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Re: [Amps] FW: FW: Triode Amps / options / tetrodes

To: "'Thomas Walsh'" <>, "'Leigh Turner'" <>
Subject: Re: [Amps] FW: FW: Triode Amps / options / tetrodes
From: "Peter Voelpel" <>
Date: Sat, 4 Dec 2021 14:17:34 +0100
List-post: <>
You are probably mixing it up with the 3CPX5000A7 (YC156/179).

The 3CX5000A7 requires 10V heater voltage at 17.5A.
Blower requirement at 2KW anode dissipation is 29cfm with 0.1" pressure

Peter, DJ7WW

-----Original Message-----
From: Amps [] On Behalf Of Thomas Walsh
Sent: Samstag, 4. Dezember 2021 13:44
To: Leigh Turner
Subject: Re: [Amps] FW: FW: Triode Amps / options / tetrodes

For that matter, a 3cx5000A7 triode also has superb IMD characteristics and
can run
at full legal limit all day long with no need to come up with a regulated
screen supply. Also no need for a socket as the tube's grid ring mounts
directly to the chassis. Can't
get more simple than that. Just power it with a stout 3kv @ 3A power supply
with at
least a 25mfd filter and you're in business. The tube does however require
at least
a 175 cfm blower which can be rather loud, but the performance more than
makes up
for it, and it will heat your basement at the same time! I see the 3cx5000A7
up on fleebay regularly for less than $300 as MRI pulls. The filament
requires 15v@15A.
My monobander hb 5000A7 amp can achieve 1500w out with only 22 w in and I've
seen 750w out with only 10w in! This will depend on the Q of the tank and
the input match, not to mention if there's any plate choke resonance. Make
sure your antenna system can handle it and don't forget to turn down the


On Dec 3, 2021, at 10:08 PM, Leigh Turner <> wrote:

On the subject of capable HF linear amplifier tubes there is an interesting
ultra-linear tetrode made by NEC Japan designed specifically for low
intermodulation television broadcast service called the 7F71RA. This
substantial and not so commonly known tube with handles achieves impeccable
IMD performance in QRO linear SSB applications and I note that one such rare
NIB/NOS specimen is currently listed up on eBay as they do from time to

The 7F71RA is in a similar class to the Eimac 4CX3000A / 8169 tetrode but
with significantly cleaner 3rd and 5th order IM specs. The NEC tube would
make a fine QRO linear for teaming with an SDR transceiver and might be of
prospective interest to linear amplifier homebrewers.  JA1VKV has an
interesting page outlining his neat homebrew amp using this tube
with just a modicum of NFB to attain superbly clean linearity performance.
And that's without applying any SDR based Pure Signal adaptive predistortion
linearization techniques.


-----Original Message-----
From: Amps <> On Behalf Of Leigh Turner
Sent: Saturday, 4 December 2021 1:12 PM
Subject: [Amps] FW: Triode Amps / options

Yep, I would rate the Eimac 3-500Z tube today's best bang-for-buck / dollar
per watt legal limit SSB amplifier tube.  A present day production 3-500ZG
graphite anode pair of 'em from the better China manufacturer sourced thro'
RF Parts or Greenstone remain reasonably priced and affordable.

Next best and very capable but more expensive triode at now eye-watering
pricing is the 8877 / 3CX1500A7. The Chinese made Greenstone versions are
more reasonably priced but still expensive.


-----Original Message-----
From: Amps <> On Behalf Of David Gow
Sent: Friday, 3 December 2021 3:08 PM
Cc: amps <>
Subject: Re: [Amps] Triode Amps

3-500z Eimac Data Sheet says Typical Operation 890 watts useful power output
CW or PEP with 3500 volts on the plate.  Maximum plate voltage 4000 volts.
Henry ran them at 4000 on the 3KA.  I had one with a pair and it would  do
2000 watts out into a commercial big dummy load and loafed at 1500.  Henry
pushed them hard but still within Eimac
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