A while ago I offered to restore my friend Richard's late fathers radio.
It's a National AE-670 radio, dating from around 1960. It's got medium wave, and two short-wave bands, and a "gram" input.
It's also a basket-case! It's been dropped at some stage in it's life, the glass dial is broken, and case front is cracked, and the woodwork's in a bad way... let's see what we can do....
At some stage, someone has added a two pin connector on the rear .... I hope that hasn't got mains on it, as it's pins are exposed....
..and it is! Connected to come on with the radio! I wonder if it was used to drive a table lamp or similar. Some TV's and radio-grams had similar sockets, although not exposed. I disconnect the socket, as it's not safe...
The chassis looks complete and largely un-molested.
Removal of the front panel knobs, and four screws underneath the cabinet allow easy withdrawal of the chassis. I also remove the speaker board, and the damaged dial glass. A Piece of veneer on the front comes away when I remove the surround. I'll glue this back later.
On this inside of the cabinet, there's a circuit diagram, layout and re-stringing information. Something looks to have eaten it a bit!
The valve line up is 6X4 rectifier, 6AR5 output, 6BE6 frequency changer, 6BA6 IF amp, and a 6AV6 AGC, detector and 1st audio amp. There;s also a 6DA5 indicator tube.
The circuit will come in handy later...
With the chassis removed, we can start on the electronics....
The chassis has quite a few waxy capacitors, which will need replacement. There's also a 3uF 300V electrolytic which is probably past it's prime!
The main smoothing can is something else... look at all those sections!
After a few cursory checks to the mains and output transformers to check they're not open-circuit, I change all the waxy capacitors for modern equivalents.
There are a couple of wax caps I can't change. They are C50, a 0.003uF and C29, a 0.05uF.
These need to be modern safety components.
C29 must be X2 rated, as it's connected across the mains. C50 must be Y rated as it's between the mains and chassis. If C50 were to fail short-circuit, our chassis would become live. Not good.
I've ordered the X2 and Y rated caps, but for now the set will function without, so the wax capacitors are simply snipped out.
You can also see the chassis has a mains transformer, so is an isolated design, unlike many British sets of the time.
There's also some rubber insulated wire that's perished. It drives the dial lamps on the front panel. It's replaced.
I gently bring the mains up via a variac and isolation transformer, monitoring the HT as I gently wind up the voltage. This allows the electrolytic capacitors to reform.
The main multi-section electolytic shows no rise in temperature, and is pronounced fit. The small 3uF cap is not in such good condition, and is replaced.
The set performs well, although the indicator is a bit dim... they never seem to be very bright thesedays...
Here's a long exposure pic!
I leave the set on soak test once I'm happy with it, and set about the cabinet.
The dial back, escutcheon and knobs get a good wash in the sink...
Where the front panel is damaged and de-laminating it's glued back together with PVA glue. The missing piece of lamination is made up with pieces of paper and glue, a bit like decoupage, until it's level. If I don't do this, the replacement speaker cloth will never sit straight.
The centre rib has been pushed in. It's repaired and glued. The croc clips will hold it all in place until the glue dries.
The speaker cone is ripped. It's been glued in the past, but has really had it. I'll get a replacement.
And on to the case...
The years have not been kind...
The piece of veneer from the front moulding is glued back...
.... and the deeper scratches filled with some fine wood filler.
Now to don a dust mask, and rub the thing down....
Looks good eh? Now to stain the wood again...
First off hoover up all the dust left from the sanding, and wipe the cabinet over with a tack-wipe.
Now, I must admit I bought this stuff ~10 years ago to paint a front door with... came out nicely too. There's still a good 3/4 of a tin left...
Now...
Step 1. Read the instructions on the tin.
Step 2. Ignore the instructions on the tin!
It does say on the tin "Apply evenly by brush along the grain" ... which is great if you're doing a front door... Find yourself a good lint-free cloth, dab it in the woodstain, and wipe it on, along the grain. It's really easy to get a nice, thin even coat like this. Not only that, but it will have dried by the time you've finished reading this paragraph!
Now that's looking good. If you want to go darker, just add another coat or two, until you get to the shade you're happy with. As it is, I think just the one coat is about right. You'll notice it's not too shiny. The woodstain gives us a satin finish, I intend to add a gloss varnish when I'm done...
