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Old 23rd Jan 2023, 3:59 am   #1
Radio Wrangler
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Default Mr Carlson does an AR88/CR88

Just spotted:

https://www.youtube.com/watch?v=kIB7pEA4eqg

He can be a bit tediously slow and nit-picking, but he doesn't miss much out.

CR88 is a post-war variant with the crystal phasing control extended to the front panel.

David
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Old 23rd Jan 2023, 10:47 am   #2
Mike Phelan
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Default Re: Mr Carlson does an AR88/CR88

Very interesting indeed, David. He sure does ramble on!

The AR88 is a lovely receiver - I've owned a couple of them over the years.
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Old 23rd Jan 2023, 12:33 pm   #3
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Default Re: Mr Carlson does an AR88/CR88

Well, he put power on it without going straight for the 'that' capacitor. (two in parallel in the AR88, for added peril)

I wonder if he knows about the tone correction capacitor risk as well?

Saying the bathtubs don't give trouble is a bit off the ball as well. But it's only part one, we need to wait and see how it goes. He certainly seems to like the old beasties. I saved up for a couple of years and bought my AR88 in 1967. Still got it. It's a rather early one, no suffix! it pre-dates the LF intro. Engraved panel and an original S meter. REME fitted a PVC harness in the early 50's.

I've been building up a set of new capacitors to replace all the paper ones. Intending to make a new block capacitor unit, case and all so the original can be archived. The bathtubs have all been leaking and seem to have attacked their rubber seals, the gunge on the outside looks just like red hermetite!

A job for sometime in the future once I'm back to stereoscopic vision.

David
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Old 23rd Jan 2023, 1:02 pm   #4
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Default Re: Mr Carlson does an AR88/CR88

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Originally Posted by Radio Wrangler View Post
The bathtubs have all been leaking and seem to have attacked their rubber seals, the gunge on the outside looks just like red hermetite!

David
Yes, mine did that. Isn't that red stuff supposed to be potentially cancer inducing?

Cheers

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Old 23rd Jan 2023, 2:24 pm   #5
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Default Re: Mr Carlson does an AR88/CR88

I happened to watch this in the early hours. Perhaps I was nodding off and wasn't paying attention properly, but I seem to think that he was intending to look at the so called bath tub capacitors - I'd have to skip through it again to confirm. I've watched odd videos of his on and off over the years and although he certainly knows his stuff, I tend to view him as a "moderniser" rather than a true restorer. I think he's probably one of the many that are the cause of the great blanket re-capping plague that seems to have originated from across the pond, although I did like the way he powered up briefly just to confirm the state of play and I seem to think that he does this more often these days than he used to. You never seem to see him actually replace any parts, the video generally cutting straight to the part where they're all done.

He has an absolute obsession with replacing any test gear sockets that aren't BNC with modern BNC types (we all know that these are generally the best types for this type of kit). I could go with this if the piece of vintage gear were going to be put into serious use and was perhaps your one 'go-to' piece of kit for regular use, but when it's just going up on a shelf as a historical display item, then I say that it's been modernised for the sake of it and ruined. I seem to remember an old Heathkit signal generator getting this treatment. However, he knows his theory and I'm not too bad with his rambling - and he seems a nice enough chap, so looking forward to what he does to the AR88. It looks to be in very good, original condition and it wouldn't surprise me if the alignment tools were still there under that cover - I thought he might find the missing screw dropped down inside somewhere.

I don't know a lot about the AR88 - there was one at a local junk sale a number of years ago which was turned on and running throughout the sale. I think there was a reserve of seventy quid on it, but it got no bids. It was still there at the next sale with a lowered reserve of fifty I think and still didn't sell. It wasn't at the next sale, so someone must have given it a home in the end...let's home so, anyway.
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Old 23rd Jan 2023, 2:27 pm   #6
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Default Re: Mr Carlson does an AR88/CR88

No-one's had it analysed, or if they have, they haven't spread the results. But the oil filling was done in an era when PCB oils were the new thing in high performance transformer oils. It's easiest to not take the risk.


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Old 23rd Jan 2023, 5:29 pm   #7
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Default Re: Mr Carlson does an AR88/CR88

I am not really into Radio but did find it very interesting.

Some nice test equipment in the background.

David
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Old 24th Jan 2023, 12:45 pm   #8
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Default Re: Mr Carlson does an AR88/CR88

Greetings all.

