Film-Tech Forum ARCHIVE: What Is This Amp?

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Posted by Bruce McGee (Member # 131) on 12-26-1999, 09:50 PM:

I just received an International Projector Corporation amplifier.

The type is NP11, (serial # 210)

It uses a pair of 2A3 outputs, a pair of 57 preamps, and a 5Z3 rectifier. Any idea how old this thing is, and where I might find a schematic for it? I am going to restore it, I hope.

I want to say this thing is from around the mid 30's, but I dont really know. It is in beautiful condition, and heavy. Other than tubes, it appears to be all original.

It was manufatured for IPC by the Electro Acoustic Products Company of Fort Wayne, Ind.

Happy birthday to me today. #43!

Posted by Erich Loepke (Member # 166) on 12-27-1999, 01:30 AM:

With the tube line-up you gave, this puts it in the mid 30s like you guessed. The 2A3 tubes are still in production overseas for audiophile amplifiers. The others are available from antique radio parts dealers from new old stock.

The power output from a pair of 2A3s is around 15 watts. Of course this was considered adequate at the time, and with the efficient speakers being used then, it could achieve loud sound levels.

You could try posting this on the electrical/mechanical forum on www.antiqueradios.com

The guys there may have a schematic laying around or at least give you some advice on restoring this amplifier.

Good luck with your amplifier!

Posted by Rick Long (Member # 213) on 12-27-1999, 02:10 AM:

Many happy returns, Burce.

The amp is from the mid to early 30's. Tubes are available from specialty electronics suppliers. Biggest problem may be finding any electrolytic capacitors for it. Tube amps used some pretty high-voltage ratings as opposed to today's solid-state stuff. Willing to bet that, if those are the original caps, the will probably be pretty dried out by now.

Posted by Ken Layton (Member # 133) on 12-27-1999, 09:29 AM:

Bruce:
For the schematic, call my buddy Dick Prather 7816 North Montana Ave, Portland, Oregon 97217-6531 (503) 289-4073. Also try John Eickhof at Northwest Theater Equipment P.O. Box 258, Wendell, Idaho 83355 1-800-341-3846 or (208) 536-5489 or fax (208) 536-5308.
For all the parts you need (including NEW capacitors) to rebuild that amplifier, go to ANTIQUE ELECTRONIC SUPPLY 6221 South Maple Ave. , Tempe, Arizona 85283 (480) 828-5411. They have a website: www.tubesandmore.com

Any amp that uses 2A3 tubes is well worth fixing indeed! You will have top quality sound for sure.

Posted by Bruce McGee (Member # 131) on 12-27-1999, 10:19 AM:

I have bought from Antique in Tempe before. The 2A3's new are 75.00 each! They also have used ones that I can afford. All the caps are available locally. All other tubes are very reasonable.
I bought several UX type used tubes from them that were just fine. They fixed a 1920's radio that someone GAVE me!!!

Ken: I'll call your friend later today, If all goes well...

Posted by Bruce McGee (Member # 131) on 01-06-2000, 07:48 PM:

I heard from Dick Prather. He says that this IPC amp is probably not a real theater amp. It was probably built for "non-theatrical" use for the old Acme, and Simplex sound machines. Figures. I hope we can come up with some kind of schematic. There are 2 blown resistors that are at least 20 watts or so. No way to read the ratings on them.

I found a spare 2A3 tube that checks OK on the tester.

The 5Z3 rectifier has plate voltage of 670 volts!

Posted by Bruce McGee (Member # 131) on 05-20-2000, 09:10 PM:

I brought this subject back to the head to say that the amp is now finished and working. Major thanks to Dick Prather for the similar RCA manual that he found and copied for me at no charge, and Ken Layton for steering me to Mr. Prather!

The amp runs well and is being used as a monitor amp for now. I am not going to use it with the Holmes!

I got lucky with the 2A3 tubes. The one that came with the amp was good. The one I found in my junk box was within 2% just as good as the other one on my tester. I replaced the 57's because the amp HOWL'd when I tapped them. The original 5Z3 was fried when the caps shorted, and I got lucky there, too with another surprise from the junk box!

I'm glad I could bring this old beauty back from the dead. It's a real work of art, and they dont make 'em like this anymore.

Bruce

Posted by Ken Layton (Member # 133) on 05-21-2000, 01:58 PM:

Bruce:
You should get some real high quality sound out of that amp! 2A3 tubes, especially the Western Electric ones are in big demand.

Posted by Bruce McGee (Member # 131) on 05-21-2000, 04:32 PM:

Ken:

Naturally, my 2A3's are RCA and National Union. Many years ago, we bought a house where the previous owner had left hundreds of new in the box tubes. There were things like 807's, 2A3's, 1625's, 1629's, etc. I had nothing that used these tubes at the time, so, I---gave---them---away.

The guy I gave them to kept them until around 2 years ago, when he sold them to Antique Radio in Tempe. Thats when I found that they had lots of tubes. I could kick myself for not simply keeping them in my own garage like he did.

Posted by Stephen Winner (Member # 8) on 05-21-2000, 08:01 PM:

This sounds very similar to the power amplifier in my Hammond organ! This amplifier was made by Western Electric though, and has an output of about 40 watts. It contains a 5Z3 for a power rectifier, 4 2A3's for final amplification, and 2 56's for pre-amplification. It is quite a good sounding amp, and keeps up with the low frequencies the organ will generate. The organ dates to 1935. It was installed when the church was built, but was given to me when they installed a new organ. I rebuilt this one because it wasn't working (that's why it was replaced). This should give you a good reference point as to the date of your amp.

The capicitiors are not too terribly hard to find if you aren't really trying to keep it authentic. This amp has an oil-filled capicitor with 3 elements. I kept it installed to keep the look of the amp correct. Underneath though I installed modern electrolytic capicitors in place of each element. These can be found at any electronic supplier for a few dollars at the most!

Posted by Bruce McGee (Member # 131) on 05-21-2000, 08:12 PM:

I wanted to maintain the original look of the amp, so I did just what you said. I installed all the electrolytics below, and left all the original stuff showing on top.

When the amp is running, the 2A3's, and the 57's have a slight blue-ish glow that pulses to the signal level. I suspect that they are a bit gassy, but its not enough to cause problems.

The 2 new 57's are matched RCA NOS from the '30's! They sound vastly better than the originals did.

The amp looks really nice in the dark. I wish you could see it.

I have a Hammond M-100 that was given to me, too. It had blown the rectifier tube, and all I found wrong was shorted caps. It has a nice sound, too. I'd love to have a Hammond with the 2A3's.

Bruce