[R-390] 5AR4 Clarification

[Perry Sandeen]

List,
I probably wasn't clear enough about my R388 rectifier tube placement. 
Jim Whartenby  was confused by my remarks.  I didn't mean to imply that there had been a location change of the rectifier replacement.
Jim disagreed with my technical belief of heat damage.  I stand corrected that the 5V4 has a cathode sleeve.  My Boo Boo.
>From personal experience I've purchased a R388 that had a melted and failed power transformer for a very small price that included a replacement transformer.
I now have 3 R388's which two are for rehabbing.  The one top cover I have schematic is totally unreadable as the whole inside top  cover is almost totally black from overheating but it doesn't seem to be from the power transformer that has partially melted on to the chassis.
even if the Xformer is still good, removing the tar requires removing the power transformer-no easy task and then removing the chassis tar. Another difficult problem.
I found from experience that the funcky top cover does work as a RF shield.  So I've got two to fabricate.
My preference for the 5AR4 is that it is smaller thus making the r388 chassis cooler.  As it's and indirect heated cathode, the rise in B+ is slower making for less stress on the filter capacitors.
Which on that point, the modern "con brothers", Nichi, Ruby, Chem, and others make light years superior filter caps.  Some electrolytics are rated for long life at 105C.
As far as  surge protection being useful, almost every PS circuit that one sees relates to some type of thermistor used in the A/C power line. 
But everyone is entitled to their personal opinions. 
Thanks for your comments Jim. I hope I've answered your question.
Perry KM6FQV

|  | Virus-free.www.avast.com |