High Power Amplifier WS19

[Rod Salter]

A long time ago I bought from a private advertisement a High Power Amp No2 for the Wireless set 19
A written description and no photos
I remember it cost a full 2 weeks pension at the time

It duly arrived by post
I unpacked it to see a hole cut in the front plate ‘for a meter’? mmm?
Next surprise, it had been fitted with a power transformer, 2 rectifier valves, choke and capacitors. The job was exceptionally neatly done. Suits me, I want to operate it off the power anyway.

It was the 4 x 807 valves type, ‘Nice’
Maybe I can crank this up to transmit a few watts


The unit was lugged to a few displays, but not working.

I kept an eye out for a suitable square meter for the hole

Eventually, I “clicked” on a box assortment of meters as I judged a square meter in the lot appeared as if it might fit
It did, but (there is always a ‘but’) the dial was for 8 amps
And that I find a strange marking in its self (I digress)

Time passes, and I was given a carton of Holden car parts, which got shoved into a corner
Again, eventually, I was ratting through the carton (I must have been bored) and low and behold a small round, wait for it - - -
The correct dual marked dial scale, you little beauty!

We have passed the bush fires and now the floods set in,
This is Australia, it is so big, and you can drive all day and be in the same state.
Bush fires at one end, floods at the other and drought still holds on in some places, while the population clings to a narrow section around the coast line.
A few weeks ago I could have played marbles any where here, and now I can’t find the way to the shed because of the long wet grass!


For the want of something to do, I benched the HP amp



With a little fiddling I got the meter movement and dial swapped over in the housings.

So far so good or how lucky they are the same internal diameter

Now to replace all the capacitors, (to be on the safe side) before powering the unit on

Then I notice that all 3 trim controls are disconnected, another mmm??

I traced and drew the circuit

First the input drive (meter trans No4) sensor is gone - replaced with the internal fitted meter?

MY Circuit



Now I struggle with all things radio, (again the buts) but that can’t be right?

I checked and checked, even to replacing some of the all same red wires with different colors so I could follow them better

Look closely at the meter wiring (some circuitry omitted for clarity)





Have you sussed it????

ONE - The meter is wired directly from bias negative (approx 30 volts) to 12 volt positive supply

AND if you haven’t noticed - - - REVERSE polarity !!!!!!

Surely the modifier had used the Amp?
Another mmm, the meter was missing, right, burnt out maybe?

TWO – The meter is across the RF choke to the network onto the cathode?

And other circuit peculiarities,

Moving on, my meter requires half a volt for full scale deflection and was fairly close to the correct reading on the low voltage when I fitted it

So, begs the question, Why have 42 volts backwards across it?

OK next
There is a bias voltage control, so OK

Another ‘but’ the “drive” from the ws19 control is in the grid

Here is the BUT, but it is wired full resistance from the input and the wiper varies the bias. I don’t understand at all,
How can that vary the drive?
Well it would, BUT also vary the bias ????
A nightmare to tune????

I searched the WWW for days about transmitters and linear amplifiers,

There is nothing like the wiring WS HP amp, I was learning fast though

Well anyway, first rewire the meter, at least with the correct polarity and
Why connect it to 12 volts?
I did not, I connected it to earth
Finding a suitable voltage dropping resistor took some time swapping values
Settled on a string to make 8.88k ohms

The face is marked for 600 and 15 volts
This resistor combination allows full scale at 30 volts

Nice - 600 less a 0 and divided by 2

Next the cathode/plate current

I rewired the meter from AFTER the RF choke to the network across the load resistor

The selector switch and meter fully rewired





Now that drive control still puzzles me

I rewired it

Full resistance from bias voltage to the grid
Once bias voltage adjusted that will remain static
The wiper to the input from the WS 19 can be adjusted independent of the bias



Let’s turn this beastie - - - ON

Connect 12 volts DC

Valves all aglow

Main switch - ON

Rectifier valves all aglow

Press to transmit

Voltage rising slowly

HISS HISS ?black snake?

Quick, switch off, I smell the smoke now

Absolutely no visible signs of anything toasted

Sneak it back on, no HT at all

Unsolder wires and check sections for the deadly short

Long time later, C5a on top of the chassis, behind the coil, yep, I missed that one
.1uf 3kv across full HT after the choke
Perfect appearance and perfect short
Sneaked a new cap in behind the disconnected original and re-solder all the wires

All voltages steady,

I changed some meter resistors to obtain a more correct reading

That leads to - never believe the color code on the resistor
One was marked 3.9k but (I like buts) measured 5.8k, I therefore went to 4.7 k and whacked the meter full over before measuring and fitting a string to make 6.2K


Also
Resistor R9a – 12 ohm 4 watt (the load for the WS19) has been toasty at some time
I replace it with 2 of 25 ohm 5 watt carbon types in parallel

There is an additional relay and the original relays have been rewired, how-ever they all work so I left them alone

I’ll need to do a transmitter section on a WS19 to really power it up

Listen for me on 3.5 something

Or maybe, I’ve got it all wrong

Cheers rod

[Bruce Parker (RIP)]

Rod, are you talking about the RF No.2 amp or something unique to Australia? There should be no gauge (square otherwise) on the No.2...

I've spent a great deal of time trying to find gauges for the various 'banana plug' types on W/S No. 9 and 11's. Usually I find the right shaped gauge as a filler that fills the spot cosmetically until I eventually turn up the right gauge. At least that's the plan. I had palpitations when I finally got a the right gauge for my 11 set.

[Rod Salter]

You are right Bruce it is a No 2 and I have edited the introductory line to add that

Maybe Hanno could alter the post header

You are also correct it should not have a meter!

and I know your joy at finding that elusive piece

I once found listed on eBay, an "old radio headphone" in a antiques shop in Hawaii at $5 us

It was the headset for a SB22 switchboard that I been searching for over years, and costing a considerably more elsewhere, if available

cheers rod

[Mike K]

Hi rod

Some of those Amps were modified for use with the 122 WS aust. In that case a meter was fitted and two of the 807s removed. The meter is a round type, similar to the 122 meter.