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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 16th May 2021, 2:30 pm   #1
stevie23
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Default Ferrograph 4 with Amp problems.

Hi! I have started looking at the 2 Ferrographs I was given. One is motorboatong and the other also has amp problems as well as a dead pilot lamp. The mechanism seems A-OK but the amplifier sounds a little quiet and distorted. The bass control makes noise and a thumping sound if turned on the slower speed and weirdly, the sound seems to come back to being cleeaner if you hold down the stop button but keep it from actually stopping. I have used, but never repaired these machines. The [very ****** shaky] video shows what is happening. I've included a drive link: https://drive.google.com/file/d/1CFq...ew?usp=sharing I'd love some advice from you other Ferrograph affictionados. How should I go about this ?
Thanks,
Steve.
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Old 16th May 2021, 2:46 pm   #2
barrymagrec
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Default Re: Ferrograph 4 with Amp problems.

Looks like a Ferrograph 2AN to me.

Check the HT voltage, it`s quite likely to be dodgy electrolytics given the age of the machine (mid fifties I would guess).
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Old 18th May 2021, 2:12 pm   #3
Uncle Bulgaria
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Default Re: Ferrograph 4 with Amp problems.

As barrymagrec says, check the HT voltage on the power supply, then the other DC conditions and go from there. My 4A was motorboating a few months ago, and I replaced the reservoir/filter dual capacitor with a modern equivalent 16/16F can from Cricklewood Electronics having worked out that the original was the culprit.

If you have an oscilloscope you can check the power supply output for ripple.

Do you have "The Manual of the Ferrograph" with the component values, adjustment instructions and circuit diagram?

Working on them, if anything like the Series 4, is a bit awkward as the heavy top plate wants to fall down all the time. The PSU in the series 4 is screwed to the bottom of the case, so has to be entirely removed with the back plate to be worked on. I had to lash up some connections to the propped-up top plate with the power supply and amplifier out of the box as I was working on mine.
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Old 25th May 2021, 2:47 pm   #4
stevie23
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Default Re: Ferrograph 4 with Amp problems.

Quote:
Originally Posted by Uncle Bulgaria View Post
My 4A was motorboating a few months ago, and I replaced the reservoir/filter dual capacitor with a modern equivalent 16/16F can from Cricklewood Electronics having worked out that the original was the culprit.

If you have an oscilloscope you can check the power supply output for ripple.

Do you have "The Manual of the Ferrograph" with the component values, adjustment instructions and circuit diagram?

Working on them, if anything like the Series 4, is a bit awkward as the heavy top plate wants to fall down all the time. The PSU in the series 4 is screwed to the bottom of the case, so has to be entirely removed with the back plate to be worked on. I had to lash up some connections to the propped-up top plate with the power supply and amplifier out of the box as I was working on mine.
Thanks Unkle B. I have now found out I have a 2A and what I think is a 3A. The 3A has a green pilot lamp. This is the one with motorboating issues... The resevoir capacitor, is this the larger of the metal cans on the power board?
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Old 25th May 2021, 3:04 pm   #5
Uncle Bulgaria
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Default Re: Ferrograph 4 with Amp problems.

It sounds like you haven't got the manual - do get hold of one as they have comprehensive lists of components, as well as photographs of the chassis with labelled parts. There's a Series 2 manual on eBay at the moment starting at 2.85 with no bids.

I've attached some pictures from my Series 4 manual. I imagine they are similar, but don't take it as gospel as I have no experience with the series 2.

You'll see in the circuit diagram the filter and reservoir capacitors C24 and C26, straight off the rectifier valve and across choke L4. On the parts list, C24 is 16F and C26 is 8F, both at 500V. I could probe the output of L4 with the machine on as it's accessible on top of the PSU chassis when the lid's up. This showed a ripple, demonstrating those two capacitors were to blame.

Now, the labelled chassis photograph shows us that C24 and C26 are both contained in a single can. It isn't possible to get those values in dual cans any more, so I used a dual 16+16F 500V can (available from Cricklewood Electronics, HotRoxUK, Watford Valves and other companies that cater to valve amplifier makers). You can see the new black can in situ in the final photograph, next to the remaining silver Drilitic dual can which still functions all right.

Edit: Just be aware if you're opening and shutting it, that the joints between the bundled cables from the fixed chassis to the tag strip on the top plate can work-harden and break. I chased a few gremlins before I realised that several of these wires had snapped at the joint, and needed to be re-attached to the tag strip.
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Old 28th May 2021, 7:01 am   #6
DMcMahon
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Default Re: Ferrograph 4 with Amp problems.

The Series 2 and Series 3 power supply circuitry is basically the same as the Series 4 schematic above, with C24 (16uF/500V) and C26 (8uF/500V) again being the filter/smoothing and reservoir capacitors respectively.

The other dual can capacitor (C29 16uF/500V & C30 16uF/500V) looks to be a bit taller, so your reservoir capacitor (C26) will be in the slightly shorter can (as shown in the Series 4 Power Unit image above).

David
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Old 28th May 2021, 10:51 am   #7
DMcMahon
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Default Re: Ferrograph 4 with Amp problems.

Interesting clip on motorboating.

https://www.youtube.com/watch?v=ThtE2hAuiIk
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