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Author Topic: AL-80b low grid current/Power output  (Read 30394 times)
K4RVN
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Posts: 261




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« Reply #15 on: November 23, 2014, 06:25:39 PM »

Hi Bob,
I have the Omni 6 plus and AL 80 B. I also have an AL 80 A. with another Omni 6 radio. These radios will not fold back on 2 to 1 SWR. Also 70 watts is about the max drive for full output as you probably know. My set up into my homebrew beam for 40 meters is putting out 1000 watts with 70 watts drive. I normally use about 65 watts and it runs about 850 to 900 watts on 40 meters. I find that the watt meter is very good on the AL 80 B and have checked it with my tuner meter and two other watt meters. I would make the following suggestions:
Tune it like you do now but use a lower drive say 50 watts to see if your watts out will drop. Then increase the drive to 55, etc. Once the max power out is indicted do not advance the drive beyond that power from the transceiver. All your power out readings as you suspect are too low compared to my amp. My plate is set on 7 plus 2 lines and the load knob is set on 3 plus 2 lines. Drive is
set on dot # 7 on the power  button on my Omni 6 plus. These numbers are for 40 meters at 7.233.00 Check all grounds on the grids where they ground on the tube. Use all the HV cautions before doing that of course. Also make sure all the solder joints on the caps, variable and fixed are good and chassis grounds are tight. Check the solder joints on your coils also.
Your tube may be soft so if you can buy a spare or borrow one it would eliminate that.   If all else fails the tuned input on the worse band could be adjusted to see if that helps. W8JI could solve this for you in a heartbeat. Good luck and keep us posted as I for one would like to add some notes in my manual for this problem once solved. Loading it heavier means turning the load control to a higher number. I often advance the load a half line after max out just because Tom said that somewhere about advancing it slightly. I tune my amp with the tune like you do on the Omni and
also the plate and load controls. That works very well on the AL 80B, A, and 811.

Frank
« Last Edit: November 23, 2014, 06:28:36 PM by K4RVN » Logged
W1QJ
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Posts: 2945




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« Reply #16 on: November 23, 2014, 07:09:23 PM »

Lower than expected Ig is normally a function of loading being too light. Regards,
Dick KH2G

Actually that's not true, it's just the opposite.  When an amp is too lightly loaded the grid current rises.  When the amp is loaded more heavily the grid current dips lower. 
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N3DT
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Posts: 1647




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« Reply #17 on: November 23, 2014, 07:31:11 PM »

It seems like everyone is ignoring the fact that the OP is only getting 45-50 Ig and 250-300 Ip. That's really low in my book. He should be getting 130 Ig and 425-475 Ip.
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K4RVN
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Posts: 261




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« Reply #18 on: November 23, 2014, 07:46:25 PM »

It depends on whether he is talking about tune or SSB position talking into the mic. I just checked my AL 80B and it is grid 80 and plate 150 in the SSB mode on voice peaks at 850 watts out on 7.163
I meant to ask him but forgot. When using the tune on the Omni 6 plus, the grid is 180 and plate 450, no ALC connected because the Omni rig does not have an ALC connection.
Lou tell the owner of the amp how to fix it and have a great Thanksgiving all.

Frank
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N3DT
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Posts: 1647




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« Reply #19 on: November 23, 2014, 07:56:41 PM »

Well, I don't know how one can tune anything in SSB mode. I use CW or FM, constant carrier, otherwise it's a guess. If those numbers in the first OP post are SSB I can't speak to that, I only tune in CW or FM mode, that may be the diff, but I don't know. That's the trouble with not being there.
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K4RVN
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Posts: 261




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« Reply #20 on: November 23, 2014, 08:29:00 PM »

The tune position on the Omni is used to tune the amp and then it is switched to the SSB operating mode or CW . I had mean to ask the op if he were in the SSB mode talking into the dummy load on his posted readings or was it the tune mode  but I forgot. The SSB would be probably 20 to 30%  of the tune readings, or  CW in actual operation. I too would not know how to tune in the SSB mode if it can be done. Also, My voltage is a nominal 240 supply, not 230. Bob have you measured yours. Mine in the summer sometimes measures 240 plus a few. My HV runs 3150 unloaded.
My amp is set on the 230 volt transformer tap . I used to have 230 here back in 1989 when I bought the AL80 A, and I just set the AL 80B on the 230 tap about 6 months ago when I bought it as the third owner. It doesn't hurt it from my experience .
« Last Edit: November 23, 2014, 09:00:37 PM by K4RVN » Logged
NO2A
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Posts: 1400




