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Old 7th September 2002, 09:56 AM   #11
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Dear np,
thanks for interesting thread. What do you think about variable bias/variable iddle current in general?
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Old 17th October 2009, 01:31 PM   #12
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are this output stage a kind of multi cascode (to avoid memory distortion) or is it a serial circuit to enhance the max Vceo?
regarded the Vceo enhance I have heard about an application note from Motorola arround 1973 - 1975. Unfortunately I haven't exactly title of this application note. Perhaps one of you know this.
Here the presently weblink for the schematic of Threshold 800A ("800 A")
Threshold-800A.jpg (image)
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Old 18th October 2009, 02:08 PM   #13
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I am looking for the parts values related to this 800A diagram: does anyone have them available ?

Thanks
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Old 18th October 2009, 05:11 PM   #14
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File Type: jpg 800a_schem.jpg (151.7 KB, 615 views)
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Old 19th October 2009, 07:31 PM   #15
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Thanks a lot Zen Mod !

Tks
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Old 19th October 2009, 10:27 PM   #16
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Quote:
Originally Posted by tiefbassuebertr View Post
are this output stage a kind of multi cascode (to avoid memory distortion) or is it a serial circuit to enhance the max Vceo?[/url]
We were using some of the faster output devices of the time,
like 2n5878/76, but the second breakdown on them was not
so good, plus of course there was a lot of dissipation going on.
The triple series kept the voltages nice and low.

That it did not seem to have been done previously was just
the cherry on top.

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Old 20th October 2009, 01:13 PM   #17
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Dear Mr. Pass, thanks for your reply.
Regarded the exactly title of the concerning motorola application note I have found an advice from the old German magazine "Funkschau" (1977 issue 4, page 61/161): By the topic "Hifi Nachrichten" ("Hifi News") is mentioned, that Motorola has developed in their European consumer labor a new concept to share the power dissipation (and the Uceo of course) and a new series of bipolar TO-3 power devices especially for the european marked (BD364/365 for 50V, BD366/367 for 60V and BD368/369 for 80V Uceo)
There is additionally mentioned, that the max. value of serial devices could be four pieces (i. e. Uceo 320V) The figured schematic is basicly the same as the push pull power buffer in the 800A
But unfortunately there are no advices of the orig. article of this application note from Motorola. Even by "datasheetarchive" I don't found this article only a list with short form data of all BjT's from this aera, see about
BD368 datasheet and Application Note, Data Sheet, Circuit, PDF, Pinout | Datasheet Archive
and open PDF file

If I have the exact title of this application note, I'm happy because I can then order a copy of this via telerent bookstore (interlibrary loan).
Thank you very much for your advices.

Last edited by tiefbassuebertr; 20th October 2009 at 01:15 PM.
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Old 23rd May 2011, 04:26 PM   #18
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I am still looking to the mentioned application note from previous post (from Motorola).
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Old 23rd May 2011, 06:05 PM   #19
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There's not really a lot to say about this. Running outputs in multiple
series/parallel is pretty straightforward, although you have to compensate
the frequency stability of some systems as you apply more series stages.

The only reason to do this is to avoid high voltage breakdown of the
devices. In the 800A it was very important to stay out of the second-
breakdown region of the bipolar transistors due to the high currents
involved. The result was very reliable - after the initial shakedown, I don't
recall seeing any failures.

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Old 23rd May 2011, 10:51 PM   #20
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similar approach is to find by the Vox "Supreme" instrumental amplifier - go to the schematic by post #79 about
2N3055 inside - commercial famous amplifier models, quasi complementary power output
The theory of operation I don't understand exactly, especially the reason, why for the Tr16 and Tr17 also was used a 2N3055 instead a medium signal type like MJE243.
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