Philco model 89 code 121 need help - Printable Version
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Philco model 89 code 121 need help - tmr63 - 06-21-2018
I am trying to understand what’s going on with a model 89 code 121 power supply.
It’s the first model. #36 tube for the oscillator. The filter capacitors are numbered C44 & C46.
I only have the rectifier tube (80) in the circuit. The tube, transformer and speaker all check out ok.
The voltages across the transformer are all in spec. when the leads are removed from the circuit.
I substituted 2 (10mf) 450V electrolytic Capacitors for the filter caps, after disconnecting the original caps.
Powering up with just enough time to take measurements then shutting down, I do not see any rectification across the capacitor C44.
( full wave 60 cycle ac) I read 110VAC 50VDC.
C46 also does not show any rectification And reads 2VAC 53VDC any help or ideas would be appreciated.
Tom R
RE: Philco model 89 code 121 need help - Radioroslyn - 06-21-2018
Hi Tom
Well the rectification happen between the plate and filament of the 80 tube. The filament of the 80 is HV+ and the center tap of the HV winding (terminal 6) of the power transformer is HV-. The caps a long w/the spkr field coil just filter the 60cy hum out.
I few points.
If you are seeing AC voltage from the 80 filament to term 6 your 80 maybe shorted.
Be sure that the caps are connected w/the + side going to the field coil. The - side connect to the center tap. In some circuits (not this one) the - are connected to the chassis.
Be sure the spkr is plugged in and that the field coil is good not open.
Check the resistance of both sections of #43
RE: Philco model 89 code 121 need help - tmr63 - 07-13-2018
Thanks for the help Terry
Everything recommended checked out ok
Turned out to be the 80 tube. Very strange. The tube had a white flakes floating about. When checked in a Hickok tester it tests almost new!
When I put in in the circuit...I turned the chassis upside down to trouble shoot. The tube plates short when turned upside down!
New tube solved the problem.
RE: Philco model 89 code 121 need help - morzh - 07-13-2018
First time you power a rectifier after a long period of not being used it takes up to 15-20 seconds for it to start conducting.
With all tubes out put the meter across the caps and wait, see if the voltage starts slowly climbing up.
If you have a Variac, start from low volts, like 50-60, gradually going to 100-110VAC. You should certainly see something within 30 sec the first time.
If not, re-check the tube, see if there is a short across the caps etc.