Anybody know what I have

[STUARTEDWARDS]

He was into photography.

[Herald1360]

The circuits made up on matrix board support the homebrew idea. It's not a technique generally used for commercial gear.

What were your late relative's hobby interests? It's clearly not a trivial piece of kit that was thrown together on a whim. Something must have justified the care and attention put into it.

The oscillator frequencies are all in the audio range which suggests nothing to do with tape recorder bias.

[PJL]

Audio amplifier for a multi-projector presentation system? They would be used with a cassette player with one channel used for audible tones that operated the slide change. Probably not right as I don't see the need for batteries if you already have slide projectors plugged in to mains.

[Lucien Nunes]

One way or another, this device seems to be closely connected with recording and replaying of what we can only assume to be audio tape. The strongest link I can think of between photography and audio recording, that involves some kind of specialised equipment, is the automated slide presentation with commentary that was popular before video recording. There were commercial products for synchronising slides with tape, e.g. using either one channel or a spare head of a stereo deck, or incorporating a head over which the tape was threaded as a diversion from its usual path through a mono deck. I can't recall if any used out-of-band tones on the audio track and a mod to the record / replay amps to filter them. An oscillator and a means of keying it was provided for recording, and a tone detector and relay for replay. One could imagine some kind of companion device to a tape deck that provided the controls and interconnections, plus a decent speaker to play the audio through, but the battery power, feedback control and the lack of a relay output and trigger button more or less blow that idea away.

The balance controls are interesting. I don't see signs of stereophony so they are either balance between two signals, the identity of which must have been so obvious to the constructor that it needed no mention, or balance as in a bridge, some kind of null control.

It's very interesting, what ever it is.

*Post crossed with above - and another anomaly for this application would be the dual headphone sockets. If it was also supposed to assist with recording the commentary, one might be useful, but two?*

[Stuart R]

I was thinking it could be some kind of training device for Morse code, with Set 1 and 2 just having 2 pole connectors - for a key maybe? But I'm not a Morse user, so not sure how it would work in practice.

Like Lucien, I thought about Slide-Tape Presentation; can see some evidence of 1000 KHz tones used via an Internet search*, but dug out my 'Focal Guide to Slide Tape' book which has no mention of tones or frequencies and just suggest 'impulses' are used.

It does suggest a keen amateur could make up their own multi-vibrator to insert a cue tone on a spare audio track to be feed to a projectionist via an earphone. Maybe this was a step further where three distinct tones could trigger different events either by ear or a decoder.

Maybe portable so it could just be used to prepare and preview a slide show at a customer's office? But battery operation seems a little too safety conscious.

If the OP still has the lids, any photos of labs or contents could help here.

SR

*Trawling the Internet for Slide-Tape Presentation and audio tones seems difficult these days. Swamped by downloadable and videos (?) of audio tones as well as plenty of hints and tips for Powerpoint presentations.

[Junk Box Nick]

I had some experience with slide/tape presentation gear in the 1970s. It was commercial gear using a single cassette deck. The audio was recorded on one track and the pulses on the other track - what would have been 'the other side'. It worked with a pair of Kodak carousel machines but there were more elaborate systems where several projectors could be used. Depending on the pulse applied a cut or a fade could be made between slides. Pulsing the tape was rather interesting as the entire job had to be done in one take. However, what I can't see on this piece of kit is the push button to pulse the tape.

This looks a very tidy job for home brew. It would be interesting to see if the lettering on the panels is applied Letraset or similar. It's very neat and has weathered well. The dials on the front look like the sort that came free with Practical Wireless or Radio Constructor and the knobs look standard hobby shop items.

[paulsherwin]

I think the slide/tape explanation is most likely, or even some sort of amateur sound movie arrangement with the sound coming from a tape recorder rather than an optical or magnetic film track. It does look very well put together for a homebrew system though, so it might be a short run commercial product, perhaps some sort of lab equipment.

[dseymo1]

But if it's for slide sync, I agree - where are the 'record slide change' button and the projector connector, and what's the feedback control for?
It's certainly intriguing!

[STUARTEDWARDS]

The catches turn it into like a briefcase.

[ITAM805]

Looks like a mixer for a couple of tape recorders? The oscillator frequency are odd but could be for line up or setting the bias over-drop, more usually 100Hz, 1kHz, 10kHz. "Feedback" could be what we now call 'foldback' ? Home made I would guess but nicely done

[PJL]

I custom built a complex tone generator for very large multi-slide projector systems back in the 80's. My wife was in the business of producing these presentations for major conferences and product launches. The slides would be produced by complex photographic equipment which allowed zooming by fading from image to image.

'Feedback' may simply mix the tone with the audio so you can hear it from the speaker. As I say, I am not totally convinced!