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Old 30th Jun 2017, 2:28 pm   #1
ukcol
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Default Ultra TR100 Transistor Six

The Ultra TR100 was (I think) Ultra's first transistor radio and according to the ERT Service Chart was released in August 1958 priced at 20 guineas (21). Jonathan Hill in Radio! Radio! says that Ultra described it as "The first completely self-contained home radio". It employed 6 Mazda "top hat" transistors the line up being:
Mixer/Oscillator XA102, 1st I.F. amplifier XA101, 2nd I.F. amplifier XA101, audio amplifier/driver XB103, and the output stage employed two XC101s. It covered the medium and long wavebands.

I was given my example by an elderly neighbour not working and rather tatty (the radio, not the neighbour).

My experience of transistor radios from this period is that they often have little or nothing seriously wrong with them; this one wasn't completely straight forward but it wasn't too bad either.

A visual inspection of the chassis showed that all was present and nothing was physically broken so I ordered some batteries. The set uses two 4.5 volt AD28 batteries wired in series to give a split 9 volt supply. The AD28 is not generally available but can still be obtained at a reasonable price from specialist suppliers.

The set is full of Hunts Mouldseal capacitors and had this been a valve set I would have replaced them all without a second thought. In transistor radios however paper capacitors have to be extremely leaky before it has any effect on performance, this is because of the low impedance, low voltage circuits employed in transistor radios - so they were left in place. I went round the electrolytic capacitors with an ESR meter and they all looked reasonable healthy.

So I connect the new batteries and switched on. There was a quiet click in the speaker at switch-on but no other sign of life. The audio stages were not working and a voltage check indicated incorrect voltages on the driver transistor. The collector voltage was low and both base and emitter voltages were high. With the transistor removed I tested it on my home brew transistor tester and it was very leaky indeed. I replaced it (an XB103) with a Mullard OC81, not original but a good electrical substitute.

The audio amplifier now worked well but there was still nothing from the receiver section, not even any noise when operating the wave-change switch. Next job was to measure the voltage on the mixer transistor and both the I.F. transistors. The mixer and the 1st I.F. voltages were close to what was to be expected. To get at the connections to the 2nd I.F. transistor I had to remove a small sub-chassis that provided linkage between the wave-change knob and the slider wave-change switch. The voltages here also proved to be good.

I then measured the forward and reverse voltage drop across the detector diode in circuit, the results were inconclusive but when I lifted the connection to one end the diode proved to be completely open circuit.

The detector diode is a CG12E and the only germanium diode I had was an OA47 which is a general purpose type. The OA47 worked very well however and I was rewarded with a lively set receiving all the expected stations on both MW and LW.

I gave the set a bit of a run after re-fitting the wave-change switch mechanism and then assembled the chassis back into the cabinet. The first time I switched on once the chassis was back in the cabinet the set was quite deaf and the audio was grossly distorted. I think Murphy's law section C clause 5 applies here, "Any intermittent fault will wait until the equipment has been completely re-assembled before putting in an appearance".

When I had removed the chassis and switched on again the fault had disappeared and the set was fine once more. I eventually observed that the fault would appear approximately one in five times that it was switched on. The fault turned out to be the on/off switch, the contact in the positive to chassis was unreliable.

In most sets this switch problem would have caused the set to be completely dead, however the split supply complicates things. With S2B open-circuit the bottom battery is out of circuit and the set runs on 4.5 volts from the upper battery. The return to the battery positive from chassis is via TR5 and the loudspeaker. The deafness is caused by the fact that the receiver section is powered from one battery only less the voltage dropped across TR5 and the loudspeaker. The distortion is because only one half of the output stage is working, See snippet immediately below.



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Dismantling the switch and flushing it out with switch cleaning lubricant failed to offer a cure. The switch construction didn’t allow me access to the back contacts to clean them by hand. I remember vaguely being aware that switching low currents (in relays for example) can leave a contact prone to oxidisation and that contacts switching higher currents are “self cleaned” so I removed the switch and used it to switch a 60W mains light bulb. After switching the bulb on and off a couple of dozen times I returned the switch to the radio. This proved to have cured the problem.

