Fender V Front Super 5B4 Heater question

[centervolume]

This amp originally came without a center tap on the heater winding. Of the 2 green leads from the PT one goes to tube heaters (except rectifier) and the other goes to ground.

I have sourced an NOS Triad RA20 for a build of this circuit. This PT has nearly identical specs and dimensions as the original 6516 PT with the exception of the heater winding which DOES have a center tap (grn-yel).

Given the 6SC7 and 6L6 pinouts, a run of single heater wire from lamp down along tubes makes sense as per the original dressing. So my question is what to do with the remaining 2 heater leads on my PT (green and center tapped green and yellow)?

Should I isolate the center tap and then take the remaining green lead to ground as per the original design?

[66Strat]

If it were me, I would update the heater wiring scheme to make use of both heater AC leads as well as the heater center tap. I would also wire the 6SC7 sockets to accommodate 6SL7 tubes. They are electrically equivalent to the 6SC7s, are more readily available, and less likely to be microphonic.

[sluckey]

If I were restoring an old amp, I wire the heaters exactly like the original and just tape up the center tap. But if I was scratch building a clone, I'd upgrade the heaters to use the center tap.

That's the same question I faced when I restored a '57 Harvard.

[66Strat]

If this is an original amp, another option would be to have the original transformer rewound.

[glass54]

+1 with Sluckey  .
I recently did a partial restoration on a Fender Princeton 6G2 s/n P05946. It has one side of Heaters to ground (near tube sockets) and the other side wired (no twists, etc). This is probably the quietest amp I have heard (almost Zero hum/Buzz/etc) with no input and Volume at max.
I commented to the owner regarding heater wiring and and quietness of the amp. I would not dare modify this amp.
It left me a little puzzled because Fender "broke" the rules that we apply to our scratchbuilds 
Kind regards
Mirek

[PRR]

> the 2 green leads from the PT one goes to tube heaters (except rectifier) and the other goes to ground.

That worked in radios with small speakers. It hums but the speaker won't reproduce the hum. For big-speaker guitar amps it was already marginal in 1950. Fender quickly shifted to a both-sides heater circuit.

Your choice: live like Harry Truman is still in the White House, or Like Ike and wire like Fenders of the later 1950s.

It's like my brother's 1941 Plymouth. It had one tail-light and no turn signals. As a Show Car, you can leave it that way, Authentic. (It's even legal to drive in most states.) However he likes to cruise modern highways, with modern idiots on the road. We put substantial lights on the back so he get does not get Toyotas in the trunk. (Side note: his car got rented for the Jersey Boys movie. He tole the set-dresser the lights were non-stock. They did stuff with black tape so the lights would not show on camera {night shot}.)

[centervolume]

This is not a restoration but a new build based on the ca 1950 schematic and layout. I am consulting original examples and so I will update the heater circuit to use the center tap.

I’m intrigued by the idea of changing octal wiring for 6SL7 rather than 6SC7. I was not aware of microphonics as an issue with the latter. Plus I have a bunch of 6SL7 to choose from.

I’ll research a bit to see how to wire these octals for center tapped heater. I’m accustomed to the nine pin layout which has the multiple pins (4,5 and 9 iirc)  for the 2 green conductors.

Octal preamp tubes are a big reason for this build so it’s a matter of diligence :)

[66Strat]

Heaters are easy. One green wire goes to pin 7, the other green wire to pin 8, and the center tap attaches to ground. This holds true for both 6SC7s and 6SL7s. It also helps to mitigate hum if you twist the wires and keep the keep the leads consistent between the tubes, i.e. pin 7 attached to one common lead and pin 8 the other.

[bmccowan]

CenterV,
I'm curious as to what happened with the EH-185 build? You asked for some advice. Got some. But then let the thread die without answering clarifying questions.

[centervolume]

Bmccowan my apologies- between the start and end of that thread the eh 185 amp found a new home and I no longer had access to it. I should have closed that thread down but I got side tracked. Thanks for following up and for your initial contribution

[bmccowan]

Thanks for the reply.

[centervolume]

sure thing - I also gave a hopefully sufficient explanation on the original orphaned thread so all the contributors could have the complete story and hopefully not be too concerned about what happened