AR88 Restoration.

[PsychMan]

Has some more fun with this. The 3 bathtubs where I have replaced the terminals are reinstalled. I noticed some newer wire on c93 where TR6 terminal D is connected, this went to chassis bypassing c93.

Also a similar wire on V6 shorting the cathode to chassis ground, I removed both of these. Not really sure why they were there, they seemed very poorly soldered also. The set has no valve changes or other mods anywhere. R20, cathode resistor for V5 read 160 ohms so that was replaced with a new 100 ohm resistor. The set seems to work better than before so I’ll leave the other bathtubs in for now, they’re restuffed but I neglected to replace the terminals when I did that. Still much more electrically, but for now I’m focusing on cleaning the front panel and regreasing the gearbox.

The gearbox is now removed and has been washed in strong degreaser and dried. I’ve sussed out the bearings but now have a dilemma. For the ball races I need some decent grease. Presently I have LM2 lithium grease, and Castrol spheerol epl2, which is also lithium based. I know the LM2 is not great as I’ve done a few record decks with them that now will need regreasing due to grease drying out. Will I be ok with the castrol stuff or should I hunt down something better. Any thoughts or reccomendations? Would ptfe bike grease be a good choice?

[G6Tanuki]

The grease I use is the "Semi-fluid" black-shiny stuff used in Land-Rover swivel-hubs.

http://www.paddockspares.com/stc3435...ot-grease.html

It's thixotropic - goes runny when disturbed but if left alone it stays put.

[PsychMan]

Looks like good stuff, and cheap. Not sure I’d be able to get it quickly enough though, I was hoping to finish this receiver over the xmas break. I might see if this is any good

http://www.halfords.com/cycling/bike...SABEgLIL_D_BwE

[G6Tanuki]

the Halfords grease may be OK - alternatively you could try this product by the WD-40 corporation [available at Screwfix]:

https://www.screwfix.com/p/wd-40-spe...se-400ml/46103

To be honest, lubrication-technology has advanced so much in the 70-odd years since AR88s were produced that pretty much anything 'modern' in the way of lubricants [excluding organic extra-virgin olive-oil] will be better than what was used on the dial-gearboxes when they were originally made.

[PsychMan]

That screwfix product looks very good, and decent reviews too. It being in a can with an applicator tube would make applying also very easy for this gearbox. That might have swung it for me, thanks!

Aside from bearings, should I apply some oil to the gears themselves? I’ve been using the radioblvd web site as guidance for this and Henry doesn’t mention doing that.

I’m taking pictures detailing removal and cleaning etc, I’ll add a little guide to this thread for future restorers.

[G6Tanuki]

Given that you've washed-out the gears and bearings with a good degreaser [and hopefully dried-off things too] then for the reduction-gears to be honest I'd suggest something really fluid because the AR88 gear-drive uses pairs of flat-punched gears with coil-springs between them to provide anti-backlash.

What you definitely don't want for the gears is any kind of lubricant that will set/go-sticky/dry-out/harden with age and stop the paired flat-gears being able to slide freely over each-other to provide the anti-backlash effect.

Grease for the spindle-bearings, sure - but for the gears themselves I would use a much thinner lubricant: "3-in-1" oil, or 5W-30 car engine-oil or similar 'runny' lubricantr is more appropriate here.

[PsychMan]

Thanks a lot G6Tanuki, I’m still relatively new to the hobby so it’s always nice to hear from others who are more experienced. I did dry it throughly with a hair drier after the degrease and wash down. I also used a spare electric toothbrush and degreaser on the gears to get all the gunk out, it was pretty mucky.

I’ve got all sorts of light oil, sewing machine oil, clock oil, various types of 3 in 1, I’ll use something light and sparingly for the gears, running dry doesn’t seem right.

I use 3 in 1 “motor oil” a lot, it’s sae 20 and is great for turntable bearings and jukebox mechs (hard to get outside of the USA however). I’ll use that for the single ball bearings, and the screwfix stuff for the ball races

[Radio Wrangler]

That's molybdenum-disulphide loaded grease. Generally used for CV joints in almost all makes. Ought to be findable in the usual car accessory shops. Sometimes called MS3

David

[PsychMan]

Progress, after much frustration, and one question

I decided to use the castrol grease I had around, and used the white lithium grease for the hard to reach ball race as I could apply without dismantling the box (futile given the events that transpired!).

Upon completion I was left with backlash, whereas before there was none whatsoever. It then dawned on me what had happened - during the adjustment of the bearing grub screws, I had loosened them too much, allowing the sprung gears to move out of place and lose their spring.

I then spent 4.5 hours dismantling the whole thing, and trying to spring load the gears to what (I think!?) they were before, what a pig of a job! I read on here about drilling holes and inserting pins to keep them in place, but I opted for wrapping some stripped bell wire around the gears and wedging it between the teeth when I had them in place. This worked very well and I was able to re-assemble the gear box and remove them once the bearings were tightened. I now have smooth operation and zero backlash.

One issue so far to tackle with the gearbox, I've reinstalled the flywheel and fitted it back to the chassis. There is a bearing bracket in front of the flywheel which bolts to the chassis and also has a little flap of metal used to lock the tuning in place via a screw on the front panel (picture attached). I cannot seem to fit this in place without it hindering the tuning operation. If I gently bend if forwards a little, it then moves freely. There doesn't seem to be much adjustment possible here unless I leave the bolts much looser than seems right. Any tips for this? I thought about either bending it very gently, or placing an extra washer behind the top fixing to bring the angle out slightly.

