Mr Carlson does an AR88/CR88 - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

ms660 · 10th Mar 2023, 1:18 pm

There was a problem with traditional sources of Mica supplies during WW2....India for instance.

Lawrence.

AnalogueMan · 18th Mar 2023, 2:52 pm

In the latest instalment he chopped open one of those caps and it was mica, not paper, inside. He did say it was unusual for mica to fail like that and probably due to thermal cycling from the nearby resistors

Radio Wrangler · 18th Mar 2023, 3:16 pm

I've chopped open various failed ones from AR88 and always found paper. Maybe these were self-selected by failing. Also the CR88 was a later set, likely made post-war and maybe trade routes had reopened. There may also be a matter of higher value ones versus lower value ones.

CR88s are rare in the UK, AR88s are common. So beware of these capacitors, not all are what they seem. Also look at the various AR88 restoration texts and notice the numbers of faulty domino Micamolds. They are also in the RF sub-chassis coil box.

So anyone restoring an AR88 still needs to distrust and test these things. If they're part of a tuned circuit, they should be mica, but for simple DC blocks and decouplers plastic film should be fine. Note that the 'that' capacitors are a parallel pair of dominoes and are known to be unreliable.

David

AnalogueMan · 18th Mar 2023, 3:30 pm

Fully agree. Each to their own, but I always replace 'that' capacitor, the HT smoothing caps and any other high-voltage bypass/decoupling caps as a matter of course no matter what type they are or seem to be. With components of that age it's not worth the risk of leaving them

Kevin Hoyland · 26th Mar 2023, 11:43 am

Episode 7 is out now and i think he has got he message regarding the paper Capacitors.

Kevin

ms660 · 27th Mar 2023, 10:24 am

It's made for TV as it were, I watched some of the saga then

Lawrence.

Radio Wrangler · 27th Mar 2023, 3:21 pm

He does drone on and is a bit too far up his own doodad about his inventions, but there are occasional gems in his output. He also gets some interesting bits of kit to work on.

From all that test gear, he can't live far from the old surplus outlets near el camino real.

He suffered from excessive set-dressing before his recent lab move. There is a limit to the amount of duplicated test equipment needed on a bench.

It's worth keeping an eye on him and Dave Jones for when something interesting comes up.

I was a bit surprised at how he wasn't aware of all the standard AR88 stuff.

David

ms660 · 27th Mar 2023, 5:06 pm

Quote:

Originally Posted by Radio Wrangler

He does drone on and is a bit too far up his own doodad about his inventions

Just a little.

Quote:

Originally Posted by Radio Wrangler

I was a bit surprised at how he wasn't aware of all the standard AR88 stuff

All factored to keep folks following.

Lawrence.

M0SOE_Bruce · 28th Mar 2023, 5:45 am

Quote:

Originally Posted by Radio Wrangler

From all that test gear, he can't live far from the old surplus outlets near el camino real.
David

He lives near Vancouver, Canada. He's been collecting (hoarding?) this equipment for a while. His focus appears to be a general audience rather than crusty old gits that apprenticed with Marconi.

Alan Bain · 28th Mar 2023, 6:53 pm

I'm sort of both sad and glad I didn't discover said surplus outlets when I lived on California Avenue (off El Camino Real) 20 odd years ago. I seem to remember luggage weight problems as it was (and those were the days when 32kg hold bags were allowed).

Radio Wrangler · 28th Mar 2023, 7:55 pm

I did, and still haven't got over the mental anguish. Only now after 30-some years has it subsided to a general regret.

David

Radio Wrangler · 7th May 2023, 9:15 pm

More video posted. This time IF alignment in fair detail. I'd have done the narrowest bandwidth as a first stab to find out where the crystal needs to be, then I'd use that frequency rather than a perfect 455kHz number for the IF centre frequency, and then work through the formal procedure with some confidence that when doing the crystal-assisted bandwidths, the centre doesn't jump. This way you can get all 5 selectivity settings with the same centre. Otherwise, if you peak up with one bandwidth and then select narrower, you don't go off tune. The IF doesn't have to be a perfect 455kHz, but it does have to perfectly agree with the crystal. Crystals may have been selected back in the day, but they aren't so available, and they have aged over the years.

David

Techman · 8th May 2023, 12:34 pm

I watched it last night and fell asleep, missing most of it. No disrespect to Carlson, I'd had a VERY long day and was tired. I'll try to watch it again properly later.

