04-13-2013, 04:56 PM
On this radio there isn't a cap from plate to ground. There is a cap (.02 mf, 700 volt) across the primary of the output transformer, including the tap that is used as a B+ choke. I used two .04 mf caps in series to make the higher voltage than the 630 volt caps I am using.
There are variants of this radio that do have a cap from plate to ground, but not this one. There also is not a cathode bypass cap, just a self-bias resistor.
As I understand from Mondial and the tube data sheets he linked to, I need a transformer with 2500 ohms primary impedance. Now, per the schematic the primary voltage is 125 V, so plate current is a tad under 100 mA. So I need a transformer that will handle 100 mA on the primary?
The total B+ current for this radio is about 20 mA when it is working properly. With the primary open as it is now, it is about double that.
What about the secondary? What impedance should I look for?
Is DC resistance irrelevant?
I'll measure the cathode current again with another tube, but I probably won't be able to do it until tomorrow evening.
Thanks to everyone for their suggestions.
There are variants of this radio that do have a cap from plate to ground, but not this one. There also is not a cathode bypass cap, just a self-bias resistor.
As I understand from Mondial and the tube data sheets he linked to, I need a transformer with 2500 ohms primary impedance. Now, per the schematic the primary voltage is 125 V, so plate current is a tad under 100 mA. So I need a transformer that will handle 100 mA on the primary?
The total B+ current for this radio is about 20 mA when it is working properly. With the primary open as it is now, it is about double that.
What about the secondary? What impedance should I look for?
Is DC resistance irrelevant?
I'll measure the cathode current again with another tube, but I probably won't be able to do it until tomorrow evening.
Thanks to everyone for their suggestions.
John Honeycutt
