Arkless Electronics
Trade: Amp design and repairs.
Sorry I was going to reply -looked at the time and realised I should have been on the road . So first thank you so much for your time -you don’t know how much I’m grateful . I understand the 2nd part of your answer and when I measured the voltage at the preamp valves there was roughly 6.2 volts . I’m not following the 1st part however due to my lack of expertise . So after the 6.3 passes through the resistors it goes to pin 8 of the 6FQ7 ? So the 6FQ7 heaters are not connected to 6.3 or am I misunderstanding . Are you an excelsior owner ?
No I'm not an owner. I'm a designer and repairer of amps etc and the "Jez" mentioned above.
I can only really comment on what is in the diagram.... my crystal ball for checking out yours from here and seeing whats different is a bit dodgy these days
According to the diagram; V1 has it's own heater supply of 6.3V AC which is floated at HT voltage. The cathodes are at HT level and this would put strain on heater/cathode insulation otherwise. ie the heaters here run from 6.3V AC BUT the whole shebang is floated at say 250V DC above ground. V1 is not a regulator or anything like that but is wired simply as a pair of diodes in series... some voltage will be dropped across these but otherwise I can see no purpose to V1 other than to prevent HT being applied to the rest of the amp until V1 warms up.
All other valves have heaters supplied from 12V DC from the regulated supply. A half wave voltage doubler takes 6.3V from the transformer and doubles it... in fact there should be about 16V ish on the smoothing caps. It then goes through a 3 pin voltage regulator to give 12V. Valves such as ECC81/82/83 have centre tapped heaters and can be run from 12.6V applied to pins 4 and 5 or 4 and 5 can be connected together and 6.3V applied between there and pin 9. If you have the rest of the schematics for the whole unit it would be useful!
The regulator circuitry for the heaters will be bloody obvious if present and correct as apart from the 12V 2A regulator on a heatsink there will be 4 large 10,000uF electrolytics!
I'm rather busy and generally turning down work ATM but this is interesting enough and not to long a job so I could fit it in as a quicky if need be.