ALBA model 70 Radiogram problems.

[trabant]

Today I've been working on the Alba 70 I bought last week re-capped it a couple were missing their paper labels and no one seems to have a schematic for it so anyway I now have it working beautifully on both long and medium Bit not a sausage on Gram. The wavechange switch simply connects two contacts for gram that's fine I'm a bit perplexed by the gram socket I have one side goes through a resistor to WC switch then on to the volume pot the other side is connected to two sockets on the back marked E presumably earth ( why two ?) Which in turn connects to the bottom pin of one valve a VMS4B I've put a new cap here possibly the wrong value I've used 47nf old cap had lost label the other end of this earth and gram socket arrangement goes through another cap a 0.1uf pretty sure that caps correct to a connection with the centre pin of the same valve and also though a resistor. Any help greatly appreciated. Please see pics .

[Station X]

The "bottom pin" as you call it of a VMS4B valve is pin 2 the control grid. A gram input could be connected here, but things don't look right to me. You have three pins all connected together, which is indicative of a common earth connection rather than an input.

It would help if you could post a picture showing the lettering on all the sockets.

[trabant]

From top to bottom the top two have Gram written between them the next two down are marked E the bottom one A obviously aerial there's also that wander plug that's where it was when I got it.

[Station X]

That makes sense, the top two pins are the ones to use for the gram input. One side of the input (the second pin down) will be earthed. You need to check the wiring from the top pin.

[Herald1360]

Does the schematic you thanked the Dutch for not provide any clues?

[Station X]

Good idea. Perhaps the OP could post an extract from the circuit showing the AF and output stages.

[trabant]

Dutch schematic is for he 56 it turns out which is slightly different however it's nearer than anything else.

[trabant]

I only come here for the sarcasm obviously lol

[Station X]

Here you go. V3 SV4B, V4 PM24M.

I suggest you check the operation of S5. It shorts the gram socket during radio operation and grounds the grids of V2 during gram operation.

[trabant]

The switch works already looked at that

[Station X]

If the diagram is correct you're looking at an impossible fault then.

The radio works, which proves that the AF Amp and output stage are working.

The switch works too.

So if you apply a signal to the gram sockets there's no reason why it shouldn't be heard from the speaker.

When you switch to gram do you no longer hear radio programess from the speaker?

[Boulevardier]

What is the signal that you are applying to the gram. input to test it?

Mike

[Station X]

Let's try another approach based on the wiring as you describe it in post #1.

Switch to gram and touch the centre tag of the volume control with a screwdriver blade. You should hear a hum or buzz.

Repeat, touching both connections to the WC switch and both sides of the resistor connected to the top gram socket.

If the buzz disappears at some point there's your fault.

[Herald1360]

Whatever you connect to the gram input has to have dc continuity (like a magnetic pickup's coil) or else the biassing for V3 will be all over the place with its grid floating......


Could this be the problem?


Try connecting a 100k resistor across the gram input and coupling the signal via a 1u capacitor and see what happens.

[Station X]

Good point, but I'm not convinced the diagram is correct for the OP's radio.

The 56 doesn't use a conventional volume control fed with an audio signal. The OP's description of the wiring to the gram socket suggests that a conventional volume control is used in his player.

[ms660]

Is the Alba 70 a TRF or Superhet?

Lawrence.

[trabant]

Superhet I presume it has no reaction

[ms660]

Cheers, I was just trying to deduce if there would be any grid bias change needed between radio and gram functions on the detector valve if it uses anode bend detection and the detector valve as 1st AF for gram.

Lawrence.

[kestrelmusic]

I am wondering whether this might be a Model 701 which is a TRF from 1936. If so, there is a Trader sheet for it, No. 73, which is of course obtainable at modest cost from Paul Stenning. It's a very pretty set anyway, well worth spending some time and trouble on. A bit like the Marconiphone I have nearly finished restoring...

[Station X]

The picture in this thread shows that it's a model 70.

https://www.vintage-radio.net/forum/...d.php?t=159081