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Old 12th August 2006, 07:48 PM   #1
Nuuk is offline Nuuk  United Kingdom
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Default Is this heater suply OK?

I am building a DC heater supply for my valve pre-amp and wanted to check that it was OK before putting the valves in and powering up.

I understand that wired in series, the heaters require 12.6 volts but I get around 21-22 when I test the circuit without the valves. I presume that with the valves in place, the voltage will be pulled down but I don't know by how much.

Here is the circuit. Is it OK to install the valves and apply power?

Click the image to open in full size.
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Old 12th August 2006, 07:53 PM   #2
wa2ise is offline wa2ise  United States
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Looks like a "constant current" supply. Should work fine with the tubes installed, just measure the voltage across each tube heater once things are warmed up. Voltage sould start out low and slowly increase until warmup is done. Don't get real worried if the voltage is excessive for a short period of time ( several seconds to a minute); tubes in manufacture are fed excessive heater voltage when first evacuated anyway.
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Old 12th August 2006, 08:36 PM   #3
Nuuk is offline Nuuk  United Kingdom
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Thanks, it's 21:39 here now so I'll power it up tomorrow morning and measure those voltages!
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Old 13th August 2006, 09:42 AM   #4
EC8010 is offline EC8010  United Kingdom
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Add a 10n capacitor from each valve heater pin to chassis and it'll be even better.
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Old 13th August 2006, 11:00 AM   #5
Nuuk is offline Nuuk  United Kingdom
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Quote:
Add a 10n capacitor from each valve heater pin to chassis and it'll be even better.
I just had time for a very quick check but I get 6.5 volts across the supply for each valve so that looks OK.

As regards the 100n caps from the pins, should they go to chassis ground or signal ground star? The two are already separated by a 100n cap.
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Old 13th August 2006, 06:44 PM   #6
EC8010 is offline EC8010  United Kingdom
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Directly to the nearest available point on the chassis (probably a solder tag on one of the screws securing the valve socket). Do this at each valve, and for each heater pin.
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Old 13th August 2006, 07:15 PM   #7
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Thanks, I'll try that next.
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Old 14th August 2006, 11:49 AM   #8
jarthel is offline jarthel  Australia
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Quote:
Originally posted by EC8010
Add a 10n capacitor from each valve heater pin to chassis and it'll be even better.

say for a common 9pin tube, heater pins are usually 4 and 5.

are you suggesting that a cap on each pin going to chassis (which I would assume is then connected to the wall socket ground)?

any reason?

thank you.
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Old 14th August 2006, 12:14 PM   #9
Nuuk is offline Nuuk  United Kingdom
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And do we put them on both pins 4 (or 5) and 8?
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Old 14th August 2006, 12:31 PM   #10
SY is offline SY  United States
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Quote:
Originally posted by jarthel



say for a common 9pin tube, heater pins are usually 4 and 5.

are you suggesting that a cap on each pin going to chassis (which I would assume is then connected to the wall socket ground)?
Since EC8010 may be a bit tied up, I'll take the liberty of answering. Yes, that's exactly the idea, pin 4 bypassed to chassis and pin 5 separately bypassed to chassis. That arrangement will bypass common-mode noise travelling up the heater line.
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