Interesting relic: Dynair line amplifier

Last year, we replaced a number of audio line amps that had been in service in our master control room for about thirty years. These were made by Dynair; and although the company has vanished almost without a trace, it was once a leading manufacturer of terminal equipment for the television broadcast industry. The line amps seemed "interesting" and had good transformers in them, so I decided to save them from the dumpster.

In search of a schematic, I contacted the present owners of the Dynair name, to no avail. Eventually, I happened upon the name and email address of Dynair's founder, Garry Gramman, who'd sold the company some years earlier. I emailed him:

Mr. Gramman,

I happened across the page about you on the "Order of The Iron Test Pattern" website while doing a websearch on Dynair. I've been looking for a schematic for an old Dynair product... Meret couldn't help me, but perhaps you could point me in the right direction. The schematics I need are for the AD-3081A audio line amplifier and the PS-3015 power supply. Thanks in advance for any advice you can offer.

Oh, by the way, I'm happy to report that our System 21 routing switcher is still in service after more than 22 years. It's only now slated for replacement.

David ______

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I received a reply the next day:

Dear Mr. ______,

The AD-3081A and the PS-3015A were developed in 1963 at the same time as the 5100 switching equipment was designed.

When I sold the Company in 1995 I did not bring any instruction manuals or schematics with me.

Since the products were, I believe, designed entirely with discrete components and single-sided circuit boards, the circuits should be traceable without too much difficulty.

I'm sorry that I can't give you any real information.

You made my day with the news that your System 21 is still in service after 22 years!

Garry Gramman

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I was hoping to save myself the trouble, but I took Garry's advice and traced out the circuit. Over a year later, I finally got around to drafting a legible schematic, and here it is:

10kB PDF

By the way, Mr. Gramman shuffled off this mortal coil only three days after responding to my email, so I present this as a tribute to him.

Pictures to come.

cool dave :thumb:

"By the way, Mr. Gramman shuffled off this mortal coil only three days after responding to my email, so I present this as a tribute to him. "

That is truly touching Dave. He was waiting for that, to be able to leave, I think. Wonderful!



But hey, now we know your last name, Mr. _______.

Totally cool, Dave! I have some UTC A22 here and I´ll try it out when I have the time. Any modern transistors you would recommend?

hey dave-

what does that thing sound like? kinda "chalky" maybe with those transformers?

dave

Rafa,

2N697 is still available and not expensive.

Dave,

I can't tell ya about their particular sonic signature since I've only heard them in the context of a noisy master control room. I don't think I'm as sensitive to these sonic subtleties as some of you guys might be, anyway. If you like, I'll bring along a frame full of 'em next time I visit, so you can check 'em out.

One thing I'm gonna do is to break out the calculator and 2N697 spec sheet and figure out if 24V operation is feasible (with upgraded caps, of course). As you can see from the notes on the schematic, the headroom isn't fantastic with a 15V supply.

Dave;

cool

Remind me never to answer questions from you.

The next 3 days may be my last.

quote: "cool

Remind me never to answer questions from you.
The next 3 days may be my last."

I think the suggestion was that Mr. Gramman was fairly close to departure when NYDave's communication occurred. Unless you are in the same condition I wouldn't worry too much ;-).

It does remind me of an old Doonesbury when Duke is being entertained in China with his girlfriend Honey translating, who informs him that the band is now going to play an undoubted American favorite in his honor, "Rocky Mountain High." Duke's thought balloon: "Lord, take me now."

> I was hoping to save myself the trouble

For four transistors, you bothered a man who should have been in the attic fixing a fan?

> been in service in our master control room for about thirty years.

The design is very silly. That must be why it lived so long. First: half the total power just goes to R11, what a waste. That means a shorted load reduces the stresses on the output transistors.

Pure class A, probably rated +18, +20dBm; pushing +22dBm at clipping. (Oh, wait, I found the footnote.) Or 10% efficiency at full power.

Gain is 12dB minus transformer loss, which is what you found.

There is local feedback, but so little overall feedback that the output impedance is highish. When it comes to "matching" versus "low-Z" philosophy, this sits on the fence.

If the silicon is clean: damm low noise. <100uV at the output, over 80dB below 0dBm.

Robust? Any transistor Beta could drop to 20 and it would meet spec. You could probably remove a transistor and hardly know it. Obviously Silicon; for 1963 this was a little daring, but for 1975 parts this thing should live forever.

Or until the electros dry out. And in fact, it would work without them, just at a somewhat higher gain.

I have a 1980 Hafler HiFi preamp. Very simple for deluxe discrete, yet its gain stage uses more transistors, far more parts, gives less output.

I am having trouble seeing the DC bias. It seems hypersensitive to Q1 Q2 Vbe and to supply voltage. I'd rush in and reduce R1, then connect it to the top of R11. That would be solid bias, but a little bit novel for 1963.

I finally got around to snapping some pics.

Frame with five amps and power supply

Closeup of amp

Note the toasty 100-ohm resistor--this is the emitter resistor for the output transistors. On some of the amps, they used a resistor of too low a wattage rating. On other amps, the problem had been corrected, either by the factory or by a technician in the field.

I'm not sure what I'm going to end up doing with these, but I thought it was only right to document them in some way for posterity, since I've found no mention of them whatsoever anywhere else.

Hey Dave, would you be interested in selling one or two modules?

Peace,
Al.

WOW are there any left in the dumpster ??? :grin: lol
nice score dave ... looks like they will be a fun experiment ..
odd coincidence ... regards ...
hope this stuff sounds as good as it looks :grin:
later
ts

Hi NewYorkDave,

would it be possible to get a copy of the schematic you traced out for the Dynair 3015A power supply?  The PDF you posted of it under the above thread seems to have been removed from your online photo album. 

Am looking to repurpose an old Dynair 2115C power supply that I pulled from a System 21 routing switcher.  Your schematic would be very helpful as a starting point. 

Thanks a lot in advance for your consideration. 

Christian

http://www.twin-x.com/groupdiy/displayimage.php?album=lastupby&cat=0&pos=153&uid=31