UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV 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.

Closed Thread
 
Thread Tools
Old 4th Apr 2019, 1:30 pm   #1
ekjdm14
Banned
 
Join Date: Feb 2019
Location: Congleton, Cheshire, UK.
Posts: 609
Default Got-at Grundig 2065 dead/high HT...

One of my current projects that I'd like to see work is a Grundig European model 2065 that I acquired at auction for £12 if I recall.

On opening the set, it has obviously been "got at" at some point in the past (plenty of fluffy dust but ferrite rod floating, damaged coil on end of chassis and the Selenium rectifier has been replaced in the past with simply a pair of diodes and no resistor... Power cord was well chewy and had an old 2-pin 5A plug so likely not been powered for a few years at least

On tentative application of power through a variac & bulb, there was some initial reforming of the electrolytic can & as I brought it up, monitoring the HT, I noted it rising over spec as I'd expected and shut down. During the short run there was obviously some activity from the amplifier section (slight hum & a buzz when measuring voltages at the EL84. Was a few days ago so can't be sure but I think it was when I measured the control grid).

Now my main question is, could it have EVER worked with just the diodes & HT presumably running around 330vDC (specced as 280) or would this "repair" have been a dead duck? I ask as it seems to me that running the HT 50v/20% above spec would damage the valves amongst other things, and the valves all check out inasmuch as they work well in my Ekco A320 which uses the same lineup minus the magic eye and plus a rectifier.

Basically I'm wondering if there's likely other damage from over-running the HT or if it likely never worked and was shelved. Obviously prefer the latter!

I get the feeling it's a quite high hour set given the blackened dial lamp, crispy state of the card behind the tuning eye and other "signs" and not 100% sure the power transformer is original but seems to be putting out what it ought to. Would be nice to get it working though just to see if it can be done, don't like the look of the switchgear as far as cleaning/carbon tracking goes though either!

Last edited by ekjdm14; 4th Apr 2019 at 1:38 pm.
ekjdm14 is offline  
Old 4th Apr 2019, 1:42 pm   #2
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,786
Default Re: Got-at Grundig 2065 dead/high HT...

Valves are tough things, and running with those HT levels is unlikely to have harmed them. The HT would have come down somewhat as all the valves warmed up fully and drew current. I wouldn't worry about it too much.

That said, it's certainly bad practice not to fit a resistor. Quite apart from the HT being too high, the reservoir cap will suffer a huge current surge as it charges up at switchon.
paulsherwin is online now  
Old 4th Apr 2019, 2:02 pm   #3
ekjdm14
Banned
 
Join Date: Feb 2019
Location: Congleton, Cheshire, UK.
Posts: 609
Default Re: Got-at Grundig 2065 dead/high HT...

Ah, that's slightly more hopeful then. I was wary to let the thing build up all the way but if that's the case then it's possible I just didn't get enough heat into the filaments to start conduction properly.

I'll try and source a suitable resistor to correct the HT before I get any further & see how it does on full mains (the worst of the caps already replaced as I had them & seemed sensible to do so at the time). We shall see what happens then. Thanks for the advice.

Edit- now I think of it, the schematic shows a bridge rectifier and what is fitted is a simple full wave pair. (heck now I wonder if it's even that or just a pair in parallel to share current in half wave)

I need to get my actual brain into gear on this one. will go and look again at it shortly and come back with photos of the dirty deeds as well.
ekjdm14 is offline  
Old 4th Apr 2019, 2:11 pm   #4
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,786
Default Re: Got-at Grundig 2065 dead/high HT...

The value of the resistor isn't very critical. You don't need to get the HT absolutely spot on, +-10% will be fine. I normally use 220R because I've got a big bag of them, but 100R-330R should be OK. Of course, some people like to get the HT absolutely right and that's fair enough.
paulsherwin is online now  
Old 4th Apr 2019, 2:11 pm   #5
Mike. Watterson
Heptode
 
Join Date: Dec 2014
Location: Limerick, Ireland.
Posts: 901
Default Re: Got-at Grundig 2065 dead/high HT...

The other issue is transformer and heater life if it's a 220V model. UK's harmonised electricity is a small - and large plus tolerance. Could be 235V to 245?

Our Irish Electricity is "nominally" 220V now. Actually it's unchanged at about 230V and can be 230V to 234V here, I had to put a suitable resistor in series with mains input on two German sets with too high LT and transformer "warming".

