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Old 27th Nov 2023, 11:26 pm   #1
Michael Maurice
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Default Decca Decola VHF tuner

This radiogram is giving me trouble!

The next thing that needs to be sorted is the radio section which consists of a VHF tuner.

5 Valves ECC85, EF41, EF41, EB91 and EM80.

There were loads of hunts capacitors which I diligently replaced except I now get nothing.

I also replaced the tuning cord.

The magic eye lights up but that’s it, no sound and no deflection of the magic eye as I tune.

I’ve powered it up from an external power supply as it's very difficult to work with it in situ.

Checks done so far HT on both anodes of the ECC85 and new valve tried.

HT on the anodes of both EF41’s. Around 90V on the G2’s of both valves.

One thing I have noticed is that the first IF valve stays virtually cold yet the second one gets reasonably hot. I’ve swapped the valves and it’s not them, I’d have expected them to reach the same temperature.

There is a small 1.2K resistor between the HT and the IF transformer but there is no voltage across those resistors.

I’m wondering if both EF41’s are also duff.
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Old 27th Nov 2023, 11:36 pm   #2
Boulevardier
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Default Re: Decca Decola VHF tuner

Quote:
Originally Posted by Michael Maurice View Post
There were loads of hunts capacitors which I diligently replaced except I now get nothing.

Are you saying that the tuner worked before you replaced the capacitors, but not after?
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Old 27th Nov 2023, 11:51 pm   #3
Michael Maurice
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Default Re: Decca Decola VHF tuner

I’ve got it working, played around with valves which I don't think were seated properly and it now works.
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