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   Home   Help Search  
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Author Topic: 811H problem  (Read 7962 times)
AK4QA
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Posts: 31




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« on: March 13, 2008, 02:07:20 PM »

Brand new out the box.  Connected to a Icom 718 with a Ameritron ATR-15 tunner and a Ameritron AWM-30 watt/swr meter.

Turned everything on and keyed (RTTY) at 20 watts.
Increased to 40.  all's well.

Increased to 60 and grid current pegs out.  

Unkey, look for smoke.  Nothing.  Start back up no problem at 40 and increase to 60 to tune.

Only can make 500 watts.  Thinking I fried a tube but why?  Also how do I know WHICH tube??

Thanks everybody.

Lee
KE4VYN

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WB2WIK
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« Reply #1 on: March 13, 2008, 02:56:55 PM »

Repeat the test without the tuner and with a dummy load instead and see what happens.

Anything's possible but it sounds like you were underloaded (on the amp) which can result in high grid current and low efficiency; this can easily happen if the tuner isn't adjusted to perfection before you start tuning the amp.

WB2WIK/6
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N3JBH
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« Reply #2 on: March 13, 2008, 04:01:17 PM »

Lee is this the case in all bands ? Also Like WB2WIK stated adjust the Load to the heavy side a bit. I would think if you are getting a good solid 500 watts now then your tubes are all  working. Try it agian and just increase the Load  some you will see grid drop.

Also read W8JI's info on tuning a Amp on his web site
W8ji.com   It may really help. Maybe it wont either but i read it any how it is good reading. Jeff
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KB9CRY
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« Reply #3 on: March 14, 2008, 06:42:06 AM »

You should adjust your tuner first using only the exciter.  Then you should tune your amp into a dummy load.  Then you apply your power to the tuner.

All amps should be tuned into a dummy load.
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AK4QA
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Posts: 31




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« Reply #4 on: March 14, 2008, 07:26:09 AM »

I guess I should have stated that I did everything you are supposed to do.  such as tune the tuner, attach dummy load, made sure my ticket was current, zipper was up....

come on guys, looking for help not a novice class
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WB2WIK
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« Reply #5 on: March 14, 2008, 07:57:18 AM »

Describe a bit more fully what happens.

You increase drive to 60W and grid current starts to peg the Ig meter?  And at the same time, the amp produces 500W output power?

Does this happen on all bands?

Does the grid current return to normal if you reduce drive back below 60W?

If, while monitoring both output power and Ig simultaneously, you crank in more loading (turn LOAD control clockwise), does that have any effect on the grid current reading?

WB2WIK/6
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AK4QA
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« Reply #6 on: March 14, 2008, 08:56:30 AM »

This event happened only once and has not reappeared.  

I get max Ip current 450mA at 57 watts in.  It does not 'pegged' like it did during event.  Slow increase yields slow Ip rise.

Have no tried any band except 80m as of yet.

Adjusting load control does not seem to have a great effect.  If you decrease down past 3 power drops off sharply.

Increasing plate gets a dip and then as per habit increase a bit more give about 500 watts.

Tubes are running about 130 degrees and no reported IMD or splatter, but of course have not worded it hard yet.

Connected ALC and operating as expected.

Thank you for your input and guidance


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AE5I
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« Reply #7 on: March 14, 2008, 09:31:58 AM »

Lee wrote:

"Turned everything on and keyed (RTTY) at 20 watts.
Increased to 40. all's well.

Increased to 60 and grid current pegs out."

Instead of raising the power to 60 watts and pegging the grid ammeter, I would recommend watching the grid ammeter as you slowly increase power and if/when you see the grid current increasing beyond where it should be, stop increasing the power at that point and increase the loading to drop the grid current to a safe level before increasing the power any further.  Once the grid current is low enough, you can increase power slowly until you've got it where you want it, keeping an eye on plate current and grid current, and keeping the plate tuning touched up all along the way.

And be sure to stop every few seconds for a cool-off period.

Good luck and enjoy your new amp!

73

Tom AE5I
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AK4QA
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« Reply #8 on: March 14, 2008, 10:01:46 AM »

Thanks Tom, but your missing the point.  There was an 'EVENT'.
Where as I was increasing input power, the grid current SLAMMED the side of the meter.  Loud buzzing like something was fried.

I un-keyed and reduced power and not seeing any majic smoke leaking, I started tuning back up.

Everything work as its supposed to, I just cant make more than 500 watts.

I'm beginning to think that this is the norm for amp rating.  Buy 800 expect 500 watts.

The thing that is a puzzle is not much deflection when I adjust the the load control.
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WB2WIK
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« Reply #9 on: March 14, 2008, 03:05:41 PM »

Try another band.  Since you evidently have a dummy load on hand, why *not* try "all" the bands to see how they behave and log setting and patterns?

Difficult to diagnose a problem when you've only tried one band.

The AL-811H uses padding capacitance in parallel with the plate LOAD control on 80m which means the LOAD control is only adjusting loading a relatively small amount.  It doesn't use any on higher bands, so has more effect.

WB2WIK/6
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N1QOQ
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« Reply #10 on: March 14, 2008, 03:05:43 PM »

Is it possible one of the tubes shorted? RTTY is a pretty tough duty cycle. I have the same amp  with a 746pro and I use a shorted plug with electronic keyer.
I'm not an expert at amps, but look at your tubes when tuning and see if they are glowing red. That might indicate if they are over heated. Maybe someone else will chime in and give a little more guidance. According to my MFJ meter I get peaks as high as 900w.
Probably more like 700w but still more than 500w.
73 Paul
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WB2WIK
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« Reply #11 on: March 14, 2008, 06:24:56 PM »

>RE: 811H problem  Reply  
by N1QOQ on March 14, 2008  Mail this to a friend!  
Is it possible one of the tubes shorted?<

::No.

However it's possible one of the tubes is open or gassy.

Since the tubes are in parallel, if one was shorted that would be that: No output, and a blown fuse.

WB2WIK/6
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VR2AX
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« Reply #12 on: March 14, 2008, 07:41:52 PM »

Lee/WB2WIK/6

May be worth checking the continuity of the padding cap/wafer switch in the 80m position. The cap itself might be intermittent, or even not be properly connected across the LOAD capacitor. If the LOAD capacitance is suddenly reduced, that could explain the grid current 'event'. The buzzing could be arcing due to the tank circuit suddenly going off tune.

VR2AX

"The AL-811H uses padding capacitance in parallel with the plate LOAD control on 80m which means the LOAD control is only adjusting loading a relatively small amount. It doesn't use any on higher bands, so has more effect."

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AK4QA
Member

Posts: 31




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« Reply #13 on: March 14, 2008, 08:42:20 PM »

Looks like 475-500 across all the bands.  How do I tell a bad tube?  The look the same thru the vent, IMHO.

Am I also correct in taking one out, clip lead the top wire to the chassie after all power removed?  uncap and replace?

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K7KBN
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« Reply #14 on: March 14, 2008, 10:24:29 PM »

Not a bad idea, AFTER you've discharged the HV supply filter capacitors.  And only use one hand; keep the other one in your pocket.
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73
Pat K7KBN
CWO4 USNR Ret.
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