Standard Beam Approach - Rebuild update

[M0FYA Andy]

James, excellent progress!
Andy

[jamesinnewcastl]

OK, made a start on the main receiver. Uninspiring piece of kit with not much on show, see pics.

Four of the valves were in good shape - probably not seen the light of day for eighty years. One has a loose top cap and one has a corroded top cap.

I've decided that I'll strip it all down to bare metal and rebuild. All resistors and caps replaced or restuffed with the exception of mica ones. I'll rebuild and just power up and go!

The metal caps covering the valves have a spring loaded (bakelite?) plunger inside, they all work perfectly. All these are squeezed down by the metal bridge device - I'm not looking forward to that!

There are three 'Westector' semiconductor diodes, not measured them yet but I won't replace them unless I have to!

Really do need to lose 'that smell'. Loads of work to do!


Cheers
James

[AlanC]

I used to have one of these receivers when I was a youth ( >40 years ago), I checked today in the cellar of my mums house where it was last seen to see if by any chance it was still lurking but unfortunately not :/ Back then (mid 70's) I used it as a tunable IF fed from the output of a TV UHF tuner to listen on the 70cm amateur band, which worked a treat. I remember that as purchased it had a fault where the local oscillator 'squegged' at several kHz and I cured it by placing a resistor in the grid lead of the valve.

The box with the multiway connector on top on the front panel had a cover with a tuning fixture consisting of a dial marked 30 to 40 Mc/s (or thereabouts) and a local control knob, but also an attachment for a flexible drive that would have allowed remote tuning from the pilot's or W/Ops position.

Best of luck with this project

Alan

[jamesinnewcastl]

Hi Alan, thanks for your best wishes.

Apparently many of these receivers sold on the amateur market for conversion to car radios and I assume for other projects such as yours. I spent many weekends wandering Lisle Street looking at what would have been brand new ex-Mod kit, pity Dad never bought any.

My receiver is in a heavy cast enclosure while there was a 'portable' version of the SBA system with everything mounted inside a single crate and that used a lighter variant of the receiver which I suspect you have described, see pic. Does that look familiar? The first variants of the main receiver used a dual flexible drive to turn a switch through preset frequencies while later versions were fully variable via a single drive

Cheers
James

[AlanC]

Hi James,

Yes that photo is spot on and apologies for the inaccuracies - it was a long time ago. Mine came from Bardwell's in Sheffield - which will be well known to anyone from this area who is into radio and electronics. Norman used to buy things from various sources known only to him that he thought would be of interest to his customers, and you never knew what to expect! Particularly, in the mid 70's there was still a lot of military surplus stuff available. One Saturday I went down and there was the R1466 all on its own and I had to have it! It couldn't have been very expensive as I was pretty broke in those days, but it was in good condition and painted in a light grey, almost cream, colour. I soon figured out the heater, HT and audio connections and found it to be working, though when you tuned in a signal it went through a number of peaks either side of the correct tuning point because of the LO problem I described earlier. That fixed, it was a good sensitive receiver. I had a n ex TV UHF tuner lying around and I knew that its IF output was at around 36Mc/s which the 1466 covered. This combination pulled in the local 70cm repeater plus UHF PMR and telemetry signals very well - slope detecting the FM of course as the 1466 is an AM receiver. Its exact fate is unknown but I suspect it succumbed to one of my parent's clear-outs after I left home.

Cheers
Alan

[jamesinnewcastl]

Hi Alan

According to the Practical Wireless article in 1956, the set could be bought for 15s with valves or 4s without. The author actually paid 10s. He was J. Stebbings - the name rings a bell but I am not sure why.

I've been cleaning my receiver this afternoon and on reading your post I was full of admiration of the work you must have put in to figure out the circuit, but looking at the pictures of your unit (attached) I can see that it is very much simpler than the one I have. This is because the fixed tuning requires several banks of variable caps and a lot of switching! Not surprising they changed the design!

Shame that you can't find your set - it is an exceedingly rare beast!

Cheers
James

[jamesinnewcastl]

Hi

Cleaning up is going nicely - see pics. When trying to remove the bumpy corrosion off of the aluminium 'cans' I found that very sandpaper left fine 'lines' in the aluminium, while a soft 'sanding sheet' of the type where the abrasive is stuck to a sponge sheet was perfect leaving no marks and acting very quickly. Great stuff.

I'd like to pick your collective brains with regard to disconnecting the bellows flexible coupling (see pic) It looks like there are two tapered pins hammered into the two holes in each end of the bellows. My question is - how do you remove the pins? Press them out somehow? Hammer them out? Something else?

