Low Voltage PT

[aajeffcote]

Just built a Twin Reverb using the iron from a 70's PA 100. Everything I read says that I have the right PT but the schematic shows 340VAC and Im running about 10 volts low. Plates have 430 to 435 on them. The amp sounds very good as is and its plenty loud but its not 85 Watts. So my question is about that PT, is there something wrong with it even though it works and sounds great, just not up to full voltage? My wall volts are normal 120ish. Also there is the yellow/red center tap wire and an orange wire that was grounded with the center tap. What is it for? Maybe thats the problem?

[Raybob]

Schematic also says plus or minus 20 percent for all voltages.  Don't see a problem.  How many watts do you measure?

[Willabe]

Also there is the yellow/red center tap wire and an orange wire that was grounded with the center tap. What is it for? Maybe that's the problem?

Your voltage is fine as Raybob said.

The yellow/red is the PT high voltage CT, the orange is for an internal shield. They both get grounded. Not a problem.

The yellow/red high voltage CT should go directly to the ground end of the 1st B+ filter cap, then to ground. This cap and CT have the most ripple voltage in the amp on them, so for the least noise wire up as above.

[tubeswell]

Just built a Twin Reverb using the iron from a 70's PA 100. Everything I read says that I have the right PT but the schematic shows 340VAC and Im running about 10 volts low. Plates have 430 to 435 on them. The amp sounds very good as is and its plenty loud but its not 85 Watts. So my question is about that PT, is there something wrong with it even though it works and sounds great, just not up to full voltage? My wall volts are normal 120ish. Also there is the yellow/red center tap wire and an orange wire that was grounded with the center tap. What is it for? Maybe thats the problem?

A PA 100 PT schematic shows 440 B+, so 430 is fine, and this difference can be accounted for by such subtle differences as, the current draw of the particular quad of output tubes you have plugged in there, or your bias. The power output can vary depending on the voltages and current through the output stage, and the extent of Class A or Class B operation, the headroom for the signal in the amp signal chain, and also the bandwidth (how much bass) the signal carries  and the size of the OT and efficiency of the speakers etc

[aajeffcote]

Very good! So its right on track. I must say I did not expect to get an answer so quickly. Thanks