Heater dillema for multi chassis phono stage.

[lordvader]

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]

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

 

[lordvader]

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]

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]

Thanks heaps for that.

I dunno why, but making cables is crazy fun
As is making amps and preamps

 

[ryuji]

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]

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

 

[lordvader]

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.