Wireless Set 128 MKII Restoration Project

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History of this Radio

Development of the Australian Wireless Set No. 128 started in early 1944 with approval for production given in July 1945. Issue to units was only after the war had ceased. It replaced the Australian No.108 as an High Frequency (HF) manpack set until the introduction of the A510 in 1955, although Very High Frequency (VHF) FM sets such as the AN/PRC-9, -10 and CPRC-26 were introduced in Australia in the early 1950's. The Wireless Set Australian, No. 108 was Australia's principal manpack set in the early days of the Korean conflict (1950-1953). The physical appearance of the US Signal Corps SCR-300-A (BC-1000) VHF FM was taken as the base for the general design of the Australian Wireless Set No. 128. There were two variants the MK-1 and MK-II, differing by the turns indicator on the antenna tuning unit.

This approach simplified sealing and placed the centre of gravity close to the body. In order to operate with existing sets and to provide long range sky-wave communication the set operated on CW, MCW and R/T in the frequency range of 2.0 - 4.5MHz either MO or crystal controlled. The RF power output is given as approximately 0.36 watt. Miniature 1.4 volt valves are used and in its construction miniaturisation was carried out as far as possible. The base of the set housed a 162/3 volt battery, similar to that used with British Wireless Sets No. 18, 46 and 68. In addition to the operation of dry batteries, provision was made for operation from a 6 volt vibrator power supply (Unit HT Vibatory No.3 Aust.) which is interchangeable with the battery compartment for use as a ground station. There is some doubt whether the vibrator power supply was ever issued as no one has ever seen it, and it is not listed in the reprinted handbook. The set appeared to be of good reputation but was noted as being 'battery hungry'. The Mk.II version of the Australian Wireless Set No. 128 had a number of improvements of which are noted a turns counter for the Aerial Loading, a rugged lightweight handset, different connectors on the junction box, throat microphone, different connectors on the junction box, headset and Morse key, and the bulky carry frame was dispensed with.

The MKII Radios Past

I ended up with two WS-128 radios. One was the MKII and the other was a MKI, The following section shows work done on the MKII radio. It was recovered from an estate back yard and was in terrible condition. Unfortunately it was outside with the cover open and the internals were suffering from some condensation and corrosion.

Before Inside the top of the Radio†††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††† ††††††††††† Before the Crystal Oscillator Section

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After a light chemical cleaning, and light abrasive blasting to remove the scale and corrosion the photos show the chassis back from the dead. The abrasive also removed scale that had jammed the variable capacitor.

Inside the top of the Radio†††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††† ††††††††††† After the Crystal Oscillator Section

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The Chassis will be protected with a coat of sealer that will mimic the original MFP coating, giving it a yellow tinge and sealing the metal. I will use an non epoxy based lacquer, with some shellac mixed in.

Before Photos of the underside††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††† †† After Chemical clean and a very light abrasive blasting

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†††††††† Before Shots of the chassis

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Technical Info

The WS128 is a low power portable transceiver that provides RT, CW and MCW for a battalion or similar unit. It is a combined transmitter/receiver complete with an internal HT/LT battery (162v/3v) when operated as a portable manpack.

The set covers the frequency range of 2.0 - 4.5 MHz and may be locked to any frequency using the 3 position flick mechanism. The transmitter is automatically adjusted to send on the same frequency as the receiver. In addition, 3 crystal controlled channels are provided and a 4th as the oscillator source.

The radio was constructed in light weight metal and does seem somewhat flimsy compared to many sets of the period.

The valve lineup is as follows:

Position

Receive

Send

V1A 1R5

Mixer

 

V1B 1R5

Oscillator

Oscillator/Mixer

V2A 1T4

1st IF Amp

 

V2B 1T4

2nd IF/Audio

Sidetone RT

V2C 1T4

RF Amp

Buffer Amplifier

V2D 1T4

Net Only

1600kc xtal oscillator

V3A 3A4

 

Modulator

V3B 3A4

 

Power Amp

V4A 1S5

2nd Det/BFO

Audio Amp RT, Osc MCW

IF Frequency is 1600 kc,

My set was missing this crystal and the crystal socket, so I am on the search to find a replacement.

