07-25-2013, 04:35 PM
Sorry Pith and others, I missed about measuring across the filter choke. Pith, I noticed you measured the voltage from plate to ground (cathode) on the 42 output tubes and got nada. Just as a test, could you do the same DC measurement from ground to the plate of let's say the 1st IF the 78 if I read the schematic properly.
I ask this for a couple reasons. One is if you were not measuring the choke at the right place ( I would measure across the two e-caps listed as 53 and 54 on the schematic, the two positive leads) only because it is strange to have that choke open up. The other reason is that the field coil being open on the speaker would also give you no voltage on the plates of the 42 output tubes BUT if it was open would allow voltage to the plates of the other tubes in the receiver. If you don't get voltage to the other plates, certainly looks like the choke, which would kill the voltages everywhere.
I hope this makes sense! Just a double check.
If indeed the choke is open and you have no DC voltage on any of the plates of the tubes in the front end, then the resistor idea to replace the choke could become a viable long term solution if you don't want to find another choke. You would need to change the value of a couple of electrolytic caps you have changed to increase their value to add back some filtering of the DC you will have lost as the resistor does not provide the smoothing out of the DC as well as a choke.
If it indeed proves out the choke is bad, you might run a WTB in the classified section and perhaps someone has one on a parts chassis.
Good luck and check in. Your learning a lot. Again, the other people responding are a lot smarter than me. Before I go off to look for what might be an expensive part I want to make certain I have done every test to assure I'm correct.
Best of luck and post a couple pictures in the clubhouse of Ireland. One place that is on my bucket list to visit.
Jerry
I ask this for a couple reasons. One is if you were not measuring the choke at the right place ( I would measure across the two e-caps listed as 53 and 54 on the schematic, the two positive leads) only because it is strange to have that choke open up. The other reason is that the field coil being open on the speaker would also give you no voltage on the plates of the 42 output tubes BUT if it was open would allow voltage to the plates of the other tubes in the receiver. If you don't get voltage to the other plates, certainly looks like the choke, which would kill the voltages everywhere.
I hope this makes sense! Just a double check.
If indeed the choke is open and you have no DC voltage on any of the plates of the tubes in the front end, then the resistor idea to replace the choke could become a viable long term solution if you don't want to find another choke. You would need to change the value of a couple of electrolytic caps you have changed to increase their value to add back some filtering of the DC you will have lost as the resistor does not provide the smoothing out of the DC as well as a choke.
If it indeed proves out the choke is bad, you might run a WTB in the classified section and perhaps someone has one on a parts chassis.
Good luck and check in. Your learning a lot. Again, the other people responding are a lot smarter than me. Before I go off to look for what might be an expensive part I want to make certain I have done every test to assure I'm correct.
Best of luck and post a couple pictures in the clubhouse of Ireland. One place that is on my bucket list to visit.
Jerry
A friend in need is a pest! Bill Slee ca 1970.