>
>>>The ITT Mackay Marine MRU-60 was a shipboard transmitter manufactured
>>>in the 1980s. It contained a 100 mW solid state exciter, a broadband
>>>100w solid state driver, and an 8877 PA. As I recall it covered 2 to
>>>30 MHz, and did not use a parasitic suppressor. I do not know if it
>>>suffered from high 8877 mortality rates. It made a lot of noise
>
>>
>>What kind of noise?
>>
>
>Well, let's see... it made a big CLUNK when the contactors kicked in,
>then the high pitched whine of the exciter/driver fans could be heard,
>followed by the sound of the blower in the PA coming up to speed.
>
>Like I said, it made a lot of noise. But I never heard it make a big
>bang, if that's what you're wondering :-)
>
For some seemingly esoteric reason, 8877s and other tubes with a
gold-plated, molybdenum grid make little noise when they sustain a
parasitic. Sometimes an arc can be heard just before the electric mains
circuit breakers open. Perhaps the resultant cloud of gold-vapour in the
envelope absorbs the electrical energy that would otherwise have produced
a big-bang?
- High-speed blower noise is pretty typical in commercial amplifiers
since they tend to be designed by engineers who use manometers and
actually read the electron tube mfg's spec sheets.
cheers, Doug
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
end
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