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Old 15th Mar 2019, 3:52 pm   #1
AmproStylist
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Default Ampro Stylist projector

Hi all
New to the forum.

I bought an old projector, wanting to repurpose it to be used as a guitar amp.

But I cut too many wires too quickly and discarded too much stuff, so I can't go back and do a puzzle.

It is an old Ampro Stylist, but I can't find the schematics for it.
I can find the schematics for "a" Ampro Stylist, but it is using different tubes than what mine is using.

Here's the one I found the schematics for.
https://www.paulivester.com/films/pr...r/amprosch.pdf

Mine has 2 35l6gt tubes instead of 2 50c5 tubes.

If anyone has the schematics for an Ampro Stylist with 35l6gt tubes I would be very grateful.
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Old 15th Mar 2019, 4:32 pm   #2
Herald1360
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Default Re: Ampro Stylist projector

From the sound of those valves, the amp from the projector is probably a live chassis one. Fine for a dedicated internal amp in a projector or record player but definitely not fine for a guitar amp without some careful modification and at least the addition of an isolating transformer to feed it whilst allowing the chassis to be earthed.

The circuit you attached definitely shows a non isolated amplifier and one intended to run from 120V mains too. For European supplies there was probably a stepdown transformer which is likely to be a non isolating (cheaper) type. I would guess that about the only useful part you'll get from the amplifier is the output transformer which at least has the merit of being one of the more expensive parts you'll need.

If you can't figure out what went where in a fairly basic amplifier, it doesn't bode well for a safe outcome to this venture without a lot of consultation and advice.
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Last edited by Herald1360; 15th Mar 2019 at 4:40 pm.
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Old 15th Mar 2019, 4:59 pm   #3
AmproStylist
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Default Re: Ampro Stylist projector

It is indeed with a live chassis.
I have the isolation transformer ready. So that is taken care of.

My problem is the "power supply".
It's a pretty weird way of doing it to my eyes.

There is no step down transformer.

Granted, I am a beginner. But I've done another projector and a couple of radios already. But this construction is weird for me, so I am asking.

I've attached two pictures of the bit I'm having a problem with.

There's a 2in1 resistor in the voltage in circuit... I don't know the proper name of this.

The purple wire is the 245v input and goes through all of the 72ohm resistance.
The white is 225v goes through 34ohm
And finally the bypass is wanting just 205v in.

There is also a 500 and a 600 ohm resistor in the chassis.

The 2nd picture is the 4 pin input.
I'm unsure which is phase, neutral and ground...
I'm going to scrap this part since I'll be installing the isolation transformer. But I'd like to know which is which so I can wire that correctly.

I'm asking as to not die. So pardon me for not wanting to die and asking because I am uncertain. I am trying to get the consultation that I need
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Old 15th Mar 2019, 6:04 pm   #4
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Default Re: Ampro Stylist projector

Quote:
Originally Posted by Herald1360 View Post
From the sound of those valves, the amp from the projector is probably a live chassis one. Fine for a dedicated internal amp in a projector or record player but definitely not fine for a guitar amp without some careful modification and at least the addition of an isolating transformer to feed it whilst allowing the chassis to be earthed.

The circuit you attached definitely shows a non isolated amplifier and one intended to run from 120V mains too. For European supplies there was probably a stepdown transformer which is likely to be a non isolating (cheaper) type. I would guess that about the only useful part you'll get from the amplifier is the output transformer which at least has the merit of being one of the more expensive parts you'll need.

If you can't figure out what went where in a fairly basic amplifier, it doesn't bode well for a safe outcome to this venture without a lot of consultation and advice.
I have to agree with this Gentleman, that this conversion isn't very feasible.
The 35L6's are only good for about three watts, even in push-pull configuration.
If you decide to pursue this project, the 50C5 is similar to the 35L6, only a different package. The pin-out diagrams are available on the net.
DAVE!
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Old 15th Mar 2019, 6:40 pm   #5
AmproStylist
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Default Re: Ampro Stylist projector

Come on guys, can we be a little positive?

To be clear. The amp does not need conversion. It plays very well as it is (was). I only have problems with the power supply.

It is using a bunch of resistors to bring down the voltage, kind of brute forcing it. There are some on the amp chassis as well besides the ones inside the projector casing.

But if it is indeed 110v, I'll skirt around that and just wire the transformer for 110v output.

So, do you guys think it runs 110v?
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Old 15th Mar 2019, 7:00 pm   #6
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Default Re: Ampro Stylist projector

I did note the isolating transformer for "phono" input, presumably used with silent films (the lack of sound track conveniently turning off the photocell output). So it could be used for a hand held input (guitar) with the input of said transformer firmly earthed.
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Old 15th Mar 2019, 7:58 pm   #7
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Default Re: Ampro Stylist projector

With a live chassis, if it is used with an isolating transformer in the audio input it is no longer a case of the transformer being used to couple a signal from a grounded record player, the input is from the metalwork of a guiar with no safety ground connection, just the player to whatever else he is touching. If the transformer fails, it doesn't just pop a fuse, it can kill.

