Why separate AC heater supplies for driver and power tubes?

leadbelly · 28th February 2006, 11:29 PM

I have seen it mentioned in threads about the benefit of using a separate transformer winding for the driver tubes than the power tubes of an amp rather than the same secondary. I mean of course specifically about instances where a single one will do and not designs where heater-cathode voltage is the issue. What's the basis of this improvement? Is it poor noise separation between heater and the anode/cathode? Is is that lower AC currents in the wire reduce EMF? I am trying to decide if it is worth the bother in my amp, the draw for the heaters of the driver tubes is 1.2A and the draw for the power tubes is 3.0A.

arnoldc · 28th February 2006, 11:52 PM

I don't know what kind of tubes you're using on your amp (DHT, IDHT) but for DHT tubes like the 2A3 when using cathode bias, I believe separate windings are required.

Having said that, I also built an EL34 amp and shared the same 6.3V heater winding with the drivers (no heater elevation) and I did not have any problems, or so I think.

I'm also interested in the logic behind it.

leadbelly · 28th February 2006, 11:55 PM

Oops, sorry, I meant indirectly heated. I can see that there are other issues for DHT.

lndm · 5th March 2006, 12:34 PM

Heater windings carry high current. This means inductive radiation can be significant where windings are near stages with low level signals. Hum is the problem. Mainly with phono preamps. You can twist the windings, and you can connect them with separate cable runs from the source. This way you avoid a string of heaters running from the same cable which then carries a high current.

28th February 2006, 11:29 PM	#1
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	Why separate AC heater supplies for driver and power tubes? I have seen it mentioned in threads about the benefit of using a separate transformer winding for the driver tubes than the power tubes of an amp rather than the same secondary. I mean of course specifically about instances where a single one will do and not designs where heater-cathode voltage is the issue. What's the basis of this improvement? Is it poor noise separation between heater and the anode/cathode? Is is that lower AC currents in the wire reduce EMF? I am trying to decide if it is worth the bother in my amp, the draw for the heaters of the driver tubes is 1.2A and the draw for the power tubes is 3.0A. __________________ Aerodynamics are for people who can't build engines. Enzo Ferrari

28th February 2006, 11:55 PM	#3
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	Oops, sorry, I meant indirectly heated. I can see that there are other issues for DHT. __________________ Aerodynamics are for people who can't build engines. Enzo Ferrari

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28th February 2006, 11:52 PM	#2
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	I don't know what kind of tubes you're using on your amp (DHT, IDHT) but for DHT tubes like the 2A3 when using cathode bias, I believe separate windings are required. Having said that, I also built an EL34 amp and shared the same 6.3V heater winding with the drivers (no heater elevation) and I did not have any problems, or so I think. I'm also interested in the logic behind it.

5th March 2006, 12:34 PM	#4
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	Heater windings carry high current. This means inductive radiation can be significant where windings are near stages with low level signals. Hum is the problem. Mainly with phono preamps. You can twist the windings, and you can connect them with separate cable runs from the source. This way you avoid a string of heaters running from the same cable which then carries a high current.

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