[Amps] Ten-Tec 425 problem

[Gudguyham at aol.com]

In a message dated 6/13/2012 3:26:53 P.M. Eastern Daylight Time,  
4cx250b at muohio.edu writes:

bought a  Titan 425 amp about a year ago and have fired it up only 5 - 6
> times.  It has always worked fine with full output. Last week I fired  it
up,
> but when I tried to tune the amp, there was no plate current  or output. I
> keyed the amp several more times and tired to adjust for  output from its
> preset set dial values. Nothing happened, no plate  current and no output.
> All of a sudden, 'BANG' and the amp went  dead.
What you did was a big mistake.  As soon as you tried the first time  and 
saw no output the next thing you should have done is this.  Key the amp  with 
no drive, check for idle current (plate current) at the same time check to  
see if the HV meter drops down a little bit from standby to keyed.  if the  
HV does not go down a little bit then you are not getting HV to the tubes.  
 Shut the amp down at this point and find out why no HV on the tubes.   
Chances are you had a open plate choke (for some reason).  There are subtle  
benign tests you can do to point to the problem.  No idle plate current and  
no deflection of HV when amp is keyed is a sure sign of no plate voltage on 
the  anodes or completely dead tubes.  Driving the amp with no plate voltage 
on  the anodes would send the grid current into the 22nd centry.