I would be interested to know how you interface the TOA amp to the
modulator tubes in my case using a pair TZ40s?
73
Mike VK2AMF
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At 02:18 AM 6/02/2025, you wrote:
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I would rip all the front-end
tubes out and drive it with a 10W TOA amplifier. You can get these cheap
on ebay and other websites.? $20 to $30 bucks. They have 4/8 and a
70v output with balanced and unbalanced and a Mic input. These work great
to drive a pair of modulators.? They also have bass and
treble.? I use several here for that purpose.
The 813s as Chuck said, wont play well on higher bands. I would not use
those. A 4-400 single is the way to go here.? You can modulate the
screen with a Dropping resistor off the plate.? No screen
supply.??? You could use the 813s as modulators
though!
Technically you won't even need a bias supply for the final. If you build
a simple sequencer with a few relays, Diodes between the coils and caps
to set delay.? You can ensure Drive appears on the 4-400 before its
keyed with B plus.? Set drive to -183 volts using a meter and a
choke right to the grid.? This will be 10 to 12 MA.?
You could Grid leak it, OR build an adjustable bias supply with negative
-75 to - 175 adjustability. I would not bother. One of my rigs has been
running 20 years with No Bias.? It has a simple over current
relay.? If drive where to disappear, it just trips.
A single will truck along at 500 to 600 W carrier No problem.
C
From: [email protected]
<[email protected]> on behalf of kc1at via groups.io
<kc1at@...>
Sent: Wednesday, February 5, 2025 5:28 AM
To: [email protected] <[email protected]>
Subject: Re: [ham-amplifiers] Dilemma
?
WOW....thanks so much for the input. Let me try to answer some of
the questions
?
Oops....its not a 350 watt modulator its a 300 watts. The thing is a
monster. Has 4 - 12au7s into a pair of 6146's then into a pair of 6080s
then the pair of 811s into a CVM-4. Can't figure out the 12AU7s. Lots of
components missing or dead ended. I'll probably just make a new front end
for it. Seems like an over kill to me.
?
truth is I've been leaning towards the 4-400 with the 813s as a back
up
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Can drive it with my 32v3. (one of 3) That's another disease i have
"Collins stuff. "
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Let me drag out my 4-400 schematics that I've collected over the last
year or so.
?
don
Mike Fleetwood
Canberra Australia and Sidcup UK.
Worldwide email address
is:?????
mfleetwood@...
