Repair of an Australian Tasma Baby from 1934

[petervk2mlg]

This is five valve compact mantel receiver designed for broadcast coverage and operation from 200-260V AC mains.

As received it was reported as working but with oscillations etc.
I didn’t try to operate it as the two core power cord was frayed and looked decidedly dicey.

Getting this chassis out of the cabinet is a labour. The electrodynamic speaker is hard wired to the chassis so it must be unsoldered (remove the cover plate over the connections and then unsolder) and then removed from the set – this is hard as not easy to get to the screws holding it in – must remove all valves and valve shields first and then jiggle!

Also when undoing this one needs to deal with the volume control which is in front of the middle of the speaker – you need to unsolder the volume control connections on the chassis. Once the speaker and the volume control connections have been unsoldered, you can remove the knobs and the bolts holding the chassis in place in the cabinet and withdraw the chassis from the cabinet.
Then unscrew the speaker baffle and remove it with the speaker attached. Only then can you remove the nut from the volume control shaft and remove the big wire wound volume pot – Note that if you do this before removing the speaker the danger is that the pot will fall backwards and damage the brittle Magnavox speaker cone.

The first area I tackled was the old power cord.
The active and neutral wires are soldered onto the connections on the power transformer directly without going through an on/off switch.
The main worry here is that the power transformer is mounted vertically under the chassis and the side connections are right up against the tuning gang. A piece of cardboard sheet has been fitted to the side of the gang to prevent shorts. Because things are so tight here it is impossible to get easy access to the power cord connections. The radio is quite compact for the age and as such there are really no easy ways to get access without removing some bits – in this case the power transformer.

I undid the 2 bolts and nuts holding the transformer place, taking care not to dislodge the spacer washers on the bolt head side of the assembly. This enabled me to carefully swing the transformer to the right, taking care not to stress any connections to the lugs on the transformer of any connections to heater wiring/ht connections to valve sockets etc.
I noticed at this point that the 59 bias resistor and bypass capacitor – an old electrolytic – were mounted on the power transformer right next to the active/neutral power cord connections
I made sure that the resistor and capacitor were not fouling the active and neutral lugs and also augmented the cardboard insulation between the gang and the transformer with a sheet of plastic cut from an old ice cream container.
Then I fitted a new 3 core power cord and ensured a good earth connection.
As the radio had been operated previously with just a 2 core cord and such close proximity to the gang the possibility of a lethal set was very real.
At the same time I cut out the old 59 bias capacitor and will fit a new electrolytic capacitor down on the 59 socket – such a position is possible with a small modern capacitor.
With all valves removed I plugged the power cord with a limiting lamp in series with the mains cord in and was happy to see the radio’s dial lamp light OK and with no untoward flashes or stress noise from the chassis.
After that it was a simple matter of replacing all the leaky capacitors in the set, although to get to the oscillator and 1st 57 and the 58 screen bypass capacitors I had to remove the can from the first IF transformer. I removed the 2nd IFT can as well while I was at it and cleaned up the screw adjustments on the compression caps on the IFTs. New grid wires were fitted to the 58 and 2nd 57.
The original wet electrolytic filter capacitors were still in circuit. Normally with radios I get these have been disconnected and new ones fitted at some time in the sets’ lives. This radio had never had a soldering iron near it and of course the electros were dried out and open circuit.
I unsnipped the leads to them, left them in place for show and fitted a pair of new 10 uF 450 volt rated ones.
A quick check of the alignment circuits improved matters somewhat. Surprising the set was pretty well spot on and reception was good, although the lack of AGC was quite evident.

Cabinet
The cabinet looked little dull, but was essentially OK – I thought I could get away without stripping and lacquering.
I first gave the case a good dust down and a wash in some warm soapy water and set it to dry outside, taking care not to let any direct sun onto it. Then a couple of applications or lacquer restorer and a rub down with a polishing cloth made all the difference.
The speaker cloth had seen better days and was thing and torn in several spots. There was nothing to be done here but remove and replace with some nice reproduction cloth.

Reassembly was straightforward but needed to be done in the correct sequence.
First install the volume pot (a 2.5K w/w job) then fit the speaker and baffle board. Solder the three wired from the volume control to the tag strip on the chassis.
To make future servicing easier, I dispensed with the hard wiring of the electrodynamic speaker to the chassis and fitted a 4 pin plug and socket. Then the chassis was slid back into he cabinet, the tuning and volume control knobs were fitted and the 4 small bolts holding the chassis in place wee refitted.
The job was complete and the radio took its place on the shelf.
I include a couple of pics and a schematic.

Peter

[Station X]

Well done Peter. It's always nice to restore an unusual set rather than a run of the mill one.

[chipp1968]

Nice looking set . the pic makes it look like normal size table model

[PJL]

That's a superb job and it is interesting to see something from outside europe.

What is notable is the IF is 445KHz whilst UK radios of the period would generally be 125KHz (apart from Phillips who took a while to get the hang of superhets).

[petervk2mlg]

The Tasma 180 radio measures 350mm X 300mm X 210mm. Not that small I guess, but by the Australian standards of the day quite small. In Australia, the console radio was king in the 1930s and far fewer mantle sets were marketed.
I've included a pic of the radio next to an AWA Radiolette "Empire State" (similar vintage)for comparison.

Peter