Tuning up an Ameritron AL-811 Amplifier for Digital Modes
HTML-код
- Опубликовано: 10 июн 2020
- Discuss this video at www.decisionconcepts.com/forums
In this video I discuss things to be aware of when using a vacuum tube amplifier at reduced power, such as when operating digital modes. I also demonstrate loading the amplifier for full drive power, such as for SSB operation, and lower output for digital modem applications. 
Наука
I have since learned to calculate plate dissipation based on plate current and HV. I upgraded to a Palstar power meter to ensure accurate calculations. I hope to do another video soon demonstrating this, as I think it's very important when operating vacuum tube amps on digital modes.
I've found that using the "tune" function to tune the amp in either WSJT-X or FLDIGI with the IC-7300 set at 25% RF out gives me about 250 Watts of output from the amplifier (as modulated by those digimode apps in SSB-D). I then knock the transceiver power down to about 22%-23% which gives me 200 Watts of output power for working the digital modes. The LOAD control then is about half an increment up from where I'd be operating if I tuned at 22%, thus the amp is running ever so slightly overcoupled when actually working digital. Grid current runs about 25ma - 28ma. No plate glow at all, and amp runs cool even after heavy use. Thanks for watching!
So what I'm confused about is, with digital modes (including in WSJT-X), output power is controlled by the volume level of the audio going into the radio from the PC and not the radios output power (drive) setting. So what do you use to determine the drive level and set the output power from the amp? In Australia were only allowed 120 watts on digital modes, but you have me very interested. BTW, great video!
@@VK5IR hi! It's some trial and error of course. You have two levels, the USB modulation on the radio, and the volume of the audio output on the computer. I'd start about 50% on both. I like to set it up so the volume slider in WSJT is about -6db or so before I see ALC action on the radio. I think mine is set about 40% MOD on the radio and 50% on the computer.
That way neither device is being overdriven and I have some play on the volume slider in WSJT-X for fine adjustment. It seems to work well!
Interesting about the 120W limitation on digital. I'm sure I've seen VK stations that must be running more power than that :)
That some great points for digital modes. I have the AL-572 with my IC 7300 . I always per tune in dummy load first. I found with my setup tunning with reduced power than near full power get the peek output and dip grid amps then reduce drive a bit and runs great, Grid current stays down and tubes make less heat. I found on AM I get wrong peek unless modulating the carrier. The dead key works FM dipping the grid. When in AM I got back swing . simple tune when speaking get me right on. also keeping drive down on AM really helps. I have Russia tubes in now. ben going strong many years. I never run full output. only for a quick full power tune then I drop drive. China has some great 572/B tubes . I have some. you can use 811H china tubes but getting hard to find now . Taylor tubes. I only have a few left. 73's
cool video about the tubes and the amp. thanks and 73.
It was very good information I have an 811 I don’t usually run it too hard but thank you and I hope you’re watching if you have any other videos God bless
Yeah I really need to do an update as I've discovered some more information, in particular how to accurately calculate plate dissipation to nearly the watt, to keep it at CCS (continuous commercial service) levels (45W per tube) which I think is desirable for digital modes. Thanks for the reminder, I'll begin working on that soon, hopefully this weekend or next week. Thanks for watching!
How are you not frying the antenna tunner? I have the same one and it is rated to only 300 watts of power.
Hi! Well, nowadays I'm generally tuning up around 225W, so that's within the 300W rating of this tuner. Also, usually I'm tuning with the tuner bypassed to dummy load.
I have run 500+ watts through this tuner though, and it worked fine, probably because I match at the antenna feedpoint to less that 2:1 SWR, then use this tuner in the shack to touch it up to 1:1.1 or so. By doing this I believe I'm putting less stress on the Versa Tuner II's components.
Obviously I'd recommend an appropriate sized tuner, but the cost jumps up significantly above 300W.
Thanks for watching!
Nice vintage computer, I see a 5 1/4 floppy drive. Nice video, thanks for sharing.
Thanks for watching! It's an IBM PC/XT, I believe this one is from around 1985. I have two, both in beaituful shape. The XT has a 10 MB HD, 5.25" 360K diskette drive, and this one has 640K RAM, ethernet installed and internet connected.
First, that tuner is not rated for the power that the map will do, and second, the meter goes between the amp and the tuner. The 300 watts listed on the tuner is transmitter input power, so the tuner could safely handle 180 watts on SSB and maybe 150 watts CW and digital. That's based on 60% efficiency of the transmitter. 300 x 0.60 = 180 watts.
My version 6 manual say never exceed 80watts exciter pg6 #9 and you should use a pulsed cw output vs solid carrier
Do you have a video about the interface between the IC7300 and Amp? I have the same equipment (IC7300 and AL-811). I am very new to this and want to make sure I am doing it correctly. I will mostly use digital. I would want to be at 50% duty cycle for digital. SSB I would max it out. Any advice is much appreciated. Thank you! De W4MTJ
I've always tuned for peak max power, then backed off the gain. I think I'm safe with that procedure. Where we get into trouble is tuning at low power, and THEN increasing the gain. At low power you can tune exactly. But, that's ok if you don't go any higher on the gain.
I've found that this actually isn't the case, and if you back off the tranceiver's drive too much, the amp will be out of tune, and thus you can easily drive the tubes beyond their specified plate dissipation limits, while driving the amp at reduced input power. I know it seems counter-intuitive but it's actually a thing, and precisely how I damaged a few of my first set of tubes. I'm going to do an update video very soon so stay tuned. You might find it interesting.. Thanks for watching.
