Japanese 100V First Watt amps - run at 240V

[Zen Mod]

by memory, present voltage at them is in range of 90-95Vdc

but, quite possible that being even lower

as you have actual amps, now with sorta properly deduced new toroids, it's easy to do what I wrote and check operating points ....... I'm lazy to cobble it together and times when I had SIT 1 on test bed are long gone and silly me lost all notes I had, before remembering to scan them and have in 'puter

what I'm certain of is that Iq is in range of 1A5, fact from Pa.

 

[Nelson Pass]

The supply caps are 100v, so 90v or so represents the upper limit.

 

[audioexplorations]

@Nelson Pass could you please advise how I should adjust these Japanese SIT1s to work optimally at 230v? Should I swap out the transformers to replicate their original config (in Japan @100Vac the channels would have seen 110Vdc), or shall I do as ZM suggested: simply adjust the course bias pot P1 to set Iq in the middle of the meter position. I believe this will set Iq where it needs to be but Vgs and Vds might be in a different spot.

I want to ensure the operating point on the SITs is where they were intended to be so I can experience these amps in their full splendour. Thank you!

 

[Zen Mod]

waiting for Pa's unequivocal blessing, just a remark that he practically confirmed what I wrote above

The supply caps are 100v, so 90v or so represents the upper limit.

and, to refresh some memory lanes:

to recapitulate:

US amp is having 36Vac + 36Vac secs, connected in series, ending in 72Vac; your pic of original US Donut is confirmed by pics I have from other source, showing same numbers
to split a hair, Donut with 115Vac primary, nowadays mains in US is 120Vac, ending in 72Vac*120/115=75Vac

Japanese amp is having 45Vac+45Vac secs, primary 115Vac on 100Vac mains, thus ending in (90*(100/115))Vac=78Vac effectively

difference between 75Vac and 78Vac is irrelevant

now, as is, you'll need to order pair of new Donuts

300VA, 230Vac primary, 75Vac secondary; or - if lookiing for ready made/standard values, you can search for 36+36Vac, and connect it in series