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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 29th Jan 2019, 10:06 am   #21
llama
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Default Re: Ferrograph 4A: Restoration advice needed

Interesting that there's solder on the pins of the R/P head. I thought all these heads plugged into 4 pins of an octal base.
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Old 29th Jan 2019, 10:51 am   #22
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Default Re: Ferrograph 4A: Restoration advice needed

I think Ferrograph normally only fitted the scket where the head was an option, as in the case of the stereo replay head on the 4Ax.
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Old 4th Feb 2019, 10:06 pm   #23
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Default Re: Ferrograph 4A: Restoration advice needed

The head has a Cyberman hat that screws on the top.

I can't see how to get the base off. It appears to be riveted, but there are wires soldered to the top of the rivets and to the screws holding the coil cores down. I'm loath to tamper with this as it looks pretty major.

The pins were soldered to rings formed in the wires. The 'dummy head' (something to do with adding stereo) plugs into a socket.

I've finished covering the case, so pictures will be forthcoming.

I've been investigating the PSU filter/reservoir capacitors as they are probably out of whack after all this time. the 16+8mfd reservoir/filter dual can will probably be replaced with a modern 16+16mfd, and the same with the oscillator dual can. I haven't got a high voltage capacitor tester and haven't powered it up.

I was interested in the circuit so was calculating what changes would happen to the filter response if I changed the LC capacitor value, and this led me to checking the anode limiting resistance on the EZ80. There aren't any limiting resistors, so I was interested to see what limiting resistance was being provided by the transformer. I think I've done the calculation wrong so would be grateful for someone to point out the error. The datasheet where I got the calculation from is attached.

Rt = Rs + n2 x Rp where Rs is 1/2 secondary resistance, n is 1/2 ratio of primary to secondary windings [1 : (n+n)] and Rp is total primary resistance. As I understand it from that diagram.

I have:

Rp = 7R

Rs = 420/2 = 210R

n = (420/7)/2 = 30

From this I get Rt to be 6510, which is rather different from the 2 x 175R to 2 x 300R the datasheet plots show.
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Old 4th Feb 2019, 11:26 pm   #24
ms660
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Default Re: Ferrograph 4A: Restoration advice needed

n will be far less than 30, n is the turns or voltage ratio not the resistance ratio.

Eg: Let's assume that the transformer is on the 245 volt tap with 245 volts going in, therefore Vp = 245, Total Vs anode to anode (according to the manual) = 480 VAC therefore divide that by 2 which = 240 therefore n = 245/240 = 1.02 therefore n = 1.02

Rt = Rs+n squared*Rp…..(+ R1) R1 is any additional surge limiter that may be fitted, that can be omitted because none is shown in the schematic.

Rs = 210 (420 as measured/2) Rp = 7 (as measured) and n = 1.02

So, Rt = 210 + 1.02*7 = 217.14 Ohms for each leg or 2 X 217.14 Ohms if you like.

So far as I can make out.

Lawrence.
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Old 5th Feb 2019, 3:53 am   #25
Uncle Bulgaria
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Default Re: Ferrograph 4A: Restoration advice needed

Thank you Lawrence, that's very helpful.

I thought there would be a relationship between the resistance ratio and the turns. I got wildly varying and worrying voltages on the secondary when putting low VAC across the primary, so reversed it. with 2 - 12VAC on the secondary, the average ratio was 1:13, when I could get a reading on the AVOmeter. (sub 1V).

If that is correct, then Rt is about 553R, with n = 6.5.

However, that's still far too high as Vaa' will be about 3kV at 240V! Surely the ratio is absolute, regardless of there being no load? It remained constant over the applied voltage range, which has confused me. I checked I am measuring the right secondaries, that go to the right pins of the EZ80 socket.

Where did you get the 480V from in the manual, and why am I not getting a reasonably measured value? I am overlooking it in the Ferrograph manual I have, if that is the one you are referring to.
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Old 5th Feb 2019, 11:46 am   #26
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Default Re: Ferrograph 4A: Restoration advice needed

The 480v anode to anode was an estimate based on the other voltages given in the manual.

I would double check the transformer primary and secondary connections you're using for establishing the voltage/turns ratio.

Lawrence.
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Old 5th Feb 2019, 4:45 pm   #27
Uncle Bulgaria
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Default Re: Ferrograph 4A: Restoration advice needed

You were right Lawrence - my error was checking the secondaries, when in fact I was using the wrong primary windings as one is on the other side of the transformer.

New values are 46R5 Rp, and a 1:2.5 ratio (30V at 12V), which gives an Rt of 282R6.

If 240VAC is across the primary, and 600V across the secondary, then according to the datasheet that's 2x300V which needs a minimum Rt of 215R. So it's in tolerance.

Correct?
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Old 5th Feb 2019, 5:18 pm   #28
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Default Re: Ferrograph 4A: Restoration advice needed

Download this and scroll down to book page 10 (section 13):

http://www.nj7p.info/Manuals/PDFs/Tu...art-4-1972.pdf

Lawrence.
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Old 7th Feb 2019, 1:20 am   #29
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Default Re: Ferrograph 4A: Restoration advice needed

Thanks again, Lawrence! Yet another PDF to add to my 'very useful' folder. I see the point of the calculation is to make sure the inrush current is limited, so it looks like all is in order now that I have the correct primary to meter. I'll take some more readings when I power it up, of course. It's good to feel one is gradually getting a handle on the hows and whys of a circuit.

Question to the floor - is there any idea of how the base comes off that head, or is it to be re-lapped with it in situ, off the edge of the lapping plate, perhaps?
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Old 7th Feb 2019, 12:01 pm   #30
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Default Re: Ferrograph 4A: Restoration advice needed

It was me who suggested the head needed relapping. I assumed it would be easy to remove the baseplate from the head as many years ago I think I did, but it was on a Series 5 Ferro which may be a different head design. I no longer have the Ferro to check the head.

Even so without a relap the machine may still perform reasonably well. Relapping just gives the best, most consistent tape to head contact and means less head cleaning. It also allows adjustment of the azimuth without the tape riding up on the ridges of old the wear groove. The old Ferro's also used the felt pressure pads which created uneven wear on the head, were more suited to the earlier tape types and with modern plastic tapes became unnecessary. At least on the record/play head, I removed the felt pressure arm entirely, but without the head relapped you may have to retain the pressure pad for good contact.
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Old 7th Feb 2019, 4:55 pm   #31
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Default Re: Ferrograph 4A: Restoration advice needed

Thanks TIMTAPE. I read on here or Tapeheads yesterday about incorrectly zeroed tape paths causing the 'characteristic keystone pattern' of wear on the Ferrograph head, which is certainly what this one has. The thing would certainly benefit from a relap according to those instructions you sent, and from what I can see the base wouldn't get in the way of the process. I'll ask at Ferrograph World in case there is a method of getting the base off without destruction!

That's interesting what you say about the pressure pads. I was up too late last night reading about the motors providing inconsistent back pressure to keep the contact with the head, hence the pads. I wondered about reducing wear by removing them, in this age of irreplaceable heads, but didn't know this could be done by using newer tape types. When it's up and running I'll have to experiment!

Meanwhile, two of the motors have been dismantled, cleaned up and lubricated...
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Old 7th Feb 2019, 5:17 pm   #32
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Default Re: Ferrograph 4A: Restoration advice needed

Quote:
Originally Posted by Uncle Bulgaria View Post
Thanks TIMTAPE. I read on here or Tapeheads yesterday about incorrectly zeroed tape paths causing the 'characteristic keystone pattern' of wear on the Ferrograph head, which is certainly what this one has. The thing would certainly benefit from a relap according to those instructions you sent, and from what I can see the base wouldn't get in the way of the process.
Yes I guess if the base cant be removed, the head would need to be relapped with the base hanging off the edge of the table, and thinking about it, maybe that's how I did it on my old Ferro 5 head.

Quote:
That's interesting what you say about the pressure pads. I was up too late last night reading about the motors providing inconsistent back pressure to keep the contact with the head, hence the pads. I wondered about reducing wear by removing them, in this age of irreplaceable heads, but didn't know this could be done by using newer tape types. When it's up and running I'll have to experiment!...
Yes the back tension changes with the diameter of the tape pack, and the larger the disparity between the hub diameter and the max diameter of tape, the greater the change. The special Ferrograph larger reel (8.25"?) must have been the worst possible in this respect.

I compromised with the pressure pads. I removed the record/play head pad but retained the erase head pad for some constant back tension on the record/play head. I also recorded with LP tape which tends to have better head contact than SP tape. This was about 40 years ago.
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Old 15th Feb 2019, 11:27 am   #33
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Default Re: Ferrograph 4A: Restoration advice needed

News from Ferrograph World:

The heads are not designed to be relapped, so Mr Martini-Yates is not convinced there would be any improvement. It looks like it's a new(er) head that's needed, which he can supply. I'll endeavour to straighten up the tape path when I get it back together so the new one doesn't have the same 'keystone' wear.

However, as I'm impecunious at present, and not back to the head-reinstallation stage, I'll leave that for now. I would like to try straightening up the old one as an exercise as well, so I'll see how that goes.

For now, I have been going through the PSU checking values after the transformer calculations. There are a number of 'Visconol-X' capacitors, some of which test open-circuit so I am replacing them with some film types I have already.

Questions:
  • I have seen reference on here to testing capacitors with a 'Megger' type machine for breakdown resistance. I might be able to stretch to one of these as the older ones are cheap. Is this worth it? At the moment all I can do is test for continuity and/or turn on the machine with the capacitor I want to test and see if the smoke comes out.
  • I like dual cans, but the right values are not available. My calculations suggest replacing the (for example) 8mFd + 16mFd PSU filter/reservoir capacitor (C24 & C26) with a 16+16mFd would not adversely affect the filtering. There are a couple more of these. Could I use 16+16mFd in all these locations? (C9/C13 & C11/C12)
  • There is a 0.1mFd, 350V 'MICAMOLD' capacitor between the AC contacts of SW3, the motor switch. Is this purely to prevent arcing? As it is on a mains AC line, though the capacitor is not between LN or L/N and Earth, should this be an X/Y type?
  • C3 is marked as 0.02mFd 360V, but in the unit it is bypassed by a resistor and a 3100pF(? - value half illegible) 'Suflex' (picture attached). What is the reason for this not being on the circuit diagram? Is it a pre-calculated snubber circuit for the speed control switch?
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Old 15th Feb 2019, 1:59 pm   #34
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Default Re: Ferrograph 4A: Restoration advice needed

Quote:
...C3 is marked as 0.02mFd 360V, but in the unit it is bypassed by a resistor and a 3100pF(? - value half illegible) 'Suflex' (picture attached). What is the reason for this not being on the circuit diagram? Is it a pre-calculated snubber circuit for the speed control switch?
From memory these are for calibrating the repro (playback) response for which components had to be individually selected in production, possibly because the tolerances on the record/play head couldn't be made tight enough to use standardised resistors and capacitors.

I think the Suflex caps are polyester and as I recall, unlike electrolytics were long lasting and reliable. I wouldn't be changing them without a good reason.
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Old 15th Feb 2019, 11:42 pm   #35
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Default Re: Ferrograph 4A: Restoration advice needed

The Suflex capacitors are probably polystyrene.

They have a good technical specification.
Apparently they are susceptible to damage if the heat from the soldering iron travels down the capacitor wire leads.
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Old 16th Feb 2019, 3:01 am   #36
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Default Re: Ferrograph 4A: Restoration advice needed

Ah yes polystyrene. Thanks for the correction Silicon.
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Old 17th Feb 2019, 5:27 pm   #37
Uncle Bulgaria
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Default Re: Ferrograph 4A: Restoration advice needed

Thanks both. It does look just like a bigger version of some modern polystyrene capacitors I have!

I fear the Dubilier Metal Mini-Cap it is paralleled with will not be as reliable. I have just finished replacing all the 'Visconol-X' types I can find. At least one measured as a short so I've not taken chances, as I have no other way of testing capacitors. This 'Metal Mini-Cap' is the same colour and design, but doesn't say 'Visconol-X'. Does that mean it is not the same construction, and perhaps a more reliable type?

What are your thoughts on my other bullet points?
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Old 17th Feb 2019, 5:50 pm   #38
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Default Re: Ferrograph 4A: Restoration advice needed

Quote:
Originally Posted by Uncle Bulgaria View Post
Questions:
  • I have seen reference on here to testing capacitors with a 'Megger' type machine for breakdown resistance. I might be able to stretch to one of these as the older ones are cheap. Is this worth it? At the moment all I can do is test for continuity and/or turn on the machine with the capacitor I want to test and see if the smoke comes out.
  • I like dual cans, but the right values are not available. My calculations suggest replacing the (for example) 8mFd + 16mFd PSU filter/reservoir capacitor (C24 & C26) with a 16+16mFd would not adversely affect the filtering. There are a couple more of these. Could I use 16+16mFd in all these locations? (C9/C13 & C11/C12)
  • There is a 0.1mFd, 350V 'MICAMOLD' capacitor between the AC contacts of SW3, the motor switch. Is this purely to prevent arcing? As it is on a mains AC line, though the capacitor is not between LN or L/N and Earth, should this be an X/Y type?
  • C3 is marked as 0.02mFd 360V, but in the unit it is bypassed by a resistor and a 3100pF(? - value half illegible) 'Suflex' (picture attached). What is the reason for this not being on the circuit diagram? Is it a pre-calculated snubber circuit for the speed control switch?
1) A megger is down to personal preference, myself I would not use one for testing run of the mill capacitors but might use one if it was a large can paper type and I wanted to know of any electrical leakage problem.

2) 16uF for the reservoir should be ok.

3) "MICAMOLD" capacitors are notorious.

4) Suflex types have been known to go open circuit or partly open circuit (very high ESR) and sometimes short circuit if there's a high voltage across them in my experience.

Lawrence.

Last edited by ms660; 17th Feb 2019 at 5:52 pm. Reason: clarification
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Old 18th Feb 2019, 4:41 pm   #39
Uncle Bulgaria
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Default Re: Ferrograph 4A: Restoration advice needed

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Originally Posted by TIMTAPE View Post
From memory these are for calibrating the repro (playback) response for which components had to be individually selected in production, possibly because the tolerances on the record/play head couldn't be made tight enough to use standardised resistors and capacitors.
I think I see now - by dint of being across the switch and the 4-pin socket, C3 is actually coming into play for the 3 3/4"/sec equalisation.
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Old 18th Feb 2019, 4:50 pm   #40
Uncle Bulgaria
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Originally Posted by ms660 View Post
1) A megger is down to personal preference, myself I would not use one for testing run of the mill capacitors but might use one if it was a large can paper type and I wanted to know of any electrical leakage problem.

2) 16uF for the reservoir should be ok.

3) "MICAMOLD" capacitors are notorious.

4) Suflex types have been known to go open circuit or partly open circuit (very high ESR) and sometimes short circuit if there's a high voltage across them in my experience.

Lawrence.
1 & 2. I'm fearful of leaving one in that could overload a part that is harder to replace. However, if you agree the change in value is not too far out of spec. then I feel more comfortable bringing it up on a current limiter and checking the voltages in use. If any of the big cans are shot, I can then replace them.

3. That sounds ominous! I'm considering replacing this with an X2 type. Is that a reasonable idea, or I could lash up an RC snubber. It seems odd they didn't do this, with the quality of the rest of the construction.

4. I'll disentangle them and check for shorts as there are two conflicting opinions on how reliable these Suflex fellows are.

Here's a hint as to how the case is coming along...
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