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 Amateur and Military Radio

Notices

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

Closed Thread
 
Thread Tools
Old 3rd Aug 2017, 12:11 pm   #1
john_morris_uk
Tetrode
 
Join Date: Mar 2014
Location: Farnham, Surrey, UK.
Posts: 61
Default AR88 (yet another!)

I've just acquired an AR88 for restoration. There's a note inside that says it was completely realigned and repaired in 2007 but more capacitirs have since developed the classic leaking oil (PCP?) symptoms. One suspect is C99/112/114 which if I read the reports correctly puts the output transformer under threat so I haven't even applied power through my variac.

However there's such a mess that I'm wondering if the main smoothing capacitors on the HT are leaking. (I'm away at the moment so can't double check.) I've started to research what to replace them with if the oil filled paper ones are gone and this is where I need some advice. When I've built GV supplies for Linear Amps I've series some electrolytics.) But it would be easy to achieve much more than 4uF per cap. I understand this stresses the rectifier valve. Any suggestions please?

Edit: I should have added that I can find any number of 450 v capacitors but with the secondary marked up at 345 volts, then when off load the HT smoothing caps could charge up to approaching 490 volts. I suppose one could add the mods I heard mentioned to ensure the HT line is never off load?

Last edited by john_morris_uk; 3rd Aug 2017 at 12:31 pm.
john_morris_uk is offline  
Old 4th Aug 2017, 7:51 am   #2
Kevin Hoyland
Heptode
 
Join Date: Feb 2009
Location: Rotherham, South Yorkshire, UK.
Posts: 559
Default Re: AR88 (yet another!)

John will you please put some Photos on when you get the time.

Kevin
Kevin Hoyland is offline  
Old 4th Aug 2017, 8:54 am   #3
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,799
Default Re: AR88 (yet another!)

The oil may be just mineral transformer oil or it mat be a Poly Chlorinated Bi-phenyls (PCBs). No-one has determined which but those capacitors were made in the era when both could have been used. The best advice seems to be to play safe and use impermeable gloves. Do not burn. Heated PCBs form dioxins which are a much bigger problem.

The existing capacitance values are fine. More C does increase peak currents in rectifiers which shortens their life.

Having an AR88 powered with the switch in 'Trans' lets the smoothing capacitors go to a ridiculous voltage, so use 630v capacitors. Plastic film types are fine. RS/Farnell had them last time I needed any.

I'n inclined to link the HT so the trans position leaves the set running.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now  
Old 4th Aug 2017, 10:17 am   #4
turretslug
Dekatron
 
turretslug's Avatar
 
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,385
Default Re: AR88 (yet another!)

A little oil goes a long way, and there's plenty in that smoothing block.... It wouldn't surprise me if it's been gently seeping past those three-score and ten rubber seals, it seems to get mentioned a fair bit and it certainly happened to mine. An AR88 in good condition is very hum-free, even using a loudspeaker with good LF response, so using more than 4uF won't achieve anything useful. (I used 4.7uF 630V plastic film types because I had them anyway, I'm sure 3.9uF would have been just as good). The fact that HV electrolytics are abundant, cheap and compact thanks to the SMPSU world seems to have encouraged some to use bananas amounts of capacitance in e.g. the audiophile world, but it's not really good engineering. (The noise limiter double diode can introduce hum when switched into circuit on some sets, but that's a different thing entirely).

The HT switch link is easy to apply with the set inverted and is a wise addition- switching the whole HT off to mute the set in "TRANS" is a rather crude and brutal way of doing things in an otherwise sophisticated design.
turretslug is offline  
Old 4th Aug 2017, 10:42 am   #5
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,951
Default Re: AR88 (yet another!)

A possible source of high voltage capacitors to re-stuff the big smoothing-block is 'motor run' capacitors

https://www.rapidonline.com/ducati-4...acitor-10-2938

though these are usually only working-voltage-rated to 450V or so.
G6Tanuki is offline  
Old 4th Aug 2017, 11:29 am   #6
turretslug
Dekatron
 
turretslug's Avatar
 
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,385
Default Re: AR88 (yet another!)

