Please help with this amp - is it really a 'widow-maker'? Isolation tranny advisable?

[Enzo]

I don't see one in the OP drawing, but some of these 35v heater rectifier tubes have a tap on them for a pilot light. Look up 35W4 or 35Z5. You could wire a 6v lamp between the heater and the lamp tap on the heater. That way they didn't have to design for the 6v lamp in series with the rest of the heater string.

Our usual pilot lamp wiring in parallel with the 6v heaters allows us to ignore burnt out bulbs. However on circuits that USE that lamp tap, it is important that a working lamp be installed. In designs that use it, they are counting ont he current through the lamp to control the overall voltage through the tube. Missing or burnt out bulb would shorted the tube life.

[nashvillebill]

Good info, Enzo, thanks, though my 200B did not have a pilot light.

[Enzo]

Yeah, not here, but since we were talking about 35Z5 et al, if someone converts a little record player amp or something that does use the lamp, they ought to know this.

[Basementplayer]

I am a total noob to tube amps and I have one of these!!! how do I tell if any one has made mine safe????

[Bruce / Mission Amps]

I am a total noob to tube amps and I have one of these!!! how do I tell if any one has made mine safe????

Unplug the amp from the wall outlet.
You might have to unsolder the speaker wires but, pull the chassis out and look at the way the power cord is wired in... if it is still a 2 wire power cord, it is probably stock anyhow.
I have found that many times these things buzz like crazy when you use a three wire power cord... not sure why but I think it has something to do with the filaments all in series as a string... but across the 120v primary winding (in parallel with the primary winding), that half way rectifier tube and the grounded end of the high voltage secondary plus the entire audio chain and all that junk is all grounded to the buzzy chassis.
I have four Lectrolab amps in here this week! WTF?