[Amps] Amps Digest, Vol 168, Issue 98

[Steve Wright]

On 27/12/16 06:00, Paul Baldock <paul at paulbaldock.com> wrote:
> I have a home brew GS-35B amp built around 5 years ago. I run about
> 4KV on the plate. I purchased 2 NOS tubes at the same time. Initially
> when I built the amp I needed around 40V of bas voltage for idle
> current of about 120mA. Over the next few years, and with little use
> the idle current gradually rose and I gradually increased the bias
> voltage to compensate and about a year ago at maximum available bias
> voltage of 54V the idle current was about 200mA. At this point I
> replace the first tube with the second tube, set the bias voltage at
> 40V and had an idle current of 110mA. Now a year later the idle
> current has crept up to 200mA (at the same 40V bias).

4KV is a fairly typical Va for GS-35b designs, but for amps that do a 
lot of hours - I wonder if that is smart.

The GS-35b is a widely abused tube - just everyone wants to buy a $99 
tube and put 5KVA into it - perfectly possible for a little while as 
long as your leaf blower doesn't drop a piston.

You are a little light on details with regard to hours, drive, output, 
and bands of operation - probably for a good reason.  ;)

Steve