R1155

[Malcolm G6ANZ]

I was given an R1155 receiver that a friend found in the back of a car he bought. It came from the same place as the R30 I previously wrote up.
So this 1155 had been stored in a barn and was in a derelict state. Not only was the rubber insulation crumbling to dust as you touched it there were a lot of randomly cut wires. Most of the severed wires were in the coil box and appeare3d to be the wires joining the coils to the switch banks. They were just neatly snipped and left . Who knows why. All the valves were present apart from the BFO and those associated with the DF.
I decided not to attempt to reinstate the DF section as there were several coils missing as well as the expensive double triode(~£100).
Firstly I had to reinstate the broken wires in the coil box and remake the old wiring. To this end I boldly removed the coil box as access was impossible with it in situ. Copious notes were made as to where the many wires joining the coil box to the chassis went. This was important as the lower frequency coils are chassis mounted and the HF coils are in the box. I also had to replace the wires going from the coils and trimmer capacitors to the wave change switch bank, again more notes and drawings.
The decoupling capacitors were 3x0.1uF in one can. I restuffed these with 500v 0.1uF surface mount type. Several of these capacitors are only accessible with the coil box removed. I checked the resistors and found that the majority were outside spec so I replaced them all, again some are only accessible with the coil box removed.
There then followed a complete rewire of the RF, Mixer and IF stages, with new capacitors and resistors. Each IF can was checked for continuity on the coils. One of the cans had a burnt out resistor, probably caused by a short circuit decoupling cap. This was replaces. As each stage was completed I checked the coils for resonance at the correct frequency all were ok.
The audio stages were next along with the audio filter which is on a separate tagboard mounted behind the front panel. Finally it was ready for power.
Here I must thank Terry (valvepower) who gave me a suitable transformer, choke already mounted on a chassis. To this I added a GZ34 and some caps to give the required HT and LT. The HT supply is strange in that the 0v is not at chassis potential but a few volt below it so giving the negative bias.
At first I used the original audio output transformer to an external amplifier. I fed in a spot frequency and tuned around until I heard it. The set was quite insensitive but a few tweaks on the tuned circuits and the IF saw a great improvement. Unfortunately one of the IF slugs was destroyed and so I couldn't peak the coil. There are 'spare' slugs in the 'Athlone ' filter which I used. The Athlone filter was fitted to filter out Athlone which transmitted on a frequency very close to the IF frequency. this filter is not needed.
Sensitivity is now about 5uV for a resolved 80% modulated signal at 7MHz.
I then fitted a 6V6 audio amplifier in place of one of the unused DF valve spaces to give a loud speaker output. The BFO unit was rewired and a new valve sourced. This was slightly different to the original one being a DL63 this has the same pinout and function just a lower heater current. Powering up it gave reasonable results. Further small adjustments on the IF coils and the LO caps improved things somewhat. SSB stations can be resolved with a bit of patience.
It's now thrown up another problem! There is an intermittent lound crackling noise ,like mains interference that comes and goes. Its not from the aerial as its present with the aerial shorted to chassis, its also all bands and on all positions of the function switch, even though some of these wafers are not connected. More investigation needed.
Overall it works

Malcolm

[Chrispy57]

Well done Malcolm - your sterling effort has brought that old girl back to life. I'm sure you'll solve that remaining problem and get a lot of enjoyment and satisfaction from your R1155.

I didn't realise there were 500V surface mount capacitors available, I've always considered that as a low voltage technology without really researching it.

I have a couple of these sets in storage that haven't really been inspected in any great detail, but one was acquired as "working" so I may get round to putting it on the bench when I have some space and time.

Cheers
Chris

[G6Tanuki]

The crackling sounds like some insulation-breakdown effect.

Your 1155 uses the cheap-and-nasty paxolin-wafer type valve sockets; I have known these to become partially conductive over the years, you can easily get grot trapped between the upper and lower paxolin sheets and this can then cause unpredictable conductive paths between the contacts. If there has been significant current-leakage for a while the Paxolin can become partially-carbonised and so partially-conductive.

Very difficult to remove this grot; when I came across it in the frequency-changer stage of one of my PCR receivers I just replaced the problematic Octal base with a nice US-made ceramic part of similar WWII-vintage.

[Malcolm G6ANZ]

G6, I agree is a breakdown of some sort. I think I've narrowed the noise down to the Frequency changer valve area. The valve itself does seem very susceptible to any touching with the fingers, or even going near it. Can a valve become internally noisy?
Chris here are some photos of the surface mount caps being assembled. A strong light, good magnifier and a steady hand are needed

[Malcolm G6ANZ]

Missed a photo out

[Chrispy57]

Hi Malcolm - nice handiwork, but where's the photo of it with 500V across it! Just kidding, but I would be a bit nervous about that personally.

Cheers
Chris

[G6Tanuki]

Originally Posted by Malcolm G6ANZ

G6, I agree is a breakdown of some sort. I think I've narrowed the noise down to the Frequency changer valve area. The valve itself does seem very susceptible to any touching with the fingers, or even going near it. Can a valve become internally noisy?

Yes. If it's one of the metallized/spray-shielded type then the wire connecting the metallizing to the pin in the base can become poorly-connected; this poor connection can cause random fluctuations in the capacitance from the valve's anode to ground, hence odd rustlings/cracklings - and in the worst case, the thing can burst into oscillation.

I've come across this with the likes of the Mazda SP61 and the generic Mullard/WWII-variant ARTH2 [a.k.a. the ECH35].

Equally, old valves can develop dry-joints in the soldering between the lead-out wires and the pins of the base [and also the top-cap leadout].

Finally, if there are any of the old-style 'shielded' connecting-leads which are made by putting a rubber-insulated piece of wire down inside of a piece of tubular braid, and wrapping a piece of tinned coper wire round the braid/soldering it to the braid for earthing, these can also corrode to become horrible ways to include both randomly-varying parallel resistors and unexplained capacitance-variation into the circuit.

[Malcolm G6ANZ]

Update on the noise problem. I decided to swap out the frequency hanger valve base as this seemed to be the root cause of the noise. Having disconnected it and released it from the chassis I went to fit the spare I had found. Problem. The mounting holes were 90' away from those on the original holder so refitting all the wiring would be difficult also it didn't fit correctly in the chassis as it had a raised ring so would not go flush. Plan B: clean the old holder. It is made from two sheets of Paxolin punched to give the correct shape holes and then riveted together with small rivets. I filed off one of the rivets and swung the paxolin into two halves. This gave decent access to clean the grot off. There was a mixture of wax and dirt, but no trace of burning or breakdown. With it cleaned and the sockets gently re-tensioned I refitted it. So far after an hour or so running listening to SSB and broadcast stations there has been no recurrence of the noise.

[G6Tanuki]

Sounds like you've fixed it!

I never really trusted those cheap-and-nasty Paxolin-sandwich valve sockets .

If your tweak hadn't solved the problem I'd have happily sent you a few ceramic Octal sockets as used in WWII US-manufactured radios.

[Malcolm G6ANZ]

I'll keep my fingers crossed that it's fixed.. You never know!

[G6Tanuki]

If it doesn't work out to be fixed, and you want to replace the Paxolin-sandwich sockets with some nice US-made WWII-era ceramics (as used in the BC348, the US-equivalent of the 1155) , drop me a PM.