The 811H of course runs 811's.  But you can swap them out for 572B's, which 
are more rugged.

The thing you have to be careful with the 811's is plate dissipation.  The 
tubes are rated for 65-watts average plate dissipation.  This is fine in SSB 
operation, but is more damaging to the tubes if you push them on heavier 
duty cycles like CW, RTTY, etc.

A lot of hams have issues with those amps if they spend too much time 
tuning.  You have to let the amp rest for about as long as you apply a 
carrier to bring the average plate dissipation down.

Another bigger issue today is the quality of the 811A tubes.  Some 
manufacturers aren't keeping the quality up.

Steve, K8SP


----- Original Message ----- 
From: "Phil Scovell" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Sunday, April 27, 2014 8:34 PM
Subject: Re: Re 811H


> Mike,
>
> That's about what I thought it would run.  I just was curious because a
> friend has one but he pushes his much harder than you do and has to buys a
> round of tubes more often than needed.  I believe he actually bought 4 of
> the 572B  tubes and then he didn't push it so hard because he didn't want 
> to
> keep buying tubes.