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LF: Once again: Field effect versus bipolar transistors

To: [email protected]
Subject: LF: Once again: Field effect versus bipolar transistors
From: "Hans-Joachim Brandt" <[email protected]>
Date: Thu, 31 May 2001 17:41:43 +0200
References: <[email protected]>
Reply-to: [email protected]
Sender: <[email protected]>
Dear all

thanks to an email from Alan, G3NYK, my eyes have been opened for a second mistake in the circuit of my complementary darlington-pair LF power amplifier in the LF Experimenter's Handbook (this one is not contained in my original drawing).
To repeat the two mistakes again for clarity:

Tr2, the upper driver transistor, is shown in the handbook with a PNP symbol but
should be NPN (as the BD235 is), and Tr4, the upper final transistor, is shown
with a NPN symbol, but should be PNP (as the BD312 is). Tr3 and Tr5 are drawn
and labelled correctly, also the ebc orientation for all transistors is correct.

Please believe me that I have not encountered problems like these when mounting
the correct transistors on the cooler and wiring them! Obviously drawing with
symbols is different, sri.

73 Ha-Jo, DJ1ZB

Alan Melia schrieb:
Hi Ha-jo, would I be right in assuming that the symbol for the upper driver
transistor Tr2 is wrong in your circuit in the Handbook also. It is shown
with a PNP symbol but the device quoted is an NPN. The ebc orientation would
be the same but the emitter arrow should 'point the other way' ??

My interest is that I have an old audio slave amp which is an H bridge
circuit and I am considering rebuilding it using effectively two of your
circuits in anti-phase. It does mean an output transformer, but that seems
a small price to pay for about 350watts linear amplification, on both 73kHz
and 136kHz.

Cheers de Alan G3NYK
[email protected]

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