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Re: [Amps] Reducing heat in tetrode amps with EBS

To: "'Paul Christensen'" <>
Subject: Re: [Amps] Reducing heat in tetrode amps with EBS
From: "Leigh Turner" <>
Date: Fri, 31 Oct 2014 20:11:15 +1030
List-post: <">>
Hi Paul,

These proposed EBS techniques you advocate using a short delay line on the
audio would work a treat...completely benign bias transitioning operation
that yields a useful dissipation / heat reduction.


-----Original Message-----
From: Amps [] On Behalf Of Paul
Sent: Friday, 31 October 2014 7:53 AM
Subject: Re: [Amps] Reducing heat in tetrode amps with EBS

One possible solution involves a digital delay line.   What is the duration 
of the typical bias settling period from full class C to third-stage class 
AB?  Perhaps 5-10 ms?  Faster?  Slower?

If audio was delayed just long enough for the amp to reach linear operation,

there would be no IMD grunge produced as a result of the EBS circuit. 
Coming out of EBS would require so-called "hang-bias," but even 10 ms is a 
very short period and not perceptible by the ear when monitoring in 

Hang-bias is a software option in my S-QSK sequencing board and is 
adjustable from 0-255 ms in 1 ms increments.  Since amp control is managed 
in software, I may try experimenting with a delay line when the homebrew 
8877 amp gets closer to completion.

Paul, W9AC

-----Original Message----- 
From: Gary Schafer
Sent: Thursday, October 30, 2014 2:14 PM
To: 'Jim Garland' ;
Subject: Re: [Amps] Reducing heat in tetrode amps with EBS

At first glance switching the bias at 1/2 watt input seems like a low value
but if you have a 13 db gain amp that puts the output power at 10 watts
during bias switching. That is only 20 db down from 1000 watts output. Your
amp is operating in a very non linear region while delivering power out that
is down only 20 db and that does not even consider transients generated
during switching.

This would generate IM products during that time. Granted the IM products
would only exist for a short time but they will still cause interference.

Gary K4FMX 

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