[VHFcontesting] [Moon-Net] Bob Sutherland 3CX1000A7 VHF Amplifier

Bill Olson callbill at hotmail.com
Mon Feb 8 16:05:24 EST 2021

My first big tube amp on 2M was a 5CX1500B. I put it in a W6PO tank circuit, grounded catrhode.... that baby DID take 40 amps at 5v on the filament.. And of course, a screen supply and a 50# fil xfrmr.. Thing worked great!! Easy KW. NOT very portable though! I think I got the tube and socket for 100 bucks that was maybe 1975? hah hah

bill, K1DY

From: VHFcontesting <vhfcontesting-bounces+callbill=hotmail.com at contesting.com> on behalf of Ron <ww8rr at charter.net>
Sent: Monday, February 8, 2021 6:20 PM
To: Terry Price <terry at directivesystems.com>
Cc: Edward R Cole <kl7uw at acsalaska.net>; vhfcontesting at contesting.com <VHFcontesting at contesting.com>; Moon-net Amateur Radio Moonbounce <moon-net at mailman.pe1itr.com>
Subject: Re: [VHFcontesting] [Moon-Net] Bob Sutherland 3CX1000A7 VHF Amplifier

Oooops....yes, 5V at 30A....another Senior moment!My 1970s 6M amp that served us well at W8VP, W9ICE, and a couple outings at W4NH is still perking along off of a Drake L4B supply.RonFrom my Samsung  S10
-------- Original message --------From: Terry Price <terry at directivesystems.com> Date: 2/8/21  12:59 PM  (GMT-05:00) To: Ron Rogers <ww8rr at charter.net> Cc: Edward R Cole <kl7uw at acsalaska.net>, Byron Tatum <bjtatum1 at att.net>, Moon-net Amateur Radio Moonbounce <moon-net at mailman.pe1itr.com>, "vhfcontesting at contesting.com" <VHFcontesting at contesting.com> Subject: Re: [Moon-Net] Bob Sutherland 3CX1000A7 VHF Amplifier Actually, 5V @ 30A same as a pair of 3-500z's which are 15A each. I used a filament transformer from a SB220 to light my 3CX1000A7 160m amp. Any of the SK-800 series sockets can be modified to remove the screen grid bypass and use them with a 3CX1000A7. If I recall, the 3CX1000A7 was a external anode ceramic replacement for the 3-1000z. The thoriated tungsten filaments were brutes, you could drive them very hard and being instant on, there wasn't much danger of stripping the cathodes like 3CX1500A7's. They draw more grid current than a lot of other tubes draw plate current!!! I was going to use them for my VHF amps until I played with the new generations of SSPA's. That decision was a no brainer!! Someday I'll sell my collection of tubes, sockets and chimneys to someone for paper weights!Terry Price - W8ZNDirective Systems and Engineering703-754-3876On Mon, Feb 8, 2021 at 12:27 PM Ron Rogers <ww8rr at charter.net> wrote:

Not to mention that the 3CX1000a7 tube requires 5 volts at 50
amps just to light the filament…..same as a pair of 3-500Zs.  That's 250 watts
consumed by the tube just to get it to "light up".

And Terry, since you mentioned the Eimac triode breach lock
socket (SK-860)…….if you can even find one of those they will cost you



From: Moon-net
[mailto:moon-net-bounces at mailman.pe1itr.com] On Behalf Of Terry Price
via Moon-net
Sent: Monday, February 08, 2021 11:57 AM
To: Edward R Cole
Cc: Byron Tatum; Moon-net Amateur Radio Moonbounce
Subject: Re: [Moon-Net] Bob Sutherland 3CX1000A7 VHF Amplifier


A 3CX1000A7 is NOT an 8877, a 3CX1500A7 is. Two COMPLETELY
different tubes, different sockets, they are more like a 4CX1000A7 which
is a breech lock socket. A 8877 is an indirectly heated cathode and a 3CX1000A7
is a directly heated cathode, like a 3-500z. Drive requirements and
input/output capacitance are different. I've built a 3CX1000A7 amp using the
classic W6PO 2m output tank but the input is much different. There was even a
design using a 3CX1000A7 on 432 but it had poor efficiency and required
lots of drive.

Terry Price - W8ZN

Directive Systems and Engineering


On Mon, Feb 8, 2021 at 11:43 AM Edward R Cole via Moon-net
<moon-net at mailman.pe1itr.com>


Bob Sutherland was W6PO, who's 3CX1000A7 (8877) amp is a classic design.
Here is the link to my 2m-8877 project which I used for several years on eme
(sold in 2018).
KL7UW 8877 Amplifier

There was a company making them at one point (do not know if they still
do).  Maybe someone else on this list can assist you on that.  I have
the original document as reprint of Eimac Amateur Service News letter in the
form of a MHTL document which I could send as attachment by direct e-mail (not
thru Moon-net).

The output circuit of my amp is stripline modification done by Harry WA4OFS
(sk) who made the RF parts for my amp as a kit.

73, Ed - KL7UW

At 06:35 AM 2/8/2021, Byron Tatum via Moon-net wrote:

      A long shot here. I am looking for info on a
3CX1000A7 VHF amplifier by Bob Sutherland (and two other authors in second
article) that appeared as a 2 part article in March 1969 HR Mag page 6 and
April 1970 page 26. What started my inquiry was discovery of a plate line
assembly from the estate of a well known Collins engineer JB Jenkins W5EU. I
recognized the assembly as from this 2 part article of which I have studied in
past. Mostly for the sake of historical reasons, and learning, I am asking these
        1. Does anyone have a copy of the
full set of plans that are offered by contacting Bob Sutherland at Eimac as
referenced in March 1969 article? I surely would like to have a set to go with
this plate line assembly.
        2. Does anyone know if any of the
complete amplifiers as offered by Al Roach W6JUK of Dymond Electronics were
ever produced? This is referenced in the April 1970 article adjacent to the
picture of the modified Henry 2K amplifier (modified by Bob Sutherland at Eimac
to incorporated 3CX1000A7 RF deck using Henry power supply).
    I am curious about the history of this 2 part article and if
there are any pieces of equipment that survived from it. I don't believe I
would care to duplicate the complex output coupling scheme and mechanics but it
is interesting to study. I would like to try and find a copy of the
construction plans to go with this plate line assembly.
Byron W5FH
936-349-6353 cell

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73, Ed - KL7UW
Dubus-NA Business mail:
  dubususa at gmail.com

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