Heater wiring (6v6)

[goldenGeek]

So I have read a lot of posts over the internet and I can not get my head around the best heaterwiring for 6v6 (or 6l6/el34 for that matter).

I read somewhere that on 12ax7/noval sockets you should go across the tube socket with the wiring to keep it as short as possible, is that okay on power tubes as well (6v6 in my case), or is that not okay, regarding hum? Is it a good thing on 12ax7s like I read or is that bad also?

[pdf64]

Constraints such as potential for increased heat stress on the wire insulation, and kV of flyback at the plate terminal may make 'across the socket heater wiring' a bad idea for power tubes, especially octals etc with a big hole.
With the low gain at the power tube control grid, the potential for reducing hum via lead dress is probably minimal; just arrange reasonable physical separation between the control grid and heater wiring, avoid close parallel runs etc.

[Phil_S]

There are many ways to wire heaters. The two most prevalent that I see are 1) where the wires are tucked into the chassis fold with short runs to the tube sockets, and 2) up in the air -- taking the shortest route. In either case, the idea is to keep the heater harness away from the signal wires. It's easy enough to find examples of both and IMO they work equally well. I'm partial to wiring in the air and putting signal wires on the floor.

I'm not sure what you mean by "across the socket." Both styles referenced above do not cross the socket. The laydown-in-the-fold style comes from the side and hugs the socket base, in the air comes from above.

Don't over think this.

[pdf64]

I think that GG may be thinking of the Merlin approved method, see http://www.valvewizard.co.uk/heater.html
RJ reports good results and has provided some pics of his implementation over in the Trainwreck section.

[goldenGeek]

I think that GG may be thinking of the Merlin approved method, see http://www.valvewizard.co.uk/heater.html
RJ reports good results and has provided some pics of his implementation over in the Trainwreck section.

Yes, almost like that, but this was in a parallel 6v6 build...

[Phil_S]

If it isn't causing a problem, leave it alone!

That said, I would not have done it that way. The heater wires are crossing very close to other wires and components. Too much chance of introducing 50/60Hz hum.

Here is a picture of how up in the air is done. I don't do it the other way, but look around and you'll find an example.

[pdf64]

Yes, almost like that, but this was in a parallel 6v6 build...

I don't think that's a glowing example of good lead dress.
The signal input wire is tight against the plate terminal.
For parallel SE, there may be a theoretical benefit (for hum cancellation) in wiring the heaters of one in opposite polarity to the other.
But for a power tube, such issues are moot, as the signal to noise ratio is so high, however bad the wiring is, it's very unlikely to cause a noticeable hum.

[Firestorm]

If the cathodes are bypassed by a cap big enough to pass 60Hz (or 50Hz) most hum will go to ground. If not, elevating the heaters shuts them up.

[pdf64]

Those techniques act on heater hum that couples with the cathode circuit, eg due to imperfect insulation.
Whereas lead dress methods are mainly to reduce heater wiring coupling with the grid circuit, which, being (generally) high impedance, is particularly susceptible to stray capacitance.

[Firestorm]

Those techniques act on heater hum that couples with the cathode circuit, eg due to imperfect insulation.
Whereas lead dress methods are mainly to reduce heater wiring coupling with the grid circuit, which, being (generally) high impedance, is particularly susceptible to stray capacitance.

Absolutely true. You have to keep grid wires clean and isolated from stray signals, heaters and especially same phase higher level leads. Hard in small spaces.