Dynatron Commodore. 1961
This set was given to me by a customer who bought a new colour TV set from my shop. This was almost twenty years ago so I thought it's about time to have a look at it.
Set was connectted up to the Philips bench power supply unit. No results but there was clicks from the loudspeaker when the waveband buttons are pressed in and out. Voltage measurements on the IF amplifier transistors revealed that TR3 has the same voltage on the base and emitter, sure enough it has a B - E short circuit. The faulty transistor is a Mullard AF116, none in stock so a Telefunken AF134 was tried instead. Success! However, the set has been twiddled, the five medium wavebands available here in the North-East are receivable but are coming in on the wrong positions on the tuning scale. BBC Radio is transmitted here on 603Khz (500metres) but is coming in on 550 metres. Same goes for the three stations receivable at the high frequency end of the band.
On long waves RTE Radio 1 can be received but not BBC R4. FM is all that wonderful either BBC R2, R3 and R4 coming in, but only just. More work to be done to this set before it's signed off.
About the TV set. The new set was a Tatung "G" series model. One of the last sets to be made in the Tatung Telford works. The "H" series was made by an outside contractor.
"the five medium wavebands available here in the North-East are receivable but are coming in on the wrong positions on the tuning scale. BBC Radio is transmitted here on 603Khz (500metres) but is coming in on 550 metres. Same goes for the three stations receivable at the high frequency end of the band."
Now down to four medium wave stations. Greatest Hits on 1152Khz has gone off the air. Might just be a temporary thing because we're having thunder and lightning in these parts.
Hi Frank, in fact the modifications had been implemented during manufacture so the set must be a late production model.
The style of the circuit diagram has the look of Ekco but I think the design of this set is unique to Dynatron in Maidenhead.
Extract from the circuit diagram showing the modifications around the FM demodulator.
Yes it looks like a Dynatron design to me, I don’t recognise it as an Ekco chassis. It must have been one of the last designs from the Hacker brothers before they left to form their own company, I think they left in 1959. TV sets at that time from Dynatron had a modified Ekco chassis, no bad thing, the T368 from Ekco at that time was a good receiver.
AM intermediate frequency checked and is correct, 470Khz. At least the Phantom twiddler has not touched the AM IFs.
Easy matter to recalibrate the medium waveband. BBC R4 is 603Khz, position the tuning pointer to 500 metres and adjust the oscillator coil L16. Adjust to tune in R4. Move on to the HF end of the tuning scale. Radio Newcastle doesn't transmit on 206 metres anymore but there's a commercial station on 247 metres, use that to peak up 250 metres. Trimmers are on the tuning capacitor. Check that R4 is still in the 500M position, adjust L16. Job done.
Long waves was not so easy. Signal generator set to 200Kc/s.(1500 metres) It's coming in on 1600 metres and adjustment the oscillator trimmer doesn't bring the 200Kc/s signal to the 1500 metre position on the tuning scale. Going have to cheat and add an additional capacitor across the LW oscillator trimmer. 75pF put things right. RTE Radio 1 is coming in on 1200 metres which is near enough to 252Khz. RTE R1 peaked up by adjusting the LW aerial trimmer.
BBC R4 is now coming in on 198Khz and RTE R1 is excellent.