Hi Guys, Its a long shot, but here goes I built a car radio from Radio Television and Hobbies in 1959, 1960. Not sure of year

It uses 4 x 7 pin miniature 12v (plate supply valves) in the RF Freq Con and IF.

One of the valves in the lineup is a 12BL6

It uses a power Transistor 2N301 type output.

It been knocked about a fair bit over the years and it looks like the mice had move through and in need of a going over.

If any of you guys with a long memory could point me to the issue, I’d be extremely grateful.

I can then order it for Silicon Chip.

Thankyou. R

This is the 1959 Karset, described in the June 59 issue, with an article on the installation in the July 59 issue.

I have the articles here and I can send to you if you need either the full article, (several pages) or just the circuit and parts list.

Harold

1959 Karset Circuit Diagram

On another note, how long were valve/transistor hybrid sets available?
I'm curious to see the circuit for this too.
I understand that for a time a valve radio with germanium output was used in battery sets to reduce overall current

On another note, how long were valve/transistor hybrid sets available?
I'm curious to see the circuit for this too.
I understand that for a time a valve radio with germanium output was used in battery sets to reduce overall current

Tended more to be in car radios, lots more noise compared to a valve especially, when used with a complimentary NPN in push pull.

https://alltransistors.com/transistor.php?transistor=2720. Did have a bad habit of dying from thermal runaway.

Thankyou so much Guys, I'll get Brad to post a picture

I didn't have any thermal issues with the output transistor in this build and noise wasn't a real issue.

From memory I did have bother biasing the output transistor up correctly.

A resistor in the coil lead fixed most of the ignition noise in the Holden, that's the model after the FJ.. the newer body shape.

On a side note do any of you guys know the History of "Roblan" makers of the Tuning Gangs I used in the 1950's

They were the only manufacture of midget Tuning Condenser I could get my hands on during that period, they were a quality unit which I
purchased in 2 and 3 Gang versions.

All the best Guys Thankyou

Now one has to be a bit cautious here. The hybrid radios normally had a "spark plate". The early NASCO (Firestone tyre & Rubber) and the Universal (Astor) Neg & positive ground & 6V /12V Models were all Valve.

The "Spark Plate" was specific to the Hybrid Radio as pretty much all of those early cars like my Zephyr have Kettering ignition. The basic form sees around a 200V spike riding on the supply. That tends to wipe out any transistor. That plate was designed to have it flash over within to suppress it.

Marc

Photo uploaded to Post 6.

Document uploaded to Post 2.

Looks like to do a good job you would have strip all the components out of the valve section and get the chassis rust cleaned and coated.

In certain areas I’ve cut corners and used the threaded end of the valve mounting bolts as earth points and should have used solder lugs under those bolts.

Even as a late 16 year old I was at my limits with the metal working with this job.

Thinking back, I talked about my experiences with the scope iron which by the way I hold dear and used on this build, I really could have done with a current day Weller for this set build because it was so crammed in the valve area.

Thankyou Harold for the circuit

Hello everyone,

As work progresses on the 1959 Karset is it first casualty replacement is the 2N250 which corroded out by the set being power transistor down in water for some time.

In trying to keep this original as I can, I did a world wide search came up with a few possibilities namely in the US and the UK.

I thought this was going to be a difficult search but there is still a few of these floating around out there , so I settled on a 2N250A version which is the final incarnation of that series.

This is coming over from the UK.

I think 2N250 was one of the first TO3 Germanium Power transistors developed by Texas Instruments in the mid 50’s .

So the work continues ….

I had a little bit of a laugh as I was reading through the original build notes , Quote, “ Provided its fairly thin, motor car lacquer can be sprayed with an ordinary fly spray and on small areas be used to give a first class finish…. etc “

Many would remember those pump fly sprayers with the horizontal canister underneath, I never tried that one but quite amusing to look back.

It is interesting to note that there are two different forms of spray gun. The thin lacquer ones tend to be the same as that old fly spray, only with a constant air supply and more knobs to control air flow and the width of the pattern; plus orientate the pattern to horizontal or vertical.

The ones for paint be it self contained, or with air supplied; pressurise the paint canister to blow the paint out. The electric one is handy as it can be used pretty much anywhere and often here, powered by an inverter.

Its a bit of a compromise but yes, the old fly spray would work.

Marc

On another note, how long were valve/transistor hybrid sets available, BurntOutElectronics asked ?

The 2N250 Germanium TO3 was developed mid 1950's,so allowing for startup production and to arrive here,I would estimate in the 2nd half of the 1950's

I would say, 2 or 3 years from 1958 to 1960,

The Radio & Hobbies all Transistor car radio was 1961.

All transistor car radios were available in the USA in1959 albeit expensive.

Back in the day it was uncertain if transistors could be made that could function on RF frequencies. Or at least be cheap enough. So these 12V plate voltage vacuum tubes were developed for car radios. There's plenty of current to be had from the car battery and alternator system for the heaters. So heater current draw was not issue there, but it would be in a battery portable radio. 12V plate voltage tubes also means you don't have to have vibrator driven high voltage power supplies. And you use the slow power transistors to drive the speaker.

Wa2ise, I'm curious about these valves.
What sort of model numbers are these?
I haven't heard of valves that can operate with such low plate voltages