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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 2017, 3:39 pm   #1
cheerfulcharlie
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Default Old Capacitor -valve tape recorder

Hi
Would anyone know the rating of this old capacitor (paper??)? it's in the bias circuit of an old Geloso valve tape recorder.

The circuit diagram just says 0.5 - I have no idea what that is referring to.

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Old 15th Jul 2017, 3:49 pm   #2
ms660
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Default Re: Old Capacitor -valve tape recorder

0.5uF...1st board pic:

http://elettronialtramonto.forumfree...72818322&st=15

Lawrence.
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Old 15th Jul 2017, 3:52 pm   #3
BillDWVA
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Default Re: Old Capacitor -valve tape recorder

Looks like a 0.5uf (microfarad) capacitor with 150V working voltage. If you just want a suitable equivalent use an axial polyester capacitor of 0.47uf as a replacement. Available from various suppliers.
Hope this helps,
Bill
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Old 15th Jul 2017, 5:29 pm   #4
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Default Re: Old Capacitor -valve tape recorder

Hi, if you can't find a capacitor rated at 150v dc I would suggest using one at a higher voltage rating.
Also I am not sure if an electrolytic capacitor would be suitable in the circuit, so a polyester cap should be a good replacement.
Are there any other capacitors in the valve tape recorder ? it is possible that some of these might need changing.
regards Peter B
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Old 16th Jul 2017, 1:35 am   #5
cheerfulcharlie
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Default Re: Old Capacitor -valve tape recorder

Thank you chaps that is most helpful.

Peter B- Yes there was a couple of rather large (old type), low volt 25uf electrolytics which I have replaced.

Bill - Your suggested replacement 0.47uf is more like it -something I understand from the modern era -thanks.

Lawrence - I had never heard of Geloso before and I don't think they made it to the UK as everything about them is in Italian..or Spanish.

I was given the machine with quote "you can have it as I keep getting shocks off it". I have to admit that when I took the cover off and saw the valves (the thought of that HT) there my heart sank.. however a more pressing problem was that both the transport and circuit board were filled to the rafters with crud which was probably now conductive? It was after I had cleaned it up that I started to fall in love with the machine (and the idea of valves), mainly because not one single rubbery bit had perished, pitted or turned to goo despite the stressful conditions they were in... then there was IMHO the simple but brilliant engineering and to top it all a 1.5 inch dia tape spool that appears to last an hour!

Hmm yes -valves I am starting to get them now.

Last edited by cheerfulcharlie; 16th Jul 2017 at 1:40 am.
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Old 16th Jul 2017, 5:33 am   #6
TonyDuell
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Default Re: Old Capacitor -valve tape recorder

Which Geloso is it? The smallest model I've seen (G255) had a live chassis (I am not joking, the mains transfomer is an autotransformer). Worse, with the (non-polaraised, continental) plug one way round the chassis is live with the tape in motion. With it the other way roundit's live with the tape stopped.

The extension speaker socket is isolated by the output transformer. The microphone socket is not isolated at all (I assume the original microphone was insulated). Listed accessories for the machine include an audio isolating transformer and a mains isolating transformer.

If this is the live-chassis model, it would explain why the previous owner was getting shocks off it.
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Old 16th Jul 2017, 1:52 pm   #7
Graham G3ZVT
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Default Re: Old Capacitor -valve tape recorder

Quote:
Originally Posted by TonyDuell View Post
Worse, with the (non-polaraised, continental) plug one way round the chassis is live with the tape in motion. With it the other way round it's live with the tape stopped.
I was weaned on live chassis radio and TV, but I don't mind admitting that I don't understand how the above state of affairs happens.

Clearly it's not the classic half-wave rectifier with the chassis connected directly to one side of the mains, so is there a bridge rectifier involved somehow? With TVs that arrangement makes the chassis effectively live all the time.

Can you explain further?
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Old 16th Jul 2017, 5:01 pm   #8
TonyDuell
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Default Re: Old Capacitor -valve tape recorder

No, it's jist a half-wave rectifier.

There is an autotransformer connected across the mains, valve heaters run off taps on that , half wave rectifier from a tap on it too. The deck motor is connected from a suitable transformer tap to chassis, the operating switch connects one side of the mains/autotransformer to chassis to complete the circuit.

So if that switch connects the live wire to chassis then the chassis is live when the motor is running. If the switch connects the neutral wire to chassis then the chassis is live via the motor winding when the switch isn't closed.

I am not sure if the service data is available 'up top'. I have the schematic and also the 'bulletin' which covers this machine. I think the latter is on the web somewhere, it's Geloso Bollettino Technico 57. I won't try to find it in case it breaks some forum rule.
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Old 17th Jul 2017, 4:07 pm   #9
BillDWVA
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Default Re: Old Capacitor -valve tape recorder

I have two of these G255 machines. One which my parents bought new when they were living in Africa in the 1950s and the other which came my way, somehow, here in UK more recently. On the first the rubber has all perished, but replacing a few caps in the other has got it working.
They need treating with care, as had been described above, because of the lack of mains isolation. Even the microphone is fully shrouded to prevent any skin to chassis contact.
Great to use stand-alone with the mike but not to connect to other (grounded) equipment, in my opinion, without special coupling arrangements.
An internet search will turn up a circuit diagram OK.
Bill
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