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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 29th Nov 2017, 12:51 pm   #41
Station X
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Default Re: AR88 Low HT

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I strongly advise you to leave the IF alignment well alone. It can be very difficult to set up even with the correct test equipment.
The whole shebang needs to be precisely centred on the narrow-bandwidth crystal.
Indeed. That's where I went wrong on my first attempt. I think only the EMER states the need to ascertain the crystal's frequency. It may not be exactly on the IF Frequency (sic).
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Old 2nd Dec 2017, 6:29 pm   #42
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Default Re: AR88 Low HT

Quick one, is there any trick to removing the main tuning knob?

Iíve removed both grub screws but itís not budging, canít see any other way to remove it. Iíve dripped some wd40 round the back and down both grub screw holes to try and free it. Before I resort to more brutal measures I thought Iíd ask first
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Old 2nd Dec 2017, 6:44 pm   #43
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Default Re: AR88 Low HT

Sometimes that's caused by a burr/deformation on the shaft caused by the grub screw being overly tightened, if it is then I usually turn the tuning knob until the end stop is reached then carefully try to rotate the knob a bit further whilst carefully pulling it off at the same time, that always worked for me on several receivers.

Lawrence.
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Old 2nd Dec 2017, 6:56 pm   #44
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Default Re: AR88 Low HT

Brilliant!

The drive seems to have a clutch type mechanism so I can turn it indefinitely. To get round this I held the flywheel still with one hand and gave the knob a twist with the other and it came straight off! I’ll remember that Lawrence, cheers
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Old 2nd Dec 2017, 7:03 pm   #45
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Default Re: AR88 Low HT

No problem, one of the last ones I had like that was on a HRO.

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Old 2nd Dec 2017, 8:55 pm   #46
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Default Re: AR88 Low HT

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Sometimes that's caused by a burr/deformation on the shaft caused by the grub screw being overly tightened, if it is then I usually turn the tuning knob until the end stop is reached then carefully try to rotate the knob a bit further whilst carefully pulling it off at the same time, that always worked for me on several receivers.
Please don't try forcing an AR88 against the endstop on the tuning gearbox. The very early gearboxes are stronger than the later ones, and the later ones are known for breaking the quadrant gear.

It's best to reach in and to try to hold the flywheel still while the grip of the knob is broken.

It's bad practice to spin these sets across the tuning range and into the endstops. It's easy to do. I did it a lot as a schoolkid and got away with it, but I only found out about the risk of damage many years later. My set is a very early one with complete circular gears throughout.

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Old 2nd Dec 2017, 9:30 pm   #47
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Default Re: AR88 Low HT

From memory on the one I had the small driving gear on the flywheel shaft is part of a slipping spring clutch arrangement so turning the tuning knob to the end carefully shouldn't overdo anything, the knob/flywheel shaft should slip, unlike the one on the HRO, once the split gears are at their limit everything stops, having said that it doesn't have the same type of flywheel kinetics as the AR88.

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Old 5th Dec 2017, 10:21 am   #48
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Default Re: AR88 Low HT

I've removed the 3 remaining bathtub units and gave them a test for capacitance and leakage using the reform/leakage tester described on this site. Nothing too shocking in terms of capacitance, some values were up to 25% higher than stated. The tub containing C76, C56, C93 tested pretty poorly. With C76 showing 15ma leakage at 350 volts, others 6ma and 3ma. Other 2 tub units tested fine for leakage with all showing well under 0.6ma.

As they were removed I gutted them anyway cutting the backs off as before. Unfortunately my nitrile gloves did manage to split during the process and I got some oil on my finger which I quickly washed off - not ideal. In terms of risk I've had a pretty negligible exposure, but all the same its a reminder to be cautious If doing any rough work with light duty gloves on! Que Sera.....

I'm in the process of fitting new caps into the tubs and hope to get them installed on the weekend. I read somewhere that while these are non polarised caps, it might be better to install them so that the outer foil is connected to the earth end. I cut one open to check this and will install this way for these units - too late for the others. I'm using those yellow polypropylene "TSE" capacitors on this receiver as I've found them to be pretty decent and have loads of them.

I found the electrically leaky tub unit, had a fair bit less oil than the others did. I'd imagine this contributed to the spillage on the case. PCB or not its horrible stuff and I will be glad to be rid of it completely!

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Old 6th Dec 2017, 11:21 am   #49
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Default Re: AR88 Low HT

For anyone who has restuffed their bathtub units, can I ask did you retain the original terminals and did you test their integrity before re-stuffing?

On the previous 3 I did, I tested for shorts to the casing with a decent multimeter. Initially I found some very high resistance showing, which I believed to be residual moisture from washing the units. A blast with WD40 or heating with a hair drier seemed to improve then finally sort this. One unit I had to leave overnight in a warm house until it showed no connection. I did also move the lead and terminals around considerably and saw no peep of a connection once this was done. I then assumed all was ok, fitted the new parts and reinstalled in the receiver, which worked just fine.

On THESE I've just opened, a few days later and I'm still seeing some high resistance between terminals and case. One I had already restuffed showed 3ma leakage with a leakage tester on a new capacitor, which suggests to me a small short there in the insulation, water based or otherwise.

It COULD well be they have been in my cold and damp workshop and this hasn't dried them out. That's my hope, because otherwise I might need to rethink what I've done on the others. I brought them into the house last night and left them under a warm lamp. Will do some further checks later.

