[R-390] Ballast Tubes in Shipment

[Jon Oldenburg]

I had 2 failures here on the 3TF7 ballast, one shortly after shipping & the second on a radio that had been in a rack for years. The original 1953 preformance reports basicly stated it was an overkill in using the  ballast regulater but in designing the radio for worst posible condition senairos it was left in. The 1953 design report is great reading to give insite to the eveolution of the R-390-URR into the R-390A. In my opinion use the tube if you have it, or insert the resistor. Any other mod should be well documented, but of course once your gone so is the documentation. I believe Noland's documentation of high hour 27/7/365 operation would suport the theroy of thermal shock failure. This is eveident to most of us as the  failure of a household light bulb, how many fail on power-up verses in use failure? Just rember that use of standby on modern line voltages increases filiment voltage so unless you use regulated power to your rack ( I used a 2-KW SOLA regulator for a number of years 115volts +- 2% untill my wife got sick of the noise) just shut it down  completly or go the 24/7 method. 

--
J.W.Oldenburg  AB9AH

"If you can't be a good example, 
then you'll just have to be a 
horrible warning."


-------------- Original message from Barry Hauser : -------------- 
> 
> I suspect failure-proneness may have to do with aging through use -- 
> filament becomes more brittle with more heating and cooling cycles? 
>