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Re: Test / GU74B tubes
Hi Jim,
The good thing about the sweet little GU74B tetrode tube is its stable high gain in grid-driven AB1 configuration with a simple untuned swamped grid input circuit....no messy band switching required on the input side. Just a few watts drive from an SDR exciter pushes the HF amplifier's output well past 400 to 500 Watts at which PEP output the tube will virtually last forever. You don't need a "sky high" idle current to get acceptable IMD equal to or better than most solid state amps; just use some cathode degeneration NFB and all's well on that score. If you specifically want a squeaky clean state of the art signal then just put your SDR exciter in "Pure Signal" mode and a feedback sampling coupler on the amp's output.....then all IM products are negated for an exemplary clean signal spectrum. These military surplus tubes were once very low cost a decade or two back, but sadly market prices have risen like they have done for all Tx tubes :-( It's the old argument of selecting different horses for different courses Jim....each tube whether triode or tetrode and the various circuit topologies have their merits in particular scenarios and use cases. The available tube choices are drying up nowadays for tube amplifier aficionados....everything has either become damn expensive, or is in the realm of unobtainium..... :-( 73 Leigh VK5KLT ________________________________________ From: ham_amplifiers@... [mailto:ham_amplifiers@...] Sent: Sunday, 26 May 2019 1:27 PM To: ham_amplifiers@... Subject: RE: [ham_amplifiers] Test / GU74B tubes Posted by: jim.thom@... But on the subject of the venerable GU74B tube we contraire withdiametrically opposite opinion.? This little tetrode is the best ham radio amplifiertubes around; > on the proviso it¡¯s used properly and within its ratings¡.. as evidenced by amp manufacturers like Acom in their immensely popular and well receivedfamily of 1 and two tube amplifiers, as well as others, and hordes of amplifierhomebrewers. Leigh##? Why even mess with a tetrode ?? ? My problem with the GU74B ......" 4CX-800"? ?is the sky?high?225 ma idle?current requirement PER TUBE !? ? And that's just to get the IMD?to acceptable levels.? That's?insane.? ?450 ma for a pair...and 675 ma for a 3 holer.? ##? Don't? mess?with the Acom? SS? amps.....? way too many problems... and?no?qsk.?? ##? Leigh,?with?your 400 W? limit,?anything will last a long??time.? ?With a 400 w? limit, a?SS amp would suffice.? Jim? ?VE7RF |
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Re: Test #5
When Y! gets goofy like that, I check the group on the web. ^^^^^^^^^^^^^^^^
On Tuesday, May 28, 2019, 7:13:36 PM EDT, 'Doug Renwick' ve5ra@... [ham_amplifiers] wrote:
Finally, after days, not hours, not one day, but days, my posts are finally appearing. Doug "The difference between stupidity and genius is that genius
has its limits." Albert Einstein "Stupidity is the most abundant element in the universe"
From:
ham_amplifiers@... [mailto:ham_amplifiers@...] ? ? I have a GU-78B that has developed a grid short. I
have determined the grid .
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Re: Test #5
Doug Renwick
¿ªÔÆÌåÓýFinally, after days, not hours, not one day, but days, my posts are finally appearing. Doug "The difference between stupidity and genius is that genius has its limits." Albert Einstein From:
ham_amplifiers@... [mailto:ham_amplifiers@...] ? ? I have a GU-78B that has developed a grid short. I
have determined the grid .
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Re: Ad Hominem behaviour in this forum thread
Yes, and George's recently publicised set of prescriptive rules and posting
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guidelines are very befitting and appropriate.. Ham radio interest group forums are intended for friendly exchange of discussion and sharing information relating to the topic; not for off-topic noise and crass and uncalled for ad hominem attacks. Speak to the topic; not gratuitously attack the person for holding view and opinion different from your own..... Leigh VK5KLT ________________________________________ From: ham_amplifiers@... [mailto:ham_amplifiers@...] Sent: Monday, 27 May 2019 10:21 AM To: ham_amplifiers@... Subject: Re: [ham_amplifiers] Ad Hominem behaviour in this forum thread Posted by: "Carl" <km1h@...> And King George III recently posted that he will be monitoring AMPS closely and blocking ALL off topic posts! Gee, like so much bandwidth is used on that long obsolete forum. Don't let the door hit you in the ass Leigh.....bye bye. There are several more modern AMP forums these days that allow pictures, audio, and even allow off topics. Carl ----- Original Message -----
From: 'Leigh Turner' invertech@... [ham_amplifiers] To: ham_amplifiers@... Sent: Sunday, May 26, 2019 7:43 PM Subject: RE: [ham_amplifiers] Ad Hominem behaviour in this forum thread It's a damn pity this now low traffic / semi-defunct ham amplifiers forum doesn't have a principled Moderator like George Fremin III K5TR who oversees the Amps group where such uncalled for rude and crude ad hominem comments are screened and deleted and rightly don't make it to the forum. Leigh VK5KLT From: ham_amplifiers@... [mailto:ham_amplifiers@...] Sent: Monday, 27 May 2019 2:33 AM To: ham_amplifiers@... Subject: Re: [ham_amplifiers] Test Now don't you start Alek...you are one of the Aussies I actually like! AND who doesn't speak like some overblown ego Brit in order to cover incompetence...or is it incontinence? Carl ----- Original Message ----- From: Alek Petkovic vk6apk@... [ham_amplifiers] To: ham_amplifiers@... Sent: Saturday, May 25, 2019 9:16 PM Subject: Re: [ham_amplifiers] Test Somebdy has forgotten to take their pills today. Bad boy Carl. :-) Alek. VK6APK On 26/05/2019 9:02 AM, 'Carl' km1h@... [ham_amplifiers] wrote: YAWN At least Rich and I were friends since about 1996 and I miss him I can't say the same about you. Go back under your GU-74B rock and behave Carl ----- Original Message ----- From: 'Leigh Turner' invertech@... [ham_amplifiers] To: [email protected] Sent: Saturday, May 25, 2019 8:41 PM Subject: RE: [ham_amplifiers] Test Indeed Joe, the forum has been quite slow since the sad demise of central protagonist Rich Measures and the Rich / Carl sideshow jousts... There's more interesting activity on the Amps group nowadays. Leigh VK5KLT From: [email protected] [mailto:ham_amplifiers@...] Sent: Sunday, 26 May 2019 10:03 AM To: [email protected] Subject: RE: [ham_amplifiers] Test No, not dead, been a bit slow, but not slow enough to worry. Joe - W7RKN -----Original Message----- From: ham_amplifiers@... [mailto:ham_amplifiers@...] Subject: [ham_amplifiers] Test Canada; the ship of fools where corruption and politics are synonymous Ham Amplifiers reflector dead? |
Leigh Turner
Scott, KB3JQQ