Monday, 10 August 2015

Revox Revamp

As is probably known by regular readers of this blog, i'm a bit of a sucker for a nice bit of surplus! So when I spotted this beauty on its way to the WEEE man, I just had to save it!

This is a Revox B261 FM tuner. Its got to be the most perfectly retro set ive seen! It makes me think of a middle aged bloke, with this and its matching amp built into a teak cabinet, huge headphones on, a pair of cords, slippers, and pipe, puffing away to a good bit of prog rock...

It had a ticket on saying 'dead', but luckily, also naming the engineer who said so! So, a quick email to him and I knew its symptoms - doesnt come on, just makes a click as from a relay on power up. OK, so, something inside is working, even just for a moment! A relay is powering up! My suspicions, as always with a vintage piece, fell on its electrolytic capacitors, and in particular, the power supply.

But first, I had to un-mod it! The XLR's and the Eddystone box of DINs shown here are all part of the non-standard build inside, part of the use this set had been put to in its earlier life.

There were also several PCBs inside as part of the mods. All came out, and theres some very nice parts on them!

 All the mod parts are shown here. Theres relays, audio ICs, audio transformers etc. With these out, the tuner is back to its 'native' state. And I could start work

 The first thing I did, was to continuity check all the internal fuses. Oh look - F4 is open circuit! Could it be as simple as a blown fuse? Rated 800mA slow blow, I didnt have any but found some 1A which will do at this stage. I replaced it, and tried the power - still dead. Rechecking the fuse showed this one had blown as well. So, checking the circuit diagram, I now knew what I was up against. F4 protected the 9.6v windings of the power transformer, feeding the +5V regulator. The picture below shows the regulator card

 Notice the missing component? C1, a 2200uF 16v electrolytic smoothing capacitor, was dead short! Thats it in front of the PCB! With it removed, I fed the LM317 regulator IC with 10v from my variable PSU, and tested the cards output - A good 5V line!
After some digging about I found a replacement 2200uF 25v capacitor that fit nicely. Soldering this in, and adding a wire link to connect two point that previously did so via the three ground lugs of the original capacitor, meant that I could refit the card and try the radio. It failed first time, but only because I forgot to replace the fuse! With a new fuse, powering it up and pressing the buttons, I now have -

Yes! Its on!
 OK, so ive no speakers or antenna attached, so I dont yet know if it actually receives or if theres any output, but it powers on, the display works, the buttons work, the LEDs work! (alright so the display backlights dont work, but they are 36v filament bulbs - i'll replace them with LEDs)

I'll test the audio another day, but i'm quite confident its working. And for the sake of a few fuses and replacing this little bugger

I have a top of the range professional grade FM tuner! And its cost me nowt!

UPDATE - Ive just slipped out, put a croc clip lead on the antenna socket, and plugged in my cans -
It sounds amazing! This sounds to me how FM should sound! This is most definitely the best thing ive every pulled out of a skip!

No comments: