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Old 8th Nov 2018, 1:03 am   #1
Michael Maurice
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Default Grundig Arundel 8055

This is one beast of a radiogram. It has 9 valves with two EL34's in push pull.


The line up is ECC85, ECH81, EF89, EF80, EBC41 EABC80 EM34 & 2 x EL84'S



The problem I have is very low sound, I have replaced all the coupling caps, but looking on google, there appears to be a 17nF capacitor, as two capacitors were changed for 10nF some time ago, can anyone shed any more light.


Also does anyone have a circuit diagram, to save me tracing one out?


Radiomuseum doesn't have anything.
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Old 8th Nov 2018, 1:52 am   #2
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Default Re: Grundig Arundel 8055

Very possibly this in Germany :

https://www.radiomuseum.org/r/grundig_8060w3d.html
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Old 8th Nov 2018, 11:27 am   #3
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Default Re: Grundig Arundel 8055

This schematic might be similar?:

https://nvhrbiblio.nl/schema/Grundig_8060W-56.pdf

Lawrence.
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Old 8th Nov 2018, 12:07 pm   #4
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Default Re: Grundig Arundel 8055

Quote:
Originally Posted by Michael Maurice View Post
This is one beast of a radiogram. It has 9 valves with two EL34's in push pull.


The line up is ECC85, ECH81, EF89, EF80, EBC41 EABC80 EM34 & 2 x EL84'S



EL34s would make it a beast- EL84s are a bit more kittenish!
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Old 8th Nov 2018, 1:16 pm   #5
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Default Re: Grundig Arundel 8055

Can anyone explain why an otherwise symmetrical output stage has one side 17nF and the other 10nF and the grid series resistor 5k and 20k ? A drafting mistake or something more?

Have you checked the cathode voltage on the output stage (suspecting the 50uF cap) - if the cap is o/c then the gain of the O/p stage will fall.

Kevin.
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Old 8th Nov 2018, 1:44 pm   #6
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Default Re: Grundig Arundel 8055

Forum member Stubbyeddy has/had the full service manual for the Aurndel , maybe worth a PM
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Old 8th Nov 2018, 2:25 pm   #7
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Default Re: Grundig Arundel 8055

Interesting circuit, Class A?

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Old 8th Nov 2018, 7:49 pm   #8
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Default Re: Grundig Arundel 8055

Hi Michael,

I have one of these in pride of place in my living room, I moved a radiator so it could go there.

It came from a house clearance in Folkestone Kent and I'm fairly confident I am the second owner.

I believe all valves are original with most having a strip of black tape from valve to chassis, I don't think it's done a lot of hours, the EM34 is bright as a button.

I have paperwork for it including,

An original colour advertising leaflet with a dealer stamp on it, A Andrews Folkestone.

Original 'Instructions for using your GRUNDIG Console.'

A photo copy of the service manual issued by Grundig Kidbrooke Park Road, London issue 1 dated 12/12/55

Have you found any info yet? I could email some photos of pages of interest to you if that helps.

The radiomuseum link has a better quality scan of the schematic but it does not include the Gramophone pre-amplifier, I think this is a mod added by Grundig London.
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Last edited by MeerKat; 8th Nov 2018 at 8:13 pm. Reason: Added more info
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Old 8th Nov 2018, 10:35 pm   #9
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Default Re: Grundig Arundel 8055

Hi Michael, there are lots of potential causes of low sound. Is it low on gram as well as radio? The best way to start is by measuring the valve voltages compared to the service data (if it shows them). That will often give a clue as to what's wrong. Low HT with or without hum can indicate rectifier trouble - looks like this might have a selenium device and these sometimes fail. Apologies if I'm teaching you to suck eggs! Cheers, Jerry
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Old 9th Nov 2018, 6:21 pm   #10
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Default Re: Grundig Arundel 8055

I took this into the workshop to measure some voltages. When I was in the customers home the sound was low and the anode voltage of the EABC80 was low at around 48V, but when I tested it in the workshop, it was around 70V and all was OK.

In the customers home, it was low on both gram and radio.

I'll take it back to the customer, re-install it and see what happens.
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Old 9th Nov 2018, 6:49 pm   #11
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Default Re: Grundig Arundel 8055

You could try changing the 200k EABC80 triode anode load as a precaution. Resistors in that position have an annoying habit of going high in my experience. No idea why though!

Ron
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Old 9th Nov 2018, 7:34 pm   #12
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Default Re: Grundig Arundel 8055

I have changed it, it made no difference at the time.
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Old 9th Nov 2018, 10:24 pm   #13
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Default Re: Grundig Arundel 8055

That's an odd one. I guess start measuring voltages again at the customer's location. There would have to be something very peculiar if it was their mains supply. Was the EABC80 anode voltage the only low one? If so and you've replace the anode load resistor then it has to either be something in the EABC80 cathode circuit, grid coupling capacitor allowing dc onto the grid causing excess current, or a dodgy EABC80. If other voltages are also down but the mains is OK and the rectifier and smoothing caps are OK I guess it's a matter of isolating the HT circuits one by one and finding what is dragging down the HT. Only other possibility I can think of is one of the HT decoupling resistors has cracked internally and is giving intermittent high resistance. Cheers, Jerry
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Old 13th Nov 2018, 1:42 pm   #14
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Default Re: Grundig Arundel 8055

Having thought a bit harder, I think I understand the odd values in the output stage grids. The EBC-41 is used as the phase inverter for the push pull stage, but in an interesting manner - it servoes the mid point (jcn of the 10n and the 2x0.8M resistors) to have zero ac swing, using negative feedback from the anode. Likely there is a bit of roll-off at LF and this is compensated for by adjusting the coupling cap to improve LF balance (this is my guess).

As for your odd result - the EABC80 is only AC coupled, so for the anode to be low, either its drawing too much current (gassy - check grid voltage, but unlikely to be intermittent? maybe it gettered after prolonged idle period..), or the 200k resistor is faulty (but you changed it already) or else the supply is not right - (corrosion on the unlabelled choke? bad solder joint, faulty electrolytic ). The output stage could be drawing too much current and pulling everything else down once warmed up.. Is the 100R cathode resistor charred? Do you get 9V at the cathodes?

The intermittency would implicated the choke. The only other thing is that the selenium rectifiers could be poor, but this would affect all the HT voltages..

Good luck!

Kevin.
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Old 13th Nov 2018, 1:50 pm   #15
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Default Re: Grundig Arundel 8055

Quote:
Originally Posted by ronbryan View Post
You could try changing the 200k EABC80 triode anode load as a precaution. Resistors in that position have an annoying habit of going high in my experience. No idea why though!

Ron
Carbon composition resistors are basically carbon dust in resin painted on a former with metal end caps. When there is more than ~50V across the ends, there is enough e-field to make the carbon granules creep in the resin, and this results in ever increasing resistance as they move towards one end. Modern metal film resistors are more stable in this regard.

I once had a Solatron TV repairman's oscilloscope - it had half a dozen resistors that were almost O/C, and then checking through every other resistor, all of the ones with >50V dc were out of tolerance.

Kevin.
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