Ok, started some electrical work today. Pulled all the tubes and started by checking the transformer and the caps. Two of the electrolytics looked fried so removed them and then did some voltage measurements on the transformer. The bottom pin outs of the transformer look as follows:

C 385V
220V CT
240V 385V
5V 5V
2.5V 2.5V
8A 2A
2.5V 2.5V

With no load on the transformer I'm not getting 385V from the pins marked above but 30V. The others all seem to be reading around 9V. I could check again with a load resistor but I think the fact I'm not getting 385V (I assume this is the plate voltage) sort of implies the transformer is gone.

So a few questions, is this the general voltage outputs from a transformer of this vintage? Am I reading this right? Second, what are the chances of finding a working transformer, or am I now destined to scrap the lot and look for another set to drop into the console?

I'm assuming that the HT for that transformer is 385-0-385, so you should find 385 across it unloaded -- that is with nothing connected to its terminals except your voltmeter.

So, if the highest voltage you're getting on the secondary side is just 30 then something is seriously amiss, such as shorted windings. There may also be leakage to the metal core which is a potentially lethal situation.

My electrical teacher would kill me. It's been so long since I've played with this stuff I've forgotten a few things. I've done a little reading and remembered. A did another measurement and the transformer is fine. 385-0-385 according to my multimeter. However, two of the caps are gone.

One indicates 8 mfd 500V (Electrolytic). However, it's huge 10cm X 3cm x 2cm. I assume it's 8 millifarads? Seems a very small capacity for such a large capacitor.

The other is 25 mfd 25V.

I assume that I should replace both with other electrolytic at a similar/identical mfd and voltage.

The other item that is broken is string for the tuning. I can replace with any old string at the right length but I'm wondering if anyone can provide some pointers. I'm sure there is one type of string that works the best.

Re: dial string, here is something that would do the trick.

http://www.ebay.com.au/itm/10-METRE-32-8-FEET-LENGTH-NYLON-DIAL-CORD-STRING-VINTAGE-VALVE-RADIOS-/320885006009?pt=AU_Electronics_Vintage_Electronics&hash=item4ab63c9eb9.

Mfd is microfarad, usually shown these days as uF.

Yes, they need to be electrolytics and those capacitances are available, although with current capacitor stock you will probably have to go above 500 volts for the 8μF one.

The rule of thumb is you can go a bit higher, but never lower.

Electrolytics are polarized and must be wired the correct way around.

Dial string needs to be of the type that doesn't go fuzzy in use. Proper dial string is available; e.g. see eBay item http://www.ebay.com.au/itm/320885006009.

Great. Thanks for the reference to the cord. I was also wanting to know the best place for electrolytic caps. I know of Jaycar but their range doesn't seem that great. Are there other stores that radio vintage people shop at that are better?

I'm looking at element 14. It appears that an 8μF 500V is a little hard to come by but a 450V 8μF or 10 is easier. I think I'll give that a shot first.

Re: 450V 8μF

Seems you missed this in my post above:

The rule of thumb is you can go a bit higher, but never lower.

That applies to voltage especially.

You'll have to Google around for capacitors. EVATCO in QLD have some. Steve Savell in WA has some. I usually get the difficult ones from Just Radios in Canada.

So, five cap changes, one 1M resistor and boom, working radio! Once I get the dial cord fixed, it will be ready to go.

One question about the antenna. There are 4 post at the back 2 and then 2. Two posts are joined with a solid connector. The other two I assumed were for an antenna but I found that only the first post seems to be required, thus a long wire antenna seems to work best. What was the regular antenna setup for these sets? Why the two pair of posts?

Finally, I have one original knob but two were missing. I assume eBay or some other supplier for some similar looking bakelite knobs?

Good to hear that you've got it working.

For a single band receiver, ordinarily you'd expect to find an aerial and an earth connector. The aerial should connect to the aerial coil associated with one gang (half) of the tuning capacitor, and the earth connected to the chassis.

I'm guessing that your set may have been designed to accommodate a loop antenna. Let us know what the 4 terminals connect to. If they go to a valve let us know the valve type and its pin.

