[Amps] 813 No parasitics

[rlm]

I would think so.  However, there have been more than a few reports of 
this occurrence with solid-state radios.  Perhaps the reason is that 
Chebyshev and Butterworth band-pass filters used in solid-state 
transceivers contain series capacitances which may short under a voltage 
transient, thereby delivering energy to the final transistors.  On the 
other hand, tuned input Pi-network capacitors are in parallel with the 
signal path, so a short to ground would seem to stop energy from entering 
the radio.  

>Okay, I'll buy this one. But I have a question. Wouldn't the low pass
>filters in the radio have some effect on reducing higher frequency
>energy from getting at the PA?
>
>Martin
>
>
>-----Original Message-----
>From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]
>On Behalf Of rlm
>Sent: 18 March 2003 20:17
>To: Tom Rauch; AMPS
>Subject: Re: [Amps] 813 No parasitics
>
>
>
>
>>
>>> Ok, you asked Skip; but let me suggest or better saying, ask, could 
>>> be the 30 MHz highest frequency for full ratings?, or maybe at lower 
>>> ratings you could have parasitics also?.
>>
>>As a general rule the most difficult to stabilize tubes are tubes with 
>>low upper frequency limits. The grid and anode leads inside such tubes 
>>are usually thin and long.
>>
>The 811A & 572B being examples.  On the other hand, G-G triodes with a 
>low-L grid that have substantial VHF gain can also become squirrely in
>HF 
>amplifiers.  The 3cx1500A7, 3cx3000A7 and the 3cx6000A7 are examples,  
>This week, I heard about a 3cx6000A7 amplifier project that was being 
>driven directly by a FT-1000D.  The amplifier made a bang.  At the same 
>instant, the finals shorted in the 1000D.  The lesson: a G-G tuned input
>
>circuit not only acts as a low-pass filter to keep VHF harmonics out of 
>the amplifier,  it acts to keep VHF energy from the amplifier from 
>travelling back into the radio and causing a problem.  
>--   Amplifier engineers would do well to pay attention when the 
>technical specification sheets say "Maximum Ratings for Amplifier and 
>Oscillator Service".  
>
>-  R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K, 
>www.vcnet.com/measures.  
>end
>
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-  R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K, 
www.vcnet.com/measures.  
end