R209 mk2

[thx1138]

Hi,

I got this R209 a few weeks back after a long lapse of radio restoration hobby..
Having trawled this forum I had the wit to order up a solid state vibrator from keith at royalSignals, which is a good start, especially to get this going properly. It certainly made a difference. Much thanks as is .

This evening I had the set running and after 2hrs the AM became more quiet as if it was on FM, ie when you tune into the carrier the resolve is like your using the wrong filter thats narrow. I also noticed cw/ssb audio is lower , not that it had been much louder to start with, but i suspect this is an issue that was well on its way to happen and finally something has kicked up.

The IF output fed into my icom indicates the rf front end to be fine albeit so my guess is more final audio amp related and I guess caps and resistors possibly gone oc or high.
Before I hack into this (carefully), can anyone point to a few things to check so I can follow through and get this lovely radio back to life.

many thanks, David

[thx1138]

Hi,
one further question. The larger value capacitors, are they bipolar or electrolyctic esp in psu section. The diagram I have isnt clear so I dont wish to put in the wrong type which would trigger all sorts of problems. Any advice re capacitors.

[G6Tanuki]

Having had several R209s, and still owning a couple - one thing these do suffer from is the decoupling capacitors going leaky - they use strange ones with a sort of grey or light terra-cotta-coloured rubbery outer.

Bearing in mind these radios are all at least 50 years old, some component replacement will be needed!

Check the voltages on the audio stages - the push-pull output is a very strange design, using two different valves (1S5 and 1T4) in a sort-of self-driving circuit with the control-grid of one half fed from the screen-grid of the other. I never really understood how it was supposed to work!

[G8BBZ]

Hi,
The electrolytics are conventional polarised components, with the exception of the large 500uF capacitor across the DC input terminals - this is a non-polarised component. You only need to fit a non-polarised component in this location if you want to retain the ability to connect the DC supply either way round. If you are happy to polarise the supply, then you can fit a polarised component in this location.
cheers
Peter G8BBZ

[thx1138]

Hi,

thanks for your advice. I was wary to do anything capacitor related as the markings are less than clear and didnt want to damage anything.
OK, I have a bundle of caps to do here.
The push pull in the audio amp had me scratching my head given how it was done. But other than that, this is a real workhorse and suprisingly selective. IF out is a great bonus too for checking things externally.

Many thanks again for help, 73s David

[G6Tanuki]

Yes you're right, the R209 is a fun little receiver. The biggest issue I had with mine was the local-oscillator being hum-modulated by the vibrator, which meant that listening to SSB signals on 14MHz was distinctly unpleasant.

A solid-state vibrator replacement (along with replacing the feeble 'selenium disk' stack rectifier with something whose performance was realistically a bit more like a set of diodes rather than leaky-resistors) solved that problem.

And I still can't get my head round the push-pull output!

[Keith]

Hi David,

I recently aquired an R209. Having masochistic tendiencies I decided to dismantle and restore the vibrator which now works fine with its reassuringly audible hum. You'll find that its performance on SSB is not ideal as it has a CW peak filter in the audio stage. I think this could be fairly easily bypassed in a reversible way if SSB is your thing. Mine is only used for receiving AM so not a problem. I too find the "self driven push pull" intriguing, but it seems to work. Another piece of innovative design is the rectification of the BFO signal to get negative grid bias for the RF gain control. This was presumably necessitated by the battery valves not having cathodes to contol.

[thx1138]

Hi Keith,

The vibrator I have is dead as you can imagine, and actually sitting on mantlepiece! it looks cool there.

The solid state vibrator is delivering a fabulously stable supply and long may it last. Best ever fix for these sets and I can imagine a WS19 set with one. (wishlist)

SSB, yes I was thinking, what do I disconnect easily, or what component that is recognisable can I find to do this.
CW is not so critical and cleaner SSB would help, incidentally (I know this isnt ideal) I used my icom 751 to align each band and maxed the RF frontend and IF stages, the results are outstanding.
RAF Volmet on 11253 is nice and loud here in central europe and even 11175 usaf is unbelievably clean to resolve.
The IF out also helps a lot for other plans with an sdr kit.

Regards David

[Keith]

I haven't tried this but you could lift one end of C78 (Mullard equipment manual designation). This will increase the overall audio gain so you might need to replace the Twin-T filter with a resistor (say 3.3 Megohm)to bring it back down again if you get any instability.