As for knobs, as far as I'm aware, we still haven't confirmed the manufacturer and model of your set. Correct me if that's not the case.

Depending on the rarity of the set, and the commonality of use among manufacturers of the knob concerned original knobs can be very difficult to obtain. You will see eBay sellers putting 40 or so knobs up for auction in the one lot, which is a difficult way to buy them unless you simply collect knobs.

A alternative is to have a replica made by one of the guys who do that. They have been mentioned a number of times in posts on this site in recent months.

A good sharp photo of the surviving knob may help.

From memory the Racophone Peewee that I had a go at, had a circuit tag board? & was a s stable as a bucket of weeping jelly. Very poor design: should have stayed with audio amps.

I think Rod Champness may have done an article in SC on one

There is a clue in the speaker, if its original. Several of the AWA speakers were built like Amplion and I am sure some were made under licence. A specific range of manufacturers used Amplion . HMV sometimes use a MSP made Jensen and others tended to use Plessey Rola.

The dial is typical of the early thirties area.

Marc

Marc,

This one has an Amplion, pretty sure original. The stations come in pretty well, with little drift. I do note the standard problem (from memory) with the simple design, stations with stronger signals are louder than stations with weaker signals (no auto gain control), so you're forever tweaking the volume. The three knobs are tone (works fine), tuning and finally volume.

I'll see if I can fix the dial cord on Sunday and then I'll send in a few more pictures of the finished product plus the old knob.

My next project will be restoring a bakelite tabletop, just need to find one with a good case but not working at a relatively cheap price.

I doubt that that is one of them, but it may have been replaced prevously? There is a very common synthetic cored string used in many radios.

An STC Caravan came in last week, with that stuff in it, I think its an early form of Nylon. I had to replace the cordage on the STC as it would not drive.

This stuff goes hard & looses its flexibily; Circuit board cleaner is also good for accelerating the process.

If it is that stuff? Get rid of it. If the spring is missing, or has sprung, salvage, or try a bearing supplier: That is where I get them.

Marc

For the antenna, the first pair of connectors, one is connected to the chassis and the other to the aerial coil. I have an AM loop from my stereo but it does not seem to work if both connectors are used. The signal just fades to nothing. I suspect that the loop of wire I have is just too low a resistance, so it's just shorting it out.

What was the original antenna like? Was it attached to a back panel or was it a long wire? What was the impedance and the resistance of the original antenna?

As for the other two connectors, which are shorted with a solid connector, again, one is the chassis and the other goes to a different coil than the first one. If I disconnect the wire, I get a 50Hz hum.

Ideas? Can anyone give me the details about original antennas?

Forgot to also ask, where can one find a volume control extender? At this point when I put the unit in the console, the right hand volume control will not poke through the front far enough to put a knob on. The tone control is similar but has a metal extender that fits over the original post so that it stick out far enough to connect a knob. Where does one find the "extenders"?

For the antenna, the first pair of connectors, one is connected to the chassis and the other to the aerial coil.

The chassis connection is an earth and is designed to be connected to a good ground such as a copper stake or a water pipe.

If you make a connection between aerial and earth you are shorting out the aerial signal completely.

What was the original antenna like?

The aerial for the average AM receiver is simply a length of wire, with the length required being determined by the sensitivity of the receiver and the receiver's location vis-a-vis the transmitter's. At Forrestville you should be able to pick up a strong signal with a metre of two of wire, if not less.

I don't have sufficient info to determine what the second set of terminals relate to. Marcc may twig to it.

It would help if we could identify/confirm the model of your set.

I think the set is a Lekmek Console 58EC. There are no markings on the case at all but the schematics that I have look very similar. I don't think I will have any time to sort out the full schematics for the foreseeable future.

The long wire + the ground stake make sense.

My next treasure hunt is to find two replacement knobs. If I can't find the extender for the volume, I'll just have to dump the old VC and replace with a new one with a longer shaft so I can get the knob to connect. Unless someone has a better idea?