restoring 59 super amp: heater question

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restoring 59 super amp: heater question

Postby centervolume on Wed Apr 27, 2016 1:56 pm

Greetings all-

I am restoring a late 50s fender super 5F4 amp. The schematic I have shows no center tap on the heater winding, so one leg goes to the tube heaters and the other goes to the chassis.

However, the OEM power transformer I have sourced for the job (triad 8087) does have a center tap. Is there any recommendation regarding either of the following?

1. isolate the center tap on my sourced 8087 and wire the 2 ends of the heater winding as per the original schematic
2. wire the heater as per the next incarnation of the super amp (6G4): i.e. running both legs to the tubes as a twisted pair and connecting the center tap to ground
a fish in the dish is worth ten in the stream
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Re: restoring 59 super amp: heater question

Postby pdf64 on Wed Apr 27, 2016 2:06 pm

'2' should be 'better, in terms of lower hum, but I suppose it may depend on how faithful (as in accurate to the original) you wish the restoration to be.
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Re: restoring 59 super amp: heater question

Postby stratele52 on Wed Apr 27, 2016 2:35 pm

If you restoring, don't mod heater wiring, keep this amp original.
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Re: restoring 59 super amp: heater question

Postby centervolume on Wed Apr 27, 2016 4:11 pm

That's what I was thinking... it's just that the 8087 PT I have has a center tap on the heater winding. I guess there was an earlier incarnation of the 8087 that had no center tap and that's what they used on the late tweeds. Maybe I'll just try the original wiring with the CT isolated and see how noisy it is
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Re: restoring 59 super amp: heater question

Postby stratele52 on Wed Apr 27, 2016 4:21 pm

Don't use the CT.
Noisy, not more than original amp
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Re: restoring 59 super amp: heater question

Postby drewleslie on Thu Apr 28, 2016 11:42 am

Easy enuff to test CV! Hook up CT and listen; remove do the virtual ground with two 100 ohm resistors and listen; remove and then just ground one heater leg and listen. As stratele52 said, I don't hear much diff. drew
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Re: restoring 59 super amp: heater question

Postby stratele52 on Thu Apr 28, 2016 12:57 pm

Original heater winding with only one wire , other is the chassis, can't use center tap or two 100 ohms resistors
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Re: restoring 59 super amp: heater question

Postby pdf64 on Thu Apr 28, 2016 12:59 pm

drewleslie wrote:Easy enuff to test CV! Hook up CT and listen; remove do the virtual ground with two 100 ohm resistors and listen; remove and then just ground one heater leg and listen. As stratele52 said, I don't hear much diff. drew

Yes it's easy to compare balanced to unbalanced when the heater system is wired up balanced.
But a 'back to stock' restoration would wire implement an unbalanced system, using the chassis as one of the heater conductors, as per http://bmamps.com/Schematics/fender/super_5f4_schem.pdf
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Re: restoring 59 super amp: heater question

Postby Dean Jr. on Thu Apr 28, 2016 7:38 pm

centervolume wrote:Greetings all-

I am restoring a late 50s fender super 5F4 amp. The schematic I have shows no center tap on the heater winding, so one leg goes to the tube heaters and the other goes to the chassis.

However, the OEM power transformer I have sourced for the job (triad 8087) does have a center tap. Is there any recommendation regarding either of the following?

1. isolate the center tap on my sourced 8087 and wire the 2 ends of the heater winding as per the original schematic
2. wire the heater as per the next incarnation of the super amp (6G4): i.e. running both legs to the tubes as a twisted pair and connecting the center tap to ground



AS I understand this, the heater filament winding consists of two legs and no center tap. The quietest operation possible here would be to lift the leg from the chassis ground and build a twisted pair for the heater feed to the tubes. Establish a virtual center tap with 100 ohm resistors from each leg to ground. IF an amp were 100% original and in excellent cosmetic condition, perhaps I leave the filament circuit stock. IF this is a player amp, I do what Leo and co. did by trying to eliminate filament noise with a center tap and twisted pairs.
Leo fender never did anything he didn't need to do if it would cost more money....and that center tap heater filament would be another expense. Leo felt that there was a need for the center tap/twisted pair filament wiring. YMMV.
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Re: restoring 59 super amp: heater question

Postby stratele52 on Thu Apr 28, 2016 9:57 pm

Dean jr , I'll keep amp original, no heater mod, noise from the heater circuit is not loud.

I just fix a Champ with heater built like that. In good shape, the amp is almost quiet, no need heater mod. And this keep the value.
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Re: restoring 59 super amp: heater question

Postby Dean Jr. on Thu Apr 28, 2016 11:13 pm

There ya go......like I said, if an amp were all-original I probably would not change it either. I just resurrected a '56 5E3 Deluxe with the heater filament grounded on one end of the winding. t here was some hum there, but that is the way it left the factory. Had it been a player with some non-originality, then I would have suggested to the owner that we change it.
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Re: restoring 59 super amp: heater question

Postby drewleslie on Fri Apr 29, 2016 11:36 am

stratele52 wrote:Original heater winding with only one wire , other is the chassis, can't use center tap or two 100 ohms resistors


agree. I was thinking of a test using two heater wires as pdf64 notes just for relative noise perspectives. drew
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Re: restoring 59 super amp: heater question

Postby pdf64 on Fri Apr 29, 2016 1:25 pm

Bizarrely, AC30s heaters were done with twisted pair wires, but then made unbalanced by linking one side to chassis 0V, near an input stage tube.
As such, it's trivial to add a couple of 100 ohm resistors and balance the system.
I can't envisage that many users, having heard the benefit of balanced heaters, would wish to revert to unbalanced heaters.
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