10th Mar 2023, 1:18 pm	#21
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 12,983	Re: Mr Carlson does an AR88/CR88 There was a problem with traditional sources of Mica supplies during WW2....India for instance. Lawrence.

18th Mar 2023, 2:52 pm	#22
AnalogueMan Pentode Join Date: Jun 2020 Location: Manchester, UK. Posts: 140	Re: Mr Carlson does an AR88/CR88 In the latest instalment he chopped open one of those caps and it was mica, not paper, inside. He did say it was unusual for mica to fail like that and probably due to thermal cycling from the nearby resistors

18th Mar 2023, 3:16 pm	#23
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 21,417	Re: Mr Carlson does an AR88/CR88 I've chopped open various failed ones from AR88 and always found paper. Maybe these were self-selected by failing. Also the CR88 was a later set, likely made post-war and maybe trade routes had reopened. There may also be a matter of higher value ones versus lower value ones. CR88s are rare in the UK, AR88s are common. So beware of these capacitors, not all are what they seem. Also look at the various AR88 restoration texts and notice the numbers of faulty domino Micamolds. They are also in the RF sub-chassis coil box. So anyone restoring an AR88 still needs to distrust and test these things. If they're part of a tuned circuit, they should be mica, but for simple DC blocks and decouplers plastic film should be fine. Note that the 'that' capacitors are a parallel pair of dominoes and are known to be unreliable. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

18th Mar 2023, 3:30 pm	#24
AnalogueMan Pentode Join Date: Jun 2020 Location: Manchester, UK. Posts: 140	Re: Mr Carlson does an AR88/CR88 Fully agree. Each to their own, but I always replace 'that' capacitor, the HT smoothing caps and any other high-voltage bypass/decoupling caps as a matter of course no matter what type they are or seem to be. With components of that age it's not worth the risk of leaving them

26th Mar 2023, 11:43 am	#25
Kevin Hoyland Heptode Join Date: Feb 2009 Location: Rotherham, South Yorkshire, UK. Posts: 538	Re: Mr Carlson does an AR88/CR88 Episode 7 is out now and i think he has got he message regarding the paper Capacitors. Kevin

27th Mar 2023, 10:24 am	#26
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 12,983	Re: Mr Carlson does an AR88/CR88 It's made for TV as it were, I watched some of the saga then Lawrence.

27th Mar 2023, 3:21 pm	#27
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 21,417	Re: Mr Carlson does an AR88/CR88 He does drone on and is a bit too far up his own doodad about his inventions, but there are occasional gems in his output. He also gets some interesting bits of kit to work on. From all that test gear, he can't live far from the old surplus outlets near el camino real. He suffered from excessive set-dressing before his recent lab move. There is a limit to the amount of duplicated test equipment needed on a bench. It's worth keeping an eye on him and Dave Jones for when something interesting comes up. I was a bit surprised at how he wasn't aware of all the standard AR88 stuff. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

28th Mar 2023, 6:53 pm	#30
Alan Bain Tetrode Join Date: Jan 2012 Location: Amersham, Buckinghamshire, UK. Posts: 50	Re: Mr Carlson does an AR88/CR88 I'm sort of both sad and glad I didn't discover said surplus outlets when I lived on California Avenue (off El Camino Real) 20 odd years ago. I seem to remember luggage weight problems as it was (and those were the days when 32kg hold bags were allowed).

28th Mar 2023, 7:55 pm	#31
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 21,417	Re: Mr Carlson does an AR88/CR88 I did, and still haven't got over the mental anguish. Only now after 30-some years has it subsided to a general regret. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

7th May 2023, 9:15 pm	#32
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 21,417	Re: Mr Carlson does an AR88/CR88 More video posted. This time IF alignment in fair detail. I'd have done the narrowest bandwidth as a first stab to find out where the crystal needs to be, then I'd use that frequency rather than a perfect 455kHz number for the IF centre frequency, and then work through the formal procedure with some confidence that when doing the crystal-assisted bandwidths, the centre doesn't jump. This way you can get all 5 selectivity settings with the same centre. Otherwise, if you peak up with one bandwidth and then select narrower, you don't go off tune. The IF doesn't have to be a perfect 455kHz, but it does have to perfectly agree with the crystal. Crystals may have been selected back in the day, but they aren't so available, and they have aged over the years. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

8th May 2023, 12:34 pm	#33
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 4,639	Re: Mr Carlson does an AR88/CR88 I watched it last night and fell asleep, missing most of it. No disrespect to Carlson, I'd had a VERY long day and was tired. I'll try to watch it again properly later.