UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

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

Reply
 
Thread Tools
Old 10th Nov 2018, 1:04 am   #1
Johnbarn
Tetrode
 
Join Date: Feb 2015
Location: Belfast, Northern Ireland, UK.
Posts: 60
Default Grundig 2068

I got this set given to me several months ago but have only started work on it this week. I downloaded the circuit diagram which called it a "Pembroke" and gave it the Model number 2068/3D but it looks pretty close to what I have. I have never worked on a Grundig before and the circuit is quite odd and it is laid out in the European DIN style. The Grundig components in the set were quite distinctive and marked with clearly readable values. Initial testing through my lamp dropper showed a heavy current drain. The two 50uF electolytics in the one can had leaked and whilst one was ok the other was showing a low resistance on an AVO. They were replaced. The HT was low and the Siemens bridge was replaced with a chunky one from RS. Further testing through the lamp dropper gave the right result - initial glow followed by a low dim. When the lamp bypass switch was closed the set gave a promising hum and one station could just be heard on MW. Then there was a wisp of smoke and I switched off immediately. The smoke was traced to a 22k 1/2 watt resistor R37 on the diagram feeding a second LS acting as an electrostatic tweeter(? - it is shown in the circuit diagram with a capacitor symbol internal to the unit).This resistor was not an original Grundig one but a typical UK three-band plus silver component the bands of which were burned. There was also a Dubilier capacitor for C70, again not a Grundig original. I tested the capacitor and it was fine. I then removed the resistor and it was reading low. I replaced it with a new one and retested the set. Again smoke from the same resistor. I switched off again and connected a meter in series with the resistor; the current through the resistor was measured at 0.084mA which means the resistor is trying to dissipate over 100W. As a next step in the process I temporarily wired in a 22k 15W w/w resistor and the set began working well on MW. The resistor was barely warm. I suspect the electrostatic LS is low and I will remove it before any further testing. Stations on the MW are plentiful but the LW BBC station is barely audible and the VHF is not operating at all.The EM81 tuning indicator is not showing anything even with a good signal on MW. I have checked the operation of the piano key wavechange and PU switches and cleaned them as much as possible with switch cleaner, though they are hard to get at. Has anyone any experience of this set and could point me in the right direction? It is beautifully made and, even though it has been "got at" at some time in the past, it is in reasonable condition inside and out.
Johnbarn is offline   Reply With Quote
Old 10th Nov 2018, 10:33 am   #2
cathoderay57
Hexode
 
Join Date: Oct 2017
Location: Bristol, UK.
Posts: 274
Default Re: Grundig 2068

Hello, I restored a Grundig 2066 a couple of years ago which is similar. Not sure your maths on the tweeter resistor power dissipation is right - if the current is indeed 0.084mA then a 22k resistor would dissipate 0.16 milliwatts. If you've made a typo and you meant 0.084A (84mA) then the same resistor would dissipate 155W. There is no way the tweeter should be passing 84mA so something is most definitely wrong there. The tweeter should be drawing minimal current so it looks as though it has gone short circuit or very low resistance. You should disconnect it straight away. There are cheap replacements available that will not look the same but will at least give you some HF sound. Although on the radio that I repaired there were no wax capacitors there were lots of plastic encapsulated paper capacitors and without exception they were all leaky. The end caps were originally sealed with some sort of white sealant but on many it had crumbled and let in damp air over the years. If the set has had a lot of use the ECC85 is probably low emission but check out all the capacitors first and replace those that need it one by one to avoid mistakes. Providing you have got HT on the magic eye and you have checked R18 (470k) then the eye has had it if it is not glowing at all (another indication that the radio has been used a lot). If the ME glows but no deflection then check the AGC voltage between R46 (2.2M) and chassis. There should be a significant change when you tune in a strong signal. If not then try again after you've changed the caps as described above. The Grundig I repaired was the best valved VHF performer I have ever come across so you should not be disappointed once you get it sorted. Cheers, Jerry

Last edited by cathoderay57; 10th Nov 2018 at 10:48 am.
cathoderay57 is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 8:48 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Copyright ©2002 - 2018, Paul Stenning.