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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 24th Nov 2018, 11:43 am   #21
jascha
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Default Re: Ferrograph S3 and S4 help with some issues please

This morning I had a go at adjusting the bias trap as instructed however I see hardly any difference when I turn the adjuster. I attached the scope to both sides of the trap just in case and also connected it directly to the anode of V4. Is it something I am doing wrong here? I did a similar adjustment on a G36 and that had more dramatic results while turning the traps. I measured onbthe scope the voltage at the erase head and it seems to measure around 70v peak to peak on the scope.
Thanks again
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Old 24th Nov 2018, 1:33 pm   #22
Boulevardier
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Default Re: Ferrograph S3 and S4 help with some issues please

Looks like everyone else is busy this morning, so I’ll give you some thoughts – must stress I’m not an expert, and I don’t have access to the circuit diagrams, so I’ll have to feel my way.

What type are your bias rejectors? I’m guessing an inductor (probably ferrite pot-core with adjustable core) with a capacitor (which may be adjustable) in parallel? So -
Are you getting the same ‘scope voltage reading on each side of the bias trap at all adjustment settings? If so then either ;
1. The trap is wildly out of adjustment
2. The inductor is either open circuit (so capacitor is passing the ac voltage) or short circuit, or -
3. The capacitor is short circuit (and passing the voltage through) or open circuit (with the inductor passing the voltage through.

Of these, I think the capacitor is the most likely culprit. So, I would disconnect one end of it and test it.

I’m only familiar with Bogen heads, and they will probably be different, but for Bogens the 70 V on the erase head is normal. The Bogen record head needs about 24 V bias at around 10 mA. That info may or may not be useful!

Sorry if I’m telling an expert the “bleedin’ obvious”, but I don’t know how knowledgable you are about these circuits – and my own knowledge is limited to dabbling with these things decades ago!

Mike

Last edited by Boulevardier; 24th Nov 2018 at 1:57 pm.
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Old 24th Nov 2018, 3:07 pm   #23
jascha
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Default Re: Ferrograph S3 and S4 help with some issues please

Hi Mike, your information is wonderful and am grateful for your help. I found that the trap was open circuit and the coil had no continuity! I luckily repaired it by using a small strand of wire and I think I’m on the path to success. I only found out when comparing readings of the coil resistance with my Series 4 which measured just under 100 ohms! On the S3 with the capacitor still in place it measured over 200k!
I’m no expert either but have been doing repairs for years and learn as I go along. One can never stop learning and I have a passion for tape recorders so why not?
I will now assemble it all together and try the bias trap adjustment again

Many thanks
Carmine
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Old 24th Nov 2018, 3:11 pm   #24
Boulevardier
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Default Re: Ferrograph S3 and S4 help with some issues please

Great! Sounds like you're nearly there - with the bias issue at least. Do keep us updated on progress.

Mike
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Old 24th Nov 2018, 3:23 pm   #25
jascha
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Default Re: Ferrograph S3 and S4 help with some issues please

Thanks Mike. Here is the trap repair on one of the ends of the coils. It’s touch and go with these things but it seems saved .
Now comes the adjustment and see what happens
Thanks
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Old 24th Nov 2018, 3:37 pm   #26
jascha
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Default Re: Ferrograph S3 and S4 help with some issues please

Thanks Mike. Here is the trap repair on one of the ends of the coils. It’s touch and go with these things but it seems saved .
Now comes the adjustment and see what happens
Thanks
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Old 24th Nov 2018, 5:22 pm   #27
BillDWVA
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Default Re: Ferrograph S3 and S4 help with some issues please

If you are after a spare inductor a chap on eBay has this assortment for sale at the moment; some look like they’ve been taken from Ferrograph sets as he’s sold heads and idlers etc.
Search for ‘Vintage choke coils filter assortment’.

Bill
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Old 24th Nov 2018, 5:34 pm   #28
jascha
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Default Re: Ferrograph S3 and S4 help with some issues please

Thanks for the info Bill. I have managed to get the coil repaired so I shall leave them for someone who might need them more than I do. The machine fixed the issue of very bright recordings too...it was the bias trap going open circuit. I am now optimizing the bias which I have done by ear but maybe have a go at doing it properly with a multimeter.
Thanks again everyone for your time and knowledge share.
C
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