Just to be clear, I'm soldering to the bit of connecting wire left from the originals, and have stuck some silicon sleeving into the grommet they come out of.
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Old 6th Dec 2017, 7:56 pm   #50
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Default Re: AR88 Low HT

Drying out has helped, but if I press on the terminal where the blob of solder is shorts start appearing - theyíre no good. *sigh*

Now to think on a new strategy, I will also have to remove the 3 I have already installed
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Old 6th Dec 2017, 8:02 pm   #51
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Default Re: AR88 Low HT

Possible solutions here in post#16 and 17:

https://www.vintage-radio.net/forum/...d.php?t=131415

Lawrence.
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Old 6th Dec 2017, 8:08 pm   #52
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Default Re: AR88 Low HT

Yes I saw those but didn’t manage to find any such chasis mount terminals which would have been ideal. The feed through capacitor idea seems quite clever, I never knew they existed.

Will see if I can dismantle or drill out what’s there and see if I can do anything with them
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Old 12th Dec 2017, 2:26 pm   #53
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Default Re: AR88 Low HT

Its not too difficult drilling out the riveted solder tags, just still deciding what to do with them. I've not been able to find anything suitable in the form of standoff terminals etc, so I'm going to see what I can do with what's left.

I've epoxyed the red/brown insulators back onto the unit, and will see if I can solder a piece of insulated wire to the tag and use epoxy or milliput to set it in place leaving some wire in the tub to attach the new capacitors.

Possible issues may be this wire coming loose from the tag when soldering the connections to the finished units. It seems they mitigated this originally by flowing LOTS of solder on to the bottom of the tag, which would require heat directly applied for some time to melt it. I will try and recreate this, but at the same time might risk degrading the epoxy by flowing lots of solder there.

My backup plan is forget the tag, use a stiff piece of insulated wire and bend back on itself to form something resembling a tag I can solder to and keep the soldering iron out of direct contact with the epoxy.

Its proving an interesting project, and I have to say if I'd known initially how bad some of these terminal seals had been, I wouldn't have bothered re-stuffing at all and would have mounted new parts on tag strip or paxolin board as others have done! I've spent so much time on these now that I feel I have to finish them to a point.

Mods, this has gotten well off topic but I'd like to keep this thread going and hopefully add some pictures. Is it possible it could be renamed to ar88 restoration, or something similar? If you don't see this I'll drop a PM
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Old 13th Dec 2017, 8:20 am   #54
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Default Re: AR88 Restoration.

Hello.
Will look forward to looking at the photos.

Thanks Kevin.
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Old 13th Dec 2017, 11:02 am   #55
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Default Re: AR88 Restoration.

Hi Kevin, I'll be sure to get some up soon. Ive struggled to get as much time on this lately as I'd like.

The approach with the bathtubs I've decided on involves removing the blob of solder from the bottom of the tag, drilling out the tag and rivet, then using epoxy to reattach the red insulator. Enlarging the hole in the insulator a little more, I then insert and glue a small (3.2mm) red eyelet crimp. It doesn't look bad and is at least similar to the original look. Capacitor leads from inside will then be fed through the crimp tube and fed through the eyelet for soldering along with the connections.

Ill put a picture up when I've finished one. Its a different approach to what most have done, and in future I think I'll just put stripboard in. Given this is an early example I want to do the best my humble abilities will allow.
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Old 13th Dec 2017, 7:19 pm   #56
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Default Re: AR88 Restoration.

I fear that the "red insulator" is itself part of the leakage problem.... so unless you can totally isolate your restuffing-efforts from electrical contact with the red insulators your leakage-problems will return.

[I've never bothered restuffing the bathtubs in my AR88s; a chunk of single-sided PCB suitably etched and fitted with "turret tags" https://uk.rs-online.com/web/p/pcb-r...tools/0433589/ makes an ideal platform for attaching axial-leaded modern components. And very much in the spirit of the original AR88 designers when they fitted the big HT-bottom-end bias resistors].
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Old 13th Dec 2017, 8:17 pm   #57
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Default Re: AR88 Restoration.

I think you're right G6Tanuki, and quite possibly its those that become leaky more than the capacitors inside.

What I'm doing will mean only the plastic part of the eyelet crimp is in contact with the insulator, so should be zero chance of that.

Its a painful process considering I have 3 restuffed tubs and now have to remove and redo them, but I cant argue with the meter readings are telling me - they simply aren't good enough. A lot better than they WERE, but 3ma leakage on a new capacitor is unacceptable - especially when the part shows 0.3ma when disconnected from the tub. I'm doing this once and doing it to last.

When I tackle the next one I shan't bother with restuffing and will do as you suggest
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Old 14th Dec 2017, 12:46 pm   #58
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Default Re: AR88 Restoration.

Thought I should add a picture of this lovely receiver, and what I'm doing with the bathtubs compared to one with original tags.

Unfortunately the receiver has the front panel off right now so this picture will have to do for now. Excuse the poor dťcor in the background
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Old 14th Dec 2017, 1:05 pm   #59
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Default Re: AR88 Restoration.

Nice solution.

Mine had a front panel like yours (smooth finish)

Lawrence.
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Old 14th Dec 2017, 3:07 pm   #60
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Default Re: AR88 Restoration.

Neat! I really like the ingenious thinking of using the plastic part of the crimp-eyelets as an 'isolator' before you get to the possibly-leaky original insulated bushing.
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