Mr Carlson lost me I am afraid.
He seems to be one of those "plug it in and switch on" brigade with nary a thought for the possible damage.
He is lucky that C-119 didn't kill the audio output transformer.
Very lucky!
Then to add insult he was playing with the power switch, specifically turning it to the transmit position while the radio was running and then back to receive.
Those of us that know the inner workings know that is a big no no. The high tension spikes caused by that action has killed many a radio.

This sort of information is readily available to the casual searcher and has been discussed here on this form alone innumerable times.

He is so lucky he didn't kill that beautiful CR-88. It looks to be in pristine condition.
Wish mine were so pretty.

Enough said on my part.
There is a raging thunder storm here now so I will say good night all.

Cheers,
Robert, VK2BNM.
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Old 24th Jan 2023, 7:03 pm   #9
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Default Re: Mr Carlson does an AR88/CR88

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Mr Carlson lost me I am afraid.
He seems to be one of those "plug it in and switch on" brigade with nary a thought for the possible damage.
He is lucky that C-119 didn't kill the audio output transformer.
Very lucky!
Then to add insult he was playing with the power switch, specifically turning it to the transmit position while the radio was running and then back to receive
While I understand what you're saying regarding these known issues, I can't fully agree.

He gave the set the lamp limiter treatment first, which was fair enough. He probably ran it for a little bit longer than I would have done for an initial test at full mains power. We all do things differently and while I think that the series tungsten filament series lamp is a very good idea, I rarely use one and after an initial inspection for anything that's likely to go bang and cause grief, I give the item full mains. I sometimes do what he did and hang a meter on the main HT line to watch what happens as the voltage (if any) comes up - I think he just probed for a voltage reading rather than have it clipped on for continuous monitoring. Once I'd got that background noise from the speaker and signs of reception, I'd have switched the thing off after not much longer than around half a minute, rather than start going through all the bands and tuning end to end of the scale, but he got away with it!

After that initial test I would have checked for any hot spots or smells and then probably lifted one end of those grid coupling capacitors and temporarily tacked a replacement in and then given the set a slightly longer test if everything else had seemed to survive the initial power up, but I'd probably still keep monitoring that HT voltage for any sudden fall off. I really don't think that the audio output valve could pass enough current between its anode and cathode to burn the output transformer out in an initial half a minute test - there'd have to be a complete internal electrode short for that to happen and would be very unlikely.

Carlson used to annoy me when he'd just go through a piece of test gear and replace all the capacitors, including the power supply smoothers without powering up or doing any initial tests, probably needlessly replacing good old electrolytic capacitors that would have lasted many more years. I'm pleased that he seems to be doing things more my way now. I also think that he may have been trying not to over complicate things too much on the initial inspection. He's a bit like a college lecturer in his approach.

Last edited by Techman; 24th Jan 2023 at 7:12 pm. Reason: Corrected description of HT monitoring.
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Old 26th Jan 2023, 10:04 pm   #10
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Default Re: Mr Carlson does an AR88/CR88

Yes, generally sage stuff, though the "meat" could have been delivered in half the time (or less)- but then I make the same complaint about most of the factual programmes on TV.... Could have done without all that narcolepsy-inducing stuff about the base panel screws- for goodness sake, someone intending to get to grips with what was once the bleeding edge of governmental-level snooping kit should be beyond that sort of thing. He did seem to be a bit precious about the possibility of others having worked on it previously, too- come on, it's 80 years old now and would have been expected to deliver the goods to a high spec. in its service life, possibly at life-or-death level, plus many years after that in possibly varying hands.

I wouldn't have hesitated for a moment to change the AF output grid coupler as an initial step- not only are they Micamolds, so they will be leaky but there's two in parallel just to make sure of it! Especially as he gave the impression of intending to make a go of the set, and the tone corrector C119 needs doing at the same time.

Still, credit to him for setting aside the time and conveying the enthusiasm to a potentially wide audience.
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Old 4th Feb 2023, 4:23 pm   #11
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Default Re: Mr Carlson does an AR88/CR88

Being these radios are some of my favorites, owning many and having brought several back to life, I'm watching with interest. I agree he should have taken the usual precautions of replacing the cap to limit possibly damaging the audio xfmr.

One thing that stood out to me was he had both hands in the radio when measuring the HV. I always clip the meter to the chassis and measure with one hand in my pocket. Bit bit a couple times - don't want to test my luck again.

That is a VERY clean and working radio he is starting with so it should be an easy update. I'll be interested to see if he does a sweep alignment of the IF.

I just finished a total reconstruction of an AR88F, stripped to bare chassis, new wiring and components. Just waiting on the front panel to come back from the painter / screener. I'd like to see what he does when presented with a basket case radio.......

