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

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Subject: [Amps] FW: FW: Triode Amps / options / tetrodes
From: "Leigh Turner" <>
Date: Sat, 4 Dec 2021 15:38:13 +1030
List-post: <>
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 maximum specs. Copy of Data sheet is yours on 
request.  The limiting factor on a 3-500z amp is the power supply and cooling.  
The Eimac data sheet specifies Eimac air sockets and chimneys.  Not for RTTY, 
FT8 or AM but an easy legal limit for SSB and CW. .

On Thu, Dec 2, 2021 at 2:45 PM gudguyham--- via Amps <>

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