Newly found VEF Spidola

[orbanp1]

Hi Steve,

Here is a full service manual for your radio with good quality schematics:
https://elektrotanya.com/orosz_vef_s...wnload.html#dl

Regards, Peter

[stevehertz]

Thanks Peter. It downloads as a djvu file and my computer doesn't seem to want to open. But I already have a good clear cct diagram. Thanks again.

[orbanp1]

Hi Steve,

I open it with "WinDjView", it is a Windows application, version 2.1. It can be found here:
https://windjview.sourceforge.io/en/.
I run it under Linux. On Linux "Okular", its native pdf viewer also opens it.
I also run "WinDjView" under W10, I have a dual-boot system. I use W10 seldom, only if necessary, and usually off the net.
WinDjView allows exporting pages as images from the document, and then I can process the image further, e.g. turn it into a pdf document of the schematics.
The Spidola service manual also has all the coil data in them.

Regards, Peter

[stevehertz]

I don't know how to do that Peter, I'm a complete computer duffer, you're talking a foreign language I'm afraid. Thanks again, like I say I have a good cct diagram and I'm fully up to speed taking it apart.

[stevehertz]

Still not been able to get around to working in earnest on this set, but I did switch it on the other day and as ever finding all the but the strongest station is difficult, but finding BBC R5 with the volume up full, I noticed that the background noise does not vary between minimum and maximum (the station itself does vary with the volume control). As indeed the background noise 'off station' does not vary with the volume control. Does that tell me anything?

[orbanp1]

Hi Steve,

Best way to start is by checking the DC operating voltages in the set.
The schematics shows the various voltages at different points, those are marked by "x.x B" where B stands for V in Cyrillic.
Those voltages are usually at the terminals of the transistors. You could measure this with a DMM.
This will tell you if there anything amiss in the amplifier stages from DC point of view.

You can follow this up with RF voltage measurements, the schematics also lists characteristic RF-levels the base (or close to) of the various transistors marked by "~X MKB" where MKB stands for uV.
For this you need a signal generator and means to measure RF voltages, like an RF mV-meter, or scope with enough sensitivity and bandwidth.
At the audio stages the levels are in "~X MB" meaning mV, and at audio frequencies.
You would need to use AM modulated RF signal from your signal generator to make those measurements.

Regards, Peter

[stevehertz]

Thanks Peter.

[Techman]

You replaced all the capacitors on the board, or nearly all of them. It's just possible that you've fitted one of the electrolytic types the wrong way round. I reckon that in a low voltage circuit like that, a low voltage electrolytic would survive connected in reverse for about an hour before giving up the ghost, so in my opinion well worth checking for this possibility. A quick and easy way to check them if you find the board layout difficult to follow, would be to go across each one in turn with a DVM while the set's powered up and see if the voltage (if any - hopefully some) agrees with the marked polarity on each of the replacement capacitors. It's a guess and a long shot and if this doesn't flag up a possible mistake, then it's down to fault finding. Background hiss from the speaker regardless of volume control would seem to indicate that the AF stages are working, but proper signal injection would confirm for certain. My set has a constant low hiss from the audio amplifier - I can't remember if it's always been like this and I haven't noticed it before, or whether it's just those old germaniums becoming slightly noisy over time.

Without checking the circuit I can't remember how many electrolytic type capacitors there were.

[stevehertz]

Good point, will check that as and when I am able to get back on to this set.