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 qrz.com
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.
Leigh
VK5KLT / VK5LT
-----Original Message-----
From: Amps <amps-bounces@contesting.com> On Behalf Of Leigh Turner
Sent: Saturday, 4 December 2021 1:12 PM
To: amps@contesting.com
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.
Leigh
VK5KLT / VK5LT
-----Original Message-----
From: Amps <amps-bounces@contesting.com> On Behalf Of David Gow
Sent: Friday, 3 December 2021 3:08 PM
To: gudguyham@aol.com
Cc: amps <amps@contesting.com>
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 <amps@contesting.com>
wrote:
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