I went and picked this up today 177 miles from the house,
nearly 24" across and it weighs a nice 44 Lbs.
11 tubes and I will get tube line up and more pics tomorrow.
It is a model PA-4
If anyone has any information on it please share,
Thank you
Peter

I remember Ampro as a maker of motion picture projectors. Your amp was probably intended for theater or auditorium use. Nice find!

--chuck

I've had an Ampro 731 tape recorder since I was a kid. Still works.

You have a good PA amplifier there. Good luck restoring it!



Larry

I figure that this one will get all the Lytic cans restuffed, here are something like 11 values on the top side, Plus another 6 or more under.
This will be a big project and I want it don't right, So I will have to clean the bench before I even think about working on this 44 pound Amp, I do not know the output rating but I would suspect 50 Watts or so.
The tube line up is,
6H6,6J7,6J7,7F7,6F6,6L6,6L6,6N7,5Z3,5V4,5V4.
So here some more pics.
I was told that this belonged to a prominent Dentist in NY and it was in his "Movie room" until he passed away some 10 years ago, It has been sitting since..
I figure it will be a heck of a fun restoration project until I want bigger speakers to handle the power.
Any information on a Ampro PA-4 Amp is desired !
Peter

Wow! Big! Nice find.

You guessed right for output wattage. With that 6F6 involved, this will be either a Class AB2 or a Class B unit (with the 6F6 as the driver for the pair of 6L6's). This was how they got 50+ watts out of a single pair of the old 6L6 and 6L6G tubes (in class AB1, a pair of them was good for only half that).

You have a nice rebuild ahead of you here. Good luck and best regards!

Larry

Indeed, this is the amplifier for the AmproArc model AA 16mm arc theatre projector. Schematic diagram is here:

http://www.film-tech.com/warehouse/ware ... category=2

-David

To say that this is sensational, would be an understatement! It's a handsome masterpiece.

I have a similar amplifier that Bell and Howell made, for the same type of service. I was fortunate enough to have a B&H service manual handy, and found the schematic. There was some gorgeous stuff made years ago!!

on the last page there is a wiring diagram but I can't make out several things, Firstly can anyone make out the Lytic can values? Secondly it looks like a date on the right hand side looking like 41' or 47', Anyone have an idea? Would love to know date and what exactly is a "Super speaker"
Would this be the correct thing and year?
http://www.ebay.com/itm/Ampro-Century-1 ... 2907wt_923
You know this will be an interesting project which appears will rock the house when done.
Thanks for the info so far! I don't know how you guys find all the info so fast !
Peter

That schematic at ****tech is of the pa-3 amplifier.

The PA-4 was Ampro's answer to the Bell & Howell model 140 carbon arc projector amplifier (the most complicated 16mm projector amplifier ever made). The Ampro is very similar to the Bell & Howell.

Good catch Ken -- I couldn't quite make out the model number on the schematic but it does look like PA-3. It seems one difference is in the tube line-up -- the PA-3 shows three 6J7 pentodes while the PA-4 shows two 6J7s and one 7F7 dual-triode. But I suspect most of the circuit is very similar.

-David

Interesting.
Looks like I have a bunch more to learn about this bugger,
It defiantly looks well built and I am hoping that it has good Fidelity,
Can one tell Fidelity from wiring diagram?
Thanks all,
Gotta clean the bench before I even think about taking it apart.
Peter

From the looks of the controls, this unit has two "standard" channels (the two controls toward the right) and one "pan"-type dual channel (center control). That would account for the two 6J7's and the 7F7 respectively.

As for fidelity, PA amps weren't particularly noted for that, but since this one was meant to reproduce soundtracks from film, it should have higher fidelity than units meant for ordinary PA work.

Larry

Not really, 16mm film soundtracks are several dB down at 7kHz. Bottom end can be very good. You wouldn't call any optical soundtrack high fidelity, and 16mm is not quite as good as 35mm (usual theatre gauge). So the requirements for fidelity from this unit would be pretty low. Plus if it's like the PA-3 it has no negative feedback.

-David

If it's got good bass response, I'll take it over the average PA amps of its time...

Larry

Cool amp! I love old pa amps, glad to see this thing sing again. I've seen a few like this on ebay recently. I've had a few boar anchors that used the whole class AB2 setup, one was a Bell that used a 6SN7 as a beefy power stage driving a transformer driving the pair of 6L6's. They claimed 55 watts RMS and 80 watts peak- I believe it. I sold it to a kid who's using it for guitar and it can certainly keep up with a Marshall very easy. We stuck GC's in it though, it originally had metal cans!

I've looked through my files of Ampro schematics and I definitely have an original schematic of the PA-4 amplifier.

There are 5 single section twist prong cans rated 40 uf @ 450 volts.

There is a single 3 section twist prong can rated 5 uf @ 300 volts (the plain section), 10 uf @ 350 volts (the triangle section), and 20 uf @ 400 volts (the square section).

The other electrolytics are:

A single 200 uf @ 150 volts

A single 8 uf @ 450 volts (probably a twist prong can)

Five 25 uf @ 25 volt tubular axials.

BTW, the schematic is dated 1948.

Any chance you can scan and send me a copy of that schematic? Or a photo copy?
It would be helpful in this process,
Yup seems like I have a couple hours to work on this one, I would actually like to restful other lytic caps before pulling these out but I doubt that I will be able to find them.
Thank you for the information above, I will write it down and keep it aside.
Peter

Your schematic is in the mail and you should be receiving it any day now.