Paxolin board under chassis of AR88

[Alan Bain]

Does anyone have a good picture of the paxolin board in an AR88 at the side under the chassis on which some resistors are mounted. The only specimen around here has a decidedly unoriginal board (ditto output transformer) and I thought I had a good photograph but cannot find it and a web search has produced many front panel photographs and a few under chassis pictures where you can see a vertical board but nothing else.

It is what I would call the "usual" type of AR88 with an engraved front panel.

[Radio Wrangler]

Originally Posted by Alan Bain

It is what I would call the "usual" type of AR88 with an engraved front panel.

That makes it an early one. Later ones with silk-screened lettering are more common. Does it have all-yellow tuning scale backgrounds as well?

David

[G3PIJpeter]

Originally Posted by Alan Bain

Does anyone have a good picture of the paxolin board in an AR88 at the side under the chassis on which some resistors are mounted.

This one? It's the only photo I have that seems to fit your request - hope it is what you are looking for.

Peter

[ms660]

Originally Posted by Radio Wrangler

That makes it an early one.

I had a later AR88D with a smooth finish engraved front panel that was an original fit (see photo below)

Lawrence.

[gezza123]

Hi Alan.
don,t know if this may be what you want ,never seen a photo of the audio board
so hope this is what you need.
gezza123

[Alan Bain]

Thanks gezza123 and G3PIJpeter this is indeed the board and I found the labelled diagram of the under chassis showing where all the Rs and Cs very useful indeed.

[Radio Wrangler]

Those resistors are droppers in the HT negative return used to create negative bias for the AGC, RF gain control and the output valve. They run rather hot, so if you do anything to them, go for physically larger parts to reduce the surface temperature.

David

[Kevin Hoyland]

See if this ok for you.
kEV.

[Alan Bain]

Regarding the "all yellow tuning scale backgrounds", I've never quite known what this means. Here is a picture of the tuning dials (carefully cropped to remove the not-very-period HP8662 adjacent, which nevertheless will be ideal for aligning it)

The tuning knob is unfortunately not original. Someone had hacked around the tuning drive and added a slow motion drive, so I have repaired the gearbox but not yet found a proper looking knob.

[mickm3for]

Hi a tuning knob on ebay now nos not cheep ouch https://www.ebay.co.uk/itm/193340783...Bk9SR87EivnfYQ Mick

[Alan Bain]

That prompted me to look for output transformers but it seems I'm not so lucky there... will have to keep using some random thing from an audio amp, but maybe I'll mount it properly rather than having it float about on its leads which seems to have been the previous repair plan....

[Radio Wrangler]

Ther's a lot more demand for audio output transformers than for tuning knobs. The transformers are fairly fragile and get destroyed if the 'That capacitor' starts leaking. RCA in their wisdom increased this likelihood by using two capacitors in parallel to add leakage!

Your photo shows an AR88 with the earlier 'all yellow background' tuning scale. The majority of sets have alternating scale backgrounds with every other scale showing yellow scale and text on a black background.

There was a release of AR88 spares sometime in the 80's and I picked up a spare set of tuning scales and a main tuning knob for my AR88, amongst a few other parts, all for pennies. They were on a stand at the G-QRP doo in Rochdale.

David

[HamishBoxer]

Don't forget that cap from the sound o/put anode to deck. Refit across the primary of o/put tx.

[trh01uk]

Originally Posted by Radio Wrangler

There was a release of AR88 spares sometime in the 80's and I picked up a spare set of tuning scales and a main tuning knob for my AR88, amongst a few other parts, all for pennies. They were on a stand at the G-QRP doo in Rochdale.

David

That was probably Colomor Electronics. In the 1990s I was going to their warehouses near Bedford, and one of them had an enormous stack of new AR-88 spares, all still in the original manufacturer's wrapping. A guy called John Reynolds (now passed away) brought the lot I believe. Where it all is now....no idea!


Richard

[Radio Wrangler]

They were indeed in manufacturer's packaging. Interesting to know a little of their history.

I suppose they're all scattered around now, which is good because the ARs potentially needing them are all scattered around too.

Thanks
David

[turretslug]

Originally Posted by trh01uk

That was probably Colomor Electronics. In the 1990s I was going to their warehouses near Bedford, and one of them had an enormous stack of new AR-88 spares, all still in the original manufacturer's wrapping.

That must have been a sight to behold! I recall on visits tio Colomor's outlet on Shepherd's Bush Road how there was always what I recognised as an AR88 output transformer at the side of the counter. There is indeed a scattering of NOS spares around at various events, I was lucky to find a still pale-colour frequency scale for an 'LF recently to replace a very darkened scale, the one on my 'D model is still useably deep yellow fortunately.

[dave walsh]

One of the gents on here had a couple of pallets worth of original MOD items including AR88 spares a decade or so ago. Perhaps it was from the same stack referred to here? I bought one or two items including an AR88 OP transformer that was mint and still sealed in the original packing. They had been described over the years as "rarer than rocking horse droppings". My technical skills are largely absent but I was intrigued, during a period when there was a sort of sudden, unexpected, demand for 88's, that some people did manage to substitute "ordinary" re-cycled OT's very successfully when it was always claimed that the originals were a make or break for restoration There is a description of how to do this on line somewhere. I last referred to the OP Tr in the "Mr Carlson does an AR88/CR88 restoration" thread of 21/1/23.

Dave W

[Alan Bain]

Thanks to all the helpful info here I can reconstruct the paxolin board (and mount it on standoffs -- I don't have the right terminals, but guess the usual terminal eyes will do), not screwed directly to the chassis like the previous bodge - which required some scraps of paxolin behind it to avoid shorting). I can try an old hifi output transformer as I don't really need the 600 ohm output.

That leaves the question of the various aerovox three-caps-in a can, or maybe more accurately three leak resistors to chassis in a can. They look like the cans are soldered so they should open up with heat from the O-A torch to be restuffed, but the terminal insulators also look decidedly ropey so I guess some kind of solution for them is needed - maybe feedthrough caps? The Mr Carlson video linked shows the caps being soldered directly to chassis but I don't think even my large ERSA iron would do that. Advice would be welcome....

[Radio Wrangler]

Have a hunt around for rivet-on turret terminals. You can make your own tag boards up and they look fantastic. You just need raw paxolin sheet a drill and a punch to form the rivet. It'll still need to go on standoffs.

David

[Alan Bain]

Found the turret terminals. Just the thing - thanks for the pointer!