Return-Path: Received: (qmail 24352 invoked from network); 12 Sep 2003 12:53:56 -0000 Received: from murphys.services.quay.plus.net (212.159.14.225) by netmail00.services.quay.plus.net with SMTP; 12 Sep 2003 12:53:56 -0000 Received: (qmail 24381 invoked from network); 12 Sep 2003 12:53:38 -0000 X-Filtered-by: Plusnet (hmail v1.01) X-Priority: 3 X-MSMail-Priority: Normal X-Spam-detection-level: 11 Received: from post.thorcom.com (193.82.116.70) by murphys.services.quay.plus.net with SMTP; 12 Sep 2003 12:51:53 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-Fake-Domain: majordom Received: from majordom by post.thorcom.com with local (Exim 4.14) id 19xnNX-0004nB-Cp for rsgb_lf_group-outgoing@blacksheep.org; Fri, 12 Sep 2003 13:50:23 +0100 Received: from [213.218.75.236] (helo=smtp07.freeler.nl) by post.thorcom.com with esmtp (Exim 4.14) id 19xnNQ-0004n1-H2 for rsgb_lf_group@blacksheep.org; Fri, 12 Sep 2003 13:50:16 +0100 Received: (qmail 885 invoked from network); 12 Sep 2003 12:50:16 -0000 X-Fake-Domain: unknown Received: from unknown (HELO w8k3f0.freeler.nl) ([62.21.151.193]) (envelope-sender ) by smtp07.freeler.nl (qmail-ldap-1.03) with SMTP for ; 12 Sep 2003 12:50:14 -0000 Message-ID: <5.1.0.14.0.20030912144356.00a19ec0@POP3.freeler.nl> X-Sender: FRE0000086604@POP3.freeler.nl X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Fri, 12 Sep 2003 14:50:33 +0200 To: rsgb_lf_group@blacksheep.org From: "Dick Rollema" In-reply-to: <3F6181A9.30807@virgin.net> MIME-Version: 1.0 Subject: Re: LF: Inverted tube amplifier Content-Type: text/html; charset=windows-1252 X-Spam-Status: No, hits=0.3 required=5.0tests=EMAIL_ATTRIBUTION,HTML_00_10,HTML_MESSAGE,IN_REP_TOversion=2.55 X-Spam-Checker-Version: SpamAssassin 2.55 (1.174.2.19-2003-05-19-exp) X-SA-Exim-Scanned: Yes Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rsgb_lf_group-outgoing@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-Spam-Rating: 1 Content-transfer-encoding: 8bit To All from PA0SE

Stewart, G3YSX wrote:

I came across an interesting concept yesterday that I thought
worthy of further consideration for an LF active antenna. The
so called inverted vacuum tube amplifier.

Consider a triode, with a positive grid and a negative anode,
with the input signal going to the anode, and the output taken
from the grid. This has a high input impeadance, very low input
capacitance, and low output impeadance. It also is more linear
than a conventional valve amplifier. These are exactly the
characteristics that are needed in an active antenna.

The downside is that although it has a power gain due to the
impeadance transformation, it has a massive voltage loss, because
in this mode the valve mu becomes 1/mu.

At low frequencies the issue with voltage probe active antennas
is not so much the voltage at the probe, but the very high
capacitive potential divider that results from the very low
capacitance of the probe, and the input capacitance of the active
device and its infrastructure. The key test therefore is whether
the voltage attenuation of the value in this mode is less than
the voltage "gain" that results from the lower input capacitance
term in the input potential divider.

Because of it's improvements in linearity, this mode is of interest
to the audio groups, particularly those interested in transformerless
valve amplifiers.

There is a writeup of the technique at

http://members.aol.com/sbench102/inverted.html

The inventor of the technique was none other than Fred Terman, who
wrote it up for proc IRE

F Terman, The inverted vacuum tube, a voltage reducing power amplifier.
Proc. Inst. Rad. Eng. 16:447-61. (1928)

In case anyone thinks that this is a misplaced April Fools Joke, there
ia also a reference to the paper in his book Radio Enginneering, although
neither of the editions that I have give any useful theory on the operation.

If anyone has access to a copy of that paper, I would appreciate a
copy, otherwise I will try to get one the next time I am in the
IEE library in London.

Stewart G3YSX

If my memory serves me right the principle of the inverted valve has been used in the past in a DC valve voltmeter for relatively high voltages causing negligible loading of the voltage being measured.

73, Dick, PA0SE