Worn Out PT?

[stratonenator]

I recently rebuilt a late 70's superlead to 68' spec with a handwired board. When I went through my diagnostic testing I discovered my heaters were only putting out about 3v or less of ac per side. I think the PT might be on its last legs, but I can't know for sure, my B+ voltage is normal at +/- 475v but recently the amp started to have a real nasty undertone going on when you play high up on the neck, nothing to serious in a band situation but for recording and practice is rather obnoxious. Any thoughts as to whether or not the PT is to blame? its my last option as I just put in new sozo 67' caps and a metro c1998 OT.

Thanks!

[elronhoover]

I recently rebuilt a late 70's superlead to 68' spec with a handwired board. When I went through my diagnostic testing I discovered my heaters were only putting out about 3v or less of ac per side. I think the PT might be on its last legs, but I can't know for sure, my B+ voltage is normal at +/- 475v but recently the amp started to have a real nasty undertone going on when you play high up on the neck, nothing to serious in a band situation but for recording and practice is rather obnoxious. Any thoughts as to whether or not the PT is to blame? its my last option as I just put in new sozo 67' caps and a metro c1998 OT.

Thanks!

Is that filament V measured with a full tube load in there? What's your wall VAC? Is the PT running very hot physically?

The 'nasty undertone' (I might steal that for a song name!) when playing up the neck is often a power supply filtering, or lack thereof issue. Whats the filter cap status in there, age, amount, etc.?

You could meter out all your primaries and secondaries on the PT if inclined, but usually a failing PT is not in a failing state for very long, it's likely either working or not..

Dave

[stratonenator]

I measured the filament with both pre-amp tubes in, sans-power tubes and also with power tubes. the filtering are sozo royal 67' capacitors and they are about 4 months old ( I doubt they have gone bad...), the layout is a 68' Cap board and they are 100mfd for screens and filter. I don't have the resistors across the screens but I have some if that might help!

Thanks!