McMichael Solarvox twin and selenium rectifier

[Boom]

The last time I smelt selenium was on an old 1400 tripler year ago and really don't want to stink the house out.

What would be the chances of the selenium rectifier in this set being ok? Are my chances of getting a good replacement even lower?

I don't have a variac so will be putting a light bulb in series with the set. I am nowhere near ready to plug the set in yet so any advise on how to bring it up slowly is welome. There are two cardboard block electrolytics in the set and I suspect that one has been a replacement for a bolt in smoothing can. I seem to recall that these cardboard blocks fare pretty well with time.

It's not all doom and gloom as the underside of the chassis actually looks pretty clean but what on earth is that coil thingy halfway up on the left which has a small piece of asbestos behind it? From the connections it looks like it has been added at some point.

The middle picture despite looking like something from a boy racers car boot is the twin speakers (energised). These seem intact and in good condition.

[paulsherwin]

I've never smelt a selenium rectifier emitting toxic gas, but I change the things automatically, though I can see that a prewar set requires more consideration.

The chances of your rectifier working well are very poor. It probably won't start gassing, but it will have excessive voltage drop at the very least. Selenium rectifiers are still made for specialist applications, but they won't look right in this set. You might as well construct a diode/resistor substitute in the normal manner, hiding it in a period style enclosure if that's your inclination.

Paul

[Steve_P]

Well it may be, but how long will it stay OK for. Stinking the house out is one thing, but the health aspects are another.

The asbestos is OK unless it's crumbly, in which case take the set outside and remove the asbestos, bag it and dispose of it sensibly. The coil, if it's got Asbestos round it, could be a resistance of some kind, such as a dropper resistor.

Go on.... plug it in and see....

Cheers,

Steve P.

[Oldtimer74]

If you take the asbestos out wet it thoroughly first before touching it.
What is the actual model number of this set?
I remember about 65 years ago having something like it with those enormous copper coil cans.
Pat

[Boom]

The label is just marked 'Twin Supervox'.

For such a huge set space is very tight inside but I've managed to free the ends of the mains cable so I'm just looking around for a piece of flex and I'll try firing it up tonight with a 100W bulb in series.

The chassis wiring seems to be covered in sticky wax stuff for insulation and is suprisingly good for its age. That coil thing has a wooden former and looks very much like an added bodge of of some sort possibly made from a length of broom handle.

If you hear a loud boom tonight from the direction of Salisbury plain it won't be the military.

[Boom]

With bulb in series I have 110V HT. Direct mains give 210V HT with transformer tapping on 200V input so I'd guess the main worry of the rectifier is probably non founded. AF stages are alive and 'hummy' but only 45V on the output valve anode. Think I'll give it a rest and think carefully if I want to go ahead with this one or not. Will be a shame if not as it is a really nice looking beasty even if the cabinet does also need completely overhauling as well.

Thanks for help.

[FRANK.C]

Hi David
What a lovely set and it appears in good condition.
I replaced the rectifier in mine, there is two diodes in it if I remember right. How are the speaker field coils? Both of mine were O/C suffering from greenspot disease. I had to rewind them.
The two coils are different, one of them forms part of the potential divider that supplies the valves screen grids.

There is a wax capacitor that will need changing inside the audio coupling transformer cover.
The cover is riveted onto a Bakelite base. I had to drill out the rivets to gain access.
The coupling transformer is a auto transformer on the diagram, on my example it was an actual transformer. This threw me for a while as I was only getting continuity between two of the three connections.


Best of luck with the restoration
Frank

[Rejectostat]

Originally Posted by Oldtimer74

What is the actual model number of this set?

Pat

From memory its model number was RV8, can't remember where I read that though. Everyone knows it as "Twin Supervox" of course.

[chipp1968]

Lovelly radio .. I wondered wwhat one looked like naked ! I presume this has the cabinet with sunray frets ?

[Boom]

Originally Posted by chipp1968

Lovelly radio .. I wondered wwhat one looked like naked ! I presume this has the cabinet with sunray frets ?

Indeed it is. Here is the picture I took as it came to me. I have started sanding the cabinet down but this is an area that I don't think I will be able to handle as well as I would like too which I feel this set deserves. I can only just about tell Oak from a lolly stick.

Interestingly the rf stages are on the right along with the aerial sockets and the af ouput is on the left. Back to front to most sets.

I've still to find out if it's TRF or a superhet.

[chipp1968]

Its a TRF , very nice , the front doesnt look too bad . I would be carefull and use nitromors on the top with wire wool .

[Ian B]

Trader sheet 557 (from Paul's data) will help.

I'm probably wrong, but I thought the early Westinghouse rectifiers as used by McMichael, Pye & others were copper oxide, not selenium, and usually used in a voltage doubler circuit.

Ian Blackbourn

[Oldtimer74]

I would agree with Ian I would have thought 1933 was a bit early for selenium rectifiers. The type fitted was Westinghouse D51 opertaing as a voltage doubler. Usually the fins on copper oxide were thinner and larger in area than those on selenium because the forward resistance is higher and so more heat disipation is needed.
Please don`t think of abandoning the project. It looks in good restorable condition.
Pat