can I safely consider these to be able to continuously supply for DC current? They seem very well made, but I'm not too keen on stressing them out too much. Would I be safe in using a single one to supply a stereo AB1 pentode/tetrode connected design using 6V6 or EL84?
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I'm on 120 volt mains here, so 120 into the 120 volt secondary, and I'll be rectifying the 480VCT primary (grounded center tap, diode per winding end) for around 320~ or so DC. I'm just trying to find the safe DC current I can draw on this configuration.
This will help you figure it out. It all depends what type of arrangement you use.
50VA isn't much, we derive the basic current available from I=VA/V so you have 50/480 which is approx. 100ma (that is the secondary AC current into a resistive load).
How you use that depends on the configuration of your power supply.
http://www.hammondmfg.com/pdf/5c007.pdf
50VA isn't much, we derive the basic current available from I=VA/V so you have 50/480 which is approx. 100ma (that is the secondary AC current into a resistive load).
How you use that depends on the configuration of your power supply.
http://www.hammondmfg.com/pdf/5c007.pdf
50VA @ 240Vac is 208mAac
Converting that to DC would make a continuous 110mAdc available. This is the maximum continuous and likely to make the transformer run pretty hot.
For cool running reduce to ~50%, i.e. 50mAdc to 60mAdc continuous @ ~320 to 340Vdc
Converting that to DC would make a continuous 110mAdc available. This is the maximum continuous and likely to make the transformer run pretty hot.
For cool running reduce to ~50%, i.e. 50mAdc to 60mAdc continuous @ ~320 to 340Vdc
50VA / 480V = 104mA rms
In a typical amp the power factor is likely to be around 0.65, so your maximum safe DC current is: 104 * 0.65 = 68mA dc. Obviously you'd want to derate that a bit for longevity.
A pair of EL84s will be uncomfortably close to that limit if you bias them at a typical 25mA each, since the average current rises in a class AB amp under signal conditions. But if they're overbuilt transformers then maybe you'll get away with it, if you keep preamp current demands low.
In a typical amp the power factor is likely to be around 0.65, so your maximum safe DC current is: 104 * 0.65 = 68mA dc. Obviously you'd want to derate that a bit for longevity.
A pair of EL84s will be uncomfortably close to that limit if you bias them at a typical 25mA each, since the average current rises in a class AB amp under signal conditions. But if they're overbuilt transformers then maybe you'll get away with it, if you keep preamp current demands low.
Ah sorry, then I missed by a factor of root 2.
50VA / 240V = 208mA rms
Divide by root.2 to allow for the two-phase rectifier = 147mA rms.
In a typical amp the power factor is likely to be around 0.65, so your maximum safe DC current is: 147 * 0.65 = 95mA dc. More than enough.
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Hmmm. Maybe a pair of monoblocks biased a little lean might be the ticket then. I'll just be using a basic capacitor input PSU, and maybe a Maida regulator for the screens, which is simple enough to lash up a single reg per output pair anyway. I might have to lash something up and see how warm it gets at a lean bias current. The preamp is likely to be a 6sl7 concertina, so pretty lax current demand there.
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I would not worry about loading-up a "control" transformer: they sometimes work 24/7 at full load in business-critical applications.
Except I never hear of "RIB" brand??
AC to DC conversion is hard on a transformer. Derate by 1.6 at least. So you can suck around 30W of DC.
6V6/EL84 are good for 12W of dissipation each, and are not typically run far into class B where power input rises. Counting screen, bias, and filtering, say each bottle can eat 14W. Plus <1W for driver. So you can run two power bottles and a little bottle. Stereo 5W audio out, or mono 14W audio out.
And a heater transformer on the side.
Except I never hear of "RIB" brand??
AC to DC conversion is hard on a transformer. Derate by 1.6 at least. So you can suck around 30W of DC.
6V6/EL84 are good for 12W of dissipation each, and are not typically run far into class B where power input rises. Counting screen, bias, and filtering, say each bottle can eat 14W. Plus <1W for driver. So you can run two power bottles and a little bottle. Stereo 5W audio out, or mono 14W audio out.
And a heater transformer on the side.
Wow, couldn't find the thread, but I suppose this is a better place for it.
So, I'm thinking with 6v6 or el84 I should be fine running a single transformer for stereo SE (ew, gross 🙄) or as one channel each push-pull. Somehow I've never actually built monoblocks, so that sounds like a fun idea, one on either end of the workbench in the garage would be handy.
So, I'm thinking with 6v6 or el84 I should be fine running a single transformer for stereo SE (ew, gross 🙄) or as one channel each push-pull. Somehow I've never actually built monoblocks, so that sounds like a fun idea, one on either end of the workbench in the garage would be handy.
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