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Author Topic: 811h Problem  (Read 5216 times)
KF5CZG
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« on: October 13, 2010, 07:14:24 AM »

Hello,

My set-up:
I am using a ICOM 746 pro, arb 704 relay and a 811h amp.  The outputs to a SWR/Wattmeter, then into 70 feet of heliax to a remote mounted LDG AT-600 pro.  The LDG is connected to a 43' S9 vertical with 32 radials.  For the arb-704 it is connected to the ICOM with the multi-pin connector and relay rca jack.  It is also connected to the 811h relay and ALC ports.  The amp puts out full power into a dummy load.  I tune the amp for max power, then throttle back to 350w during normal ops.  Exciter drive is around 40w.

Problem (which is intermittent):  While on 40m SSB and running 350w the swr (out of the blue) jumps up and then the grid current meter, which is below 100ma, starts bounces back and forth and hitting the stops on the high end.

I opened the 811h and looked at the tubes (did not remove them).  They looked clean and I did not see any melted caps, diodes or resistors.  Also, I was not running the ALC arb-704 connection to the amp....I am trying this now.

Has anyone experienced this?  This may not be an amp issue.  MY guess is the LDG may be getting RFI exposure or I may have ALC issues.  Any suggestions would be appreciated. Thanks.
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KD8GKR
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« Reply #1 on: October 13, 2010, 07:50:23 AM »

Do you have another antenna other than the vertical? Did you run the amp on a different antenna configuration before the S9 vertical? Or, is this a all new setup?
My guess is tuner.
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KD8GKR
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« Reply #2 on: October 13, 2010, 07:53:16 AM »

I know with yaesu radios, you normally don't have to run the ALC connected. I am not sure about Icom radios.
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K0BG
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« Reply #3 on: October 13, 2010, 08:16:21 AM »

The ALC is not the problem, as I too think it is the tuner. Or, it could easily be a bad coax connector.

By the way, you don't need the 704 at all. The 746 has jacks for both the key line, and ALC.
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KF5CZG
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« Reply #4 on: October 13, 2010, 08:17:53 AM »

I just got off the phone with Mike at Ameritron.  He believes one of the tubes may be failing due to the grid current oscillation.

I have used the amp for a year with the S9 antenna and with a 150 foot end fed NVIS with no problems.

I have three 572b tubes that I plan to drop in later this week.  Will also check the grid resistors.
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KF5CZG
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« Reply #5 on: October 13, 2010, 08:39:58 AM »

I used the arb-704 for my first rig (TS-430S), so I already had it and therefore kept using it. 

The LDG AT-600pro has no problems with 100w ssb or the digital modes.  It works great.  I did have to adjust the swr threshold for 30m.  It was set at 1.1 and on 30m it would continually tune and not lock down a setting - of course, I dont use the amp on 30m.
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KD8GKR
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« Reply #6 on: October 13, 2010, 10:35:05 AM »

Does it do this while transmitting into your dummy load. when you said it puts full output into a dummy load is why i think we are leaning toward something between amp and antenna. keep us posted....
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KF5CZG
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« Reply #7 on: October 13, 2010, 11:34:32 AM »

I have tuned the amp into a dummy load on 40m and switched to SSB and cant seem to replicate the problem....Also, I am using the MFJ power injector to get power to the LDG AT600pro....No problems, getting power all the way to the tuner..So, my heliax and connectors are good.  Thx.
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W7SMJ
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« Reply #8 on: October 13, 2010, 02:34:45 PM »

I have a similar situation, S9 vertical with an auto tuner (not LDG) at the base, and have seen a similar problem.  It was definitely the auto tuner and a reset fixes the problem.

I would try tuning the appropriate frequency and then disconnect the power to the LDG so it latches and keeps the same match.  Then see if the problem reoccurs. If it doesn't, reapply power and continue testing.  If you have another recurrence then that's probably pretty strong evidence it is the auto tuner.

73,
Scott
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W8JI
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« Reply #9 on: October 14, 2010, 03:16:30 AM »

I just got off the phone with Mike at Ameritron.  He believes one of the tubes may be failing due to the grid current oscillation.

I have used the amp for a year with the S9 antenna and with a 150 foot end fed NVIS with no problems.

