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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 12th Oct 2022, 8:16 pm   #1
EF80TVVALVE
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Default Pathe Vox Amplifier

Hi all

Well I'm carrying on with perusing the 9.5 sound route, I'm still working through the Son but a Vox projector came along at the wrong time and I decided to buy it. I was intending on buying one when I had finished the Son but I decided to go for this one and give myself too many projects as usual.

Unfortunately someone has been at it before and removed all of the amplifier components but left the chassis in place. The main lamp has been replaced and a separate exciter fitted powered by a DC supply. The PEC has been replaced by a late B&H cell leading off to a female RCA plug.

I'd like to maybe rebuild an amplifier back inside the casing so that it can be returned almost to how it should be. My intentions will keep the B&H cell and use this as the input to the amplifier. I'm just wondering if anybody has any advice or can suggest any circuits that will work well, I'm sure I can go down the valve route without much trouble which would be nice, something like a Mullard 3-3 maybe?

I also need to know if anybody can provide data for the B&H cell, I presume it doesn't give much output and may need a lot of gain from an amplifier. With this in mind I can think of how the front end of the amplifier should be so that it gives enough gain for a nice amount of volume.
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Old 13th Oct 2022, 9:00 am   #2
rontech
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Default Re: Pathe Vox Amplifier

I had a couple of B&H 601 etc series. They had mullard EF37A 's as the first stage amplifier.
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Old 13th Oct 2022, 2:26 pm   #3
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Default Re: Pathe Vox Amplifier

Yes, if I remember correctly the 601 uses a regular PEC but I'm sure this later cell will give a similar output. I did try to measure it with my multimeter last night and got a peak of around 20mV. I'm sure the 3-3 circuit would work quite well, possibly with an extra EF86 at the front to allow another stage for more gain.
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Old 13th Oct 2022, 7:30 pm   #4
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Default Re: Pathe Vox Amplifier

You need a high impedance mic sensitivity amplifier. A bare 3-3 won't cut it, but and extra EF86 should be fine. Is the cell one of the later B&H solar types?

The original Vox amp is a strange design - the amp ran at full gain all the time and volume was controlled by a shutter over the PEC!
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Old 13th Oct 2022, 10:14 pm   #5
Cruisin Marine
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Default Re: Pathe Vox Amplifier

Please excuse my ignorance, but for the sake of myself and others- what is a PEC?
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Old 13th Oct 2022, 10:42 pm   #6
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Default Re: Pathe Vox Amplifier

Photo Electric Cell...

As it has been completely stripped I would be inclined to forget originality and go for a few ebay modules from china. That's quite a chunky power supply so maybe it could power the amp too.
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Old 13th Oct 2022, 11:40 pm   #7
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Default Re: Pathe Vox Amplifier

Quote:
Originally Posted by Cruisin Marine View Post
Please excuse my ignorance, but for the sake of myself and others- what is a PEC?
A PEC is a photo electric cell.
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Old 14th Oct 2022, 10:09 am   #8
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Default Re: Pathe Vox Amplifier

Thanks all for offering your thoughts. Wd40addict, yes the cell is the later B&H solar types, I believe a popular modification with some projectors a few years ago as there were many spare. Not too sure why people thought it as an upgrade really, a well restored original amp will do the job fine.

PJL, that was the initial thought, the Maplin power supply provides DC for the exciter lamp. Building a valve amplifier in the casing isn't so much for originality, too much modification has been done to allow for it to be returned to its original state, but I thought it would make an interesting project to build a small valve amplifier in there being as the chassis has been left in situ. Buying some cheap amplifier boards is still very much on the cards if it proves to be an unviable project. I do think something along the lines of the Mullard 3-3 keeps things nice and simple though and could be assembled in there with little problem.
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