RAP 646 Radio UK

[HamishBoxer]

Paul has the data top right of this page, not sure re alignment but should be on same. YES, it is on.

[Herald1360]

Alignment frequencies are given in the data but there is no specific alignment procedure specified so presumably the "standard" way for this vintage of set applies.

[paulsherwin]

Yes, you should be able to realign it like any of the AA5s you're presumably familiar with. However, it may not need realignment unless somebody's been twiddling.

[Vecher1]

Jerry, That would be great if you could do it.. I do have the schematic and layout..

Skip

[cathoderay57]

Hi Skip, OK, I'll have a go. There are plenty of people here to peer review it . The one thing I can't do is produce a layout diagram of the chassis showing exactly where each coil and trimmer is. I used to have one of these radios a few years back, but sold it and didn't keep my restoration notes, so I can't do a visual match between the circuit and the physical layout. It ought not be too difficult though for you to work out which trimmer and which coil is which, from the circuit. I'll post the procedure and annotated circuit parts in a day or two. Cheers, Jerry

[cathoderay57]

AFAIK the IFTs only have trimmer capacitors, although the circuit diagram looks as if they have cores of some sort but maybe not adjustable? Can anyone who owns one of these please confirm this, before I go any further? Cheers, Jerry

[ms660]

In the service info I'm looking at some of the component numbers in the layout for RFI don't tally up with some of the component numbers in the schematic for RFI, ie: the capacitors in the RFI schematic are numbered C1 through to C11, in the layout for RFI it shows two C9's but no C8 and no C11 either, it also shows a C12, there's no C12 marked on the schematic for RFI.

I would guess that the other C9 in the layout is C8 in the schematic and that C12 in the layout is C11 in the schematic.

So far as I can make out.

Lawrence.

[cathoderay57]

Thanks Lawrence; the service info you have got seems to be the only version in circulation and so the errors are likely to be universal. I've drafted up a first version of the procedure and attached it below. Any comments or corrections welcomed. The values of components for the dummy aerial were lifted from the Trader Sheet for the Barker 88 which has the same Mix/Osc and IF valves. However, the coils will have different characteristics and so the chosen component values might be sub-optimal, but probably provide better matching for the RAP 646 than not using a dummy aerial at all. Cheers, Jerry

[ms660]

Sounds ok so far.

IF trap?

Lawrence.

[cathoderay57]

Originally Posted by ms660

IF trap?

Good point, thanks. I'll do an update in a bit. Jerry

[cathoderay57]

Here's version 2 which includes alignment of the IF rejector/trap. Jerry

[ms660]

Lawrence.

[Vecher1]

Thanks you ALL. This will help a lot.

Skip

[Vecher1]

Ok finally finished up recap of radio.. so plugged it in.. brought up on variac... AND? mostly does not work.. no volume on most bands except the LW band.

I did do a if alignment and that went fine..

I was able to hear my signal generator on the LW band at 300khz and 150khz

but no signals or sound on all other bands?? Maybe band switch? i will look at it and clean it.. hopefully that helps...

Any suggestions?

Skip

[cathoderay57]

Hi Skip, sounds as if it isn't giving up without a struggle. Dirty contacts or a broken wire on the band switch are possibilities. If the padder capacitors (C8 and C9) at the bottom of the SW3 and MW oscillator coils are bad then that could cause the symptom on those bands, although it should still work on SW1 and SW2. Also worth checking continuity of the antenna and oscillator coils, although it is rather unlikely that more than one would be o/c. Check also the voltages on the 6K8 anodes, grids and cathode. There are no reference voltages in the service data but experience will tell us if the voltages that you measure are reasonable. A simple check is to try connecting the antenna wire to the top cap of the 6K8 and see if you can hear anything on MW (broadcast) band - that's assuming you still have some AM stations in your area! Cheers, Jerry

[Vecher1]

Ok Think I might have found the problem The wire on Pin 6 ( plate) of the 6K8G broke off so re-soldered it and will put back on bench.

More to follow,,

Skip

[Vecher1]

Ok Everything seems to work better can RX signals on all bands.. or Signal generator..


Need someone who has worked on this radio to tell me where the adjustments are.. what coil is what i will take a few pictures and post.. Thanks

Skip

[Vecher1]

OK Was able to figure out what coil was for what band.. Alignment went smooth after that..

So its done Really nice sounding radio Chrome cleaned up nice

Thanks to all who helped without your assistance it would have been much harder.. I will take some pictures and post in a few..

Skip

[cathoderay57]

Good job, well done!