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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 20th Nov 2018, 7:17 pm   #1
jascha
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Default Ferrograph S3 and S4 help with some issues please

Dear Forum team,

May I please ask for some assistance in trying to bring my 2 Ferrographs up to spec? Before I carry on I must mention that both machines have been fully recapped and valves have been checked for their conductivity.
They both run well however there are areas where they can improve and need some help please.

Ferrograph Series 3A/N issue:
1.Noisy erasure and thinny sound quality during recording. The machine fully erases a tape however there's a residue of background noise, above the expected hiss and this results in quite poor S/N ratio during recording. I have only tried to tweak the bias pot on the oscillator board but improvements were only slight. Turning the pot fully clockwise improved matters slightly but recordings still sound on the thin and bright side. I have not touched any of the eq pots or the adjustable coil.
2. Signal meter sticking: The meter tends to stick around the mark 2-4 area of the meter. I have taken it apart due to the fact that the glass was pushed in so i put that right and checked for the meter movement that it is free and seemed all very smooth, however in action it keep sticking which is quite annoying when trying to make a recording. Any ideas please? Thanks

Ferrograph Series 4 issue:
1.Poor winding power especially starting the machine close to the end of a reel. Comparing with the S3 I have the results are inferior. I have oiled the motors and they seem to run freely however they don't seem to have much pulling power perhaps. Could it be voltage related? I have not done any measurements yet
2. Erasure of prerecorded material is not fully erased and some traces of previous recordings remain. I have cleaned the heads thoroughly however the problem remains. Are there any adjustments in connection to the erase circuit? I do have a scope that I can use to test however I need some guidance as to what I am looking for to find this fault if that helps.

Thanks so much in advance.
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Old 21st Nov 2018, 1:20 am   #2
ben
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Default Re: Ferrograph S3 and S4 help with some issues please

Quote:
Originally Posted by jascha View Post
Ferrograph Series 4 issue:
1.Poor winding power especially starting the machine close to the end of a reel. Comparing with the S3 I have the results are inferior. I have oiled the motors and they seem to run freely however they don't seem to have much pulling power perhaps. Could it be voltage related?
Not worked on the models you have, but I have found that if headbridge entry and exit fixed tape guides are very worn, having flat spots for instance, they place extra drag on the tape that can cause this. In some cases you can loosen and rotate them to expose a new surface.
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Old 21st Nov 2018, 9:42 am   #3
BillDWVA
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Default Re: Ferrograph S3 and S4 help with some issues please

I’ll do my best to make some suggestions:
1) Poor sound quality. First thing is to check that this is caused during recording by playing a tape pre-recorded on a known good machine. However as much of the circuit is common to ‘record’ mode as well as ‘playback’ the first test would be to trace the audio signal through the various stages to find where the degradation occurs. Another test would be to inject an audio signal from another source and monitor it to check its quality. Distortion or low ampilification may be caused by bias voltage on one or more of the amplifier valves being out of range caused by an out of spec resistor. I only have a diagram for a Series 2 in front of me but the components to check would be the resistors from cathodes to chassis and control grids from the anode circuit of the previous stage. You mentioned that the sets have been ‘recapped’; There is a possibility that the bias trap is out of tune now and the audio output stage is being saturated by bias current when it is in ‘record’. This can be checked by hooking up your ‘scope to amplifier side of the trap (a capacitor and variable inductance in parallel - L3 and C22 on this circuit). You will see the oscillator waveform when the set is switched to ‘record’ and the inductor has to be adjusted for a minimum bleed-through. I don’t think that the equalisation circuit would cause such noise unless something was badly out of spec. Was the machine OK before it was ‘recapped’? Always best to replace one component at a time, testing as one goes.
2) Sticking meter on these can only be some mechanical locking. If it is a Sifam meter then it is high-quality instrument, from my experience. Check again for a bent needle or end stops - these get squashed in by a detached glass.
3) Incomplete erase; Low oscillator output? Poor plug/socket connection or dirty contacts? misaligned or very dirty head?
4) Weak winding; Have you checked that the brake is fully releasing? Turns-counter drive gear binding?
Hope this helps?
Bill
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Old 21st Nov 2018, 12:07 pm   #4
jascha
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Default Re: Ferrograph S3 and S4 help with some issues please

Hi guys,
Thanks so much for your help. I shall go through the suggestions carefully however I can give an update as to what I already discovered. Firstly on the S4 (with the poor erase) I had a jammed bias pot and therefore had to take out the PS and free up the pot. Whilst I had it out I decided to swap the power supply units to see what happens and bingo... the S4 erased a tape fully . So my suspicions that it’s a faulty erase head have been eliminated. There are two capacitors on the unit that are 4000pf and 10000pf which I suspect could be leaky? I did not change these caps as they are not the type that usually get replaced. My focus is now on these caps as I had changed the other leaky caps.
I shall report back as I go along.

