Triang 'Red Box' transmitter

[Dodgy Geezer]

Does anyone know ANYTHING about the old Triang radio system - the one in the big red metal box?

It is an early valve system, with a very low component count, but seems to have a lot of control buttons. I can't imagine that it's a true tone multi-channel, but it looks like it could use some odd signalling process...

[PaulJ]

No, I never discovered what all the buttons were for but I converted one anyway and used it as a ground based tranny....... As you said there is not much in there, which left plenty of room for the conversion, so I left the original electronics "for posterity".....

But there was still plenty of room in the other half so it doubled as a lunch box .......

Paul

[Dodgy Geezer]

Yours looks to have a different valve, and I can't see a crystal there. My one has a big fat crystal attached to the valve base, stamped 27.255, which is somewhere around Blue.

What mark is yours? Mine is a Radiomaster II, and it has a small original grommet hole in the side for what might have been a remote handset.

The white button closes a circuit from a small aerial coil to a light bulb - that was a common signal strength indicator. The blue button adds some capacitance somewhere. The black button connects to the pot - - perhaps the filament current? and the green one looks to be associated with the switch marked Pulse.....

I wonder what voltages were used? My valve is a DCC90....

[PaulJ]

Mine is a "Radiomaster Mk1" and I can confirm that there is no crystal. The valve is a Brimar 3D6-1299. There is no hole in the side of the box but one of the buttons on the top was fuggered and I replaced it with a socket, into which I plug a remotely operated button. As you can see, there is sundry other wiring in there, all of which I have left. Most of it was for batteries but I have no idea which batteries or what voltage they may have been......

Paul

[Dodgy Geezer]

Looks like HT - 90v, LT-1.5v. That's my DCC90 anyway... Your circuit looks a bit more complex than mine...

[Dodgy Geezer]

I've sketched the circuit for the Radiomaster 2. Which looks odd....

On the left is the circuit (such as it is). On the right is a simplified view of the switching (minus a few simpler switches.

What would be interesting to know is:

1 - how do the electronics work?
2 - what do the various switches do to the output signal?
3 - therefore, what must the receiver look like?

I haven't put in any component values - I can read a few, but some completely escape me. In particular, I don't know if the cap joining the rest of the circuit to the bottom of the aerial coil is even a cap or not... and I guess that the component across the valve terminals is a resistor...

[Phil_G]

Just guessing here: could the HT rise be delayed by the pot & capacitor until its high enough for the RF stage to 'fire' and transmit carrier, in doing so it drains the HT capacitor and stops transmitting, removing the discharge so the cap charges again - in a repeating cycle, rather like a unijunction transistor oscillator? the pot would control the charge timing and therefore the gap between RF bursts - ie mark/space proportional control - and the buttons give full continuous carrier or no carrier? Its nothing more than a guess... meanwhile I've asked the experts on the Vintage Radio Repair & restoration Forum, fingers crossed...

[Dodgy Geezer]

May be worth mentioning that early R/C either worked by sending a single 27mhz pulse to trip a control, or by sending a string of pulses varying the gaps between them to give a 'progressive' signal..

I suspect that the Radiomaster had one button for left and one for right. The extra gromett might have been for a pulser box...

[Dodgy Geezer]

A little post script on that circuit. I have drawn a resistor across two of the valve terminals, and a capacitor connected to the bottom of the aerial coil.

Both of those are a similar components - you can see the one connected across the valve terminals as the brown ceramic object with s[;ashes of paint just next to the two 4.7k resistors on the valve base, and the other lying along the brown paper coil former next to the silver aerial coil.

I guessed that they may be a resistor and a capacitor, but I really don't know...

[PaulJ]

Dodgy, I've sent you a pm........

Paul