[R-390] R-390A ballast replacement

[Bob Camp]

Hi

As I have said before the tubes are the last thing we are going to run 
out of on the R-390A's. They are a glut on the market. With a properly 
sized series resistor the inrush current into the tubes on the ballast 
tube string will be significantly less than on the other tubes in the 
radio. Opinions vary widely about just how important this is.

There is a lot of data on the care and feeding of large transmitting 
tubes. There is not much real hard data on receiving tubes. Certainly 
they do wear out from inrush related issues. They also wear out from a 
lot of other causes. The inrush stuff mainly causes the filament to go 
open (or rarely short) circuit. That makes an inrush failure fairly 
easy to spot. I can't say I have seen a lot of dead receiving tubes 
with open filaments. I don't think I have ever seen one with a straight 
shorted filament. They seem to go from low emission or gas long before 
the filament opens up. Obviously this relates to how long you leave it 
on each time you turn it on. Somebody who turns the radio on and off 
ten times an hour is going to have very different results than the guy 
who leaves it on 24/7.

I have no particular problem with putting solid state stuff into 
radios. I do have a problem with putting it in when there are other 
equally good alternatives. I also can see no logic to putting it in 
when it degrades the operation performance of the radio. If you are 
going to put in a solid state ballast then put one in that does a full 
wave process with a couple of mosfets rather than diodes. That gets 
away from the noise issue. It also gets the complexity up there quite a 
bit. I have seen assembled versions for sale in the several hundred 
dollars price category. If it's going to double the price of the radio 
a gizmo better do a lot more than a two dollar (at most) fixed resistor 
....

	Enjoy!

		Bob Camp
		KB8TQ


On Feb 12, 2005, at 11:59 AM, charles bolland wrote:

> Bob,
>
> So what you are saying is that the resistor that I
> now have installed
> is good enough?  I was worried about wear on the other tubes with 
> turning
> the receiver on etc.