Now we need to re-create the black front, with the fade towards then centre. we can do this with some black aerosol paint. The end result is the given a coat of lacquer.
I'm rather pleased...
During all the cabinet work, I had a thought... Gram input. Be nice if it was bluetooth....
There's precious little on MW and SW these days, and this would give the receiver a bit of a lift!!
Enter the BK8000L bluetooth module and adaptor board.
A simple 7805 power supply is built up on some perfboard. The keen eyed amongst you will notice there's only a single diode. The board uses half wave rectification. This is because the board is to be powered from the heater winding on the transformer. One side of this winding is referenced to chassis ground, so we can't use a bridge rectifier. The module only uses about 50mA when it's running, so there's not a lot of smoothing required either (220uF seems to work well).
The module's left and right output "positive" outputs are coupled together via two 0.1uF capacitors, and the signal fed into the gram socket.
It works really well :)
And the radio reception isn't affected by it either!
The speaker board gets a nice piece of blue cloth glued, clamped and clipped into place....
... groovy ....
The hole where the magic eye pokes through is given a coat of PVA glue. This will make it stiffer, and easier to cut. It'll also stop it from sagging after I've cut it.
It's left to dry.
Meanwhile, the X2 and Y class safety capacitors have arrived......
... and are duly fitted.
Now onto the dial glass... it's in a bad way ...
in fact it's in three pieces...
The rubber grommets are removed from abound the holes for the control shafts, as they've gone hard and have shrunk. I'll find some new ones...
But what to do about the broken glass? I've had very little success over the years attempting to glue it. Superglue is just too brittle. Epoxy works, but has to applied thickly to get it to stick and the results are generally not nice to look at.
My mate Stephen showed me this glue the other day. "It'll stick anything" he says. It comes in a pen, and is cured by the UV LED mounted in the end....
Further research show people have been using it to repair broken and cracked mobile phone digitisers, as a sort of stop-gap repair.
What have I got to lose?
Having carefully cleaned the edges of the broken parts with isopropyl alcohol, I apply a line of the glue from the pen, and shine the UV LED at it...
It allegedly cures in 5 seconds...
I'm sceptical...
... but it works superbly!
Where the glue ran out of the join when I put the two halves together, there's a bit of a bead, which is very slightly soft. The packet says the stuff can be shaped, sanded, drilled, polished and painted... so I clean up the surface with a bit of wire wool.
I repaint the rear of the dial, where it's supposed to be opaque, with some black paint, as some of this was damaged when the glass was broken.
At this point, the dial breaks again, in the middle of the "V" ... there was a hairline crack there before... It again glues well...
Now onto the speaker. It's a 20cm x 12cm elliptial. It's shot. Not only is the cone torn, but the edges are all breaking up. It's also 3 ohms. Digging about in my box of spare speakers turns up a couple of similar sized speakers, but they're 8 ohms. I asked the usual sources and put out a couple of requests on various forums for something suitable. No good. eBay was not forthcoming either. Then, whilst googling I found this ....
I'm lucky enough to have a branch of Halfords locally, so I popped down, and picked one up...
It's a similar size, and 4 ohms... near enough. Notice on the label it states "Min. Input 20 watts" .. I've only got 4 or 5 .... I'm sure they don't mean that really ..... only one way to find out!
The speaker is mounted up onto the speaker board and fixed back into the case. The output transformer was originally mounted on a bracket mounted to the old speaker. I'll worry about that later ...
Now to refit the dial-glass. This was originally mounted by two rubber grommet type mounts, located on the four holes around the holes where the control shafts pass through, on each end of the chassis, as shown here .....
The rubber has long since turned into some kind of gunge... I had a look in the box of rubber grommets, and selected a couple of these conical shaped things. They're designed for accepting wiring looms though the bulkhead of cars. I used a few on the mini...
A grommet is fitted to the hole in the chassis, and the conical grommet cut to size.
The output transformer is mounted to existing holes that fix the front bezel to the cabinet and speaker board. The dial lights are re-fitted, and the magic eye back into it's spring-loaded holder.
The bluetooth receiver is glued to the bottom of the cabinet.
... the back replaced, and it's given a thorough testing. The "min 20 watts" label on the speaker proves to be meaningless, as I thought.....
First thing of note was the damaged mains cable ...
