[Amps] 3-500 tube question

[R.Measures]

On Jul 3, 2004, at 9:01 AM, N7uvh at aol.com wrote:

> Hi guys..great reading.
>
> I have a sb220 with the original tube Eimac 3-500z.   I think i have a=20=

> short
> in one tube.  Keeps cooking the rf chock on pin 4 of tube to ground. =20=

> So what
> I am wondering if it is ok to buy a 3-500ZG   to replace it.

=F0  Yes, Patrick, but the grid to gnd chokes should be replaced with=20
fusable resistors to protect the tubes.  Also, the grid bypass C should=20=

be increased by c. 1000pF per socket.  The suspect tube should not be=20
discarded unless a grid/filament check with a high-potential tester=20
confirms that the breakdown is <5kV. Better parasitic suppressors might=20=

help.  An article on my Web site describes problems & fixes with the=20
SB-220.
>
> thank you
> n7uvh  (first time in a amp)
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org