Thanks again guys
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Old 21st Nov 2018, 3:47 pm   #5
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Default Re: Ferrograph S3 and S4 help with some issues please

Ps: I have so far checked the caps on the power supply/oscillator unit and all seem to be fine. The bias adjustment pot was totally jammed at half way and have freed it up but the only way I can get a full deep erase is to turn the bias adjustment fully clockwise which of course affects frequency response! Arghh! I swapped both the EL84 and EZ80 just as a curiosity (although they had passed the test already) but the result remained the same. It’s a low output from the oscillator perhaps? How can it be measured please and what should I expect to measure voltage wise?
Thanks again
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Old 21st Nov 2018, 5:01 pm   #6
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Default Re: Ferrograph S3 and S4 help with some issues please

Apologies for my previous post... of course the erase head which I thought I had cleaned well yesterday had another layer of muck that I had not cleaned well enough and that did the trick in regards to the erase issue. So annoying spending time fault finding when it was a simple thing such as cleaning the erase head PROPERLY!
Phew!
I shall look into the other issues and post back. Thanks again
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Old 21st Nov 2018, 5:32 pm   #7
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Default Re: Ferrograph S3 and S4 help with some issues please

Have you replaced any capacitors in the oscillator circuit? If so, are you sure you've used the correct types? Some of them will almost certainly need to be silvered-mica (or perhaps there's a modern equivalent of s.m).

I can remember a couple of times when I got this wrong. In the first, when we had a recorder on which the oscillator wasn't working at all, I quickly traced the fault to a shorted s.m. cap, and absent-mindedly replaced it with another type, since we didn't have an s.m. small enough to easily fit. No oscillation (still), so I started looking for another fault - until I twigged to the problem. Managed to squeeze in a larger s.m. of right value and all was well. The other case was with a Mullard Type C valve tape preamplifier (truly excellent circuit). I carelessly used a ceramic instead of the specified s.m, and sometimes the oscillator would work, and other times it just wouldn't start - until I replaced it with s.m..

Even if yours still has the original s.m.s and they're measuring OK, it might be worth replacing them - they might be breaking down on load - I'm not familiar with the Ferrograph circuits, but those circuits have to handle quite a bit of power to set up the field in the erase head.

Mike
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Old 21st Nov 2018, 5:40 pm   #8
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Default Re: Ferrograph S3 and S4 help with some issues please

Hi Mike,
Thanks for your reply. The silver mica caps are still there (4000pf & 10000pf). I took them out and checked them for both capacitance and leakage and they’re fine. The other 2 caps on the oscillator board (0.1uf) were replaced by mustard type caps which I know perform well, and they replaced the original leaky caps. All the caps were leaky and a good idea to replace them I felt. I also checked for out of spec resistors and replaced as necessary. As Bill mentioned it might be a good idea to check the bias traps as due to a recap job the alignment might be out. I had to do the same procedure on my Revox G36!
I am unsure whether to tweak the equalisation pots as in the Ferrograph manual they strongly suggest not to touch these as they come out carefully set from the factory. However a bias adjustment is necessary I feel to ensure that the machines record well.
Thanks for the experience shared re caps!
Carmine
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Old 21st Nov 2018, 5:56 pm   #9
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Default Re: Ferrograph S3 and S4 help with some issues please

I wouldn't touch the equalisation at this stage - definitely sounds like an HF oscillator issue, so focus on that. Have you put a scope on it, and do you know what the ac voltages should be? (or compare scope readings between the working and non-working one).

Unless, that is, the Ferrograph circuit has some sort of clever interaction between the record equalisation and HF oscillator (I've never seen that). I don't claim to be any sort of expert on these circuits.

Mike
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Old 21st Nov 2018, 6:54 pm   #10
jascha
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Default Re: Ferrograph S3 and S4 help with some issues please

I won't touch the Eq pots and will try to do some more work on the Ferrographs during the weekend.
Just to update: Both machines playback very well and in regards to the Series 4 all it might benefit from is optimizing the bias for recording (perhaps set it to BASF LGS35 or an equivalent tape of the era. Also making sure that the break clear the spool carriers (which I think they fully do) to address the issue of the slow wind towards the end of the tape. I have cleaned the tape path but it did not make much of a difference.

The series 3 needs calibration for recording purposes as the recordings are coming out very bright so considering that the electronics needed a number of components changed, the biasing etc might be the issue.

