Radiogram identification and Circuit info - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Chiltern · 9th Jan 2023, 1:33 am

Quote:

Originally Posted by Nickthedentist

Is the arm on yours plastic or cast alloy? The former are very brittle by now!

Nick, the plastic arms were brittle even when new. My parents had a Sobell radio gram in the 50's and the plastic lugs for the cartridge mounting failed very quickly, however BSR were contacted and they sent a die cast replacement.

The plastic arm originally fitted with a HGP37 cartridge, still have many discs played on this, including the 1st LP the family bought, and they are still playable with reasonable quality, so not too 'groove grinding', specially considering the playing weight.

Alan

Brockie · 9th Jan 2023, 11:13 pm

Quote:

Originally Posted by Simon Gittins

If you want to try using the original electrolytic capacitor, it should be reformed at its working voltage using something like this:
https://www.vintage-radio.com/projec...-reformer.html
A modern ESR tester won't check it at its working voltage.
The capacitor pictured would be fine as a replacement.

Ooh interesting. Might knock one of those up... Thank you Simon.

Brockie · 9th Jan 2023, 11:14 pm

Quote:

Originally Posted by joebog1

Paul, I use F&T caps for all chassis mount caps. I've been using them for about 40 years and NEVER had a failure.

Joe

Awesome - thanks Joe - have just ordered one in case needed

Brockie · 10th Jan 2023, 9:14 am

All parts on order.. Just waiting on the postie to rock up with the goods.. should hopefully be before the end of the week....

Many thanks to everyone for their help and advice, as always. Still learning as i go

A confirmed list of the valves contained....

X79
6BA6
6AT6
EL84
U50

So with regards to the "audio coupling cap (that capacitor)" - where would i be looking for this? Are we talking ceramic here, mica or ??. With no cct diagram, I am guessing it would be somewhere around the 6AT6 and EL84 Grids?
Thanks

Cobaltblue · 10th Jan 2023, 9:25 am

It would be connected to the EL84 grid.

The original is likely to be a wax paper capacitor or a hunts mouldseal, or some such similar.

If you take an under chassis picture around the audio stages (EL84, 6AT6) area, many members can point you to the likely suspects.

Cheers

Mike T

Station X · 10th Jan 2023, 9:26 am

Quote:

Originally Posted by Brockie

So with regards to the "audio coupling cap (that capacitor)" - where would i be looking for this? Are we talking ceramic here, mica or ??. With no cct diagram, I am guessing it would be somewhere around the 6AT6 and EL84 Grids?
Thanks

Please see post #6.

dazzlevision · 10th Jan 2023, 9:29 am

That capacitor would be the one connected to the control grid (g1) of the EL84 valve - pin 2 (counting clockwise when looking at the underside of the chassis).

There might be a low value series resistor connected to pin 2 as well, but "that capacitor" will have one end going to EL84 pin 2.

Use a Polyester or Polypropylene axial lead type, rated at 400V dc.

The photo of the same chassis I had will give you an idea (posted earlier in this thread). It's the yellow one on a small 3 way tagstrip fixed to the inner side of the right hand chassis vertical panel, with a 220k resistor at one end and a 470k resistor connected at the other end.

Brockie · 10th Jan 2023, 10:11 am

Thats typical. I was going to say pin 2 of the EL84. However didn't want to get it wrong in front of those that have a decent knowledge and experience on these things.

Thanks dazzlevision/Cobaltblue/Station X - yes it's the waxy on the right side, which is good news since I have a Polyester 400v axial replacement on the way.

Brockie · 15th Jan 2023, 4:16 pm

So - no better way of spending a weekend than the theraputic replacement of 66 year old Waxy Capacitors. All now replaced (Including "That" one)

Just trying to work out how best to mount the 32+32 Capacitor, since there is no way the terminals will fit through the tiny triangle cut in the chassis since the newer one is a lot bigger (32mm diameter rather than the 25mm of the old one - wouldnt be do bad if they had punched a larger hole in the chassis - however alas not!) - Am currently thinking down the line of mounting sideways on the internal underside of the chassis, with some short wires to the original connection points. Will leave the existing hunts Cap in there for show, however just migrating the wires off onto the new one.

Power cable still to be replaced (Think it was 2004 when these changed to Brown/Blue)... however it is still in pretty good nick... might just reterminate. As per dazzlevision's rebuild, i have a fuseholder that i will stick inline just to make things a little safer - not sure what to rate it at though - maybe i will power up and measure the current drawn, and base it around that...

Slow progress, however going well

Nickthedentist · 15th Jan 2023, 4:18 pm

Quote:

Originally Posted by Brockie

Power cable still to be replaced (Think it was 2004 when these changed to Brown/Blue)... however it is still in pretty good nick... might just reterminate.

More like 1970-ish for flexible cables! But unless it's faulty or not up to the job, why not re-use it? It's part of the set's history, after all.

Brockie · 15th Jan 2023, 4:23 pm

Quote:

Originally Posted by Nickthedentist

Quote:

Originally Posted by Brockie

Power cable still to be replaced (Think it was 2004 when these changed to Brown/Blue)... however it is still in pretty good nick... might just reterminate.

