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Old 20th Mar 2019, 2:49 pm   #66
Uncle Bulgaria
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Join Date: May 2016
Location: Cornwall, UK.
Posts: 2,315
Default Re: Ferrograph 4A: Restoration advice needed

I've certainly seen some of the marvellous Pathe-and-similar films that cover everything from the manufacture of Blackpool Rock to how to remember to shoot 3 rads in front of Messerschmitts! In this case, I wouldn't want to be taken for such a greenhorn that I was worried about a few volts here and there, but it was strange to me that the HT could be well within tolerance, yet some of the Va values could be 50% out and still have normal function.

I then thought that the DMM is 'auto-ranging': does this load the circuit differently, as with using an AVO with the "ohms/volt*full scale" because there will be a different full-scale requirement when the digital meter trips to the next higher range? Or doesn't it work like that because the display is not a current-driven pointer?

Thank you Bill - I see you've popped over to Tapeheads as well! I'm really pleased with how this is turning out, so thought plastering some more pictures around the place would help anyone else in a similar situation. I know when I first started pulling this apart I couldn't find any reasonable images of a 4A's innards from anyone on a similar journey so there was a lot of trial and error.

I need to do what you've done and show the changes on the circuit diagram - the trouble is I haven't got it printed large enough to add to yet, so I've just got notes, highlighted components and bundles of paper! I prefer how the Ferrograph manual labels the components with their numbers for the accompanying list, rather than how Vortexion have done it.

Advanced question: The replay head is mounted on four screws over a bar to allow it to tilt sideways. (The space for the dummy head with its spring-loaded octal socket seems the much better design for adjustment). What is the process to get the best response and get the head perpendicular to the tape?

After a forum search I get the principle, and I have TIMTAPE's handylap manual which covers the theory of azimuth/zenith etc. I have no other reel to reel in a usable or calibrated condition to produce a tape but I do have an oscilloscope I could use under instruction if that helps.
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