Discussion in 'Amateur Radio News' started by KM9G, Jul 7, 2021.
And we all know what happened to him....
McAfee is dead...
I've got 9 tube amps, from a little AL-84 (600 watts) to a Johnson Thunderbolt (2K+) and a half dozen old Drake radios that tune the same way and have found the fastest way that I can peak them is by locking the mic on and putting a 1000 hz tone in front of it, which I generate via a phone app. As stated above, it is done at full power to not waste time with incremental tweaks. Radio first, then amp - about 5 seconds each.
I didn't come up with this method - I read it somewhere on the web and gave it a shot. I like it better than those pulsing tone generators that go into the audio line of a mic that are sold as "Tube Savers)
You don't have to buy a pulsing tuning aid; you already have one - it's the "dits" side of your paddle.
Those with CW allergies can either buy a paddle or get the pulser.
Say it again for those in the back!
John McAfee did not kill himself.
That works, but a single tone ssb signal is no different than CW key down or FM as far as tuning and duty cycle goes.
The Johnson Thunderbolt isn't anything like "2K+" -- it's rated 1000W DC input power and in Class AB1, which is its normal operating class for linear service, is about 55% efficient, for 550W output power. It can be overdriven to more than that, but then linearity (and resulting IMD) suffers and I wouldn't do that. The 4-400As are only running at 2200Vdc anode voltage (for tubes rated 4000V), so it's actually pretty underpowered. The tubes themselves could produce far more power, but the amp really can't.
The T-bolt is also far more complex to tune up, with coarse and fine loading controls, "grid" peaking, etc. The Johnson recommended tuning procedure reads like a novel.
I owned a very "mint" T-bolt from the late 60s to about 1978 or so and treated it with care. But it doesn't tune up like today's common grounded-grid amps do. The big "plus" of the T-bolt is it has so much power gain, it can be driven to full output (in the "tuned grid" mode) by a 10W exciter, 17.4 dB power gain. Current FCC regulations on commercially sold amateur amplifiers for use below 50 MHz don't even allow that much gain!
Can we have a multiple choice question now please?
Actually it's got to be because that applies to your TX valve PA output stage, 6146's and all that.
And they don't run (generally) in Grounded-Grid. Class A, A/B outputs aren't affected that way.
That's the best I can do. Am I right? I'm too dog-tired to know. If not, please don't be offended.
And here's a pic of Tuning-Cap arc-over damage in a TL-922 amp I just found on eBay.com
You can buy it now if you like.
My story and experience:
I had an Ameritron AL-811H, first generation (say mid-1980s) 800 watts. I got it on a trade from a local yahoo swapper scrounger. First thing I did was buy a set of matched 811s for it; I put them in and let them cook for about 10 hours on 110 VAC. Second thing I did was drop a 220 VAC 20A line in the office to feed that amp. Third thing was I did the 10 meter modification. I remember I had a special radio shelf made for the office that matched the Pottery Barn furniture - so the YL Version 1.0 was happy... 16 inches deep and with a stabilizer in the lower to hold the weight of the Amp and 35 amp Astron.
Oh boy, things worked well until that ill fated morning!
I rolled out of bed to check-in to the US Navy Marine Corps Net on Forty, I was tired, groggy and not quite awake, so being slow on the tuning, with ~50 watts driving into the 800 watt setting I did pop one tube while tuning up! I was too slow tuning down the reflected; that one tube was probably not annealed properly. When it popped, it was quite loud and stunk to high heaven! My YL Version 1.0 got mad as a wet hen. The catastrophe took out a couple of resisters under the socket, as well as a couple two-three disc caps. I was able to run it after the smoke settled, as the other three would tune up just fine. I had my Elmer fix it, and he put a couple of sacrificial diodes under each tube, as per a modification out on the free domain. I should not have been so cheap on the tubes, I got the matched set from RF Parts for $200.00 (50.00 each) as comparted to the 572B which were $85.00 each at the time - the 572B is a more robust tube and can handle more abuse.
3 pieces of advice from KQ1V
First: make a settings cheat sheet. I created a MS-Word cheat sheet that, after tuning each input setting in the rear of the amp, I jotted down the settings for the amp and the tuner. I even went to Staples and had it laminated. Worked exceptionally well.
Second: you really can't be too slow on the manual tuning!
Third: always and continually check the SWR meter, forward and reflected. In fact, always check all meters tuners, amp and power supplies... good data points.
That's my story, and I'm sticking to it!