When handling a radio chassis I generally try to leave the tuning capacitor fully meshed to avoid the risk of bending the vanes. The switch fault had distracted me enough to cause me to not take this precaution and I now found the RF section of the tuning gang was shorting out at about half rotation. It was straightforward although a bit fiddley to sort the tuning gang out.

That was the electrical work complete (something completely within my comfort zone) but now I came to the cabinet.

I decided it was about time I had a go at cabinet work and this seemed a good set to learn on.

The cabinet was generally grubby and the top of the wooden surround was rough and worn. The metal part of the carry handle was badly corroder and the bright on the tuning knob was missing.

After cleaning the cabinet I lightly rubbed down the wooden surround and then brought the colour back with dark tan shoe polish. A good polish of the cabinet ensured that the polish would not come off when handling the radio and improved the finish. The metal part of the handle was rubbed down to the metal and the sprayed with several coats of a brass coloured paint aerosol.

Lastly I needed something for the tuning knob bright. The only convex bright I had in my knob box was too big and then my wife suggested she may have a button that would do the job. She found one the right size and shape, all I had to do was removed the “stub” from the back and spray it with the brass paint. Finally I glued it to the knob with hot melt glue.
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Old 30th Jun 2017, 3:32 pm   #2
Phil G4SPZ
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Default Re: Ultra TR100 Transistor Six

Wow, Colin, that looks fantastic! Nice write-up too and a good description of the fault-finding.

I also have one of these sets, which also had a dicky on-off switch but otherwise just needed new connectors, batteries and a clean. Sadly the tuning scale on mine has deteriorated due to being stored in the previous owner's damp garage.
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Old 30th Jun 2017, 3:43 pm   #3
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Default Re: Ultra TR100 Transistor Six

Thanks Phil,

That's a shame about the tuning scale on you set, would it be possible to make a replacement if I take a high definition picture for you of the scale on my set?
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Old 30th Jun 2017, 3:52 pm   #4
Phil G4SPZ
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Default Re: Ultra TR100 Transistor Six

That's a very kind offer, Colin. We're away till the end of next week, but when I get back I'll take a photo of mine to show you. It seems to have started off as a bronze background, but has turned partly black. It will be nice to compare!
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Old 30th Jun 2017, 4:03 pm   #5
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Default Re: Ultra TR100 Transistor Six

There seem to have been a few versions of this set. Mine (in the todo pile) has the bronze tuning scale background and a metal rod handle which attaches to the sides of the case. I must say Colin's version looks better!
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Old 30th Jun 2017, 4:11 pm   #6
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Default Re: Ultra TR100 Transistor Six

I think yours will be a TR101 Paul.

http://www.radiomuseum.org/r/ultra_t...r101tr_10.html
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Old 30th Jun 2017, 6:20 pm   #7
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Default Re: Ultra TR100 Transistor Six

You are absolutely right
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Old 30th Jun 2017, 8:39 pm   #8
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Default Re: Ultra TR100 Transistor Six

That's helpful, Colin. Mine is also the 101 version, with the wire handle, so the tuning scales are different.
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Old 30th Jun 2017, 9:35 pm   #9
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Default Re: Ultra TR100 Transistor Six

I have one these in the roundtuit pile, it looks in good physical shape, but I have not tried powering it up yet.
I am amazed you can still obtain the batteries, I had plans to use two 3 slot AA battery holders for mine.

I will have to unearth it to see if the dial is the same as yours, if so I will try to scan it for you.

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Old 30th Jun 2017, 10:50 pm   #10
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Default Re: Ultra TR100 Transistor Six

ukcol

Thanks for that informative & very helpful article.

I have two of these and one is a bitsa for spares but the other works but has lowish volume and has been left unresolved for some time but now, because of your post, I'm now energised to complete it.

Rgs Tony
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Old 1st Jul 2017, 12:37 pm   #11
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Default Re: Ultra TR100 Transistor Six

Good tip about jolting switches back into action, thanks!
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Old 2nd Jul 2017, 7:50 am   #12
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Default Re: Ultra TR100 Transistor Six

Hi Terry,

At least having a donor set means you have a reasonable chance of having a good original component if one of the top-hat transistors turns out to be duff.

Hi Sue,

Thanks, it won't work in all cases of course and certainly won't work with switches in mains sets that are already operating in high voltage high current conditions.
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