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 Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players

Notices

Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

Closed Thread
 
Thread Tools
Old 10th Dec 2020, 12:48 pm   #21
DMcMahon
Dekatron
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

While you are in there I would recommend you visually check out capacitor C35 (0.01uF) to see if it is a paper type, the grid coupling capacitor for the output pentode V5B (ECL86). Worst case if the capacitor is very electrically leaky then could cause circuit damage.

For good measure also would check out C12 (0.1uF) the grid coupling capacitor for V5A the triode section of the V5 valve.
DMcMahon is offline  
Old 10th Dec 2020, 1:01 pm   #22
TerryB44
Pentode
 
TerryB44's Avatar
 
Join Date: Mar 2013
Location: Liverpool
Posts: 102
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

Hi David,
I read the section about grid coupling capacitors or "that Cap" as it seems to be referred to. You mentioned about these earlier. Would that be C35 on the ECL86, V5A?
TerryB44 is offline  
Old 10th Dec 2020, 1:04 pm   #23
TerryB44
Pentode
 
TerryB44's Avatar
 
Join Date: Mar 2013
Location: Liverpool
Posts: 102
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

Oh, your post popped up just as I posted my question! Thanks.
TerryB44 is offline  
Old 10th Dec 2020, 2:27 pm   #24
TerryB44
Pentode
 
TerryB44's Avatar
 
Join Date: Mar 2013
Location: Liverpool
Posts: 102
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

Had a visual check on C35 and C12. C35 looks to be covered in a waxy substance and doesn't look brilliant but that means nothing I suppose. C12 looks to be in better condition. Both are in really awkward locations being underneath other components. Can you tell if they are paper from the pictures?
Here is C35.https://www.vintage-radio.net/forum/...pictureid=4514

Here is C12.https://www.vintage-radio.net/forum/...pictureid=4515

Last edited by TerryB44; 10th Dec 2020 at 2:41 pm.
TerryB44 is offline  
Old 10th Dec 2020, 8:37 pm   #25
DMcMahon
Dekatron
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

C35 almost certainly looks wax covered paper so I would replace. You can cut through the legs to make it easier to remove the old capacitor and unsolder the leg remnants at the valve pins.

C12 looks like a yellow mustard type which is not paper (polyester foil/film type), these normally do not leak and should be fine.

David
DMcMahon is offline  
Old 10th Dec 2020, 10:19 pm   #26
TerryB44
Pentode
 
TerryB44's Avatar
 
Join Date: Mar 2013
Location: Liverpool
Posts: 102
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

Thanks David. I'm just waiting for the parts to arrive now so I can make a start! I assume it would be best to start with the two cans and see what difference they make, and then progress on from there, right? Which type (construction) of cap would it best to replace C35 with?

Last edited by TerryB44; 10th Dec 2020 at 10:37 pm.
TerryB44 is offline  
Old 11th Dec 2020, 12:25 am   #27
DMcMahon
Dekatron
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

Almost any modern axial Polyester/Ceramic/Polypropylene metal film etc.

I personally like Polypropylene.

If possible give C35 some priority because if it was really bad from electrical leakage point of view it could damage the output valve/output transformer (worst case).

When replacing the can capacitors would make sense to measure (if you have a multimeter) the resistance of the associated resistors connected to them, just to make sure none are really abnormally low/high.
DMcMahon is offline  
Old 11th Dec 2020, 12:36 pm   #28
TerryB44
Pentode
 
TerryB44's Avatar
 
Join Date: Mar 2013
Location: Liverpool
Posts: 102
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

Good morning David,
Thanks for the recommendations. I've checked the resistors associated with both cans and they measure ok, so while I was at it I checked all resistors and the only one that reads incorrect is R41 2.2M which only reads 0.05 on the 20M scale. It's colour coded red, red, green in the photo of C35, second from right. Am I not measuring correctly or is it a faulty one?
TerryB44 is offline  
Old 11th Dec 2020, 4:08 pm   #29
TerryB44
Pentode
 
TerryB44's Avatar
 
Join Date: Mar 2013
Location: Liverpool
Posts: 102
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

Just double checked with a better multimeter and the result is the same. Checked R1 which is also 2.2M and that reads ok, so I guess R41 has gone open circuit has it?