More like 1970-ish for flexible cables! But unless it's faulty or not up to the job, why not re-use it? It's part of the set's history, after all.

Fair point - hadn't thought of that!

Brockie · 19th Jan 2023, 9:17 am

So I thought i would slowly (Via Variac) increase the power on this in the hope that the existing old hunts 32+32uF Cap would reform. Wound up slowly over around 12 hours.

After 12 hours I connected a loudspeaker (just one i had laying about), and no matter what volume it was set to I was getting a loud rasping noise from the speaker. Figured this might be caused by a smoothing capacitor which looks like a Hunts.

So - Swapped out (all be it temporarily for the meantime) for the 32+32uF I had ordered, but was considering whether to change or not. As if by magic, life! I had a radio with no issues (even though it seems a bit deaf). Not sure on whether the dial matches up with the frequencies - a job for later.

So now the "amp" seems to be up and working, time to turn my attention to the Turntable.

10th Jan 2023, 9:14 am	#24
Brockie Triode Join Date: Nov 2018 Location: Risca, South Wales Posts: 48	Re: Radiogram identification and Circuit info All parts on order.. Just waiting on the postie to rock up with the goods.. should hopefully be before the end of the week.... Many thanks to everyone for their help and advice, as always. Still learning as i go A confirmed list of the valves contained.... X79 6BA6 6AT6 EL84 U50 So with regards to the "audio coupling cap (that capacitor)" - where would i be looking for this? Are we talking ceramic here, mica or ??. With no cct diagram, I am guessing it would be somewhere around the 6AT6 and EL84 Grids? Thanks

10th Jan 2023, 9:25 am	#25
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,864	Re: Radiogram identification and Circuit info It would be connected to the EL84 grid. The original is likely to be a wax paper capacitor or a hunts mouldseal, or some such similar. If you take an under chassis picture around the audio stages (EL84, 6AT6) area, many members can point you to the likely suspects. Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

10th Jan 2023, 9:29 am	#27
dazzlevision Dekatron Join Date: Sep 2003 Location: Near Swindon, North Wiltshire, UK. Posts: 3,608	Re: Radiogram identification and Circuit info That capacitor would be the one connected to the control grid (g1) of the EL84 valve - pin 2 (counting clockwise when looking at the underside of the chassis). There might be a low value series resistor connected to pin 2 as well, but "that capacitor" will have one end going to EL84 pin 2. Use a Polyester or Polypropylene axial lead type, rated at 400V dc. The photo of the same chassis I had will give you an idea (posted earlier in this thread). It's the yellow one on a small 3 way tagstrip fixed to the inner side of the right hand chassis vertical panel, with a 220k resistor at one end and a 470k resistor connected at the other end. Last edited by dazzlevision; 10th Jan 2023 at 9:37 am.

10th Jan 2023, 10:11 am	#28
Brockie Triode Join Date: Nov 2018 Location: Risca, South Wales Posts: 48	Re: Radiogram identification and Circuit info Thats typical. I was going to say pin 2 of the EL84. However didn't want to get it wrong in front of those that have a decent knowledge and experience on these things. Thanks dazzlevision/Cobaltblue/Station X - yes it's the waxy on the right side, which is good news since I have a Polyester 400v axial replacement on the way. Attached Thumbnails

15th Jan 2023, 4:16 pm	#29
Brockie Triode Join Date: Nov 2018 Location: Risca, South Wales Posts: 48	Re: Radiogram identification and Circuit info So - no better way of spending a weekend than the theraputic replacement of 66 year old Waxy Capacitors. All now replaced (Including "That" one) Just trying to work out how best to mount the 32+32 Capacitor, since there is no way the terminals will fit through the tiny triangle cut in the chassis since the newer one is a lot bigger (32mm diameter rather than the 25mm of the old one - wouldnt be do bad if they had punched a larger hole in the chassis - however alas not!) - Am currently thinking down the line of mounting sideways on the internal underside of the chassis, with some short wires to the original connection points. Will leave the existing hunts Cap in there for show, however just migrating the wires off onto the new one. Power cable still to be replaced (Think it was 2004 when these changed to Brown/Blue)... however it is still in pretty good nick... might just reterminate. As per dazzlevision's rebuild, i have a fuseholder that i will stick inline just to make things a little safer - not sure what to rate it at though - maybe i will power up and measure the current drawn, and base it around that... Slow progress, however going well

19th Jan 2023, 9:17 am	#32
Brockie Triode Join Date: Nov 2018 Location: Risca, South Wales Posts: 48	Re: Radiogram identification and Circuit info So I thought i would slowly (Via Variac) increase the power on this in the hope that the existing old hunts 32+32uF Cap would reform. Wound up slowly over around 12 hours. After 12 hours I connected a loudspeaker (just one i had laying about), and no matter what volume it was set to I was getting a loud rasping noise from the speaker. Figured this might be caused by a smoothing capacitor which looks like a Hunts. So - Swapped out (all be it temporarily for the meantime) for the 32+32uF I had ordered, but was considering whether to change or not. As if by magic, life! I had a radio with no issues (even though it seems a bit deaf). Not sure on whether the dial matches up with the frequencies - a job for later. So now the "amp" seems to be up and working, time to turn my attention to the Turntable.