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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 3rd Dec 2015, 11:38 am   #81
turretslug
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Default Re: RCAF AR88LF (GR-17) Project

RCA showed some attention to detail as regards screening- whilst they didn't go to town in quite the way of e.g. the Scott Laboratories SLR shipboard broadcast receivers, the oscillator coil box was a separate-walled construction to cut down on common circulating currents that might have resulted if it was just a fourth section of the main RF box, and there's an insulating coupling between the two four-gang sections of the main tuning capacitor, again eliminating common RF impedance, however slight.

A phrase that sometimes crops up in AR88 articles is "no expense spared"- I really feel that that's a mis-understanding and decidedly missing the point, rather it's an excellent pragmatic exercise in cost-effective performance. Where it matters, state-of-the-then-art techniques and materials are used, such as the low-loss, low temperature-coefficient polystyrene coil formers and associated components, the then-new low-noise RF pentodes with good HF performance and the gas-filled stabiliser, coupled with sound circuit design. Otherwise, the construction is simple mild steel foldings and established components and techniques- whilst it might have seemed a posh and expensive radio to the man in the street, it's nothing like the engineering almost for-the-sake-of-it jewellery that is the mark of a lot of military kit- notoriously, the gear-box resembles a product of the alarm-clock industry, albeit with split gears, rather than the almost over-the-top precision laboratory approach of the contemporary Telefunken E52 . It certainly fits the bill of the most believable account of its origins- that it was a pre-war high-performance commercial receiver intended for quantity production that was chosen by time-poor wartime authorities for its capability of being produced in very large numbers in short order- i.e representing good "bang for buck".
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Old 3rd Dec 2015, 4:24 pm   #82
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Default Re: RCAF AR88LF (GR-17) Project

The lack of local oscillator radiation is in marked contrast to the contemporary National HRO, which is renowned for sending the local oscillator signal up the aerial.
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Old 3rd Dec 2015, 7:13 pm   #83
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Default Re: RCAF AR88LF (GR-17) Project

Indeed: in past times I can recall published HRO mods involving a series-tuned 'trap' a so when listening on 14MHz the 3rd harmonic of the LO didn't unduly perturb UK Channel-1 VHF TV.

[The WWII-era TCS12 receiver thankfully didn't cover 14MHz - given that it used a 12A6 power-output-valve as its local-oscillator [Why? Why?] I can only imagine it would have generated some serious level of 3rd-harmonic-power too!]
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Old 13th Apr 2016, 3:17 am   #84
David Dunlop
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Default Re: RCAF AR88LF (GR-17) Project

Just noticed this morning on the UK eBay site that an AR88LF that was listed a few years ago as complete, seems to have suffered a mysterious fate as just the cabinet is up for sale. It is interesting for couple of reasons:

- The SN is C-00013, making it perhaps the earliest known AR88LF and it was built sometime in 1943.

- Although there is some indication the exterior of the cabinet may have been repainted, or touched up, the interior looks quite original. If it is, the black paint used on these cabinets was definitely not the same as used on the AR88 Series speaker cabinets. As posted earlier, the speakers original black paint dries to the look of black granite crystals. The paint on the inside of this cabinet looks like a semi gloss finish with a very fine texture.

If anyone is curious to have a look, the eBay item number is: 201559774428

In the interim, not much has been done with my AR88LF recently, but I did finally sign up for some classes earlier this year and wrote my Canadian Basic Amateur Radio Exam. Passed with Honours so hope to get my two 19-Sets back on the air later this year.


David
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Old 13th Apr 2016, 10:08 am   #85
turretslug
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Default Re: RCAF AR88LF (GR-17) Project

Well done on the exam result- very satisfying to achieve a milestone like that.

Shame about that orphaned cabinet though, I suppose it's just part of the slow but steady attrition of venerable survivors- I wonder if a leaky Micamold did for the output transformer and maybe other things, or a duff smoothing block killed the mains transformer. Looking on the more venal aspect of things, anything with an HT transformer is vulnerable to breaking nowadays and as old mains transformers fail and traditional-type transformer makers disappear, the hyenas will only become more ravenous. Sadly, I suspect that much of the latter-day tube-mania represents a short-lived and disposable distraction in return for the irredeemable loss of classic technology. A cynic might feel that someone decided that they could achieve a double whammy by selling the transformer to the must-have-tube-amp crowd, and then flog the case off on the grounds that many rack-mount AR88s are devoid of one.

At least folk on the likes of this forum appreciate things for their historical and cultural context.
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Old 13th Apr 2016, 10:13 am   #86
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Default Re: RCAF AR88LF (GR-17) Project

While I wouldn't go breaking up an AR-88 - unless already stripped of parts - I don't think the AR-88 is in any danger of being lost to history. A large proportion of vintage radio collectors have one - often in very nice condition (I do myself). And they turn up regularly on Ebay.


Richard
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Old 23rd Jul 2016, 3:51 pm   #87
David Dunlop
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Default Re: RCAF AR88LF (GR-17) Project

Haven't been on eBay for a while, but for some reason a few weeks ago I went in to have a look and stumbled across a chap in the USA selling an RCA AR88LF Data Plate in very good condition. 1944 dated, which goes well with my receiver and speaker, but obviously not the correct serial number. He also threw in a caution plate, which he was not certain went with the AR88LF, but what the heck.

Now I have to think out the best way to remove the existing serial number from the plate and have the correct one for my receiver added. The correct SN for mine is 'C-00335', so technically the 'C-0' starter could be kept and just the last four digits changed, but this process might just look too obviously modified. I think the best thing would be to clear the entire original number and reapply the correct one.

I have been thinking the best place to have this work done, might be one of the local jewellery/silversmith shops that do high end engraving. Any thoughts, experience or suggestions on this would be greatly appreciated.

While I think of it, can anyone advise the correct type of screws used to mount the data plate? They are probably identical to those used on the speaker data plate, but I do not have a clue about correct length, thread etc. for ordering any from a supplier.

David
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Old 23rd Jul 2016, 7:50 pm   #88
M0FYA Andy
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Default Re: RCAF AR88LF (GR-17) Project

A few years ago I noticed that someone was selling used AR88 spares, and realised he must have completely dismantled a receiver into component parts, so I made a note of what each part sold for as his auctions finished over a week or so.

The total he got was more than £500!

Now to carefully dismantle an AR88 would probably take a couple of days, but there's a message there.................

Andy
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Old 23rd Jul 2016, 9:41 pm   #89
David Dunlop
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Default Re: RCAF AR88LF (GR-17) Project

There is a lot of sense to that, Andy. The biggest negative to this series of receivers is the brutal weight of them for shipping. I think it tends to drive the price down a great deal for a complete one. To my knowledge as well, there is only one seller around I can think of with a massive supply of NOS spares, so if one has the time patience and skill, a complete disassembly of an AR88 could prove very profitable.

Just wish there were more of the tools available for them. I am still one short for my receiver, and then only have to figure out where the two stored on the tuning cover actually went.

David
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