On Sep 1, 2004, at 8:59 AM, Bill Fuqua wrote:
That gives me an idea. I have a Thunderbolt and if I go to solid state
rectifiers, a capacitive input filter and then wire up the 866A's in
parallel but in series with the filtered output I would still have
the light show and more output. Just have to have higher voltage
filter capacitors and bypass the filter choke.
Bill -- For SSB, this is a good plan -- provided the Tune-C will stand
the extra potential and the PS filter C is increased in value to make
up for eliminating the choke filter. However, with a C-filter, a
stepstart might be a good idea to limit the turn-on surge. Also,
4-400As need c. 800v on the screen to take full advantage of their
emission.
cheerz
73
Bill wa4lav
At 09:17 AM 9/1/2004 -0600, John T. M. Lyles wrote:
The 1960 vintage Heathkit Chippewa amplifier model KL1 was a dual
4-400A amplifier which worked well in class AB1. It was described in
Electric Radio magazine a few years back, with some modifications to
improve it. I believe that there is an online index to ER which you
can look up, and order a back issue. I believe that earlier W6SAI
Radio Handbooks (like 21st edition) elaborated on the craft of
building tetrode amplifiers. About that time the 3-500Z was really
becoming a favorite, as a grounded grid zero bias (low bias) class B
amplifier. Setting up tetrodes for best IMD and linear operation
requires a bit more care, as you have both a screen and control grid
bias voltage to deal with. Some have found that grounding the grid
and screen for RF (and applying the DC bias to both) and driving the
cathode is a good way to handle a 4-400A. The Johnson Thunderbolt
amplifier had 4-400As but it ran them in AB2 at too low an anode
voltage, leaving it short of output and prone to being overdriven
(causing IMD).
I have a Chippewa that I am going to restore someday, as it got
"modified" by someone. I saw another one that had been converted to
grounded grid, but wasn't interested as it had been too modified from
original, and for that an SB220 or Drake L4 would be adequate.
Problem with Chippewas is that they had a separate huge power supply
chassis with 866As and it is usually missing or burnt up.
73
john
K5PRO
Message: 1
Date: Tue, 31 Aug 2004 18:23:08 +0200
From: "ON5KM" <on5km@planetinternet.be>
Subject: [Amps] search 7527A design
To: <Amps@contesting.com>
Message-ID: <005601c48f76$d160a020$a284efd4@computer>
Content-Type: text/plain; charset="iso-8859-1"
hi ,
who has a link or info to a good stable design using 1 or 2
7527a's (qb4-1100 or 4-400) ??
all info welcome .
tnx on5km stef
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Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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