'Radio Jacks'

[TonyDuell]

In the 1960s (I think) some companies -- Truvox was one -- sold what they called 'Radio Jacks', a cheap way to record a radio programme.

They seem to have been crystal sets, often switch-tuned, that plugged into the microphone input of a tape recorder (which of course could handle a low level signal). I think they earthed via the tape recorder, there was a terminal for a long wire aerial.

I read somewhere, though, that they gave better results than a simple crystal set, presumably there was some filtering after the detector diode.

Does anyone have such circuit diagrams? Was there ever a magazine project to make one (seems quite likely)?

[G6Tanuki]

There were several designs for these published in Practical Wireless backin the 60s, both as simple crystal-sets and one- or two-transistor reflex sets [typically using an OC44 as the first (reflexed) transistor, one or two OA81 diodes as the detector, and an OC71 as the second transistor].

I'm sure I also remember one using the ZN414 in the 70s.

Attached screengrabs are from Jan.1964 Practical Wireless.

[Sergeauckland]

I've just had a look inside my Truvok Radio Jack, and it's quite horrible!

There does seem to be some RC filtering, but the internal structure is so fragile, I wouldn't want to move any parts to see what's connected to what.

There doesn't seem to be any insulation between the internal parts and the metal case and some of the components' connections look like touching the case.

I tried mine a few years ago with a few metres of cable as an antenna, but couldn't get anything out of it. Now that I've got a pantry TX, I'll try that when I have a moment.

S.

[G6Tanuki]

The Sinclair "Micro-FM" was also advertised as having two output jack-sockets, one being for headphones the other being for connection to a tape-recorder/external amplifier.

[Graham G3ZVT]

These are a testament as to how quiet the RF environment was back then!

[G6Tanuki]

Yes, I think any supposed 'better quality' from recording with what was basically an amplified crystal-set was predicated on two things:

1] You were only trying to record from a local, high-powered BBC transmitter.

2] The potential audio bandwidth of a crystal-set or a RF-amp/reflexed radio feeding a crystal-set could be better than that of a traditional AM broadcast-radio with its usual sideband-clipping in the IF and subsequent post-detector filtering to give that mouthful-of-porridge sound seemingly preferred by old people.

In the late-60s I used my father's Philips tape-recorder to record baseball-games that were being broadcast on Medium Wave by AFN in Germany. You wouldn't have known they existed if your only signal-source was a "radio jack" thing with a few feet of wire as the antenna.

[Hartley118]

Originally Posted by Graham G3ZVT

These are a testament as to how quiet the RF environment was back then!

My recollection is of problems with whistles from bias oscillator harmonics beating with the station. FM was a wonderfully quiet revelation for radio recording.

Martin