[Amps] What Do you think?

[Jim Thomson]

Date: Thu, 8 Sep 2016 21:44:18 +0000
From: Bill Turner <dezrat at outlook.com>
To: Amps group <amps at contesting.com>
Subject: Re: [Amps] What Do you think?

Something is wrong with the numbers. 3500 V at 500 mA is 1750 watts DC
input. If you were measuring 1500 watts RF output, that would be an
efficiency of about 86%, which is impossible with a class AB linear
and highly unlikely even if operated class C. 

I would recheck the meter calibration before buying. 

73, Bill W6WRT

##  I agree, something is amiss...and it might be the B+ meter...and /or the
plate current meter.   You could temp place a fluke DVM  in series 
with the existing analog 0-1 A meter to get an accurate p;ate current reading. 

##  Most of those  0-1 A dc ammeters are fairly accurate.   The B+ meter
could easily be out to lunch... typ caused by using carbon comp resistors 
in the series string for the B+ multiplier..for the B+ meter.   They will typ drift
30% on the high side.   That means your B+ meter  will be reading way down
on the low side of the actual B+ voltage. 

##  The other concern is the tubes, and availability. Half decent 4-1000s   are rare. 
3-1000 Zs  are very rare.   If  4-1000s  used, typ no load B+ is 4800-5500 vdc. 
They require a lot more drive than a 3-1000Z.   3-1000Z  sucks a lot more idle current,
and requires more bias vdc. 

##  If it has  2 half decent tubes in it, plus some spares, you are probably ok.   Any Single 
3-1000 Z or  4-1000  will do an easy 1800-2000 w pep out.   Any 2 x holer, with 200 w
of drive should be aprx 4-5 kw out... provided the xfmr is big enough.

##  the B+ meter would be easy to fix, if outa whack, just use the correct resistors for the string.

Jim   VE7RF