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

To: Leigh Turner <>
Subject: Re: [Amps] FW: FW: Triode Amps / options / tetrodes
From: Thomas Walsh <>
Date: Sat, 4 Dec 2021 05:44:24 -0700
List-post: <>
For that matter, a 3cx5000A7 triode also has superb IMD characteristics and can 
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 
a 175 cfm blower which can be rather loud, but the performance more than makes 
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 
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 drive! 


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 time. 

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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