Pre amp heaters

[Soupdragon666]

Hi all.
Looking for some sage advise if possible.
I was looking at my old dead amp, its an Ashdown(before they became Hayden)Peacemaker 60 to see if the schematic differs from the pcb. It does.
The four preamp valve heaters run off a 12.5 volt regulated supply.
On the pcb valves 1 and 2 Pins 4 are 12.5 v positive, valves 3 and 4 Pins 4 are 12.5 v negative and all valves Pin 5 go to earth.
Now on the schematic, valves 1 and 2 pin 4 positive, pin 5 to earth. However valves 3 and 4 are pin 4 to earth and pin 5 to the negative.
Is this an error on the schematic or does either way round work.????
I have built 1 amp from a kit and 2 JCM 800 2203 following the Ceriatone layout but all the heaters were wired to the transformer.
Hopefully the schematic is attached below.

ashdown-peacemaker-60-amplifier-schematic.pdf

Any help in raising my knowledge would be great.

Cheers

[thetragichero]

that shouldn't matter as long as there is roughly 12.6v potential difference between pins 4 and 5

[Stevem]

If the amp ever worked before then they can not possibly be wire the way you discribe because then that regulated 12.8 volt D.C. Supply would be partially shorted to ground thru the heaters of the pairs of tubes you say are wired differently!

[PaulD]

If the amp ever worked before then they can not possibly be wire the way you discribe because then that regulated 12.8 volt D.C. Supply would be partially shorted to ground thru the heaters of the pairs of tubes you say are wired differently!

Not sure what you mean. The heaters are a resistive element and nothing would be "shorted". As stated above it makes no difference which way round they are wired, as long as one end is more positive than the other current will flow and they will get hot!

[thetragichero]

if you take a look at the heater supply on the schematic there's both a negative and a positive voltage regulator (7812 and 7912) with the 0v point being common. half of the preamp is off the positive side, half of the preamp is off the negative side
my vote is that this is a red herring

[PaulD]

if you take a look at the heater supply on the schematic there's both a negative and a positive voltage regulator (7812 and 7912) with the 0v point being common. half of the preamp is off the positive side, half of the preamp is off the negative side

I think that was fairly obvious from both the OP's description of the circuit and the schematic. The OP's question was about whether it mattered which of the valves heater pins (4 or 5) was connected to the 0v rail and the answer is no, it makes no difference whatsoever.

[trobbins]

Possibly an easier pcb routing concern than actually sticking exactly to the schematic - or just a typo.

[chief mushroom cloud]

looks fine to me, they prob just keeping the bi-polar supply current balanced
if you actually measured voltage between pins 4 & 5 on all those ECC83s, you would read ~+12.6V

[Soupdragon666]

Thanks a lot for the comments.
Makes sense that it could be the design of the pcb.