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

[Leigh Turner]

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 at contesting.com> On Behalf Of Leigh Turner
Sent: Saturday, 4 December 2021 1:12 PM
To: amps at 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 at contesting.com> On Behalf Of David Gow
Sent: Friday, 3 December 2021 3:08 PM
To: gudguyham at aol.com
Cc: amps <amps at 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 at contesting.com>
wrote:

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