Heater dillema for multi chassis phono stage.

lordvader · 27th January 2012, 03:58 AM

So I'm currently working on a phono preamp, that's using 4 c3g tubes.

Originally, I was going to use a single case, but it was starting to look VERY squishy, so I'm going to gut an old preamp that I no longer use, and house the power transformers in that.
I figured an 8 pole speakon connector will suffice, wired something as follows :

1 : Safety earth
2 : HV
3 : HV (ground)
4 : Heater (6.3V)
5 : Heater (0V)
6 : 15V (voltage ref for regulator)
7 : 15V (ground)
8 : unused

What occurred to me, was that I've only got enough connections for 1 heater winding. If there is enough current (the winding is a 3A winding), can I run all four tubes of the single winding ? Each c3g uses about 0.4A, so there's plenty of overhead ...

Another question, is it better to rectify near the transformers and transfer DC, or transmit AC, and do the rectification in the main chassis ?

grufti · 27th January 2012, 04:44 AM

Rectifying near the transformer is better in my experience. CCS circuits should be on the main chasis, if you use them.

lordvader · 27th January 2012, 04:51 AM

Thanks for that ...

Actually, if I rectify near the transformers, I can tie to 0V lines together, freeing up a connector for a second heater winding ...

That will make my speakon look like this :

1 : Safety earth
2 : 230V
3 : 15V
4 : 0V
5 : Heater (6.3V)
6 : Heater (0V)
7 : Heater (6.3V)
8 : Heater (0V)

I'll double up on the 0V lines in the cable itself, so the 230V and 15V lines may be twisted around a 0V line. Or would shielding the umbillical mitigate that necessity ?

ryuji · 27th January 2012, 05:06 AM

twist each heater winding in the umbilical and shield the entire umbilical, you can pretty much be positive you are not picking up any RF/hum at that point

lordvader · 27th January 2012, 05:26 AM

Thanks heaps for that.

I dunno why, but making cables is crazy fun

As is making amps and preamps

ryuji · 05:43 AM

Quote:

Originally Posted by lordvader

Thanks heaps for that.

I dunno why, but making cables is crazy fun

As is making amps and preamps

It indeed is a lot of fun. I had just finished rebuilding my 6cb6/807 based 5 channel amplifier and im already considering changing out the 807's for gu-50's i got laying around.. its certainly an addiction

grufti · 28th March 2012, 05:32 AM

Have you finished your amp yet? How did it turn out?

lordvader · 28th March 2012, 05:45 AM

No, I haven't sadly

I haven't been able to dedicate too much time to it. It is close to finished though.

They layout is pretty much done (for both PSU and preamp), and everything is screwed down, so what will be left to do is the actual wiring, then the testing, then the listening.

27th January 2012, 03:58 AM	#1
lordvader diyAudio Member Join Date: Mar 2002 Location: n/a	Heater dillema for multi chassis phono stage. So I'm currently working on a phono preamp, that's using 4 c3g tubes. Originally, I was going to use a single case, but it was starting to look VERY squishy, so I'm going to gut an old preamp that I no longer use, and house the power transformers in that. I figured an 8 pole speakon connector will suffice, wired something as follows : 1 : Safety earth 2 : HV 3 : HV (ground) 4 : Heater (6.3V) 5 : Heater (0V) 6 : 15V (voltage ref for regulator) 7 : 15V (ground) 8 : unused What occurred to me, was that I've only got enough connections for 1 heater winding. If there is enough current (the winding is a 3A winding), can I run all four tubes of the single winding ? Each c3g uses about 0.4A, so there's plenty of overhead ... Another question, is it better to rectify near the transformers and transfer DC, or transmit AC, and do the rectification in the main chassis ?

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27th January 2012, 04:44 AM	#2
grufti diyAudio Member Join Date: Jun 2004 Location: Hillside	Rectifying near the transformer is better in my experience. CCS circuits should be on the main chasis, if you use them.

27th January 2012, 04:51 AM	#3
lordvader diyAudio Member Join Date: Mar 2002 Location: n/a	Thanks for that ... Actually, if I rectify near the transformers, I can tie to 0V lines together, freeing up a connector for a second heater winding ... That will make my speakon look like this : 1 : Safety earth 2 : 230V 3 : 15V 4 : 0V 5 : Heater (6.3V) 6 : Heater (0V) 7 : Heater (6.3V) 8 : Heater (0V) I'll double up on the 0V lines in the cable itself, so the 230V and 15V lines may be twisted around a 0V line. Or would shielding the umbillical mitigate that necessity ?

27th January 2012, 05:06 AM	#4
ryuji diyAudio Member Join Date: Feb 2011 Location: massachusetts	twist each heater winding in the umbilical and shield the entire umbilical, you can pretty much be positive you are not picking up any RF/hum at that point

27th January 2012, 05:26 AM	#5
lordvader diyAudio Member Join Date: Mar 2002 Location: n/a	Thanks heaps for that. I dunno why, but making cables is crazy fun As is making amps and preamps

28th March 2012, 05:32 AM	#7
grufti diyAudio Member Join Date: Jun 2004 Location: Hillside	Have you finished your amp yet? How did it turn out?

28th March 2012, 05:45 AM	#8
lordvader diyAudio Member Join Date: Mar 2002 Location: n/a	No, I haven't sadly I haven't been able to dedicate too much time to it. It is close to finished though. They layout is pretty much done (for both PSU and preamp), and everything is screwed down, so what will be left to do is the actual wiring, then the testing, then the listening.

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