[Boatanchors] We do live in a solid state world

[Singley, Rodger]

To add a little to Carl's excellent advice:

One of the mistakes commonly made by newcomers to vintage gear using sweep tubes as linear finals is to try to extend tube life by running them at lower power.  This is a good idea BUT only if you load it to normal input and then reduce power through reducing drive.  If they are not loaded to normal output, then the screen current will soar and this is usually the most fragile element in sweep tubes.  If you own and use a lot of gear with these finals building a pulse type tuneup device would be worthwhile.  This provides a pulsed tone at full drive but with a low duty cycle to allow tuning with less stress for the rig and the operator.  Adding a cheap cooling fan is also an excellent idea to increase the life of these stressed out tubes.

I keep charts for all of my most used rigs and this makes tuneup very fast.  If I end up with settings far removed from the logged values then there is either a rig/antenna problem or (more likely) operator error.  I built my homebrew "big" linear amp with turns counter dials for the roller inductor and vacuum tuning cap and a 6 to 1 vernier for the load cap.  With this amp, setting to the logged settings is close enough since there is 2400 watts of available plate dissipation and a fast acting electronic protection circuit that takes it offline if any parameter goes outside of safe values.  For class C AM Carl is dead on correct concerning modulation quality (and also avoiding subjecting the mod transformer to unnecessarily high voltage spikes).

My two biggest shocks in recent radio history were a: at a club meeting a member brought in a miniature straight key Christmas tree ornament.  One of the new hams knew it was a Christmas tree ornament but had no idea what it was.  And B: Tuning and loading is a lost art.  I guess it shouldn't surprise me but it was so much a part of my Novice experience in 1975 since only a few rigs (like the Heathkit SB-104 and Signal One CX-7) allowed transmit without tuning.  I guess one of my current university students might be equally stymied by trying to cue a stylus to a certain point on an LP or loading tape on a reel to reel deck :)

Rodger WQ9E


-----Original Message-----
From: boatanchors-bounces at mailman.qth.net on behalf of Carl
Sent: Sun 9/19/2010 10:37 AM
To: Rob Atkinson
Cc: boatanchors at mailman.qth.net
Subject: Re: [Boatanchors] We do live in a solid state world
 
Ford has been over the top several times Rob, in print and on various 
forums.
With a Willie Billie 8 call sign he cant be expected to know very much about 
the "old days" except what he can read.

I certainly dont remember many amateur affordable commercial loads for open 
wire line or the ready availability of high power 300-600 Ohm terminators in 
the "old days" when I ran PP 250TH's. The common practice on AM was to tune 
up on a long winded gasbag such as W5PYT and it wasnt a quick process as 
today. First tune the various stages of the Viking I and then the input and 
output tanks of the amp.

These days DX list nets are a good place to tune while on CW there are 
always holes to be found except maybe in a contest.

These days I have a chart on each modern amp that lists dial settings for 
each band and mode as a start but it still requires a few seconds of carrier 
to be sure the grid current is safe and tweak the tuning. Adding another 
signal in the middle of a split frequency pileup isnt going to bother anyone 
(-;

For the boatanchor amps, and another Vking I or II, 32V2, etc,  it still 
takes a bit of time but similar charts are used to get close. What many fail 
to realize is that with Class C AM the tuning is critical for good 
modulation. Its also obvious that very few use a modulation monitor scope.

Try tuning an ART-13 into a dummy and then to an antenna and expect it to be 
proper.

I remember when sweep tube rigs arrived and most OT's tuned them like an old 
Class C rig, taking forever and cooking the finals on a regular basis. Its 
the same today with noobies getting into boatanchors and finding that new 
finals will cost them a good part of their  paycheck.....or welfare or 
disability check.

Carl
KM1H