Last edited by TerryB44; 11th Dec 2020 at 4:30 pm.
TerryB44 is offline  
Old 11th Dec 2020, 4:28 pm   #30
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

Maybe a poor connection to R41 and R41 is open circuit (in effect)

Lawrence.
ms660 is offline  
Old 11th Dec 2020, 5:20 pm   #31
DMcMahon
Dekatron
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

Depends if your 0.05 reading is a 0.05 ohms, i.e. effectively a short circuit or 0.05 MOhms (50k) or effectively an open circuit indication on that particular meter.

Terry you need to disconnect one end of R41 and recheck. If the volume control R40 (think it is volume) is at one end and switch S2 is made (do not know what this is) there is a direct path from the top end of R41 to earth/ground so then giving a very low resistance reading across R41 (bottom end of R41 connects to ground).

David
DMcMahon is offline  
Old 11th Dec 2020, 5:29 pm   #32
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

He's deleted the 51meg measurement he quoted from his post....

Lawrence.
ms660 is offline  
Old 11th Dec 2020, 5:33 pm   #33
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

So far as I can make out R40 is the source monitor volume control in record and a tone control in playback, S2 is shown in record mode.

Lawrence.
ms660 is offline  
Old 11th Dec 2020, 5:34 pm   #34
DMcMahon
Dekatron
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

I did not see the 51Mohm stated.
DMcMahon is offline  
Old 11th Dec 2020, 5:39 pm   #35
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

Quote:
Originally Posted by DMcMahon View Post
I did not see the 51Mohm stated.
He stated that both his test meters indicated 51meg when connected across R41, after which the post was edited for whatever reason.

Lawrence.
ms660 is offline  
Old 11th Dec 2020, 6:02 pm   #36
DMcMahon
Dekatron
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

Yes as you say in that case maybe a bad connection or R41 open circuit. The repeat measurement of R41 with one end disconnected should prove one way or the other.

Now see the reference in the manual to the tone control/source monitor volume.

David
DMcMahon is offline  
Old 11th Dec 2020, 6:10 pm   #37
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

I don't have the full manual but do you know why pin 1 of the output DIN socket is DC connected to the grid of V5a?

Lawrence.
ms660 is offline  
Old 11th Dec 2020, 6:17 pm   #38
TerryB44
Pentode
 
TerryB44's Avatar
 
Join Date: Mar 2013
Location: Liverpool
Posts: 102
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

Hi David,
R40 is a tone/monitor control and the switch is the rec/play mode switch. I've put the switch in record mode and the reading is zero which would indicate a direct route to ground, so in play mode with the switch off I get a reading of 0.05M which varies if I turn the tone control R40 to a max of 0.42M. So without as you say disconnecting it I'm not going to get a true reading, plus I'm wondering if this might be a bit of a red herring anyway!

UPDATE: It was a red herring. Cut it carefully on the earth connection side so I could re-solder it together and got a reading of 2.6M, so it's ok.

Last edited by TerryB44; 11th Dec 2020 at 6:38 pm.
TerryB44 is offline  
Old 11th Dec 2020, 6:26 pm   #39
DMcMahon
Dekatron
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

Quote:
Originally Posted by ms660 View Post
I don't have the full manual but do you know why pin 1 of the output DIN socket is DC connected to the grid of V5a?

Lawrence.
I wondered exactly the same when I saw it, do not know, maybe Terry has the User manual which may explain.

David
DMcMahon is offline  
Old 11th Dec 2020, 6:38 pm   #40
DMcMahon
Dekatron
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

Quote:
Originally Posted by TerryB44 View Post
Hi David,
R40 is a tone/monitor control and the switch is the rec/play mode switch. I've put the switch in record mode and the reading is zero which would indicate a direct route to ground, so in play mode with the switch off I get a reading of 0.05M which varies if I turn the tone control R40 to a max of 0.42M. So without as you say disconnecting it I'm not going to get a true reading, plus I'm wondering if this might be a bit of a red herring anyway!
Yes looks like a red herring.

The parallel calculation of 2.2M with 547k (R40 500k + R39 47k) = 440k (0.44M).

David
DMcMahon is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 5:54 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.