Tom
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Old 4th Feb 2023, 4:26 pm   #12
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Default Re: Mr Carlson does an AR88/CR88

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Originally Posted by turretslug View Post
credit to him for setting aside the time and conveying the enthusiasm to a potentially wide audience.
Agree!

Tom
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Old 14th Feb 2023, 6:10 am   #13
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Default Re: Mr Carlson does an AR88/CR88

Greetings all.

I haven't replied for a while as I have been in hospital.
I agree that Mr. Carlson is good to bring forward the idea of people being interested in repairing older communications radio equipment.

I do strongly dis-agree with the idea of just plugging it in and switching it on!
Yes, he had a lamp limiter in use but that will not protect the audio output transformer.
If you don't think the audio transformer is a big deal in an AR-88 receiver then try to buy one. Good luck with that!

I have wondered if Mr. Carlson has done some checks on the radio before he started to film his video segment. Quite possible as the man is not an idiot.

If capacitor C119 fails it will put full HT across the primary of the output transformer.
I have experience with AR-88 radios. 2x "D"s and 2x "LF"s. 3 restored and the 4th at the end of my bench now waiting patiently.
The 3 restored ones have had the C119 caps replaced before power up.
The precaution of changing the output valve grid cap is an excellent idea.

Have to look around at the information on the net and if you are a beginner at this stuff use the search function on this excellent forum.
If in doubt ask questions on this forum. It is chock full of friendly people who are happy to save you from the "Gotcha's" that can destroy your radio.

Here's another gotcha for the plug it in and switch it on brigade. North American R-390A receiver.
Just plug it in and switch on.
Do a knob twist to see if it works.
And wipe out 4 Collins mechanical filters.
If you can find them maybe over $1k.
Ouch!
A very common fault is capacitor C553. Plate coupler between an IF stage and the bandwidth switch. The other side of that switch is the 4 Collins mechanical filters.
The R-390A nominal HT is 250V. C553 is 0.001Mfd 300V waxed paper.
Not much free-board.

Just remember. Do the research before plugging it in.
"Fools rush in where experienced techs fear to tread".

Just my thoughts.
I know some will disagree and some vigorously but it is how I do it.

Cheers all.
Robert VK2BNM.
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Old 14th Feb 2023, 7:59 am   #14
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Default Re: Mr Carlson does an AR88/CR88

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Being these radios are some of my favorites,
Tom
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You being on your side of the Atlantic, I assume that's a CRM-R6A overseeing your operations. There are a few of the AR8516L variants in the UK, but they have a number of issues. Gorgeous lookers, though.

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Old 14th Feb 2023, 3:30 pm   #15
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Default Re: Mr Carlson does an AR88/CR88

I have nothing like the technical expertise and useful info shown here but I do remember that [like the R1155] these sets enjoyed a boom in demand about a decade ago. It had always seemed to be a "given" that destroying the O/T was amazingly easy and the TR's were as rare as could be, as Robert says at post 13*.

I did notice that one or two individuals carried on regardless and were lucky plus some people then employed and relatively modest non standard O/P transformers with good results. The assumption, up to then, was always that if an original could not be sourced, all was lost. There is a least one article somewhere focussed on how to get around the failed O/T problem. In discussion it was suggested that maybe the Output Stage itself was a bit of a design fault in the rush to production at the start of the war and rather than modify them all, it was possible that, when an overload occurred, it was just easier to get another tranny from the stores! As good an explanation as any other perhaps.

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Old 17th Feb 2023, 2:48 am   #16
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Default Re: Mr Carlson does an AR88/CR88

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Quote:
Originally Posted by thoyer454 View Post
Being these radios are some of my favorites,
Tom
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You being on your side of the Atlantic, I assume that's a CRM-R6A overseeing your operations. There are a few of the AR8516L variants in the UK, but they have a number of issues. Gorgeous lookers, though.

David
Hi David,

I have two 8516's - no "L", not quite sure what the "L" signifies.

The one I did a few years back is completely redone, works well and looks just as good. The second that I got this past fall is in various states of disassembly on the bench right now. Finished replacing all of the paper caps and now I'm addressing the mechanicals.

I picked up a CRM-R6A this past fall as well and that is next up on the bench after I finish the 8516. Probably another month or so. Need to get some dials made for the 8516....

I don't have the patience or "teaching" personality it takes to do videos loke Mr Carlson does otherwise these would make great videos....

