Is this heater supply OK?

Nuuk · 12th August 2006, 07:48 PM

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?

wa2ise · 12th August 2006, 07:53 PM

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.

Nuuk · 12th August 2006, 08:36 PM

Thanks, it's 21:39 here now so I'll power it up tomorrow morning and measure those voltages!

EC8010 · 13th August 2006, 09:42 AM

Add a 10n capacitor from each valve heater pin to chassis and it'll be even better.

Nuuk · 13th August 2006, 11:00 AM

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.

EC8010 · 13th August 2006, 06:44 PM

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.

Nuuk · 13th August 2006, 07:15 PM

Thanks, I'll try that next.

jarthel · 14th August 2006, 11:49 AM

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.

Nuuk · 14th August 2006, 12:14 PM

And do we put them on both pins 4 (or 5) and 8?

SY · 14th August 2006, 12:31 PM

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.

12th August 2006, 07:48 PM	#1
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	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? __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

12th August 2006, 08:36 PM	#3
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	Thanks, it's 21:39 here now so I'll power it up tomorrow morning and measure those voltages! __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

13th August 2006, 09:42 AM	#4
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	Add a 10n capacitor from each valve heater pin to chassis and it'll be even better. __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

13th August 2006, 06:44 PM	#6
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	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. __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

13th August 2006, 07:15 PM	#7
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	Thanks, I'll try that next. __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

12th August 2006, 07:53 PM	#2
wa2ise diyAudio Member Join Date: Apr 2005 Location: NJ	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.

14th August 2006, 12:14 PM	#9
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	And do we put them on both pins 4 (or 5) and 8? __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

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