MadModder

Today I had few extra hours and plan was max. results with minimal effort.

I could not locate thick enenough aluminium for support, I mostly used 30x30 mm 2 mm thick L-profile.

Mechanically it appears fine, but I haven't tested it yet electrically.

Magnetic tape is now 2 mm off the sensor. Plan is to file 3 mm bolt holes oval just enough to bring the tape near the sensor but avoid physical contact.

Still two separate items left: X-axis and configutation.

 Ohh my I laugh so much, Tom you are a comedium. 

So the next thing to work out is how to transport this megalith (97 lbs not including the 'desk mount' case!) the entire length of the UK while retaining some confidence that it won't be smashed to smithereens 

Meanwhile have a fragment of the circuit showing a few of the pesky filters that need aligning :

Years back I had a great interest in Communication Receivers - in fact I had quite a collection of what other followers of electronics would disparagingly call 'boat anchors'.

Before re-housing the workshop and moving here (11 years ago) I reluctantly disposed of most of them, but I could not bare to get rid of my Racal RA17. This receiver, made in 1957, is iconic. At the time it was probably the most stable communications receiver and was priced accordingly. Used in huge numbers by the armed services and many 'listening posts' it played a large part in our cold war defence 'snooping' on the Eastern Block.

Why was it so stable. Well it used the 'Wadley Loop' designed by Trevor Wadley (a South African) at the invitation of Racal, and uniquely used a single crystal generating many harmonics, to control two local oscillators whose drift would self cancel. (a VERY simplified description)

I don't remember when or even where I got mine, but I have found traces on the Internet of me asking questions back in 2002, so it was before then !

Now it's been packed up for those 11 years. The capacitors and resistors in these sets are well known not to age well, and I do recall dimly from before I packed it up that it would benefit from some TLC - leaky capacitors and resistors changing value all contribute to reducing sensitivity and selectivity.

I've decided that at last I must get this unit back into commission, but sadly I no longer have the RF test gear that I did, and this set has some very complex filter networks (100 khz, 37.5 & 40 Mhz) that need sweep generators to set to the accuracy demanded.

So, biting the bullet, I'm planning  to 'out source' the work to one of the very few people able to do it. This will include replacing all electrolytic capacitors, all paper capacitors above 4.7 nF, replacing all carbon resistors, and re-aligning the filter units.

It's had a few 'modifications' where non original sockets have been substituted for more common ones, and those mods will probably be reversed if possible.

To whet your appetite have a few pictures taken today when I pulled it out of the eaves storage where it's been all these years:

Well I stood there pushing the bell for hours hoping for a brew, but gave up and found a cafe 

I was probably out  making really slow progress on a doorbell...