Looking through the .pdf data sheet for those Ducati caps, it states that they can indeed be used with DC voltages of (root 2)x the rated AC voltage- as one would expect but it's nice to see the manufacturer state it in print. They ain't exactly a king's ransom, either, and if they're rated for motor run use then smoothing HT in a radio that draws around 100mA should be an easy life. Small enough to safely and comfortably get three in the original can volume, too.

Last edited by turretslug; 4th Aug 2017 at 11:37 am. Reason: Spurious word!
turretslug is offline  
Old 4th Aug 2017, 12:38 pm   #7
HamishBoxer
Dekatron
 
HamishBoxer's Avatar
 
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 8,923
Default Re: AR88 (yet another!)

Brilliant idea to use those caps, certainly won't fail in a hurry.
__________________
G8JET BVWS Archivist and Member V.M.A.R.S
HamishBoxer is offline  
Old 4th Aug 2017, 1:43 pm   #8
john_morris_uk
Tetrode
 
Join Date: Mar 2014
Location: Farnham, Surrey, UK.
Posts: 61
Default Re: AR88 (yet another!)

Thanks for the responses. Capacitors ordered.

I expect I'll get sone other questions and I've got to check the sweep function on my Hewlett Packard signal generator when I eventually get round to setting up the IF.

Of course if anyone had an S meter I could buy I would be very interested. I appreciate they are like hen's teeth (The original one started full scale and started biased back to zero if I understand the circuit correctly....)
john_morris_uk is offline  
Old 4th Aug 2017, 1:46 pm   #9
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,192
Default Re: AR88 (yet another!)

Quote:
Originally Posted by john_morris_uk View Post
Of course if anyone had an S meter I could buy I would be very interested. I appreciate they are like hen's teeth (The original one started full scale and started biased back to zero if I understand the circuit correctly....)
That's correct. A right hand zero meter was used. A left hand zero meter mounted upside down will serve the same function.
__________________
Graham. Forum Moderator

Reach for your meter before you reach for your soldering iron.
Station X is online now  
Old 4th Aug 2017, 1:59 pm   #10
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,799
Default Re: AR88 (yet another!)

I took a quick photo of an original one in my AR88 (not original cabinet colour, but I was a youngster at the time...)

The legend says "Decibels above 1 microvolt"


David
Attached Thumbnails
Click image for larger version

Name:	AR88 003.jpg
Views:	190
Size:	45.8 KB
ID:	147357  
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now  
Old 4th Aug 2017, 2:21 pm   #11
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: AR88 (yet another!)

Here's the one in the AR88 I had, not an original AR88 S meter but it's right handed and the right sort of colour.

If I remember right my old Hallicrafters SX28 and SX17 also had right handed S meters.

Lawrence.
Attached Thumbnails
Click image for larger version

Name:	rcaar88d.jpg
Views:	173
Size:	72.3 KB
ID:	147358  
ms660 is offline  
Old 4th Aug 2017, 6:07 pm   #12
john_morris_uk
Tetrode
 
Join Date: Mar 2014
Location: Farnham, Surrey, UK.
Posts: 61
Default Re: AR88 (yet another!)

Quote:
Originally Posted by Kevin Hoyland View Post
John will you please put some Photos on when you get the time.
Will do; when I can work out how to do it on this forum!
john_morris_uk is offline  
Old 4th Aug 2017, 11:16 pm   #13
AC/HL
Dekatron
 
AC/HL's Avatar
 
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,637
Default Re: AR88 (yet another!)

Chapter and verse!
https://www.vintage-radio.net/forum/...ad.php?t=77650
AC/HL is offline  
Old 5th Aug 2017, 9:07 am   #14
HamishBoxer
Dekatron
 
HamishBoxer's Avatar
 
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 8,923
Default Re: AR88 (yet another!)

