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

[R L Measures]

On Jul 20, 2006, at 7:07 AM, Mike Schatzberg wrote:

> Hello Amp Fans:
>
> I have experimented with "grid fuse", while investigating grid  
> equalization
> and trying to eliminate the need for using matched pairs of triodes.
>
> 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.

Mike S.: We use 30-ohm, 0.25W resistors as fuses and they will carry  
normal SB-220 grid current without changing value.  With serious  
mistuning, they will darken but remain intact.
Were your failed resistors slow-roasted, or did they just blow open  
suddenly?
>
> ...ilman/listinfo/amps
>

R L MEASURES, AG6K. 805-386-3734
r at somis.org