[TonyDuell]

This is my first real restoration of a radio. I've done repairs, I've restored other electronic devices, but never done a full restoration on a radio set. So me being me, I picked something fairly complicated. A Trio 9R-59 shortwave set. I don't think this set justifies the name 'Communications Receiver'.

I bought it at a sale at the Dulwich museum. It was described as 'works, but has been got at'. When I got it home I removed the top and bottom covers and had a look. Most of the passive components had been replaced but the soldering was terrible. And I didn't like :

No mains fuse (holder missing, effectively shorted out)

Mains wiring joined with uninsulated solder joints in mid-air

Two core mains lead fed through a strain-relief bush and then knotted.

Bare component leads connected to HT+ crossing over bare wires connected to the chassis. HT insulation should not be by luck.

So I wasn't going to power it up in that state. It needed a rebuild.

The first hint for anyone working on one of these sets is that it was sold in the States as the 'Lafayette HE-30'. The manual for that set is rather more detailed than the Trio one, it includes parts lists and alignment data. So in general I worked from that.

With the covers off, I could make a start. Fortunately I noticed that the dial glass just slides in place. I removed it and stored it before it fell out. Then pulled all the valves and kept them in order just in case the inter-electrode capacitances were different enough between identically-numbered valves to upset things. The chassis will not rest on the bench upside-down, it stands on the adjusters of the IF transformers. But I made some 'legs' from Meccano angle girders fixed to the top cover mouting holes. So I could work on the set in comfort

A large part of the under-chassis area is occupied by the coil pack. After desoldering a dozen wires it was disconnected. Next I disconnected the BFO/Q-multiplier sub-chassis. Unscrewed the 4 screws for that and took it out. Removed the band switch knob and bushing (DO NOT forget to slide the nut, washer and earthing clip over the spindle when refitting the coil pack), undid the 6 screws for the coil pack (one hidden by the BFO unit which is why I removed that first), moved the coil pack to the side, unsoldered the earthing braids and took it out.

Then I started with the mains transformer connections, removing cut off ends of wires and rewiring things neatly. I added a fuseholder from the junk box which I connected in the neutral mains wire (!). The circuit diagram shows the mains switch in one wire and the fuse in the other so I kept it like that. I did fit a new 3-core mains lead with the earth wire going to a solder tag under one of the transformer mounting nuts. Yes I know it should be a dedicated bolt but that it not really an electrical requirement. Then I worked through the power supply, tidying up the wiring and removing, sleeving and resoldering any componet leads that could short.

Then working backwards through the stages starting with the audio output. I made layout diagrams, desoldered everything, cleaned up the tags (removing cut-off wire ends, etc) and reassembled it. Fitted a few NOS resistors when the originals were too mangled. And replaced 'that capacitor' anyway.

After doing the audio/detector stages I moved back to the IF amplifiers. The first problem was that one of the IF transformer mouting nuts was missing. The stud (fixed to the transformer can) was 3mm diameter but a normal M3 nut didn't fit. In the end I re-mounted the rectifier valve holder using normal M3 nuts and bolts and used one of the original nuts thus freed to fix the transformer. Then the IF gain control needed repair, the shaft was cut too short for the knob to fit. As I discussed in another thread here, it's a 10k reverse-log taper pot. The original track together with the spindle/slider from a pot in my junk box made an electrically correct part with a long spindle.

Alas the knob was designed for a 6mm spindle, not a 1/4" one. But it was easy enough to drill the knob out to 6.4mm, whereupon it fitted perfectly.

The RF/Mixer/Local Oscillator stages had been totally mis-wired, it wasn't worth making a diagram of what was there.I removed the components and re-wired according to the circuit diagram. In the process I found the RF amplifer control grid series resistor (should be 47 ohms) was a 47nF capacitor meaning said grid had no DC path to anywhere. And there were a couple more similar errors.

I didn't do much on the coil pack as I didn't want to upset the alignment. I did replace the tatty wires that connect it to the rest of the receiver and also sleeved the wires of the 33 ohm resistor in the oscillator circuit.

The BFO unit had not been touched so I left it alone.

Next I refitted the coil pack and BFO and connected them all up. Put the valves back in, connected a length of wire as an aerial and a small speaker and powered it up.

I was not expecting it to work, after all I'd removed and refitted just about all the components and must have made mistakes, right? Wrong!. After warming up, I could receive signals on all the bands.

As to whether it is 'finished', I think it could do with re-alignment, but I don't have a suitable RF signal generator. That will have to wait. But I am still pretty pleased with getting it working first time.