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« Reply #21 on: November 23, 2014, 10:14:19 PM »

If you`re absolutely sure the Omni 6 is delivering full output to the amp,and the hv is normal,the tube must be soft. You`ll never get anywhere near rated power with only 45-50ma grid current. 
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NC5T
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Posts: 44




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« Reply #22 on: November 24, 2014, 05:37:53 AM »

Good Morning and thanks again for all the replies.

  When I tune the amp, I use the "tune" feature of the Omni 6+ and this is how I checked it to get the measurements. This feature is the equivalent of CW keydown and is used to set the transmitter power, check SWR, set your antenna tuner, and tune an amp no matter what mode (SSB, CW, Fm) you have the radio set on.  Just to make sure it is working properly I have also tried it on CW with the same results.

  My 220 is actually 232VAC with no load.  I ran a fresh breaker and used 10/2 for the line.  I have not measured the drop under load, but I can give that a try just to see how much it drops when I key the amp to see if it is the line.

  I will also take a look at all of the ground connections again just to make sure they are all still good.  I had some issues when I first got the amp, soft 120VAC line caused softstart resistor meltdown and I had a bad connection on a diode causing T/R issues.  After fixing these issues I went through it and everything else was good.

  With this being my first amp, I wasn't sure if the low grid current/load setting and low output was a sign of a bad tube or if it could be another problem.  RF Concepts has the 3-500ZG for $135 and even if the problems I am having are something else, it wouldn't be a bad thing to have a spare tube anyway.

73,

Bob
NC5T
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W8GP
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Posts: 353




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« Reply #23 on: November 24, 2014, 06:41:51 AM »

Try driving it with 100 watts and see what changes.
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K4RVN
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Posts: 261




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« Reply #24 on: November 24, 2014, 07:19:39 AM »

Bob, thanks for the info. A number 10 is good for 30 amps usually so no problem there, also 3100 volts is up to spec on HV as I sure you know from the manual.  Your HV numbers are great. You should have also changed the fuses from 20 amp fuses to 10 amp fuses when switching to 230 volts. Radio shack has them here. My dedicated 240 line is number 12 and good for 20 amps so you should have very little swing on your 230 volts . Although this is your first amp, you chose a good one in my view and by your replies you know what to look for and listen to some suggestions after weighing their values,
I have come to the same conclusion I wrote in my first reply #15 that your tube may be soft and suggested that you buy one or borrow one to eliminate that problem. Rf Parts gives a one year warranty on their 3-500 tubes and that's what I am using in my AL80B.
I have found the AL 80 B manual to be the best of the three Ameritron amps I have owned. I would suggest that you check on page 18  especially item #4. Where it gives you the max operating
grid current of 170 mA for CW and 0 to 75 mA for SSB operation as the SSB grid current depends on the operators voice somewhat. Let us know if the new tube solves your problem. I have two
Omni 6 transceivers, and also think they are great rigs.

Frank
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N3DT
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Posts: 1647




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« Reply #25 on: November 24, 2014, 07:34:20 AM »

I know nothing about the Omni, I do know that my TS2000 has a 'Tune' mode by pressing the antenna tuner button (AT). However, when I do that with the TS2000, it only puts out 5 or 10 watts CW, I forget which, no matter what mode the TX is in and also engages the antenna tuner. You do not want to use the transceiver's antenna tuner with the amp, the swr into the amp should be good without the TS2000 or even the Omni antenna tuner (if it has one). If your transceiver shows swr while transmitting make sure it's in that mode while keying the transmitter and note that the swr is low into the amp, if it isn't the TX will fold back power. I know when I got my AL80B, it had never been used on anything above 20M because the input SWR was high on 15/17  and the AUX wire was still in place. I had to adjust the tuning for the 4 high bands and cut the 10/12M wire, I didn't mess with the 20/30 input because it was good on 20M and I don't use the amp on 30M. I'm not sure there is a good balance between 20 and 30 anyhow. I'm not sure any of this applies to you NC5T, but I do know if you're putting 70 W into the amp, the swr is good into the amp and you're getting those Ip, Ig and PO numbers, something is wrong.
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W1BR
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Posts: 4179




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« Reply #26 on: November 24, 2014, 07:57:16 AM »

Try driving it with 100 watts and see what changes.

