[Amps] Reducing Ameritron AL-800H blower noise?

2 2 at vc.net
Mon Jan 27 05:27:41 EST 2003

>>2 wrote:
>>> Gold sputtering is caused by vhf/uhf parasites.
>>>Overdriven at HF can not cause gold sputtering.  AT UHF, maybe.
>>How do you know that? If there is a difference due to frequency, what is 
>>the physical reason for it?
>**  note: The "letter about parasitics" Mr. Foote refers to mentioned 
>that the resistance of the 8875s; VHF parasitic suppressor resistors had 
>changed from 100-ohms to over 400-ohms in a period so brief that the 
>outside of the resistors showed no sign of overheating.  Richard Kaller, 
>W7MOI suggested that such a phenomenon might be caused by a brief VHF 
>parasitic oscillation because each resistor was virtually shorted at HF 
>by c. 0.07uH of L..
>  In a telephone conversation, Mr. Foote said that the gold sputtering 
>problem was encountered during the 8877's development.  After autopsying 
>a leaky tube, the 8877 project engineers concluded that thin layers of 
>gold were evaporating during brief bursts of a high frequency oscillation 
>condition.  I agree since I have seen this problem in a number of 
>autopsied 8877s.  My guess is that the frequency of oscillation could 
>well be above 300MHz, where the 0.1pF of feedback is c. 53-ohms.  
>  To address your question:  Considering that the stored energy in a 
>typical amp's filter cap is c. 150-ohms,  ... ..

Bozo Alert:   This should have been 150-Joules.  sorry

-  R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K, 

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