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Old 1st Feb 2017, 4:33 pm   #1
mastercare
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Default RTVC all wave Signal Generator

Hi all, I've just joined the forum, hoping I can get some help.
There was an old post a few years ago, where a member had the exact same problem. It all lights up, but I have low voltage on the output of the selenium rectifier, about 39v. When I disconnect it and measure the tx winding there is about 52v AC.
I tried, as mentioned before, using an 1N4007 diode in place of the selenium rect. but no joy.
can anyone remember this discussion?
Here are some piccys to jog your memories.

Cheers
Paul
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Old 1st Feb 2017, 4:50 pm   #2
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Default Re: RTVC all wave Signal Generator

This could be the one: https://www.vintage-radio.net/forum/...d.php?t=112751
The HT would appear to be quite low. What did you measure with the 1N diode in place and did you disconnect the selenium one for the test?
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Old 2nd Feb 2017, 8:09 am   #3
mastercare
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Default Re: RTVC all wave Signal Generator

Hi thanks for getting back to me. Yes I measured about 38V with the 1N4007 in place that's with the selenium diode out of circuit. I've got some new caps arriving they're 5uF 100V working as they seem very suspect. Would these make the DC side low?

I think what confuses me, is if there's only 52V AC on the TX winding how do we end up with nearly a 100V DC as mentioned in post by old geezer if all is working?

Cheers, Paul.
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Old 7th Feb 2017, 3:16 pm   #4
Phil G4SPZ
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Default Re: RTVC all wave Signal Generator

The diodes and capacitors could have been configured as a voltage doubler rectifier?
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Old 7th Feb 2017, 8:24 pm   #5
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Default Re: RTVC all wave Signal Generator

There are three versions of this generator (at least). Yours, one with acorn valves and one with an ECC81. The only circuit I can find is the last one: http://www.richardsradios.co.uk/acton.html, which uses a higher voltage transformer with a bridge rectifier.
52VAC with a half wave rectifier should produce a higher DC voltage (1.4x I think) so possibly the reservoir capacitor is open circuit, or very leaky. Either is possible with kit of this age.
PS. It's also known as Acton, as this is where it was made.
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Old 8th Feb 2017, 2:22 am   #6
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Default Re: RTVC all wave Signal Generator

Hi and thanks for replies.

I looked at the Acton, but I don't think it's mine, as my sig gen has only 2 valves and they are VR135 x 2.

I replaced the caps across the load R and the DC voltage has now come up to 63V, the AC on the transformer was 52 VAC, so it all makes more sense now.

I still have no oscillation anywhere, I'm not sure if the valves are gone I can't seem to find any other suspect parts.

Cheers, Paul.
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Old 8th Feb 2017, 10:02 am   #7
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Default Re: RTVC all wave Signal Generator

Some voltage readings from the valves might help.
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