RCA AR88 Comms Receiver.

[Scotch24A]

Recently acquired an ar 88
-what is the best aerial to use with this set?
-what should I be able to hear on bands 5 and 6?
-what is the easiest way to clean the wave band switch contacts: it is v.crackly when turned.
Thanks
Scotsch24A

[paulsherwin]

These are complex professional communications receivers, in addition to being 75 years old. Has it been restored?

[G6Tanuki]

Congrats on your acquisition: properly fettled thay are still good receivers despite being 70+ years old.

Best antenna? What do you want to listen to? if you're after 'general coverage' then a long-wire anything from 10 50 100 feet long will work well; connect it to the A1 terminal and link the A2 abd E terminals together.

If there's a specific frequency you want to concentrate on - let's say one of the HF amateur-bands, a half-wave dipole connected using coax cable to A1 and A2 terminals, with E left unconnected, is the way to go.

What are you likely to hear? That depends - right now the sunspot cycle isn't really perking so the HF bands are in the doldrums, but you should be able to hear plenty of signals during daylight hours around 14 - 14.35MHz, and occasionally there is also 'Sporadic-E' propagation which livens-up the 28 to 28.5MHz band with lots of Euiropean stations.

[Scotch24A]

Originally Posted by paulsherwin

These are complex professional communications receivers, in addition to being 75 years old. Has it been restored?

It looks as though it has been tampered with-the tuning capacitor top shield is missing,as are the tuning tools ;although the colour coded capacitors look original albeit a bit sticky and leaky-I guess they will need to be replaced in the non too distant future.
Scotch24A

Thanks-what about cleaning the band switch contacts?
Scotch24A

[HamishBoxer]

Try a long wire aerial and De-Oxit to clean the switches. See previous posts as there is a lot of work needed on these to be reliable and not take out expensive output transformers etc. Really, make sure the work is done Before applying power.

[paulsherwin]

Any contact cleaner can be used to clean the switch contacts - Servisol is most common in the UK (don't use ordinary WD40). I'd advise against using the radio in this state though.

[Scotch24A]

Thanks
Scotch24A

[Scotch24A]

I have been advised to replace the C119 capacitor(3000 pf)-what is the voltage rating-is it 240 v or greater.
Thanks
Scotch24A

[Radio Wrangler]

The HT voltage can go well over 300v if you put the system switch into 'Trans' so you need to be comfortably over this as a rating.

ALSO don't fit the new C119 where the old one was. If it fails, it will probably destroy the output transformer. Replacements are pretty much only available along with the restt of an AR88. So instead, fit it across the primary of the output transformer. It will do the same job here (tone correction) but if it fails, there is no damage. RCA missed a trick.

Also consider C118 and C122. These are in parallel. The parts are shaped to look like mica parts but are actually paper and known to fail, turning the audio output valve hard on. This can destroy the output transformer and the mains transformer. one 10nF 600v will replace the pair of them.

David

[Scotch24A]

Thanks David
Scotch24A

[Scotch24A]

David
Are the primary terminals on the output transformer marked-they appear to be 3&4 on the circuit diagram.
Thanks
Scotch24A

[turretslug]

Yes, they are numbered on the output transformer (or should be, the specification of the transformer changed slightly over the production run to include a 600 ohm winding, it's always possible that there may be the odd exception to the rule in this set that was produced in large numbers over a short time-span) but the turret tags are pretty close together and occupied by the relatively thick wiring. It's likely to be easier to connect the capacitor between pin 3 (anode) of the output valve's socket and the output (lower voltage) tag of choke L50. This is what I did, a typical wire-ended axial capacitor like the 2700pF 1600V Philips polycarbonate that I used should reach.

[Radio Wrangler]

There are a couple of different circuit diagrams and a couple of different output transformers, depending on model and variant. One end of the primary goes to HT rail, and the other end goes to the output valve (usually 6V6) anode.

The bad (RC original) place for the tone correction capacitor is from the anode to ground. The good place is from the anode to HT.

David

[Scotch24A]

Thanks ,David and Turretslug.
Scotch24A

[Scotch24A]

Help- my ar 88 has suddenly gone silent-not even a crackle from the waveband switch.
The dial lights work but there is no glow from the two rear valves(5Y3GT and VR150 )-the other valves(metal) warm up as expected.
I’ve no idea what the problem is-where do I start looking?
Thanks
Scotch24A

[turretslug]

With those symptoms, one possibility is that the tape filament of the 5Y3GT has fractured, usually where it loops back down one of the anode cavities. They can get quite brittle with age.

Another is dry-jointed filament pins, octal-base types are quite prone to this.

[Station X]

Use your meter to check the 5Y3GT heater voltage and heater continuity.

[Radio Wrangler]

If the 5Y3 has failed, there will be no HT supply. Without HT, the VR150/30 will not light. The other valves are all heated from a 6.3v winding on the mains transformer. The 5Y3 runs form a separate 5v winding.

So it all fits.

Other faults could be a bad joint in the 5v heater circuit for the 5Y3, loose valveholder contacts in that circuit or (rather unlikely) a failed 5v winding in the transformer.

Beware of very high AC voltages on some other pins of the 5Y3 socket. Maybe check the resistance between heater pins of the (removed) 5Y3 with an ohmmeter first? I'm a fully paid-up coward and if there's a safe check, I'll go for that one first.

David

[Scotch24A]

Thanks for the advice.
Scotch24A

[falcon123]

i recently had a 5y3 in a philco give up the ghost. i restored it to operation by flowing solder into the little hole at the end of the pin. i did them all while i was at it. i dont know who made your tube but this does seem to happen, the wires from the glass envelop desolder themselves from the pins SOMETIMES and is easily rectified and costs very little but your time