I have three 572b tubes that I plan to drop in later this week.  Will also check the grid resistors.

Mike unfortunately missed hearing a key clue. You said the SWR meter kicked up.

This can ONLY happen from a bad antenna, antenna tuner, feedline, or something after the power meter.

If SWR kicks up, so can the grid current meter.

Reinforcing the logical conclusion you have an antenna system problem is your test that shows things are OK on a dummy load.

73 Tom

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KF5CZG
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« Reply #10 on: October 14, 2010, 07:06:30 AM »

Tom,

Would have to agree with you.  The Amp operates just fine into a dummy load and into my manually tuned NVIS.

I made three lengthy contacts on 40m back on the S9 Vert and 811h last night. I did not see any problems this time. 

This is what I did differently:
 
a.  Added a crap load of chokes on the remote LDG AT-600pro power, Tx and ANT lines
b.  Used the ICOM 746pro and 811h ALC connections
c.  Reduced the LDG AT-600pro SWR threshold one notch (from 2 down to 1.7)
d.  Tuned the Amp for max power into a dummy load (600W RTTY Mode)
e.  Reduced drive power to achieve 250W RTTY into a dummy load
f.  Made a very small load/plate adjustment that increased power to ~275W RTTY, placed amp in stand-by per Ameritron - use to never do this
g.  Switched to the S9 Antenna
h. Cycled power on the AT-600pro
i.  Auto tuned, using RTTY mode, the AT-600pro on the exact 40m SSB freq that I planned to use
j.   Turned Amp on and quickly adjusted drive power to 275W RTTY, checked SWR (was 1.2)
k.  Operated off and on for 20 minutes or so and could not duplicate the issue


According to Mike at Ameritron if you tune at max power and then reduce drive as much as I do, then you should retune with minor adjustments....Like I said, I never did this before.


I will continue to tinker. 

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W8JI
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« Reply #11 on: October 14, 2010, 10:31:00 PM »

According to Mike at Ameritron if you tune at max power and then reduce drive as much as I do, then you should retune with minor adjustments....Like I said, I never did this before.


Only on RTTY or FM and only retune a little. Don't retune for CW or SSB when you reduce power.
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KF5CZG
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« Reply #12 on: October 16, 2010, 08:44:11 AM »

Now, on a similar topic....I just put three 572b's into my 811h amp lat night.  lit them all night in stand-by mode.

This morning I started tuning the amp into a dummy load.  I get 600W RTTY but the grid meter pegs to the right everytime I key up, but it also settles back down to about 100ma.  Again, when I key up the grid meter hits the stop on the right then immediately settles down...This is in RTTY mode using a dummy load.

I know I took a risk putting Taylor 572b tubes into my 811h.

The no-load plate voltage is good...1650v

Any comments??

kf5czg@gmail.com     Jim
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W8JI
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« Reply #13 on: October 16, 2010, 08:08:34 PM »

Now, on a similar topic....I just put three 572b's into my 811h amp lat night.  lit them all night in stand-by mode.

This morning I started tuning the amp into a dummy load.  I get 600W RTTY but the grid meter pegs to the right everytime I key up, but it also settles back down to about 100ma.  Again, when I key up the grid meter hits the stop on the right then immediately settles down...This is in RTTY mode using a dummy load.

I know I took a risk putting Taylor 572b tubes into my 811h.

The no-load plate voltage is good...1650v

Any comments??

kf5czg@gmail.com     Jim

If you put three tubes in the 811H and left one socket empty, it really screws up the neutralization badly! That may not be it, but it could be.

You should do a similar mod as this one:

http://www.w8ji.com/arc_protection_al572.htm

to the 811H.

A pin to the right is either loss of proper load on the amp, something oscillating, or maybe an open grid resistor.



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KF5CZG
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« Reply #14 on: October 16, 2010, 09:25:29 PM »

Tom,

In the eham post titled "tuning the 811h amp"b you stated that installing 3, 572b tubes was ok...Did i miss something?  What I observed with 3 572b tubes is that max output is difficult to achieve, especially on SSB. 

I ordered another 572b.  By the way, my 811a tubes looked great after one year of operation.  Many thanks.
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