@@SWRadioConcepts What @azcharlie2009 stated is from the design engineer himself. Tune all the way up to max input, then reduce input until desired amp output is reached. You tuning to 35w and then reducing to 25w is what he says not to do.
Thanks for your insight. I have the 811H. Correct me if Im wrong please. Per your video I am tuning at 20 watts out from the rig then adjusting the plate,load and plate again for max defection. Then increase the load slightly then I reduce power out from the rig to 8 watts which seems to give me close to 200 watts. Your method acually gives me higher wattage going out from the amp then the conventional method. I also dont understand plate glow. Thanks again!
8 watts seems a bit low for 200 W output, but I don't have an H. I'm concerned about increasing the load AND reducing power. If you reduce power, you are in effect increasing the load which requires more capacitance, and would normally mean naturally a lower numerical setting on the load control.
I think I would try tuning at 10 Watts exciter power and see where you're at with RF power out of the amp. You are more than halving the exciter power after tuning and I'd be concerned about that. At these power levels you're probably fine either way anyway, but efficiency might be affected.
After i made this video I discovered through trial and error that I should be tuning at even lower exciter power than I was in this video. I touched on that in my other comment below.
@@SWRadioConcepts thank you for your reply. I now tuned with 10 watts drive and got about 110 watts out. The plate was 300 and the grid was just above 10. Does that sound right to you?
@@dougburrell Grid is most important and 10 is barely bumping the needle, plate seems high in comparison but I think the 811 can handle max 750 if I remember correctly so that's fine. Is 110W maximum RF out at 10 watts? If you want 200 then I'd go ahead and retune at 15 W and see where it's at.
@@SWRadioConcepts Thanks for your help. I think I will leave it at 10 watts. Sometimes my digital tx last 4 minutes on FLDIGI. I really appreciate you getting back to me.
@@dougburrell oh yes, with fldigi I would definitely keep it where you have it, 10W. I've been very hesitant to use my 811 with fldigi at all. That's a reason I kind of regret not getting the 811H for more headroom for fldigi modes. I'm glad you came across my video because tube amp tuning for anything less than full out 600W, 800W, etc., isn't well documented in my opinion.
How is the Amp connected to the 7300,?
Very nice video! 73 de IU2IDU
I got a IC-7300 and will get an AL-811H soon. Now, you got a tuner between radio and amp, and a tuner between amp and antenna at the same time? Is that necessary? I have not seen anyone doing that before. Thanks for the help.
It's not necessary, though you wont get 1:1 from radio to the amp's input because its not that perfect. Maybe 1.3 - 1.5 to 1. So it's nice to be able to touch that up. Plus it's nice to have an autotuner when I'm not running the amp. Mostly I used it because I happened to have an extra one, but i am glad it's there. My follow up video to this about digital ham radio does a better job explaining it.
Thanks a lot for the help.
@@SWRadioConcepts "you wont get 1:1 from radio to the amp's input because its not that perfect"
I have an AL-811H, there are tuning slugs on the back just for this issue, though you have to choose between 20 and 30 since they're on the same slug.
Doesn't the 811 have this?
@piquat1 yes it does have those tuning slugs. I was wondering this myself, issues between bands that are in the same slug aside, why wouldn't one eliminate the tuner between the radio and the amp and use the slugs to tune the match between radio and amp?
Very nice tutorial but I'm a little confused about the mfj 929 when it's only 200watts and you were tuning the AMP for over 200watts. Educate me pls I wish I was wrong
Yeah, my subsequent video did a better job explaining the setup. The IC-7300 is connected to the MFJ 929 directly. Then the 929 is connected to the input of the amp. So the 929 shows the power between the radio and the amp - less than 100 possible watts. The other MGJ tuner is connected between the amp's output and the antenna. Sorry I confused myself when making this video.
Im amazed that you have a tuner on top of that amp. Mine gets way too hot to do that.
Really? I never noticed the temperature, but actually I've never checked. It has never felt warm to me while using the tuner. Do you have a similar amp?
Mines on back order., nice video .WD8ODO
Kinda weird that we don’t adjust load for max rf before increasing drive to 60.
placing a tuner between your rig and the amp is not necessary.
Digital modes were designed for use with low power. Their nature is to be functional at 25 watts or less. There is no reason whatsoever to use a linear amplifier with digital modes! Doing so just makes a mess of our crowded bands! This is especially true for the FT4 FT8 modes!
(1600*300e-03-300)/3=60W which is about the limit for anode dissipation per tube👍🏻
Whatever W8JI says, that's what we should do....
Normally I agree, and he does slightly touch on the subject in his supplemental tuning documentation, but isn't specific enough. You *must* tune the amp at the power you intend to operate. Do not tune at max power then drop the exciter power significantly, or you'll be out of tune and damage tubes - trust me from experience.
@@SWRadioConcepts Yes, happened to me too. New tube s just arrived. TNX 73
What? Seriously dude...too many tuners in use.
i have mobile phone for digital mods.. Whats the point
For digital modes ft8 you only need 40-50 w
well, the way the bands have been acting, 50watts is right about the minimum amount required to successfully work DX over 5000mi, I'd say more like 75-100W might get you heard a lot more easily, assuming your antenna is very efficient...
Russian rebranded tubes 😅😅😅.. Can see them miles away...