Any INFO re Army Oscillator Beat Frequency No 8

[dave walsh]

Designated as FHL ZD00187

I've just aquired one of these in a rather poor state inc two smashed valves. Main range seems to be 10-600 Kc/s hence IF alignment? Google turns up a faint reference in association with the 31 set MK2 but not much else apparently [my search skills are poor but no circuit/handbook so far]. Anybody know this one? Black [or was] with white panel, central circular f scale and meter above [output volts]. Seems familiar somehow-might have seen it in Radio Bygones or a similar mag Any comments welcome.
Dave W

[dave walsh]

The more I look at the worse it seems, in some respects anyway-especially the electrolytics but it's interesting!
Dave W

[AC/HL]

It it's dedicated test equipment, it might be in the 31 manual itself.

[dave walsh]

Yes especially as the one ref seems connected to that manual but I can't seem to get the whole thing to open on the page or access it through the VMARS site but that could be my incompetence Thanks for coming back on this anyway Bill..
Dave W

[G3VKM_Roger]

Dave,

I downloaded both the 31 Set EMERs OK but they are of little help as the BFO is just mentioned as being a preferred piece of test gear. There is a small section that deals with checking the audio characteristics of the radio using the BFO but that doesn't contain any info on your gear.

Regards,

Roger

[dave walsh]

Thanks for that Roger-very good of you to check and it has established that the info is not there after all. Hopefully something will turn up. I don't think it's that critical as the unit shouldn't be that complex, it's just that there is so much input from enthusiasts and official sites like VMARS these days I kind of assumed that something would be out there. The last time I was able to help someone with a Type 3 PSU there was no shortage of info Perhaps I've got a rarity [unlikely]. You can tell it's been in the Army with the "OSCILLATOR BEAT FREQUENCY" title reverse
Dave

[trh01uk]

Dave,

well its not a lot of help, but I have turned up the first of a series of EMERs on the item. See enclosed.

It will give you a little bit of info about what it does, and the valve line-up. You would need EMER Tels Z702 to get a schematic, layout and parts list. EMER Tels Z704 to get repair information. I don't have either of them, I'm afraid.

These beat frequency oscillators were common before a reliable way of directly generating an audio sine wave with constant amplitude had been devised. Much easier back then to mix two RF oscillators and extract the difference frequency.

Richard

[dave walsh]

On the contrary Richard, that's extremely helpful info you've dug out-plus it shows anyone interested what the BFO Unit looks like. Your explanation of it's use is a further bonus as well! I might try a direct request to VMARS. Their site is being re-vamped and they point out that not everything they have is on line yet.
Thank You,
Dave

Clearly I'd got the wrong end of the stick re IF alignment mistaking the Output Impedance for the range !!! but a useful audio Sig Generator [when working at least].

[ronbryan]

A BFO will also give wide frequency coverage without band-switching. This can be useful when sweep testing audio equipment for instance. I recall that the Danish firm Bruel and Kjoer made a BFO for that purpose.

Ron

[m0cemdave]

Originally Posted by ronbryan

A BFO will also give wide frequency coverage without band-switching. This can be useful when sweep testing audio equipment for instance.

Not only that, but it's quite easy to provide a sweep from 20 - 20k Hz with a logarithmic scale.
B&K made various generators of this type, which could be swept either by hand or from a link to a chart recorder.

[dave walsh]

Interesting additional comments chaps-thanks-the [Chart Recorder] plot thickens
Dave