I'd want a monitor scope on an amp that is running a single 3-500Z with more than 60 or so watts drive.  I can drive my SB-220 to well over 1kW output using an Omni VI that is set for 85 watts max  power output.

Pete
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WB2WIK
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« Reply #27 on: November 24, 2014, 08:56:26 AM »

Thanks for all the responses!  I have tried to answer each question below.

W8JX:  The SWR raises a little on the radio, from 1:1 to just under 2:1 at the worst, 80M, and it varies by band a bit but not much.  I checked it with the antennas and got pretty much the same result.

WA7PRC: When I tune the amp, I use the tune feature on the Omni 6+, and then tune for max output with first the plate and then the load caps.  The amp is the only thing on a fresh 220 line so there is very little drop in AC to the amp.

The higher I turn the load cap, the less grid current, and power out I get.  I am not sure if this is what was meant by loading it heavier.

I have always gotten good reports on the audio, but I did go ahead hook up the scope and it didn't see any issues, even with full drive, so I think I am good with the way the ALC is set.

Thanks for the help on this.  I wonder if I am worrying about nothing, or is this an indicator of some issues with the amp or tube?

73,

Bob

NC5T





I've had an AL-80B since it was new in 2001 and let me add a couple of things:

1.  The way the ALC is set is meaningless if you don't have the ALC line "connected."  Without it connected, it doesn't do anything.

2.  Drive the rig harder.  Your rig should be able to output 100W, so use that.  Drive it with 100W and I'll bet the grid current rises.  When it does, adjust the LOAD clockwise, which will increase output power and also reduce grid current, then re-peak the PLATE tuning, and peak the LOAD again.  This is a reiterative process and must be re-performed when you change drive power, change bands, or change frequencies within a band by more than a few percent of the operating frequency.

I can easily drive my AL-80B to >200 mA Ig with enough drive; then I bring it down by increasing the LOADing (which is clockwise, or less capacitance).

If yours can't do that, I'd say you have a weak tube.
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K4RVN
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Posts: 261




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« Reply #28 on: November 24, 2014, 11:25:12 AM »

David, the Omni 6 plus has no internal tuner, older rig built in the 90s and early 2000 and has no ALC making the AL 80B ALC useless with this rig to control it. Also unlike some Kenwoods and Icoms I have owned it will not fold back on higher SWR. Just passed that info along since you mentioned you were not familiar with the Omni by Ten Tec. The Tune position is convenient so you don't have to have a key and use the CW position. It has a button to push also for CW and one for SSB. It is possible to have the SSB or CW button mode engaged and still push the tune button to load the amp. Back when the Omni was built they were top notch with a cost of about 2300 for the standard unit without the extra filters. They pretty much hold their own now with more modern rigs. I often see people who reply ask what transceiver is being used to drive an amp with a problem. Different radios load different ways and connect to the amp in different ways. I use a MFJ interface on one of my amps left over from a previous old Heathkit amp and an Icom 7200.
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N3DT
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« Reply #29 on: November 24, 2014, 01:15:48 PM »

If I drive my AL80B with 100W the grid protection circuit kicks in immediately. About the max I can put in mine is maybe 85W and that's driving the thing to over 1KW when tuned for max on Plate and Load.

As I've said before, I'd reduce drive to reduce Ig if it's too high, increasing the LOAD control will reduce the Ig with more than necessary drive, but that Pin also has to go somewhere. I'd rather run the amp more efficiently and use the load to reduce the PO only slightly.

RVN, yes, I am totally unfamiliar with the Omni, I was just thinking if it operated anything like mine, but didn't know, just shooting in the dark.
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