Hi all,I have not had to deal with to many speaker problems but I need some advise, I have a RCA 29K unit worked fine until last night I switched it on and nothing No Sound, checked around and found huge drop in voltage after the field coil checked the field coil for the required 1630 ohms and it was there but the winding coming out of the field coil ( I believe is the Hum bucking coil reads shorted) to check I removed the speaker and inserted a 10 watt 1750 resistor to check , and the voltages came back to normal , so I will have to replace the speaker now the wires coming out of the field coil(hum bucking?) go to a smaller transformer mounted on the speaker then to the voice coil, will I have to use this smaller transformer on the replacment speaker to acheve the desired impedance?
Thanks for your help
Elton

Hi Elton

Wonder if the field shorted to your speaker frame? A hum bucking coil is usually a few turns and reads near zero ohms.

Can you insulate the speaker frame from chassis and see what that does? If shorted to frame there will be B+ voltage on the frame.

The smaller one is an output transformer. Yes, you still need to use this. It matches your output tube to voice coil of the speaker. This output transformer is also connected to B+. It's possible its winding shorted to the core?

Norm

:Hi all,I have not had to deal with to many speaker problems but I need some advise, I have a RCA 29K unit worked fine until last night I switched it on and nothing No Sound, checked around and found huge drop in voltage after the field coil checked the field coil for the required 1630 ohms and it was there but the winding coming out of the field coil ( I believe is the Hum bucking coil reads shorted) to check I removed the speaker and inserted a 10 watt 1750 resistor to check , and the voltages came back to normal , so I will have to replace the speaker now the wires coming out of the field coil(hum bucking?) go to a smaller transformer mounted on the speaker then to the voice coil, will I have to use this smaller transformer on the replacment speaker to acheve the desired impedance?
:Thanks for your help
:Elton

Norm , after further checks it turns out my field coil is reading correct so I just pluged it in without the speaker side, and the voltages went to normal the minute I plug the output side in the voltage drops, the output trans reads arout 300 ohms on both sides of the primary and less than a ohm on the voice coil side do these readings sound OK? I have checked and re-checked the resistors and caps associated with the output so the only thing left is the output transformer , but how could it pull down the voltages so much?
:Hi Elton
:
: Wonder if the field shorted to your speaker frame? A hum bucking coil is usually a few turns and reads near zero ohms.
:
: Can you insulate the speaker frame from chassis and see what that does? If shorted to frame there will be B+ voltage on the frame.
:
: The smaller one is an output transformer. Yes, you still need to use this. It matches your output tube to voice coil of the speaker. This output transformer is also connected to B+. It's possible its winding shorted to the core?
:
:Norm
:
:
::Hi all,I have not had to deal with to many speaker problems but I need some advise, I have a RCA 29K unit worked fine until last night I switched it on and nothing No Sound, checked around and found huge drop in voltage after the field coil checked the field coil for the required 1630 ohms and it was there but the winding coming out of the field coil ( I believe is the Hum bucking coil reads shorted) to check I removed the speaker and inserted a 10 watt 1750 resistor to check , and the voltages came back to normal , so I will have to replace the speaker now the wires coming out of the field coil(hum bucking?) go to a smaller transformer mounted on the speaker then to the voice coil, will I have to use this smaller transformer on the replacment speaker to acheve the desired impedance?
::Thanks for your help
::Elton

Hmmm....sounds like C35 and/or C37 have shorted?????

When you can't find something wrong with the speaker or its output transformer, and plugging in the speaker (equipped with output transformer) causes voltages to drop, suspect tone condensers on the plates of the output tubes. When you plug in the speaker's output transformer, you effectively connect the tone condensers to B+. If either is shorted, it'll load down the B supply.

Thomas