[G6Tanuki]

It's possible that you've bolted the gearbox back in place positioned slightly differently to when it was first fitted.

Loosen the fastenings between the gearbox and the chassis and wiggle it about a bit while at the same time refitting/adjusting the dial-lock-screw bracket, to try and find a position where both are happy.

It can only take a few thousandths of an inch movement to go from free-running to binding.

[PsychMan]

Cheers, I think that might have been the case. I tried slackening the nuts right off again and tightening the bolts that attach the box to the tuning capacitor housing first, THEN doing the bolts under the chassis. It might be slightly better, but not much. In the end I've left the top nut on this bracket slightly loose and it seems to move freely now, it will do, for now at least. If it becomes a problem again I will revisit.

Panels back on and has cleaned up nicely (pic attached), the engraved lettering looks nice and white now without the yellowing of before. This was achieved using a soft toothbrush and a little fairy liquid.

I'll be focussing now on electrical stuff, it generally works on all bands but performance is weak. Some bands need the RF gain very high or they're near enough silent. Few more fake micas to deal with, and the screen resistors. I'll also test any other resistors and do some voltage checks to see where I am.

[Keith]

Looks fantastic! (certainly puts mine to shame)

To be honest, I always leave the RF gain at maximum and let the AGC do its stuff. The only exception is receiving SSB/CW where there's not enough BFO injection and the only way is to back the signal off manually.

[turretslug]

I recall having to do something similar after a drive-train overhaul- anything more than a gentle nipping-up of the drive-to-chassis securing nuts obviously distorted things too much, at least it's secure to the capacitor frame itself! RCA obviously knew that things were a bit flimsy and prone to distortion here, hence the riveted piece of angle along the fly-wheel slot in the chassis. The drive-train is a bit of a weak-spot generally with its (albeit split) "alarm clock" wheels and lack of end-stop mechanism (other than the VC gang itself ). The Scott RCH gear-train currently on the bench here is about three times the mass of the AR88's, with much thicker, precisely machined split wheels and geared end-stop dowels. It's also floated from chassis in both horizontal and vertical planes on springs- possibly a stipulation in a maritime receiver subject to heavy seas and/or blast. Even the supposedly lowly CR100 has much sturdier framing, compact layout and end-stop provision. I think the AR88's design budget was under pressure at drive-train stage....

[PsychMan]

Small update

I got round to doing the screen resistors, and found all but one horrendously out of spec. 33k resistors reading as much as 200k and 300k!

Interestingly, what I've found generally with resistors in this receiver is the larger bodied type almost always seem to have gone high. The one screen grid resistor I didn't need to change was a smaller type and read 34k so I left it in.

Still a lot to do, but for now its set up with a 50 foot antenna and is pulling in far more than the little 15 foot one in my workshop. I've been unable to resolve any SSB. I am new to comms receivers and have tried the methods advised on here (manual mode, selectivity up, AF gain max, CW mode and driving with the RF gain). I seem to get lots of signals on band 5 and 6, but unable to tune them into anything meaningful, just BFO whistles and not much else, could well be alignment, which is on the to-do list. What I can receive is clearly off based on the dial readings, and I did recalibrate all that when I reinstalled the gear box

[ms660]

Try the 40 meter Ham band on range 3 between 7 and 7.2MHz, plenty of Ham SSB on there now as I type, use Hack Green SDR as a guide, Ham transmissions will be lower side band (LSB) on the 40 meter band.

Lawrence.

[PsychMan]

Thanks Lawrence, I'll have a go on band 3, which seems to perform much better for me than 5 or 6.

[ms660]

You might need to increase the BFO injection, I seem to remember with mine I used twisted wire gimmick capacitor.

Lawrence.

[turretslug]

Whilst RCA were quite proud of the "mechanical bandspread", it's very much a pre-SSB tuning rate on the higher bands, and takes a light and precise touch on the tuning to get the received signal on the sweet spot for intelligibilty- all the while juggling the RF gain to keep the signal level optimum. The manual talks of "electrostatic" BFO coupling- essentially meaning that the BFO gets into the IF amp by being physically close to it! Also symptomatic of pre-SSB design. I believe some post-war models addressed the injection level shortcomings with a few pF of coupling between BFO and 3rd IF amp.

All the same, there's a certain satisfaction in resolving SSB with all the variables involved- there are lots of articles on the theme of product detectors and receivers from the pre-SSB era, but many would argue that that's spoiling the fun and missing the point!

[Keith]

My copy of the circuit diagram (not sure if it's for the D or the LF) shows a connection from pin 4 of the BFO to point "A" and thence to a suggestion of a capacitor (dotted) in the grid circuit of the 3rd IF. Now pin 4 of a 6J5 is designated as n/c, but it is next to the anode (P) on pin 3, so maybe this is the "electrostatic" coupling referred to. I guess this would be a convenient place to add a few more pF.

[Radio Wrangler]

Ah, I just noticed when I read 'Engraved lettering' With an engraved panel, that AR88 is a very early one, and lo and behold the photo shows the all-yellow tuning scale.

Most AR88s have silk-screened labelling and tuning scale that alternates light/dark bands up the frequency ranges. Only the very early ones have the scales all the same.

The front panels are also copper-plated under their paint.

David