>
>
>
>Gentleman, could Han's problem not be a huge SWR on the output of the
>tube, unrelated to anything more exotic?
>
>Ian ZS6BTE
>
A too-huge SWR is indicated by the Loading-capacitor being at one of its
stops when the amplifier is tuned up.
>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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>
>
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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