Metropoulos Forum

Hello everyone, I am starting a new build on a JMP 50 watt (68 lead spec) and I am trying to decide on which PT I should get. I notice that on some of the PT's listed for this model have an extra 100 volt primary tap along with the standard 120/220/240 inputs. What is the purpose of this? Is this simply for areas that have 100 volt service (which I didnt know existed) or can you use this tap with a variac to achieve a lower voltage on the secondary? I have been searching for several days now and can not seem to find an answer so I thought I would check with you guys first before making a purchase. Thanks for any info you can provide on this.

I finally found my answer on the Classictone site today. It turns out that the 100volt winding is for use in Japan. Guess I wouldn't need that option!

but does the 100volt tap lower the plate voltage at all compared to 120volt, I have the same transformer and I just got a variac and I want to lower it. right now im at 436vdc unbiased@120vac, so will the 100volt tap variaced to 100vac input lower the plate voltage, or will it still be the same as the 120vac input?

Using the 100VAC primary tap with the US 120VAC wall voltage will raise all the secondary voltages.

Can any part of the amp get damaged if you use the 220vac tap with an actual 120vac supply?

If there is enough voltage for the heaters than probably not. Every thing just will be lower... B+, bias, heaters...
ADA preamps run this way. ~4vdc for heaters and less than 200 volts for B+.