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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 16th Nov 2017, 7:53 pm   #81
Boater Sam
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Default Re: Oh No! Not another howler.

So, Lawrence, Bush were pushing their luck with the AC41 having nothing to stabilize the IF amp?
Their other sets all seem to have a different circuit, The DAC41 circuit does not differ so much from the AC41 and yet they used a grid stopper.
Aligning the "B" set, it is very easy to send it into the same sort of oscillation as the "A" set, the IF transformers tuning have to be staggered slightly.
The disconnected IF transformer padder is strange, it has never been removed, it is a tight fit in the can and there is no way it could of been flexed, Its the square wire Lemco mica cap and the lead was broken through right next to the rivet.
As this set had good rubber wiring, the original looking valves, original large dial bulbs and no signs of repairs, I wondering if it failed very early in the sets life.
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Old 16th Nov 2017, 8:30 pm   #82
ms660
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Default Re: Oh No! Not another howler.

I've no idea Sam, but although the AC41 and DAC41 use the same spec valves (heaters aside) at least one of the DC operating conditions is wildly different between those two models for those valves, also I suspect that the DAC41 has to deal with a wider percentage fluctuation of the HT for the different mains taps that may be employed as there is no mains tap for the rectifier input.

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Old 17th Nov 2017, 11:51 pm   #83
Skywave
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Arrow Re: Oh No! Not another howler.

To select a few remarks [edited in places] made by Boater Sam:

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Originally Posted by Boater Sam View Post
► So I feel vindicated: if Bush found the need [for a grid stopper] in the DAC41, the stability of the IF amp must have been marginal.
► I'm bored with Bush short superhets with less than good performance.
► These 2 sets . . . are not anything special; performance is not the best and they were obviously made very much to a low budget.
Your frank remarks echo mine entirely.

Al.
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Old 4th Dec 2017, 7:05 am   #84
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Cool Re: Oh No! Not another howler.

Thanks, Al, its nice to be right for once!
Both the AC41s now work well, they have been soaked for 2 days before I left.
Just to keep my hand in I restored a couple of AC11s as well, similar sets in many ways to the AC41.
But they are rock stable.
The screens on mixer and IF amp valves are separately decoupled, though trying this on the AC41 made no difference at all.
No grid stoppers either.
When I get back in spring I will get down to examining these 2 models, there must be some significant differences. I think the IF transformers are different.

We are always right until proved wrong by someone who is convinced he is right when in error.

Sam.
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