Restoring A Westinghouse Model H-743t4 tube radio

[dmr]

Hi!! I am in the process of restoring a Westinghouse Model H-743t4.

I have replaced the filter capacitors. The other cap were 10-A = 20uF @ 150V the 10- B was 40uF @ 150V I replaced them with a 22uF @160 V and a 47uF @160v.

Using two meters, one meter to measure the input AC voltage and the second meter to measure the DC output voltage. Using a variac I ramped up the voltage to 115 V.

Watching the dc output voltage from pin 7 of the 35W4 rectifier tube it measured 147.8 v. The schematic says it should be 130 vdc. The radio has no sound or stations.

Can someone give me any advice on where to look now for the problem?

Thank you!!

New member

dmr 

[Sandbagger]

Nov 9, 2014 18:47:31 GMT -5 dmr said:

Hi!! I am in the process of restoring a Westinghouse Model H-743t4.

I have replaced the filter capacitors. The other cap were 10-A = 20uF @ 150V the 10- B was 40uF @ 150V I replaced them with a 22uF @160 V and a 47uF @160v.

Using two meters, one meter to measure the input AC voltage and the second meter to measure the DC output voltage. Using a variac I ramped up the voltage to 115 V.

Watching the dc output voltage from pin 7 of the 35W4 rectifier tube it measured 147.8 v. The schematic says it should be 130 vdc. The radio has no sound or stations.

Can someone give me any advice on where to look now for the problem?

Thank you!!

New member

dmr 

Ok, this sounds like a 5 tube AM table radio, and not a CB, but that's ok, we love all tube radios. Sounds like you are off to a good start. Whenever you get a B+ voltage that is significantly higher than what it's supposedly be, it indicates that a load is missing somewhere. Usually a resistor changing value or a bad (or underbiased) tube is the usual cause. It would be helpful to have a complete schematic with voltages at the various points to compare to, and a signal generator to use to find the bad stages. If you are getting no sound at all, it may be as simple as an open speaker, or a problem with the 50C5 audio amp circuit. A simple touch of the volume control's wiper with a metal screwdriver should produce a hum out of the speaker. If not, your problem is most likely in the audio amp.

[Deleted]

Nov 9, 2014 19:03:01 GMT -5 Sandbagger said:

Nov 9, 2014 18:47:31 GMT -5 dmr said:

Hi!! I am in the process of restoring a Westinghouse Model H-743t4.

I have replaced the filter capacitors. The other cap were 10-A = 20uF @ 150V the 10- B was 40uF @ 150V I replaced them with a 22uF @160 V and a 47uF @160v.

Using two meters, one meter to measure the input AC voltage and the second meter to measure the DC output voltage. Using a variac I ramped up the voltage to 115 V.

Watching the dc output voltage from pin 7 of the 35W4 rectifier tube it measured 147.8 v. The schematic says it should be 130 vdc. The radio has no sound or stations.

Can someone give me any advice on where to look now for the problem?

Thank you!!

New member

dmr 

Ok, this sounds like a 5 tube AM table radio, and not a CB, but that's ok, we love all tube radios. Sounds like you are off to a good start. Whenever you get a B+ voltage that is significantly higher than what it's supposedly be, it indicates that a load is missing somewhere. Usually a resistor changing value or a bad (or underbiased) tube is the usual cause. It would be helpful to have a complete schematic with voltages at the various points to compare to, and a signal generator to use to find the bad stages. If you are getting no sound at all, it may be as simple as an open speaker, or a problem with the 50C5 audio amp circuit. A simple touch of the volume control's wiper with a metal screwdriver should produce a hum out of the speaker. If not, your problem is most likely in the audio amp.

I have restored these. There are called All American Five (AA5). After the first one, I started to notice a pattern of resistors being over tolerance or way out. And this was with the power off. So being that there are not that many in an AA5, I replaced all the resistors and all the caps. Then spray Deoxit on the pots and switches. You'd be amazed of the results if all the tubes are good.

That voltage is not that out of the ordinary. Tube rigs had a much high varying of voltages and solid state.

That is the easy part. The hard part is the cosmetics. Good luck.

I have one posted on the internet somewhere, if you are interested.