John, hit reply then manage attachments to up load pictures from your desktop folder etc.

Forum will re size them as required.
__________________
G8JET BVWS Archivist and Member V.M.A.R.S
HamishBoxer is offline  
Old 7th Aug 2017, 11:45 pm   #15
john_morris_uk
Tetrode
 
Join Date: Mar 2014
Location: Farnham, Surrey, UK.
Posts: 61
Default Re: AR88 (yet another!)

As requested, some photos. A few shots of the underchassis to start with.

Contrast the cover for the RF stages (that's had a few moments work with acid metal cleaner and wire wool and a rinse of fresh water with a few minutes on the Aga) with the rest of the metal work.

You can see where a previous person has made several repairs and replaced various cap's.
Attached Thumbnails
Click image for larger version

Name:	IMG_0888.jpg
Views:	191
Size:	60.3 KB
ID:	147521   Click image for larger version

Name:	IMG_0889.jpg
Views:	188
Size:	111.8 KB
ID:	147522   Click image for larger version

Name:	IMG_0890.jpg
Views:	197
Size:	146.3 KB
ID:	147523  
john_morris_uk is offline  
Old 8th Aug 2017, 10:59 am   #16
Kevin Hoyland
Heptode
 
Join Date: Feb 2009
Location: Rotherham, South Yorkshire, UK.
Posts: 559
Default Re: AR88 (yet another!)

Thanks John for taking the time to put the photos on the Thread.

Kevin.
Kevin Hoyland is offline  
Old 8th Aug 2017, 11:05 am   #17
PsychMan
Octode
 
PsychMan's Avatar
 
Join Date: Jun 2013
Location: Fleet, Hampshire, UK
Posts: 1,764
Default Re: AR88 (yet another!)

If the oil has left a mess, you should find the spray version of jizer does a good job of removing it.
PsychMan is offline  
Old 8th Aug 2017, 11:48 am   #18
john_morris_uk
Tetrode
 
Join Date: Mar 2014
Location: Farnham, Surrey, UK.
Posts: 61
Default Re: AR88 (yet another!)

Thanks. I hadn't tried that.

Whatever it is it's put very light corrosion on the chassis. I've tried white spirit as a solvent but the best results so far have been with Screwfix metal cleaner and rinsing with water.

The problem is that Screwfix metal cleaner is an acid and I don't want to get it near the wiring loom, coils or IF cans etc.

Metal work I can remove and clean separately comes up almost like new...
john_morris_uk is offline  
Old 8th Aug 2017, 11:51 am   #19
john_morris_uk
Tetrode
 
Join Date: Mar 2014
Location: Farnham, Surrey, UK.
Posts: 61
Default Re: AR88 (yet another!)

I've also found that whoever sorted it previously didn't appear to check any (or many?) of the resistors. Some of the sample few that I've checked are way off. E.g. 560R (R13?) is 1.2k
john_morris_uk is offline  
Old 8th Aug 2017, 2:47 pm   #20
PsychMan
Octode
 
PsychMan's Avatar
 
Join Date: Jun 2013
Location: Fleet, Hampshire, UK
Posts: 1,764
Default Re: AR88 (yet another!)

Yeah its horrible stuff. It hadn't corroded mine, but the stuff that came out of the smoothing block had a tar like consistency when cool, could be a mix of the oil plus the potting compound.

In the process of re-doing the smoothing block and bathtubs on mine, just too much going on and workshop issues preventing progress at the moment. As my workshop is quite damp, I daren't leave my receivers in there, so each bit of work I do I have to hump the damn thing in there then back out again!

Will look forward to seeing your progress. I had some problems removing the innards of the smoothing block myself, tried immersing in boiling water and all sorts, the contents just wouldn't budge. Hope you have better luck !
PsychMan is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 4:43 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.