No, this is too dangerous to do.

David
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Old 15th Mar 2019, 8:01 pm   #8
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Default Re: Ampro Stylist projector

It's important that you don't die Ampro and clear that you are uncertain, hence the concerns expressed already! Advising you about a doubtful conversion under these circumstances, via photographs and without any confidence in your design might be difficult as it risks passing on the responsibility to others.

The fact that it's intended for use with a guitar just adds to the mix. The problem IS the power supply as you say but in more ways than one. It's not an accident that valve electric guitar amp's don't employ live chassis circuits, with or without an "isolating" transformer tacked on the end. You may need to read up on this one before going any further, in your own interests.

Dave W.

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Old 15th Mar 2019, 8:17 pm   #9
AmproStylist
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Default Re: Ampro Stylist projector

How do I make it safe?


I have a store bought amp.
This is the schematic to it.
http://4.bp.blogspot.com/-ElQP_uSdAd.../GA5+stock.JPG

On that, the ground is connected directly to the ground of the three prong socket. But the cable that came with it is two prong.. does that mean that this could potentially kill me as well since there is no real ground?

Last edited by AmproStylist; 15th Mar 2019 at 8:36 pm. Reason: Added a question
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Old 15th Mar 2019, 8:38 pm   #10
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Default Re: Ampro Stylist projector

Actually your forum name needs to change! The description is of the 'New Educational', this runs an AC/DC style amp straight off the mains with a voltage selector as described above and a mains voltage lamp. The earlier 'Educational' had the same amp, but no voltage selector. The 'Stylist' runs from a 110V autotransformer powering both amplifier and lamp.

As the name suggests the Educational models were aimed at schools and saved weight and complication by doing away with the autotransformer and using a mains lamp. The downside would be a less bright picture.
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Old 15th Mar 2019, 9:16 pm   #11
dave walsh
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Default Re: Ampro Stylist projector

You may need more knowledge and experience to make either of them at all safe. Ampro. It's not being kept secret but "lets be positive" isn't really the right approach. Being positive [voltage wise] is actually what you need to avoid, especially on guitar strings.. maybe in damp conditions? The projector doesn't seem suitable anyway and the amp you have is basic to say the least. Mains Transformers were [and still are] expensive so it wouldn't be realistic or safe to build a proper PSU in now anyway. This is a Forum that gives advice but not blindly.

50 years ago, in the UK, AC/DC circuits were used in thousands of Radios, Record Players and TV's to enable the use of different mains supplies and save on costs. [You can read them up here or elsewhere]. In fact this was very safe as no metal parts were exposed and people were more cautious. Even if the power leads were reversed and the chassis was live it was ok but certainly would never be allowed these days.

Amps and Tape recorders though, or anything you could plug into externally-like a microphone, guitar or person, always had a full conventional PSU with a MAINS [not isolating or auto] transformer circuit used for safety and with an earth lead.

Dave W

Last edited by dave walsh; 15th Mar 2019 at 9:27 pm.
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Old 15th Mar 2019, 10:15 pm   #12
AmproStylist
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Default Re: Ampro Stylist projector

Quote:
Amps and Tape recorders though, or anything you could plug into externally-like a microphone, guitar or person, always had a full conventional PSU with a MAINS [not isolating or auto] transformer circuit used for safety and with an earth lead.
Could you please explain to me the difference between a MAINS and an isolating transformer?
Because as I understand it there is no real difference between the two. An auto transformer is different, and I understand why.
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Old 15th Mar 2019, 10:36 pm   #13
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Default Re: Ampro Stylist projector

The "store bought" amp circuit shows how it should be done for safety- there's an isolating mains transformer and the ground pin of what looks like a standard "kettle connector" is taken to the chassis and the audio input ground side. It also (interestingly) uses dc for the valve heaters presumably for hum reduction without needing to be particularly careful about heater wiring layout or voltage balancing.

To answer your safety question about the two prong mains lead- Yes there is the possibility of a dangerous situation if the insulation in the mains transformer were to fail or if a mains live wire were to come loose and touch the chassis. With no ground, all could still work but the amp and its signal input could become live. With the ground correctly connected such a fault would blow fuses or take out an RCD rather than electrocute you. In general, safety requires that there must be a minimum of two independent failures before any part of equipment can become live. This is normally achieved either by double or reinforced insulation or by grounding any accessible conducting parts. There is always the possibility here that someone has deliberately compromised safety to get round a hum loop problem rather than solve it correctly by wiring layout or using a suitable signal ground separating interconnection such as an audio isolating transformer.

