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

[Peter Voelpel]

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

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.