>
>On Mon, 20 Apr 1998 17:56:30 +0100 Peter Chadwick
><Peter_Chadwick@mitel.com> writes:
>>>The way I was taught is that you key the amp with no drive and vary
>>the
>>caps all around and look
>>>for a kick in the plate or grid current.
>>
>>Also decrease the bias so the tube is running a fair bit of plate
>>current -
>>say 1/3 to 1/2 rated dissipation so the gm is high.
>
>If the air flow is available I run to almost full rated
>dissapation....why play around? Once I ship an amp or a repair I prefer
>to not see it again.
>
>>
>>Then if it's stable unloaded, as Carl says, it should be OK. Unless
>>(until?), of course, after time on 10 metres, the suppressor resistor
>>cooks and goes high, and the parasitics appear.
>
It seems to me that even a 100% increase in Rs would not make much
difference in the performance of a VHF parasitic suppressor.
>With overstressed 2W carbons for R, I agree. But with 5W metal oxide
>available at a fraction of the cost of 2W carbons why not change when the
>cover is off? If you want to spend the time measuring the R of an
>antique, why not just upgrade at the same time? I dont even bother
>wasting my time to measure the old ones any longer.
>
Is it a waste of time to measure the resistance of a seemingly-critical
resistor? . . There are two types of damage to Rs. It is my opinion
that when there is cosmetic damage and less than a 50% change in
resistance, 28MHz operation is usually the reason. However, if there is
little or no cosmetic damage, and a large increase in resistance, higher
frequency energy is the culprit. .
cheers
Rich...
R. L. Measures, 805-386-3734, AG6K
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