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Old 20th September 2013, 10:52 PM   #1
kevinkr is offline kevinkr  United States
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Default Doug Self: Wireless World Magazine Article Archive

Many of you may not be aware of the archive although it has been discussed in a number of older threads here, a reminder:

The Wireless World Archive

Take a look at the April 1961 10W stereo amplifier article and note the bootstrapped plate load resistor in the first stage. (I honestly cannot recollect ever seeing it applied this way in a tube power amplifier.)
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Old 21st September 2013, 12:58 AM   #2
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Gee Kevin - am I that old .....

This was more often used at the time, although I am not sure in commercial circuits. I used it several times. [More often used these days is feeding the pentode g2 (bypassed) d.c. wise from the succeeding cathode to achieve a maintained operating point for the input pentode - but you will know that.]

Also used then was a tertiary NFB (unloaded) winding on the OPT. One could then apply >30dB nfb with stability, with only some loss in h.f. because the voice coil winding was not also in the loop. Distortion of <0,05% could easily be achieved with pentode outputs this way before the UL mode became the preferred thing.

Thanks for that reference. Brings back memories .....
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Old 21st September 2013, 01:37 AM   #3
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The Marantz 8B uses tertiary NFB windings.

Not that long ago, someone posted a schematic for an AC/DC unit that had tertiary NFB windings. For AC/DC stuff, that's high end. The fact that some folks had DC house current was the only legitimate reason for AA5 radios and other equipment lacking power transformers to exist. I've got to believe money was the primary motivation behind the AA5, etc.

Lest anybody think DC house current is "ancient history", parts of NYC's Greenwich Village had DC power into the 1970s, at a minimum. I'm guessing Tom Edison's generation equipment used in his Washington Square Park incandescent lighting demonstration was still on the job.
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Old 21st September 2013, 02:43 AM   #4
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Hi Eli,

Yah .... and these days we seem to be moving back in that direction, what with the development high efficiency super bright L.E.D.s and "green movements".

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Old 21st September 2013, 09:58 AM   #5
Merlinb is offline Merlinb  United Kingdom
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Quote:
Originally Posted by kevinkr View Post
Take a look at the April 1961 10W stereo amplifier article and note the bootstrapped plate load resistor in the first stage. (I honestly cannot recollect ever seeing it applied this way in a tube power amplifier.)
That sort of bootstrapping was indeed rare. It seemed to appear very suddenly in the press in 1961 (see the January article), with a few articles appearing on it through 1962/3, after which everything turned transistor anyway!

Last edited by Merlinb; 21st September 2013 at 10:01 AM.
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Old 21st September 2013, 04:21 PM   #6
kevinkr is offline kevinkr  United States
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Use of bootstrapping definitely caught my attention!

Parts of Stockholm apparently had DC as well into the late 1960s. Friend told me that they actually had rotary converters to get 220V 50Hz in the basement of their building.
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Old 22nd September 2013, 02:28 AM   #7
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Use of bootstrapping definitely caught my attention!

Parts of Stockholm apparently had DC as well into the late 1960s. Friend told me that they actually had rotary converters to get 220V 50Hz in the basement of their building.
Genuine rotary convertors or motor generator sets?

As this article explains, genuine rotary converters work best at 25 Hz. Yes, 60 Hz. was used too, and there were complications.
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Old 22nd September 2013, 02:49 AM   #8
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Apparently it is getting late, my laptop just deleted my entire reply..

Definitely conversion from DC to AC, I would suspect motor gen sets.. I was 12 at the time and have no idea of his relative level of knowledge.

Yeah, I have a couple of books on 25Hz rotary converters once in use on the NYC subway system. The last time I rode they were still running.

Lots more here: www.nycsubway.org: Rotary Converter Power Technology

and Amtrak: http://en.wikipedia.org/wiki/Amtrak%...n_power_system
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