You do want a series resistor between rectifiers and 1st capacitor too, maybe about 150 Ohms. Depends on set HT current consumption.
Mike. Watterson is offline  
Old 4th Apr 2019, 2:46 pm   #6
ekjdm14
Banned
 
Join Date: Feb 2019
Location: Congleton, Cheshire, UK.
Posts: 609
Default Re: Got-at Grundig 2065 dead/high HT...

Just had a closer look and certainly the mains transformer is not original. It's a Douglas branded item with 200/220/240v primary taps (on 240 so a good start) then secondary looks like a couple of 6.3 tappings with some mess of bridging together and a 250mA fuse and 250-0-250 with the diodes wired as a full wave rectifier.

This would explain the absence of the bridge rectifier then, and possibly the high HT. Will add photos shortly but just going to disconnect it and investigate the transformer under no load condition & decide where to go from there. Thanks
ekjdm14 is offline  
Old 4th Apr 2019, 2:56 pm   #7
cathoderay57
Nonode
 
Join Date: Oct 2017
Location: Bristol, UK.
Posts: 2,358
Default Re: Got-at Grundig 2065 dead/high HT...

Hi Dan, I repaired a Model 2066 last year which is similar in many respects. I agree with Mike as the heater voltage on mine was about 7.5v so I used a 100R 5W resistor in series with the mains to drop heaters closer to 6.3v and coincidentally reduce the HT a little bit. As yours is not the original transformer you should not need to use a mains series resistor. If it is the same as the 2066 it has an electrostatic tweeter connected to the HT so watch your fingers! The tweeter is unlikely to be working but there is loads of info on this Forum about repairing them with new foam. Once I got the 2066 working it gave the best FM reception of any valved set I have encountered.
cathoderay57 is offline  
Old 4th Apr 2019, 5:32 pm   #8
ekjdm14
Banned
 
Join Date: Feb 2019
Location: Congleton, Cheshire, UK.
Posts: 609
Default Re: Got-at Grundig 2065 dead/high HT...

Thanks for the encouragement, transformer is out and testing it with no load at 245v on the variac (average line voltage here) the outputs give around 6.8v for the filaments and 280-0-280 from the 250v side.

Strangely high given the transformer was fed from it's "240v" primary tap but not horrendous. I'm wondering though if it would affect the set's operation being run from a centre tap transformer and full wave rectifier as opposed to the original setup.

Phone is updating so I have to wait to recover my photos from it, but it's not pretty... I'm wondering if it'd be worth finding a more suitable transformer for the set before continuing much further, or perhaps the current one would stand being run from one "250" tapping into a bridge rectifier with the 0v tied to the chassis to get the set functioning and ascertain whether a replacement is worth it or indeed necessary (the Douglas unit looks like a universal thing though and doesn't fit well at all on the chassis).

Thanks for the info about the tweeter, I'll keep my hands out of that when the set's powered up & have a look at how to fix it if/when I discover it's u/s.
Attached Thumbnails
Click image for larger version

Name:	IMG_0946.jpg
Views:	164
Size:	86.2 KB
ID:	180879   Click image for larger version

Name:	IMG_0947.jpg
Views:	154
Size:	97.3 KB
ID:	180880   Click image for larger version

Name:	IMG_0948.jpg
Views:	152
Size:	82.3 KB
ID:	180881   Click image for larger version

Name:	IMG_0949.jpg
Views:	144
Size:	105.5 KB
ID:	180882   Click image for larger version

Name:	IMG_0954.jpg
Views:	149
Size:	89.1 KB
ID:	180883  


Last edited by ekjdm14; 4th Apr 2019 at 5:44 pm. Reason: Add photos
ekjdm14 is offline  
Old 4th Apr 2019, 7:16 pm   #9
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,786
Default Re: Got-at Grundig 2065 dead/high HT...

If you're measuring these voltages off load then they will be a bit on the high side. I don't think you have anything to worry about.

What's wrong with keeping the existing 250-0-250 arrangement and just adding the missing resistor?
paulsherwin is online now  
Old 4th Apr 2019, 9:06 pm   #10
ekjdm14
Banned
 
Join Date: Feb 2019
Location: Congleton, Cheshire, UK.
Posts: 609
Default Re: Got-at Grundig 2065 dead/high HT...

