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Old 14th Oct 2019, 8:57 pm   #1
music-centre
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Default Problem with Dynatron RG38 Radio section

Hello All,
Although a Radiogram I am posting this in the Radio section as its only concerned with Radio reception.
I am being really optimistic with this one I know but I wondered if anyone has had a similar fault to this on one of these.

The FM band is fine with excellent reception as are all the AM bands most of the time but using it on MW it will occasionally reduce its gain so that on a fairly weak station the volume is reduced to hardly anything,the volume gradually reduces over a few seconds.

Changing wavebands always brings it back so I thought dirty switch contacts, after cleaning them twice no difference.

I have since found that touching the contacts on the Ferrite rod Aerial with a screwdriver will get it back as well as once just touching the chassis with a screwdriver with me holding the shaft did.

AGC fault perhaps?

I have only changed the output valves grid coupling capacitors.I cant seem to find a manual for it, just wondered if someone has had experience with one of these and could narrow down the area I should be looking- I don't really want to go on a mass capacitor changing exercise if possible.

I have tried swapping the 2 RF/IF valves and cleaned the valveholders, no amount of banging the chassis will produce the fault.
Thanks,
Steve.
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Old 15th Oct 2019, 11:11 am   #2
Nuvistor
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Default Re: Problem with Dynatron RG38 Radio section

With these type of faults I used to connect test equipment up to various locations and leave running and note the changes when the fault occurred. No use connecting the meter etc when the fault occurs, the connection very often clears the fault.
Time consuming but it usually gives enough information to localise the fault.
Once localised it was easier to changed the components in that section, working on the principle that a few R and Cís was cheaper than another few hours with the test setup.
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Old 15th Oct 2019, 1:26 pm   #3
music-centre
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Default Re: Problem with Dynatron RG38 Radio section

Hello Frank,
Thanks, yes thats probably the only way its going to be found.
Its so unpredictable, I left it running for 8 hours last week and it didnt do it but yesterday did it twice in 15 Mins.

I will have to set the chassis up somewhere with some speakers, not the best thing to get out of the cabinet and the mains transformer is separate in one of the speaker enclosures!
Cheers,
Steve.
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Old 15th Oct 2019, 5:37 pm   #4
Silicon
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Default Re: Problem with Dynatron RG38 Radio section

I had symptoms like this in a PYE P75.

I traced it to a preset capacitor in the RF stage.

A slight rotation of the adjustment screw seemed to cure it.
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