Mixed technologies radio.

[Amie]

Double post.

[Murphyv310]

One of the last products made and marketed by the old EMI company was a portable radio which employed three low consumption valves and two OC72 transistors.

I suppose done that way because the three transistors that would be needed for the signal stages, were to costly?

It has other benefits.
The use of a class B output stage with transistor output reduces power consumption on lower volume levels than a DL96 will have on the HT battery.
HT batteries were expensive so removing the output valve will greatly reduce costs for the consumer, a big selling point. Low voltage batteries were much cheaper plus the filament current saving as well.

[Murphyv310]

Hi.
I made up a frequency changer today with a single 1J42A. The RF was derived from a ferrite rod with a medium wave coil and I used the tuning winding fed directly to one grid of the 1J24B, initial testing of this part was done with the anode and G2 fed from HT with their own respective load resistors, the G2 was decoupled with a 1nf. Good signals were seen on the anode. Next was to make up a local oscillator. I've been told in the past that using the second grid of the 1J42A won't work properly in this type of circuit. Me being me decided to try it and see what would transpire. A suitable coil was found in a couple of boxes of oscillator coils I got from Ed Dinning. The wiring was simple with one winding of the coil between G2 and HT and its secondary to the second G2 via a 100pf cap and the earthy end grounded. At this point I was using a resistor as anode load. Immediately on applying power the oscillator ran.
So next I cobbled in a RS midget IF transformer. After some rough alignment the RF carrier was seen on the scope of my local on the output of the IF transformer, also the two adjacent stations were seen when tuned, tracking though is bad at the moment and this needs some work. So we can see the 1J42A will work as a frequency changer. Next was to try it into the TA7642 and I was able to drive a set of headphones from it. Tuning is pin sharp and obviously there is no bleed between the local and the next closest station.
Next is to get the tracking right an then transfer this to a more permanent construction method than it all over the bench.
I'll post a diagram of the FC later on.

[Murphyv310]

As promised.

Still some work to be done but even like this it works, very stable too.

[Amie]

Interesting, well done

No questions yet, just hopefully be able to ride towards an interesting design on your coat tails Trevor!

[Murphyv310]

Hi.
The Local Oscillator it rather hit and miss, get the ends of the band OK and the oscillator stops mid band cobbling up a separate oscillator with another 1J42A could be the answer with its output fed into the mixer G3 if I decide to strap both grids together or fed to G1b. Will see over the next few days what transpires.

[Amie]

Hi Trevor.

As you've a stated your intention is a hybrid design, you could include a stabilised transistor local oscillator to feed the dual control pentode....

Just a comment from the peanut gallery

[Murphyv310]

Hi Amie.
When I did the single 1J42A pantry tx I initially used an LC tunable circuit. The stability was really uncanny with only a few Hz drift after a few hours, even voltage drop from 9 to 6v made only a few tens of Hz difference, filament voltage made no difference to drift. Using a separate osc is the best way I think as I can tie the two split control grids, also able to get a good level of injected signal.

On a slightly different note I remember your dad asking me if he could repost my circuit of the panry tx on the Radioboard forum, seems like yesterday.

[Amie]

Hi Amie.
When I did the single 1J42A pantry tx I initially used an LC tunable circuit. The stability was really uncanny with only a few Hz drift after a few hours, even voltage drop from 9 to 6v made only a few tens of Hz difference, filament voltage made no difference to drift. Using a separate osc is the best way I think as I can tie the two split control grids, also able to get a good level of injected signal.

I would be interested to know what level of oscillator signal on the dual control rod pentode would be required for efficient conversion, have you fed one separately from a generator and measured?

On a slightly different note I remember your dad asking me if he could repost my circuit of the panry tx on the Radioboard forum, seems like yesterday.

I don't know when that was but even though he's been gone over two and a half years, I still wake up thinking he is still here, I know you will understand....

Thanks.
Amie

[Geordie McBoyne]

In 1961 Pye employed a transistor in the sync separator in the V700A series TV receivers.
Sales brochures promoted the "Transistor Synchronised" feature in the sets.

Geordie McBoyne.