I had a similar problem with a Heath SB-220 on 10 meters. Turned out I did
not have the loading control advanced enough by far.
Regards, Mike N4NT@chartertn.net
----- Original Message -----
From: "Ian Roberts" <ITR@Nanoteq.co.za>
Cc: <amps@contesting.com>
Sent: Thursday, August 10, 2000 4:46 AM
Subject: Re: SV: [AMPS] SB1000 parasite question for Tom and Rich+
|
|
|
| Gentleman, could Han's problem not be a huge SWR on the output of the
| tube, unrelated to anything more exotic?
|
| Ian ZS6BTE
|
| sm5ki wrote:
| >
| > How can a new 3-500Z tube, pushed to around 250 watts output, power
glow?
| >
| > How can two different new tubes behave in exactly the same way?
| >
| > And if the tubes are weak as the owner says, they should draw low
current
| > and not glowing at all?
| >
| > Is this not an indication the problem is in the amp not the tubes? My
| > swedish made copy of the COLLINS 30L-1 had glowing 811s on 80 when the
| > tubes were at the same time selfoscillating on around 50 MHz. Could this
SB
| > 1000, if it has parasitics, behave in the same way?
| >
| > The reason could be the parasitic choke changed value due the
temperature
| > effects or capacitive coupling beetween the filament bifilar choke and
anode
| > on the higher bands?
| >
| > If the zener is shorted, the tube draws more zero signal current and has
| > higher small signal gain. The chances for a parasitics to start is thus
| > higher especially when the new tubes have higher gain at the parasitic
| > frequency.
| >
| > That his SB 1000 has a broken ceramic switch may, of course, be an
| > indication that something is wrong causing the problem?
| >
| > Maybe he did not burn-in the tubes long enough?
| >
| > How are the chances the parasitic has now ruined the new tubes cathodes?
| >
| > This amp is in another city some 500 kilometers from the home QTH and I
had
| > no chance to see the amp and help my friend with the problem.
| >
| > These two EIMAC tubes were taken out of sealed cartoons and they were
thus
| > new and looked very much unused.
| >
| > Tnx in advance fellows and 73s de Hans SM5KI
| >
|
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