This is personally hilarious to me since Paul Penfield was one of my (very excellent) instructors at MIT... but he taught field theory at the time... I didn't know he had dabbled in audio.
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |
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| 1962 | I love to cook with wine. Sometimes I even put it in the food.
Jim, Genuinely odd. I have never seen an amp of that era before that did not use a transformer coupled speaker. Wonder if these speakers were originally special built to handle the DC, and also higher impedance. 40 Ohms comes to mind. I notice the volume control is connected in a conventional manner; didn't they use to turn it around because of the relatively low base input impedance?
I have a 1962 Lafayette Electronics catalog. Sometimes fun to look at.
Back then I built a class-A amplifier for my '61 Renault Dauphine using one of those Delco door-knob Ge power devices. I used a choke load and capacitively coupled to the speaker. Actually sounded pretty decent.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
I'd almost forgotten those power transistor things. Kind of an inverted stud package. Probably a better thermal design of package than 99% of what's in use these days.
Best regards, Spehro Pefhany
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On a sunny day (Wed, 16 Jun 2004 14:07:46 -0400) it happened "Tam/WB2TT" wrote in :
High Ohm or speakers have been used here. A bit later in the beginning of the sixties there even was a kit here you could buy with an amp that looked a lot like that.
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Yep, even had a guide pin to keep them from rotating while torquing them up.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
I have a 1969 RCA Transistor Manual. It shows some transformer coupled audio amplifiers. Unfortunately, the manual is too recent, because it already has silicon power transistors in it. Wish I had the old GE manual. That contained vintage stuff. I seem to recall somebody did have an all PNP push pull direct coupled amplifier (no NPN EF); that would have been the predecessor to the quasi complementary.
I have the 1964 "GE Transistor Manual". It shows some output stages using both an output transformer and a driver transformer. But it also shows some totem pole outputs using all PNPs, but with some small-signal NPNs in the signal path.
The only old RCA manuals I have are either CMOS or tooobz ;-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Just for kicks I ran SWCAD on an all PNP output stage. It does work. Without much thought to biasing, I was getting about 18V p-p into 10 Ohms from a -24V supply. Requires a diode in the collector circuit of the ce half. I saw no obvious crossover distortion.
Before my time but I would have expected to see transformers at every turn, considering the high price of trs then. Well, either that or valves - somewhere I've got an oldie proudly badged as 'transistor', and yes, it contains 4 or 5 valves.
I would go for a quite different germanium design myself though. Class B output pair driven by an LM324, nothing else, no biasing. Works very nicely. People always think it will distort badly but it doesnt. Took me a bit of thinking to figure out why.
Back in high school, I knew a guy who had a Renault Dauphine and he was
6 foot 8. I could never figure that out. Today most people wouldn't be caught dead with a French car. Next to the Yugo...
The Delco 2N278 TO-36 on a big heatsink, and a big choke were standard on the back of those GM radios of those years. I replaced quite a few of those transistors, got a lot of white silicone goop on my hands. Screwed up an occasional mica washer, too.
I hated to work on Caddy radios because of all the air conditioning ducts that were in the way. Since it was a class A circuit, with heavy collector current, the germanium trtansistors tended to get out of hand when the environment get hot. Did you notice in the schematic in the URL above, that the DC was also across the headphones? I don't think I'd like to have DC thru a pair of headphones, they might singe my ears! Someone should've put a 1000 uF cap in series with the headphone jack.
I've got an interesting story about one of those TO-36 transistors. There was an old guy who lived in a trailer park who kept bugging my ham buddy and I about building a circuit for him. He was half-baked, said he wanted a metal detector circuit that would work at a certain frequency, so he could find gold in the soil. He said that he needed a transistor that would do so and so frequency, and he was trying to get one from the electronics store. The guys at the store pulled a joke on him, gave him a Motorola 2N278 that was all gold plated, so it looked really cool. It was a burned out transistor from a car radio, and they told him that that little stud on the bottom next to the threaded stud had to go into a hole in a waveguide so it would put out RF.
My ham buddy and I were in high school, and we were always in need of funding so even tho we knew this guy was a crackpot, we put up with him to see if we could make some money. Well, he gave us that power transistor and told us what he needed, and we looked at each other incredulously, and knew that someone at the store was pulling a joke on him. But they didn't charge him for the transistor so they weren't doing anything illegal.
We tested the transistor, and tried to convince the old guy that this was just a burned out power transistor, and that it wouldn't work as he thought. But his mind was made up that he could get that transistor to put out RF into a waveguide. Sorry to burst his bubble. but it was just a useless, burned out 2N278.
There _are_ germanium NPN power transistors. CBS's 2N1296 is one example (of which I have a few). But the usual was to use two PNP germanuim power transistors in the standard totem pole circuit, with a PNP and an NPN for the drivers.
I have an old amp that used germanium output transistors, and some clueless tech tried to use silicons. It turned into a transmitter, putting out above the AM broadcast band.
On occasion you can find the GE manuals for auction on Ebay. Going rate seems to be less than ten bucks includiong shipping. Just keep your eyes open for them.
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