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Author Topic: Heathkit SB100 (Ameritron A80)  (Read 12141 times)
W1QJ
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Posts: 1515




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« Reply #15 on: September 21, 2013, 03:34:32 PM »

Thanks to all of you for your comments and advise.  Checked for the parasitic problem and appears there is none.  The final test I did was with no drive and triggering the transmit relay and adjusting the plate and grid controls through spectrum with no change in current.  With the transmit relay keyed, the tube starts glowing red instantly and after a few seconds will blow the fuse.  From all of your comments on the subject, it leads me to believe that the tube is in fact shorted out and needs replaced ---ugh---

How did you perform a parasitic test if the fuse blows within seconds of turning the amp on?  Please explain.  Thanks
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WB6WSQ
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Posts: 16




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« Reply #16 on: September 21, 2013, 04:11:14 PM »

I performed the test as G3RPZ suggested by adjusting the plate and load control and saw no difference in the current.  I actually have about 10 seconds before the tube glows bright red and the fuse is ready to blow.  I keep opening and closing the relay by shorting it out multiple times while adjusting the controls full allowing a couple seconds between activating the relay each time for the tube to stabilize.
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W1QJ
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« Reply #17 on: September 21, 2013, 11:13:09 PM »

Hmmmm......ok, I would get a good tube in that amp and move forward to having some fun.
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G3RZP
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« Reply #18 on: September 22, 2013, 01:35:22 AM »

I agree with W1QJ - you need a known good tube.
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W1QJ
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« Reply #19 on: September 22, 2013, 04:27:47 AM »

Yeah, I think a good known tube is needed to remedy this amp.  If the amp simply lost cut of bias then the plate would eventually get red but it would not blow the fuse.  SO I don't think lost cut off bias is the problem.  For the fuse to blow there has to be a major short in the tube somewhere between the elements of the tube and probably involving the plate.  I doubt a parasitic is the problem especially if the blows without going into the transmit mode.
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WB6WSQ
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Posts: 16




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« Reply #20 on: September 22, 2013, 10:15:36 AM »

Guess it is time to let the moths out of the wallet and head down to the tube store!  Hey, we tried real hard and I do appreciate all the feedback.

Bob
WB6WSQ
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WB6WSQ
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Posts: 16




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« Reply #21 on: September 22, 2013, 10:29:15 AM »

All in all for what it is worth though, I fired it up again yesterday on 20 meters for the Scandanavian contest.  Made contact with Sweeden and Finland with CW after not getting through barefoot.  RST and serial number and it held long enough.  Made me feel a little better.  Thanks again all for the help.
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