Cossor 935 audio section - UK Vintage Radio Repair and Restoration Discussion Forum

Cobaltblue · 7th Dec 2021, 8:34 pm

This is going to be a slow job.

I am still in full time employment and have a busy personal life so please bear with me.

I have removed the audio amp from the set as the first move. It's not at all obvious on this set how to remove anything

There is a multiway connector and 5 wires soldered on.

It's clear this was a bespoke unit calling on as much of the standard parts bins as possible.

The amplifier consists of two chassis bolted back to back with two mains transformers and rectifiers.

One transformer seems to feed the radio whilst the other is mainly concerned with the audio output.

The whole set uses a real mix of valves but those on this chassis are Loctal (B8B) and B8A.

7Y4, 67PT, 67PT, 7C6, 7Y4.

Cheers

Mike T

Cobaltblue · 10th Dec 2021, 10:52 am

Not had much time to progress this.

Done some cold checks and started to draw out the circuit.

One of the to mains transformers is Open circuit on the mains side. (The one mainly concerned with Radio) but there is a bit more coupling between the two power supplies than I thought it seems to be a sort of "shared supply"

The transformers look to be identical to the transformers used on the Cossor 500/520 series of sets (and others).

Sort of expecting that you can see the puddle of wax in the second picture.

The output transformer seems a bit small for 12W but a pair of EL41 is capable of that so we will wait and see its certainly going to fall short of HiFi.

The Choke on the "Radio" power supply chassis appears to be a second Audio output transformer just used as a choke the DC resistances and connections appear to be the same as the output transformer used on the Amplifier side of the Chassis.

The Amp is drying out at the moment whilst I source parts hoping to get the TV and Radio Chassis out next week to let them dry out over Christmas.

Cheers

Mike T

Cobaltblue · 14th Dec 2021, 9:49 pm

After a bit of a struggle due to the confined location I have now removed the radio.

Again had to cut wires the radio chassis looks a nightmare to service.

Cheers

Mike T

7th Dec 2021, 8:34 pm	#1
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,865	Cossor 935 audio section This is going to be a slow job. I am still in full time employment and have a busy personal life so please bear with me. I have removed the audio amp from the set as the first move. It's not at all obvious on this set how to remove anything There is a multiway connector and 5 wires soldered on. It's clear this was a bespoke unit calling on as much of the standard parts bins as possible. The amplifier consists of two chassis bolted back to back with two mains transformers and rectifiers. One transformer seems to feed the radio whilst the other is mainly concerned with the audio output. The whole set uses a real mix of valves but those on this chassis are Loctal (B8B) and B8A. 7Y4, 67PT, 67PT, 7C6, 7Y4. Cheers Mike T Attached Thumbnails __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

10th Dec 2021, 10:52 am	#2
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,865	Re: Cossor 935 audio section Not had much time to progress this. Done some cold checks and started to draw out the circuit. One of the to mains transformers is Open circuit on the mains side. (The one mainly concerned with Radio) but there is a bit more coupling between the two power supplies than I thought it seems to be a sort of "shared supply" The transformers look to be identical to the transformers used on the Cossor 500/520 series of sets (and others). Sort of expecting that you can see the puddle of wax in the second picture. The output transformer seems a bit small for 12W but a pair of EL41 is capable of that so we will wait and see its certainly going to fall short of HiFi. The Choke on the "Radio" power supply chassis appears to be a second Audio output transformer just used as a choke the DC resistances and connections appear to be the same as the output transformer used on the Amplifier side of the Chassis. The Amp is drying out at the moment whilst I source parts hoping to get the TV and Radio Chassis out next week to let them dry out over Christmas. Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

14th Dec 2021, 9:49 pm	#3
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,865	Re: Cossor 935 audio section After a bit of a struggle due to the confined location I have now removed the radio. Again had to cut wires the radio chassis looks a nightmare to service. Cheers Mike T Attached Thumbnails __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk