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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 15th Jul 2022, 12:28 am   #1
phil_fw
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Default Starting out with a Ferrograph series 4

Hi guys, Something of a novice with valve equipment. I started looking at the Ferrograph 4. I read a lot of threads first and have the circuit diagram. The EZ80 rectifier tube was cracked so I replaced it. Turned it on briefly.. and the EZ80 was arcing some so I turned it off quick. I do need to put together a lamp limiter. I wondered if taking out both smoothing capacitors would provide some insights and perhaps lead to an unsmoothed HT value I could read. Turned it on and the EZ80 seemed to be behaving itself. The heater was gently glowing. There was a faint smell coming off the mains transformer and faint noises (heating wax perhaps) so I just knocked it off again quickly. The fuse didn't blow and I wonder if these were possibly normal and just not noticed when the device was all boxed up in regular operation. Anyway.. I figured I would leave it there until the replacement caps arrived. The schematic is quite hard to interpret - for me and I am not sure how to fault find. I figured I would start with the power supply unit first. I do need to make a capacitor discharge wand as well before going much further.
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Old 15th Jul 2022, 1:23 am   #2
Lucien Nunes
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Default Re: Starting out with a Ferrograph series 4

If the unit hasn't been used for a while and/or the smoothing capacitors are the least bit suspect, I would check / reform / replace them before powering up. The rectifier arcing is a fairly sure sign of leaky caps shorting the HT rail to ground and can rapidly destroy the rec and then the mains transformer. The previous rec might have been overheated and damaged by the same cause. Likewise the noises and hot smell from the transformer are signs of distress and might indicate that the leaky cap is still hammering it, or that it has already been damaged and has shorted turns. Pull the rectifier out, leave it on for 30 mins and confirm the transformer stays cool.

Original reservoir and smoothing capacitor cans are often perfectly usable once reformed. Looking around me, six out of seven pieces of valve equipment in the dining room are working fine with their originals, only one was irretrievable. The key is to reform first, before the caps get cooked by the leakage currents and before they cook the rectifier and transformer. I prefer to reform the caps directly, rather than by throttling the mains supply with a lamp limiter. The lamp is excellent for damage-limitation if a catastrophic breakdown should occur, but it's a blunt instrument as far as reforming is concerned.

I have a couple of purpose-made capacitor reforming tools but sometimes use the unit's own mains transformer and rectifier with a pair of resistors as a voltage divider and the downstream HT load disconnected. The key to reforming is not to push it. As soon as the current gets too high, the capacitor heats up and much of the good work of reforming can be undone. Of course, you might have decided to replace the caps because there are signs of physical deterioration such as bulging seals or electrolyte leakage, or as a matter of principle. I would do so for a unit that was going to be powered up all day every day in someone else's studio, for example. But for a tape deck for my own intermittent use I would have a go at reforming.

Also, before the HT comes up properly for the first time, have you changed the output valve coupling capacitor?
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Old 15th Jul 2022, 1:57 am   #3
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Default Re: Starting out with a Ferrograph series 4

You could have a look at my Ferrograph 4 thread here: https://www.vintage-radio.net/forum/...d.php?t=151194

As a relative novice as well, I took it apart completely (every nut, bolt, and motor) and repaired it with patient help from ms660 and others. I have numerous pictures, notes and videos if you need help.

The most important thing is to have "The Manual Of The Ferrograph" which is a hardback volume with lots of useful lists and photographs beyond the diagram, including tables of DC voltage conditions. Take notes, draw diagrams. Everything is BA, so have a set of BA spanners.

It is possible to measure some of the DC conditions with everything in the case - you can clip voltmeter leads onto exposed joints on the L4 choke to measure HT straight off the rectifier, for example. For others, you have to remove the power supply chassis. Measure what's wrong before replacing anything willy-nilly.

First things first: what IS wrong? If Lucien says it's the smoothing/rectifier capacitors, he's probably right. I had to replace mine after I'd been using my deck heavily for a while. It measured OK originally, and better once reformed, but gave up the ghost. It's C24/C26, which I replaced with a Cricklewood 16µF+16µF can. You can see the new black one in the photograph.

The output stage coupling capacitor is C15 in the amplifier section, marked in the diagram. You can see in mine I've replaced that with a modern yellow polyester type.

But before all that, check the transformer as Lucien says.

Good luck! If I can do it, you certainly can.
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Old 15th Jul 2022, 10:05 am   #4
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Default Re: Starting out with a Ferrograph series 4

As with any mains powered equipment there are potentially dangerous voltages present internally, particularly with valve equipment.

In addition to the 240 volts mains supply voltage, the AC voltage supplying the 2 anodes of the EZ80 rectifier valve can be up to 700V (half that with respect to ground), this comes from the mains transformer secondary winding, I do not know the value on the Series 4 but it will be at least 500V.

The DC HT voltage from the EZ80 cathode could be close to +300V (higher with no load or poor smoothing).

So if you intend to do any live voltage monitoring then proceed with great care and caution, i.e. your personal safety should be your main consideration & priority.

David
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Old 15th Jul 2022, 10:22 am   #5
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Default Re: Starting out with a Ferrograph series 4

Thanks for the helpful comments. It will be a slow process for sure. I should have mentioned that I took it apart first - the capstan motor rubber mounts are perished and will have to be replaced.
To simplify the fault finding I separated the power supply and amp stages. I jumped across pins 8 and 6 on socket 4 to power up. I figured I should check out the power supply in isolation before moving on. My amplifier module is disconnected right now. So the problems are all in the power supply at the moment. I think a pin out map of the transformer would be useful. I am going over it with my voltmeter to see how it is.
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Old 15th Jul 2022, 10:25 am   #6
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Default Re: Starting out with a Ferrograph series 4

Thanks David, Yes I am taking it very easy and obtained a decent voltmeter first, with well insulated leads. I have a healthy respect for the high voltages going on, and always check the capacitors are discharged before proceeding with any poking.
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Old 15th Jul 2022, 10:45 am   #7
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Default Re: Starting out with a Ferrograph series 4

Thanks for that - yes... I have been reading it for a while! Very informative
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Old 15th Jul 2022, 12:40 pm   #8
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Default Re: Starting out with a Ferrograph series 4

Quote:
Originally Posted by Lucien Nunes View Post
Pull the rectifier out, leave it on for 30 mins and confirm the transformer stays cool.
I will do that Lucien. I do have the amplifier module disconnected and have taken both smoothing capacitors out of the circuit. I figured there was a lot less to go wrong at this point. I will pull out the rec and check the transformer.
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Old 15th Jul 2022, 7:56 pm   #9
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Default Re: Starting out with a Ferrograph series 4

If you can do it safely, by clipping meter leads across the EX80 anodes (with power off) then switch on to see what AC voltage you have from the transformer and to make sure the voltage does not decrease over the 30 minute transformer temperature check period.

This could help to verify if any shorted turns.

David
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Old 15th Jul 2022, 8:51 pm   #10
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Default Re: Starting out with a Ferrograph series 4

The mains transformers in these machines are incredibly robust having been wound to very high standards at the Simonside factory it rare to find a failure. My money is on the HT caps.


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Old 16th Jul 2022, 6:40 pm   #11
phil_fw
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Default Re: Starting out with a Ferrograph series 4

The EZ80 seemed to be shorting so I changed it out. The smoothing capacitors were rotten inside as well so I changed them too. The HT DC is reading OK now and the transformer is behaving normally.
I was thinking of checking the bias oscillator next. I suppose I can feed the signal into my oscilloscope. I was just wondering what sort of voltage I would see coming out of it.
cheers
Phil
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Old 16th Jul 2022, 10:51 pm   #12
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Default Re: Starting out with a Ferrograph series 4

Looking at the capstan parts... I have a feeling something is amiss. There is a big brass roller and the capstan. The capstan is just bare metal. I guess the rubber has come off. Is there some kind of rubber sleeve that fits over the capstan post?
Thanks
Phil
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Old 17th Jul 2022, 12:02 am   #13
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Default Re: Starting out with a Ferrograph series 4

For the bias the manual states 53 -58kHz, 6.5 -12.0V RMS measured at deck tags 3 and 1, with correct value for actual head indicated on deck under the flywheel.

Erase voltage is 32 - 40V RMS measured at deck tags 1 and 2.

For your comparison using scope you will need to convert your peak to peak readings to RMS.

The bias and erase signals should be clean and stable sine waves.

David
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Old 17th Jul 2022, 12:14 am   #14
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Default Re: Starting out with a Ferrograph series 4

Not sure about the capstan but believe the pinch roller was all metal on some of these early machines.

David
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Old 17th Jul 2022, 1:18 am   #15
phil_fw
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Default Re: Starting out with a Ferrograph series 4

Thanks David.

I did make something of a mistake with the capstan. I was getting confused with the series 5 which is sitting on the floor. The series 4 does have a rubber roller that makes contact with the brass pinch roller. The series 5 looked like a bare metal capstan but there is a thin layer of rubber still on it.. and it does contact the brass roller in the play position.
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Old 17th Jul 2022, 11:29 am   #16
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Default Re: Starting out with a Ferrograph series 4

Waiting for parts I put the series 4 down and had a look at the series 5. The power supply features this Plessey capacitor - 8uf and 16uf. I am curious about the connections. The body is insulated and has a connection on the top. I suspect none of them are going to earth as far as I can tell. This is trickier than the can ones I found on the series 4. I would appreciate help with this one.
When powered up the series 5 power unit just seems to put out 45v of DC.

Thanks
Phil
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Old 17th Jul 2022, 11:49 am   #17
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Default Re: Starting out with a Ferrograph series 4

Quote:
Originally Posted by phil_fw View Post
Waiting for parts I put the series 4 down and had a look at the series 5. The power supply features this Plessey capacitor - 8uf and 16uf. I am curious about the connections. The body is insulated and has a connection on the top. I suspect none of them are going to earth as far as I can tell. This is trickier than the can ones I found on the series 4. I would appreciate help with this one.
When powered up the series 5 power unit just seems to put out 45v of DC.

Thanks
Phil
The switch solenoid (L1) is connected in series with the HT-ve supply, that's why the -ve connection to C33 and C34 isn't connected to ground, it's connected to the center tap of the mains transformers HT winding.

Lawrence.
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Old 17th Jul 2022, 12:40 pm   #18
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Default Re: Starting out with a Ferrograph series 4

Quote:
Originally Posted by phil_fw View Post
When powered up the series 5 power unit just seems to put out 45v of DC.

Thanks
Phil

Sounds very low. Series 5 manual indicates 285V at input of smoothing choke L5 (C34 junction) and 275V at output of L5 (C33 junction), both in Playback mode and measured with respect to chassis.

David
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Old 17th Jul 2022, 12:54 pm   #19
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Default Re: Starting out with a Ferrograph series 4

Thanks for that Lawrence. I will trace the wires back. Being colour blind is a handicap... but I find I manage if I study the schematic closely.
Cheers
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Old 18th Jul 2022, 11:30 am   #20
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Default Re: Starting out with a Ferrograph series 4

Be careful of the interconnecting wires. I found that repeated movement from opening and closing the case, and moving the chassis resulted in fatigue cracking at the plugs, and the tag strips on the deck.
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