Looking for informations on Marconi TF2331 Distortion Factor Analyser

[bembel]

Hi all,
I found a Marconi TF2331 Distortion Factor Analyser that need to be fixed, I googled and found nothing (free).
Any documentation is welcome (Schematic, Op Manual, block diagram, detailled spec or calibrating procedure.)

Thanks

[bembel]

Hey englishmen, where are you ?
Nobody ever used this one ?

[EC8010]

I scrapped one about fifteen years ago, but didn't keep the manual...

[bembel]

did you use it ?
Thanks

[EC8010]

No. As far as I remember (this was a while ago), you had to manually tune to null the fundamental, then you could measure how much distortion was left. I think it was good down to 0.01% or -80dB. Shortly after acquiring the Marconi I bought a much better test set for £40 + VAT that automatically nulled the fundamental and did a host of other things as well, hence the scrapping of the Marconi.

[bembel]

Thanks EC8010, Could you confirm that the only internal oscillator is for calibration purpose. ---> So no an ext. gen. must be used ?
And that the output bananas are the distortion results (fundamental substracted) intented for oscilloscope display ? 1M outputZ ?

[EC8010]

I can't remember about the internal oscillator, but if you try measuring its distortion, you'll soon find out if it's any use. Linear Technology (IC manufacturer) had some application notes with circuits for low distortion oscillators. For valves, you probably only really want 1kHz (general THD test), 30Hz (finds output transformer problems), and 10kHz (finds driver slewing problems etc). The monitor output will be fine going into the standard 1M input resistance of an oscilloscope and I thoroughly recommend that you use it - the shape of the distortion waveform tells you an awful lot about what caused the distortion.

[bembel]

Thanks a lot EC8010, I will recieve this Marconi unit soon, and your answers permit me to debug some contradictions the sender told me.
Thanks again.

[EC8010]

You're welcome, but please remember that I'm going from memory of something fifteen years ago - I could easily be wrong.

[bembel]

Your input is very appreciated anyway EC8010 ! (even an unsure one from memory is still better than no-one at all).

To close the subject I forgot to say that I wonder what use have this "supply" pot ? here's a picture attached (this is the right-upper most pot).
Any idea?
I wonder also if in the "Cal mode" you need to loop I/O or if it is internally done (any memory of this ?).

thanks again.

PS: still looking for Schem/doc/manual.