[Amps] Grid fuses (was: Life and gain of 3-500Z)

[R L Measures]

On Jul 20, 2006, at 8:08 AM, Peter Voelpel wrote:

> Hi Mike,
>
> No wonder the resistors opened.
> At 100mA grid current there are already 0,27W heating them up. Most
> resistors are rated with their wattage at a 25°C environment.
> Grid current usually is one third of anode current in grounded grid  
> linears.
> I always directly ground all grids with wide copper straps to the  
> chassis
>

Are these wide straps non-inductive?
> 73
> Peter
>
> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps- 
> bounces at contesting.com] On
> Behalf Of Mike Schatzberg
>
> I believe what I tried at the time was about a 27 ohm 1/4 watt  
> resistor.
>
> What I found was that the resistor was very sensitive to grid  
> current peaks.
> The value that I selected for use with a pair of 3-500ZG triodes,  
> in an SB
> 220 amplifier, seemed to be very sensitive to slight over drive, or  
> so it
> seemed.
>
> The resistor would open circuit perhaps once in 3 months, while I  
> tested
> this system on the air in daily use.  I can only assume that high  
> current
> peaks caused it to open, I never heard any arcing or other anomaly  
> from the
> amp.
>
>
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R L MEASURES, AG6K. 805-386-3734
r at somis.org