To achieve the same result with your live chassis amp designed for 120V mains you would need a suiutable 230-115 mains isolating transformer to feed the ac supply to the amplifier. With this in place, then the chassis and signal ground of the amplifier can and should be connected to the mains safety ground.
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Last edited by Herald1360; 15th Mar 2019 at 10:51 pm.
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Old 15th Mar 2019, 10:40 pm   #14
AmproStylist
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Default Re: Ampro Stylist projector

Quote:
Originally Posted by Herald1360 View Post
The "store bought" amp circuit shows how it should be done for safety- there's an isolating mains transformer and the ground pin of what looks like a standard "kettle connector" is taken to the chassis and the audio input ground side. It also (interestingly) uses dc for the valve heaters presumably for hum reduction without needing to be particularly careful about heater wiring layout or voltage balancing.



To achieve the same result with your live chassis amp designed for 120V mains you would need a suiutable 230-115 mains isolating transformer to feed the ac supply to the amplifier. With this in place, then the chassis and signal ground of the amplifier can and should be connected to the mains safety ground.
Thank you!
That's exactly what I was planning to do.
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Old 16th Mar 2019, 12:12 am   #15
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Default Re: Ampro Stylist projector

From the information in #3 this amplifier is from the 'New Educational' and runs on 245/225/205, not 110v. A 230:230v isolation transformer would be required.
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Old 16th Mar 2019, 9:46 am   #16
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Default Re: Ampro Stylist projector

Right, that's sorted voltage-wise, then.

So.... back to the original question, does anyone know whether a schematic can be found to help put the amp back together?

The audio side will be relatively standard but the exact power supply configuration could be "odd". At a guess, the ac feed to the rectifier will be taken off the resistor dropper chain at the 205V tap probably via a series resistor and there will be further resistors from there in series with the heater chain to limit the heater chain current to 150mA. Another possibility is that the rectifier feed comes direct from mains- this would explain the "6-8W" output claim.
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Old 16th Mar 2019, 11:49 am   #17
AmproStylist
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Default Re: Ampro Stylist projector

The 50C5 and two 35L6GT tubes in this amp add up to an even 120V heater voltage connected in series.

I think the 50C5 is being used as a rectifier.

The 205V that comes in right now is run through a 500ohm resistor right after the on switch for the amp.

I'm starting to think I could just feed the whole thing 120V straight from my transformer, bypass the 500ohm resistor, and it should work? It would kind of make sense. To me at least.
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Old 16th Mar 2019, 1:05 pm   #18
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Default Re: Ampro Stylist projector

Not quite. The 50C is the oscillator used for the exciter lamp. The mains input is dropped from 245v to 205v by the 72R resistor. The 205v is directly rectified by a selenium rectifier to produce the HT for the amp. The 205v is also dropped by the 500R resistor to give 139v to run the series heater chain.

A 4 pin input connector was common on cine gear Earth, Neutral and 2 Lives, one to feed the amplifier and motor and the other to feed the lamp. This meant that an external transformer could be used to run a 110v lamp for a public show or similar to give greater brightness.
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Old 16th Mar 2019, 1:09 pm   #19
AmproStylist
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Default Re: Ampro Stylist projector

Do you have the schematic?
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Old 16th Mar 2019, 1:26 pm   #20
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Default Re: Ampro Stylist projector

Re your question about Mains/Isolation and Auto transformers Ampro [post 12*]. It's good you seem to recognise that an auto Tr isn't protective as it just taps off a different voltage without isolation [common in 60's record players]. This is my explanation re the others but I claim no expertise].

I can see that the mains and Isolation Tr's may look the same to you. The difference, as I understand it is that an Isolation Transformer is primarily a safety device. They are used on Building Sites and when repairing live chassis or doubtful equipment in the workshop, to avoid harm. Standard valved equipment used a "Mains" Tr [yes they are all mains] designed to be incorporated within the amp itself. You would usually get mains in and out [or even more perhaps 350v on a hefty guitar amp] to be rectified for the valves. Yes that is also [by definition] isolated with two windings. There is no direct connection to the chassis and importantly, the metal work can now be earthed but the function/usage is different. You could still get a leak across a mains transformer [unlikely] but it would blow the fuse via earth so that's another safety factor-not just the electrical separation.

An Isolation Tr relies on that factor alone and is built accordingly. It's often bulkier and usually intended for external use only [like some medicines]. There's a lot more to this in some applications but that's beyond my basic understanding, why I'm generally cautious re advising anyone and there are warnings on electrical sites. "Be careful out there" as the Duty Sargeant always said in a certain well known cop show!

Dave W

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