The sets cover the 80 meter band so it will be used at the next Field Day if I can get it going.

††††††††††††††††††††††††††††††††††††††††††††††††††††††††††† Diagram††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††† ††††††††††† Operating Instructions

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The WS-128 MK1

As the MK1 looked to be an easy option to get going first while I worked on the MKII chassis cleanup, I started to get the MK1 going. This seemed to have been a workshop donor as many little things were missing from the receiver. The first thing was that all of the coil slugs had been swiped. After some searching a donor source of parts was supplied by my collogue Ray Robinson.

The MK1 coil slugs and the MKII coil slugs are different sizes, they are close but there is about 60 thousands of an inch difference, and the MKII slugs are too small for the MK1. The chassis and Front panel were a lot better on this set. Although as it turned out there was a lot wrong with the set. The shots below show the front panel and chassis top and bottom.

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Electrical Restoration Notes MK1

After playing with the receiver section, a donor supplied by Ray Robinson, yielded the cores I needed, and I have found that the size of the MK1 coil slugs and MK2 coil slugs is different by about

60" of an inch. They are not interchangeable; the MK2 ones are too small for the MK1.

After a number of small faults including the choke missing from the filament string for the oscillator tube, and other small parts cut out or missing, cut wires, the receiver is finally going well, of note the radio is not very stable on CW, the chassis is very flimsy, and if you move the set on the bench it varies the tune. This may be better once it is in its case. I managed to obtain a nice Handset for the radio. I tried it and now I know why these radios were not known for great reception. The handset as a receiving device is totally useless, it is more useful as a weapon rather than receiving signals. The modern headset I have been using, I say modern 1977, is light years ahead of the STD hand set for this radio. I was listening to 3.7000 CW and the volume had to be turned down to ľ as the signal was so strong. With the STD headset, I had to turn up the gain to hear anything, and then all I could hear was static, the volume control is actually a RF gain control as it controls the screen grid voltage to the RF lineup, and turning up the gain to maximum is basically useless. I suspect that the other headset type with the throat mike is far more sensitive, as the old Phone type hand set with the electro magnet steel disk speaker is no good on this radio.

 

I now have focused on the TX. After fixing a few faults with broken caps, I managed to get a Carrier out. RR furnished me with a 1520 KC Crystal, Not 1600, but I was able to tune the IF to that frequency, and re-tune the RX to track. Once I had that installed I had a signal, just no Audio or CW MO...! I did the normal thing started at the Mike transformer fed a signal in and tracked it. I managed to get a Signal down to the capacitor that fed the 3A5 modulator stage. So the Speech Amp seemed to be working, although on the grid of the 3A5 I had nothing on the other side of its feed capacitor I had a signal. I pushed a signal into the Grid, and Nothing out of the plate...? Screen volts were Ok,? Took the tube out, tested it, It had emissions. The answer was, Tubes when tested in the basic tube tester, do not check if on the input grid has a short..! That tube had a short or partial short on the input grid, when I removed the tube the signal appeared at the grid pin on the socket. After fixing this issue, I then had AM TX output with Audio :-0 Although the modulation depth is not as good as I would like at the moment itís a start.

 

Note: If you ever have to get at the BFO / Mike Amplifier tube base, itís almost imposable. I had to remove the can from the chassis not an easy task to fix a pushed through pin on the tube socket. Next I will be looking at fixing the CW MCW tone. The MKII should be child's play.

Other Places to See a Wireless Set 128 !

See: http://www.vk2bv.org/museum/

and: http://www.vk2bv.org/museum/ws128.htm

and: http://www.tuberadio.com/robinson/Australian_radios/

 

 

 

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