Roberts RM-33 table radio

[stephanie]

I finally got around to sorting this one out.

http://www.vintage-radio.co.uk/image...berts/rm33.jpg

The picture belongs to Paul Stenning (as did the radio).

Since I received it back in 2003, the radio had been sitting on my living room shelf. So this past Friday I decided to finally get around to sprucing it up to turn it into a functional device.

It was basically working, although from having sat around, it needed some cleaning of some controls.

First was to replace the mains flex. The original had been snipped so that a 5" stump remained. Back when I received the radio, I had attached another longer chunk of flex to this stump and fastened it in place with "splicing caps" (it's an American thing, don't ask ).

To replace the flex, you have to un-do all the screws holding the power supply and radio chassis in the wood case. These are at the bottom of the case.

Remove the tuning and volume knobs also (the tuning knob can be a little tight on the shaft, so be gentle). Also, undo the fixing nut for the earphone jack and disconnect the speaker leads (these are press-fit sleeves that fit over the terminal lugs on the loud speaker). The push buttons stay on. No need to remove these. In fact, if you try to remove them you could probably break the plastic mounting on the switches.

The flex goes through a strain relief grommet on the P/S chassis and passes over to the radio chassis to connect to the switch behind the volume control. It's a 2-pole switch -- first I've ever seen in a domestic radio.

All the radios I've worked on that use a combined power switch & volume control have single-pole switches.

To get at the volume control, you have to undo the screws that hold the band selector switch buttons in place and also the screws that hold the circuit board to the metal frame. Unfasten the strain relief grommet on the power-supply chassis.

Save the grommet, you're going to need it later on. The replacement piece of flex was 0.75mm with a black jacket(instead of the original 1mm white stuff) but the strain-relief gripped it properly.

Also, uncouple the VHF-band tuning mechanism. This one is relatively easy, since the section for VHF uses a potentiometer that couples onto the shaft of the tuning condenser used for MW & LW.

Be careful upon moving the band selector switches out of the way because these are connected via a flat flexible PCB (basically a plastic ribbon with the conductive traces printed on it). You don't want to be breaking this or you're in deep crud.

Once these are safely out of the way, you can undo the nut that holds the control to the metal chassis. Give yourself some slack with the wires so that you can easily unsolder the flex from the switch terminals.

While you're attaching the flex, make sure to give the metal chassis frame a bit of a wipe-down. It seems to have a tendency to grow metal "whiskers" for some reason. Picture a magnet covered in iron filings.

After the flex is soldered and secured, screw back everything in place and then join and align the VHF tuning potentiometer with the AM condenser so that they're tracking properly. Tighten the grub-screw that holds the shaft-coupling in place, but be careful since the shaft is plastic. Snap the strain relief grommet back into place after passing the flex through the hole in the P/S chassis and THEN at the end, you can screw on a new plug.

The tuning pot could definitely use a shot or two of control cleaner, which I gave to mine. Work the tuning control back and forth through the entire range. This will cure drifting and scratchiness when tuning on VHF.

After that, squirt some a little bit of cleaner into each adjustment for the VHF preset stations. These things are made up of a metal worm gear with a plastic "nut" of sorts that rides in the grooves. The worm gear on mine were tarnished, so while the control was soaking up the liquid, I used a small piece of tissue to wipe the black deposits off the metal.

This also cured the drifting on the pre-set stations.

Reassembly was basically a reverse of disassembly, except it was a bit more of a chinese puzzle, trying to get everything inside all squared away. Remember to also

Now all it needs is a new AFC switch (the original won't latch when pressed) and an FM wave-rod, although it seems to work quite well with the three segments that are still left on it.

[Paul Stenning]

Hi Stephanie,

I'm pleased you got it sorted eventually! I assume you have a 117V to 230V transformer there?

Double pole mains switches are fairly common here - I think they have been a requirement for many years.

If anyone is confused about the mention of a tuning pot, this set has a varicap tuner on FM. The vertical row of buttons select either the pot on the tuning control or one of five presets that are accessible from behind. The AFC button is also on the back and allows the AFC to be switched off when tuning the presets. I don't think the AFC button is supposed to latch - I think you press it when tuning (to turn the AFC off) and release it afterwards.

There is a little clip on the back which is intended to hold a small screwdriver for adjusting the presets - but this is invariably missing.

[stephanie]

I'm pleased you got it sorted eventually! I assume you have a 117V to 230V transformer there?

Yup!! I've got two at home, in fact. A 2,000 watter and a 200 watter.

I've got grandiose plans to wire up me workbench for 220 volts. Brought back a bucketload of surface-mount and in-wall sockets from my vacation in South Korea.

The Korean 220 volt (two round pins) in-wall sockets are compatible with our boxes.

There is a little clip on the back which is intended to hold a small screwdriver for adjusting the presets - but this is invariably missing.

I always thought that clip was for holding the aerial in place when folded down for shipping.

I'll play around more with the AFC button tonight.

Also. I'm wondering....we have a VHF station at 104.3 mhz. Since this radio's dial only goes to 104, I'm wondering if it's supposed to be able to normally pick up 104.3 or will it just stop at 103.9/104.0 thereabouts and not pick up anything higher.....

Otherwise I'd have to re-adjust the coupling on the tuning mech.

[Sam]

Originally Posted by stephanie

Also. I'm wondering....we have a VHF station at 104.3 mhz. Since this radio's dial only goes to 104, I'm wondering if it's supposed to be able to normally pick up 104.3 or will it just stop at 103.9/104.0 thereabouts and not pick up anything higher.....

Otherwise I'd have to re-adjust the coupling on the tuning mech.

You should be fine. On the valve and transistor sets I have with FM I can tune quite a bit beyond the end of the scale. For instance, my Hacker Harrier stops at 100MHz, but I can reach 102MHz (at least I think I can, the station there is at home in Norfolk, rather than in Durham! ) 0.3MHz should be no problem.

Sam

[ppppenguin]

Originally Posted by stephanie

I've got grandiose plans to wire up me workbench for 220 volts.

I thought most US homes had split phase 110-0-110 available. Heavy loads like tumble driers would be wired to the "outers" to run on 220V. Or have I got it all wrong? It's a while since I've been to NY - must go again in the not too distant.

I think I've got an RM33 tucked away somewhere - you're inspiring me to dig it out and have a go!

[stephanie]

Originally Posted by ppppenguin

I thought most US homes had split phase 110-0-110 available. Heavy loads like tumble driers would be wired to the "outers" to run on 220V. Or have I got it all wrong? It's a while since I've been to NY - must go again in the not too distant.

You're correct. That's how it's done here. The resulting 220 volts would not have a neutral connection like the British & European services do.

However I live in a flat. I only have 110 volt service (one leg of the 110-0-110 service) across live and neutral with a very undependable earth connection.

At some sockets the earth connection has broken - I can explain more about this in a separate thread. To restore that, it would require replacement of the entire cable inside the wall. In these cases I'm using 2-pin sockets in order to prevent any earthed devices from being used on those (although I can sometimes use a "cheater plug adapter" to lift the earth from an appliance if absolutely necessary )

I can't use heavy-duty air conditioners or electric dryers in my flat unless I were to run them with a high-wattage transformer.

I think I've got an RM33 tucked away somewhere - you're inspiring me to dig it out and have a go!

You should. It's quite a nice radio to listen to afterwards.

[mikelect]

Ot Closed