Discussion in 'Amateur Radio News' started by KM9G, Jul 7, 2021.
You can still do that, sure. But it's probably better to tune for maximum output.
Good advice...but I believe you meant..."You can't be too FAST." No more than 5-seconds key-down and 15-seconds cool-off for your 811s unless you want them to suffer infant mortality.
All this tune-up mess makes an even stronger argument for a solid-state amp. I have a KPA500 and I never touch it - instant on, no tuning and instant bandswitching from the radio or software. Check my bio; my previous stations featured the AL-811 (1993 station) and the AL-811H (2005 station). In fact, AES shipped the 811H with the tubes sitting in the sockets with no protection around them; three of the four tubes were shattered in transit.
That was a bad way to ship anything with tubes in it.
SS amps are great, and the KPA500 is a fine example, assuming you have well-matched antennas. If not, prepare to invest in a tuner, and manual ones still require adjustments. Auto-tuners don't, but at the kW level can cost $600 or more, so that's just part of the deal.
Having already owned old amps with 811As (Heath Warrior, Gonset GSB-201, etc) I wouldn't spend a dollar on any of them today: The tubes aren't as good as when RCA made them (which stopped 40 years ago), and they're just too fragile. 85 year-old design. I'm amazed "anybody" (well, the Chinese) make them today. But no matter how hard they try, they're not what the old RCA 811As were.
OTOH, a 3CX3000A7 can run 3kW output power just loafing along, is nearly indestructible, and not expensive. If you've never used a Henry 8K Ultra...it's auto-tune (internally) and can run 4kW output power all day long, with a toooob. Unless your antennas a terrible, it wouldn't need a tuner.
The 3x3 is nice. Mine is in the garage so the tune up procedure is kind of tricky. Dump 100 watts into it, stop in the kitchen to make a sandwich on the way to the garage, tune up the amplifier, eat sandwich, go back to the kitchen and rinse the plate, stop at the restroom on the way back the to the shack, unkey transmitter.
It's very important to do this quickly before the transceiver or coax overheats.
I have the KAT500 matching tuner. Once trained it's as "instant" as the amp, but I also understand that the auto-tuner doesn't have the wide matching range of a good manual tuner. While the KAT500 is rated for more than the KPA500 can put out into 10:1 mismatches, I can't bear a mismatch that bad with any tuner - so I cut and hung more wire antennas to cover bands where my first doublet was horrible (the lesson here being one antenna really can't do it all).
Into a 3:1 or better match the KAT500 is rated for 1000w - and that's the condition I've achieved, with multiple antennas, on every band/segment I work. Also, with prices going up, the KPA500 may still be more money than an AL-811H (and I still don't believe that 4th hole gives any real advantage), but the KAT500 is the same price as a 3kw MFJ matchbox, and less than (or at least the same as) a Palstar.
I will admit there is something alluring where tubes are concerned, but anymore I'd rather skip the knobs. If I could justify the purchase I'd get a KPA1500, but I can't. The KPA500 provides that first 7dB of gain (same as a 3-hole 811), has no knobs and takes up less desk space, even with the tuner under it. That's how I rolls today. Saying the Elecraft K-line is a "500 watt transceiver" is not hyperbole!
Yes Steve, it is a lot different than amps from the '70s and '80s and I prefer them over the T-Bolt which is truly a PITA to play with. The Drakes I mentioned are all mated with L-4Bs and one L-7 for the TR7 (I'm a bit eccentric regarding matching equipment). The T.B.. was acquired to compliment a Viking II with the 250-42-1 attenuator (again, Matching pieces!).
I'd found a mod replacing a couple of the screen regulators with the ones it was designed for (Johnson reduced the power to meet FCC regs by changing two of five regulator tubes to lesser voltage ones) while also replacing the bias tube with a higher voltage one causing lower idle current thus bringing it up (back) to full power and, pushing it hard, it puts out a substantial signal. I tried it with a Drake T-4XB and about 50 / 60 watts in SSB it is a beast. I've heard you can run it in class C, with a bit more drive, to squeeze even more out.
I keep spare a set of 4-400As just in case though - I already blew up an old L-4 by pushing beyond its ability. Both 3-500s popped and the PS erupted in flames. Now That was an interesting experience I'd not like to see again!
Yes Travis, that's right but, I don't have a key connected and my older radios do not have FM, just SSB, AM, CW. I do at times tune the 922 with FM through a 940S and that works out just fine.
If y0ur Amp is changing its mind due to weather, that is your antenna not the amp. My Experience here anyway seeing that issue and fixing it.
Sometimes that not a problem, it's the "nature" of the antenna.
The SWR changes on my doublets when it rains because their both fed with 300ohm ladderline; my tuner "sees" that and changes with it. It's not at all extreme, and goes back to "normal" when the sun comes out and dries out the ladderline. If your antenna is coax-fed and you have no ladderline, there's a problem.
the 11 meter crowd tunes everything to the right and 250% hello audio!
Real hams don't run amplifiers. Improve your antenna set up and then if the station still can't here you turn off your rig and go do something else.
Tom is the go to ham for Ameritron amplifiers. No one knows more about them than him. He's an expert in most facets of amateur radio.
The T-bolt is a bit of a beast at 120 lbs dry.
Not sure about the screen regulator change...the B+ in that amp is only 2200V and there needs to be a large differential between anode and screen voltage to prevent excessive screen current as more cathode emission will be drawn to the screen and dissipated. 4-400A's can run "bright red" anodes 24h/day and in old broadcast service as amplifiers or modulators they often were run that way...for years. But you have to keep grid and screen currents low, that's what destroys them.
Tuning up the T-bolt, I found tuning by watching output power and screen current "only" is very sufficient and never spent any time looking at plate current.
Enjoy the old hardware!