Thanks again to all
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Old 21st Nov 2018, 8:41 pm   #11
BillDWVA
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Default Re: Ferrograph S3 and S4 help with some issues please

Hi, was reading your question again about the winding. If you are experiencing sluggish rewinding then it may be a case of ‘They all do that, Sir’. My Series 4 struggles to start rewinding when only just into a spool, especially a nearly full 8 1/4” and worse when cold. I’ve got used to having to give it some help or unthreading from the tape path and just letting it wind via the left guide. Once the take up motor is up to the usual roasting hot state after playing an entire reel it flies back. Old, sticky or draggy tape will sometimes lock solid through the guides.
Keep the reels turning....
Cheers,
Bill
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Old 21st Nov 2018, 9:28 pm   #12
jascha
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Default Re: Ferrograph S3 and S4 help with some issues please

Hi Bill,
I think you’re right there! They all do it . My S3 however seems to be a bit more upbeat in this respect and hence my enquiry. Could it be that the S3 has less load on the motor due to the counter being belt driven rather than the S4 type of counter? It’s just a guess.
The reels are always turning and shall carry on doing so
C
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Old 22nd Nov 2018, 1:50 pm   #13
Ted Kendall
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Default Re: Ferrograph S3 and S4 help with some issues please

I think Ferrographs of this vintage have the correct bias voltage reading for the fitted head stamped on the underside of the deckplate. This of course may vary with the tape type, but is at least a starting point.
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Old 22nd Nov 2018, 6:03 pm   #14
jascha
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Default Re: Ferrograph S3 and S4 help with some issues please

Isn’t bias dependant on the type of tape used?
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Old 22nd Nov 2018, 6:14 pm   #15
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Default Re: Ferrograph S3 and S4 help with some issues please

Yes it is - that's why manufacturers always specified a particular type of tape as optimal for their fixed-bias machines.

I think there are some quality freaks who would even insist that it's dependent on the type of programme material - so, for example, set the bias to either optimise frequency response, or maximise dynamic range, or minimise distortion.

Last edited by Boulevardier; 22nd Nov 2018 at 6:42 pm.
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Old 22nd Nov 2018, 6:59 pm   #16
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Default Re: Ferrograph S3 and S4 help with some issues please

The bias setting marked on the machine would would have been for their badged "Ferrotape" which was probably EMI H77 or near offer.
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Old 22nd Nov 2018, 9:29 pm   #17
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Default Re: Ferrograph S3 and S4 help with some issues please

At the time, most reputable tapes were very similar in bias requirement - divergences started with the introduction of low noise tapes on the domestic market.

With the general introduction of stereo equipment, setting bias at 10kHz instead of 1kHz became more common, as the overdrop was sharper and made channel matching easier. The sweet spot is pretty universally recognised - 1dB overdrop at 1k or 4-5 at 10k is the best compromise between output, distortion, noise, self-erasure and dropout.
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Old 23rd Nov 2018, 12:25 am   #18
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Default Re: Ferrograph S3 and S4 help with some issues please

Re excessive background noise, these old Ferrographs had a tendency to magnetise their own head due to switching impulses when changing function. I had this problem with my old Series 5. It's mentioned in the manual. You're supposed to turn the rotary function switch in a certain way to minimise this.

If it hasnt already been mentioned, have you properly demagnetised the heads and tape path, with a decent demagnetiser tool? I'd say especially with an old Ferro, a good demagnetiser tool is essential.
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Old 23rd Nov 2018, 2:38 pm   #19
jascha
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Default Re: Ferrograph S3 and S4 help with some issues please

Thank you all for your kind responses. Much appreciated.
I do have a decent Teac demagnetiser but only demagnetised the playback/record head, not the erase head. I did some swapping over of the oscillator unit between recorders and the problem did not shift. I did improve matters regarding erase on the S4 which was down to a dirty head however I still have to address the recording brightness on the S3. I guess I will need to check the bias trap setting since the machine was recapped and also some resistors replaced. I have 2 Ferrotapes (one of them still sealed) but I think I will adjust for best performance using something like an LGS 52 or LGS 35.
I never biased a Ferrograph properly apart from tweaking the bias pot by ear.
How about the Eq pots? Are they really untouchable?

Cheers guys again
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Old 23rd Nov 2018, 3:05 pm   #20
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Default Re: Ferrograph S3 and S4 help with some issues please

I agree, if you've changed components in the oscillator circuit, or even swapped the board from the other machine, then re-setting the bias trap should be a priority if you haven't done so. If significant bias voltage is finding its way through the trap and back into the record amp output stage, it can cause havoc with its operating conditions.

Mike
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