Not a lot really I suppose, just the transformer isn't particularly neat looking & the wiring needs to be redone anyway as the way the diodes are just flapping around and uninsulated is a bit makeshift even for me. Too tired now but will give it another check over tomorrow bringing it up slowly to limit inrush before I get the resistor & see what the HT settles at if I let it run for more than 30 seconds at full mains. Will see how it settles down & decide where to go from there. Thanks
ekjdm14 is offline  
Old 4th Apr 2019, 9:25 pm   #11
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,786
Default Re: Got-at Grundig 2065 dead/high HT...

I certainly agree that you need to tidy it up with something like a tagstrip.
paulsherwin is online now  
Old 5th Apr 2019, 9:19 am   #12
G0HFCFrank
Pentode
 
Join Date: Oct 2011
Location: Oldham, Greater Manchester, UK.
Posts: 167
Default Re: Got-at Grundig 2065 dead/high HT...

Dan,
Could you not reduce the HT by leaving one diode out and running on half wave rectification?
Just a thought,
Frank C.
G0HFCFrank is offline  
Old 5th Apr 2019, 9:45 am   #13
ekjdm14
Banned
 
Join Date: Feb 2019
Location: Congleton, Cheshire, UK.
Posts: 609
Default Re: Got-at Grundig 2065 dead/high HT...

Paul, a tag strip would be an ideal solution if I keep the current setup, would fit with Grundig's way of doing things too.

Frank, I was thinking along those lines but as Paul mentioned it may not be that bad if I let the set warm up properly. May get a chance for further playtime later today, thanks
ekjdm14 is offline  
Old 5th Apr 2019, 10:22 am   #14
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,786
Default Re: Got-at Grundig 2065 dead/high HT...

Half wave rectification won't reduce the HT, it just means the smoothing caps have to work harder. You are inventing problems for yourself where none exist.
paulsherwin is online now  
Old 5th Apr 2019, 11:04 am   #15
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Got-at Grundig 2065 dead/high HT...

Leaving one diode out would increase the ripple voltage, that would make the HT lower.

If you intend to run it with the higher than normal HT I would make sure that the EL84's anode dissipation isn't over it's limit.

Lawrence.
ms660 is offline  
Old 5th Apr 2019, 5:01 pm   #16
Mike. Watterson
Heptode
 
Join Date: Dec 2014
Location: Limerick, Ireland.
Posts: 901
Default Re: Got-at Grundig 2065 dead/high HT...

The only sensible way to reduce the HT is a series resistor. Using half wave puts MORE stress on the first Electrolytic cap and peak voltage is about the same.
Mike. Watterson is offline  
Old 5th Apr 2019, 6:22 pm   #17
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,786
Default Re: Got-at Grundig 2065 dead/high HT...

Agreed Mike.
paulsherwin is online now  
Old 5th Apr 2019, 6:32 pm   #18
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Got-at Grundig 2065 dead/high HT...

I agree with that too, going half wave would reduce the HT but increase the ripple voltage as has already been stated.

Lawrence.
ms660 is offline  
Old 6th Apr 2019, 9:02 am   #19
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,786
Default Re: Got-at Grundig 2065 dead/high HT...

Why would it reduce the HT? The peak voltage would remain the same, but would only occur on alternate cycles, so the reservoir cap would have to work harder. The smoothed DC should be the same if the reservoir cap is big enough.
paulsherwin is online now  
Old 6th Apr 2019, 10:06 am   #20
G0HFCFrank
Pentode
 
Join Date: Oct 2011
Location: Oldham, Greater Manchester, UK.
Posts: 167
Default Re: Got-at Grundig 2065 dead/high HT...

"Why would it reduce the HT? The peak voltage would remain the same, but would only occur on alternate cycles, so the reservoir cap would have to work harder. The smoothed DC should be the same if the reservoir cap is big enough."

An interesting point Paul, 'common sense' would suggest that as only 1/2 the energy is being supplied to the circuit then the reservoir voltage would drop depending on the load current. Also, as the rectifier (valve or solid state) only conducts when the anode voltage is higher than the cathode (=reservoir voltage) then the half wave can only supply the same amount of energy as the full wave by turning on for a greater part of the half cycle which in turn means a lower average or rms voltage.
That's my take on it and I'm happy to be corrected.
Frank C.
G0HFCFrank is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 4:48 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 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.