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Old 3rd Sep 2019, 12:57 pm   #12
DonaldStott's Avatar
Join Date: Aug 2015
Location: Glasgow, UK.
Posts: 1,328
Default Re: Kolster-Brandes MR10

So having replaced C38 and C39, the A.F. coupling capacitors, it was time to put all the valves back in place and try a live switch on, via the lamp limiter of course.

The K-B MR10 behaved very well when the lamp limiter was switched to Lamp - initial lamp brightness which gradually dimmed as the valves heated up and then some of the brightness gradually returned as the valves reached operating temperature. And of course the main thing is that the set "sounds alive".

I had the usual strong signal for BBC Radio 4 but not much else - really nothing at all on any of the other bands!

Switched the lamp limiter to Direct which increased the signal strength and made the set bulbs glow brighter - but still nothing on any of the other bands!

A quick visual inspection showed that there was no sign of life from V1 (12AT7) a dual triode in the FM section. Carefully touching the valve confirmed that there was no heat whatsoever? Don't know to what extent the lack of FM will be down to the fact that the internal plate aerial is not attached?

Another couple of initial observations: -

1. Even with the volume turned right up this set is (currently) very quiet so some more gain somewhere would be welcomed.

2. The treble pot is very scratchy with dead areas even after a good squirt or two of De-Oxit - why is the tone control and not the volume control coupled with the on/off switch?

Now we can move on to measuring the valve voltages along with the values for any suspect resistors or capacitors. A few of the Hunts look suspicious e.g. one is cracked, and these may need to be replaced.

In two of the pictures in my Post #9 above there is a large blue electrolytic capacitor which looks fairly new - just wondering if this is a replacement and why?
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Last edited by DonaldStott; 3rd Sep 2019 at 1:03 pm.
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