Cheers
James

[mole42uk]

Originally Posted by jamesinnewcastl

Hi

I'd like to pick your collective brains with regard to disconnecting the bellows flexible coupling (see pic) It looks like there are two tapered pins hammered into the two holes in each end of the bellows. My question is - how do you remove the pins? Press them out somehow? Hammer them out? Something else?

Are they not roll pins? I think I see a slit on one side - that means they are a 'spring' fit into the hole and could be pushed out, maybe holding the shank of a slightly smaller twist drill in a pair of pliers.

[Sparky67]

If they are roll pins James, a bit difficult to tell exactly, they might be quite tight. Using a drift which fits the external diameter of the pin and tapping them through with a small hammer should get them out without damage. Something like THIS imperial set perhaps?


Martin
G4NCE

[jamesinnewcastl]

Hi Chaps

Thanks for the replies. They don't have a hole through the middle, there is a slot but only on one and it looks like just a mark. One end protrudes more than the other so I was thinking a tapered pin? Sorry the pic is too good.

I was a little worried about damaging the bellows by hammering away only to find there was a 'right way' to do it. But I will try giving it a little tap!


Cheers
James

[M0FYA Andy]

James,
Given that you can't support the part the pin is in easily as it is in fresh air in the unit, hammering may be unsuccesful and cause damage. It might be better to make a tool akin to a small G-clamp to squeeze the pins out?

Andy

[Ed_Dinning]

Hi James, as previous suggestion about a G clamp, with a clearance hole in the "anvil".
Once moved off the taper they should com free easily.

Ed

[ex seismic]

A couple of washers over the thick end of the pin and squeeze with water pump pliers or some such?

Gordon

[Jon_G4MDC]

Andy's post #31 is the way to do it. There were commercial devices like that.

[jamesinnewcastl]

Hi Chaps

I like the press idea - I have a small vice that might just get in there with some washers. I'll have a hunt around as it's surprising what items can be pressed into service (ah a pun)!

Cheers
James

[jamesinnewcastl]

Hi All

I've started working on the Main Reciever now. It isn't wired the same as the standarad given in the AP and has several more components added. I can't find any documents showing official modifications. I've mapped out what the changes are and most look like alterations to the AGC response which I know was 'fiddled' with. However, one modification takes an output from the second IF stage - there was never any need for this so I am assuming that the receiver I have was used for experimentation.

My question actually is for anyone who might be able to explain why a lot of effort has gone into a bank of variable capacitors when none seems necessary? The photos attached show the capacitors in question. Seemingly all you need to do is to use a screwdriver to adjust the shaft through the hole provided in the cover plate. However there appear to be 4 spring loaded clamps for one row of the capacitors along with what look like three screws to set the height of the cover plate. This clamping would seem to be the point of the cover plate.

Any ideas? Is this a standard thing to do? It seems like an expensive thing to do too.

Cheers
James

[jamesinnewcastl]

Bit more explanation - the brass coloured parts are a spring material pivoted in the center by a fixed screw. The large headed screws probably adjust but I dare not fiddle. The capacitors affected are not in circuit together so I don't suppose that there is any interaction involved between the pairs.

James

[Jon_G4MDC]

Looks like fine adjustments. Set coarse by rotating the main ceramic C then adjust the spring paddle for fine tweaking using the stray capacitance between it and the "hot" terminal.

[jamesinnewcastl]

Hi All

Just a short update on the Main Receiver restoration. I've decided to restore it to the standard of that shown in the first Aircraft Publication. The one I have has a number of modifications which were designed to increase performance rather than function.

I need a full strip down and I plan to change the capacitors that might be dodgy but to give it a fighting chance all the resistors must be changed too!

So here is my first attempt at recreating the resistor type used in the receiver. I started with appropriate sized plastic tube, spayed with plastic primer, then painted with model kit enamel colours for the body. The pics attached show my Dremel made into a small 'lathe' for cutting all the bodies to the same length. Next a few bodies were fed onto a long bolt separated by washers and put in a drill chuck. By ty-wrapping the trigger the bodies were turned and a paintbush held up to paint the colour bands.

Next a resistor put inside the tube and the ends sealed with wood filler and shaped. This isn't the most refined method and I've damaged the paint on the prototype but I am pretty pleased at progress so far! Shame that the new resistors have such thin lead wire.

The new resistor is shown lying next to an original 1k. I need to colour the wood filler next and get matt paint!

Cheers
James

[AdrianH]

Just a question, and this will depend on the dissipation in each resistor, but could you run into issues with the resistors cooking, as basically you are insulating each one, stopping any cooling the resistor may have.
I ask as i have a need to get some vintage looking dog bone resistors and was considering doing something similar.

Adrian

p.s. the effect you have got is very good.