04-07-2016, 10:38 AM
I am not sure I understand something.
http://www.nostalgiaair.org/pagesbymodel...022404.pdf
In the voltage chart (page 2) it lists pin1 of the 25Z5 rectifier at -20V measured relative to the B- (tuning cap frame is what they use for convenience).
This is the voltage separately rectified for the Field coil. How can it be negative?
Granted the voltage used is between the Neutral AC pin and the Pin1 (the 25Z5's Cathode) and there will be some bias between the B- and the Neutral (due to the big choke between them with some 500 Ohm DC resistance) but then the voltage developed from the rectifying is quite large (100V or so) and even with some negative bias the voltage measured relative to the B- should be positive.
Another thing is, unlike the rest of the heater voltages (6.3V and 25V) between pins 3 and 4 for the rest of the tubes, the 25Z5 heater voltage is listed as -20V. Which is 1) implies DC, 2) should be 25V.
I am puzzled a bit.
PS. A negative voltage does indeed develops first across C19 which is unnerving. It reaches to about -12V , then starts dropping and eventually goes to +100V when measured relative to the Neutral (which is totally weird).
PPS. again, warming up takes very long time, 2 minutes or so. Weak rectifier might be the culprit but it is not totally weak, it is in fact OK or close to it.
http://www.nostalgiaair.org/pagesbymodel...022404.pdf
In the voltage chart (page 2) it lists pin1 of the 25Z5 rectifier at -20V measured relative to the B- (tuning cap frame is what they use for convenience).
This is the voltage separately rectified for the Field coil. How can it be negative?
Granted the voltage used is between the Neutral AC pin and the Pin1 (the 25Z5's Cathode) and there will be some bias between the B- and the Neutral (due to the big choke between them with some 500 Ohm DC resistance) but then the voltage developed from the rectifying is quite large (100V or so) and even with some negative bias the voltage measured relative to the B- should be positive.
Another thing is, unlike the rest of the heater voltages (6.3V and 25V) between pins 3 and 4 for the rest of the tubes, the 25Z5 heater voltage is listed as -20V. Which is 1) implies DC, 2) should be 25V.
I am puzzled a bit.
PS. A negative voltage does indeed develops first across C19 which is unnerving. It reaches to about -12V , then starts dropping and eventually goes to +100V when measured relative to the Neutral (which is totally weird).
PPS. again, warming up takes very long time, 2 minutes or so. Weak rectifier might be the culprit but it is not totally weak, it is in fact OK or close to it.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
