supply voltage out of spec

[George Snyder]

I have a '69 sceptre in good working order (sounds great). But I'm worried about using it because the schematic indicates 500v at the first filter cap (30 uF) but I measure 560v. As the cap can is rated at 525v I'm afraid this voltage level will over stress it (it's the original). I read somewhere that these old amps were designed for lower line voltages than are present today. Do any of you see similar voltages in your vintage Sunn gear? Should I invest in a variac (or just play during brownouts)?

[Don T.]

Hello:
 Lots of things can account for 560v at the cap. Diode rectifier in place of the tube type for example. My Sceptre runs 560v also and did take out the cap. I replaced it with a surplus 600v unit on a terminal strip. There is a source in Denver I believe that has replacement caps. Check the old postings for info.
Don T.

[George Snyder]

Thanks to Don T. for the reply. The rectifier is the original 5AR4 tube type. I noticed that the filament supplies (5v and 6.3v both) are 10% over nominal. I considered a separate cap with higher voltage rating but would like to keep unit as stock as possible. I think since all the supply voltages are around 10% high the variac set to about 110v should put me in spec. Anyone have any experience with variacs and older amps?

[Greg Z]

My sunn 1200's with Diodes instead of the 5ar4's is running 595v b+.
I just upped the first cap to 600v, no problems so far.
 I run it daily for 3 to 4 hours for the past 5 months.

 Greg z
to thine own sound be true