Tom
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Old 9th Mar 2023, 2:26 am   #17
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Default Re: Mr Carlson does an AR88/CR88

Episode 3 is out.

He's replaced the main reservoirs and the bathtubs, found some livelier 6SG7s and run into a crackly audio problem.... Along with flickers of the VR150/30 regulator.

It's our pal, THAT capacitor.

So Paul doesn't seem familiar with the 'that' capacitors in valved audio stages in general. Nor does he seem aware that 'Micamold' capacitors are 100% mica-free and just crappy paper jobs hyped up by marketing.

I notice that he's wary of the oils in some capacitors without saying why.

It's interesting watching him discover stuff we're well aware of, but as he replaced the bathtubs on sight, as well as the big block smoother, he has been using prior knowledge of certain components. So I think he genuinely isn't familiar with all the usual players and we're getting to see him diagnose them from scratch.

Good footage of 6K6 grid glowing and darkening, shot through convenient hole in the top mica.

David
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Old 9th Mar 2023, 3:45 am   #18
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Default Re: Mr Carlson does an AR88/CR88

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So Paul doesn't seem familiar with the 'that' capacitors in valved audio stages in general.
I've been following this. I actually thought that he had replaced 'that' capacitor, but I could be wrong and would have to check back. I seem to think that he is familiar with grid coupling capacitors from the odd video I've seen of him working on standard vintage broadcast receivers.

Personally, I would have left the bathtubs in place and perhaps mounted a small tag strip on one of their vacant connections, fitting a small tag strip on each one to mount the replacement capacitors, rather than doing it the way he did, but his way does look neat. However, not everyone is going to have a soldering iron hot enough to reliably make all those 'direct-to-chassis' soldered connections, so it would be a tag strip for each one if I was doing it, I think, and leave the chassis itself untouched. I take his point regarding the fact that those bathtubs could leak in the future, but seeing their unstressed condition, I would have risked leaving them in place and just electrically disconnected, using a vacant tag on each one to mount a small tag strip for the replacement capacitors - I was glad to see that he then contradicted the 'leak' theory by leaving the main block in place and just disconnecting it...I think there's a low risk of leakage once they're out of circuit and I take his point regarding heating the terminals causing possible leakage, although again, I personally think this is low risk.

I must admit that when that crackling (which he referred to as 'static') started, I immediately thought of the typical sound of a failing audio output transformer - fingers crossed that it's not that!

To sum up, I think his series on this receiver is probably going to be one of the best (if not the very best) 'go-to' diary (or 'how-to') for anyone wanting to do a repair/restoration on one of these sets, perhaps viewed in conjunction with this thread to take all the different views of others on board before deciding on the exact path to take. I don't agree with absolutely every method he uses in his 'restorations' and I do feel that he's sometimes more of a 'moderniser' than true restorer, but there's no doubt that he knows his stuff and we all have different opinions on how things should be done. He's not old enough to have been brought up and trained in valve (tube in his case) technology, so he's obviously had to teach himself, or perhaps been lucky enough to have had someone older to mentor him in the technology.

Although I've seen a few of these receivers around over the years, I've never actually had my hands in one myself - perhaps I should have bought that one I mentioned at the junk sale, just for the experience, although I'm trying to avoid any more boat anchors these days.
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Old 10th Mar 2023, 12:57 pm   #19
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Default Re: Mr Carlson does an AR88/CR88

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I actually thought that he had replaced 'that' capacitor, but I could be wrong and would have to check back.
In fact he hadn't.

I happened to see his latest video on the CR88 receiver last night - I'd only seen the previous one where he'd replaced those bathtub types when I made the above post.

I seem to think that those flat type of capacitors with the 'domino' type markings aren't necessarily mica types like you might think they are, but are actually paper and foil like the traditional ones that we all know and love - he certainly thought they were the more reliable mica types. He should cut one open (like he's said he's going to do with a bathtub at some stage, although I think most of us have seen these opened up before) and see what's inside. In fact, I've got a feeling that I may have got some of those 'domino' marked capacitors in a jar somewhere, so if I find one (or some) I'll test one and if it shows as being leaky, I'll cut it open and have a look at the innards, just out of interest.
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Old 10th Mar 2023, 1:03 pm   #20
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Default Re: Mr Carlson does an AR88/CR88

Those are the notorious Micamold capacitors. No mica was inconvenienced in making them, just paper. Whether they were a wartime measure to conserve mica supplies or whether they were just a profiteering marketing scam, I'm unsure. I'm quite certain that they are rubbish.

You may be wasting a valuable jar!

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