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Re: [Amps] AL-1200 Pop

To: Ed Briggs <>
Subject: Re: [Amps] AL-1200 Pop
From: R.Measures <>
Date: Wed, 7 Jul 2004 06:53:04 -0700
List-post: <>

On Jul 6, 2004, at 7:19 PM, Ed Briggs wrote:

It could be lots of things. But I recently had this problem and it turned
out to be the tube.

Symptoms:  Pop in standby, at power up.
                   Visible flash, apparently coming from RF compartment

 I do not see how a defect inside the tube could cause a flash in the RF out compartment.

                   Occationally, damage to B- clamping diodes.
                   No carbon or other charring

Differential Diagnosis:  Remove tube; apply power.
                                   Never happened with tube removed

 That shoots down the bad blocker C theory.

Alternative theories: Parasitics

 Ed -- The 3CX1200A7 does have twice as much feedback C as an 8877 and 33% more feedback C than a 3-500Z. Does this AL-1200 have a "neutralization" circuit?
                   Dust, humidity, spiders and other bugs,
                    finger grease on the tube chimney
                    bent chimney clips
                    Cracked or damaged blocking capacitor

Actual Cure:
            Replacement of the tube.

 If the replacement tube happened to have slightly less VHF-gain than the original tube, it would have less of a tendency to regenerate at VHF and cause HF tank arcing. On the other hand, VHF parasites normally increase the Ωs (ohms) of the suppressor resistor, but this one was reportedly within tolerance. .

Apparently, Ameritron has seen this before and replaced the tube w/o charge
(under warranty). The tube was returned to Ameriton
for testing and 'tested good' but promptly failed when re-inserted in my
amp. Ultimately, my tube went back to Eimac.

 My guess is that the tube was not defective, and that it had more VHF gain than average.

(Yes, I know, you shouldn't have seen a flash for a tube arc, but there was
an arc. It may have been a reflection
of the step start relay arcing,

 Not likely. Step-start currents are mild by design. / cheers

or perhaps the light of the internal arc
through the ceramic)

Happy hunting


----- Original Message ----- From: "Dana Roode" <> To: "AMPS" <> Sent: Sunday, July 04, 2004 9:25 PM Subject: [Amps] AL-1200 Pop

I just finished replacing the open frame relay in my old AL-1200 with the
Ameritron relay PCB mod. Put it all back together, seemed to work fine,
tuning on 40m. Moved to 160m, had the Amp in Standby while I set the
power on the exciter. Heard a loud Pop - exciter power only.

I turned the Amp off for awhile, then tried it again. It still works
I opened it up looking for a visibly bad component, none found.

Any ideas what this might have caused a Pop in Standby? Should I worry?


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Richard L. Measures, AG6K, 805.386.3734.

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