[R-390] V509 runs hot

[David Wise]

I had intermittent jumps on mine too, which I traced to a bad mica cap.

V509 section B (pins 6-7-8) is the IF Cathode Follower.  According to the voltage charts, it has 185V on the plate and 4.3V on the cathode.  4.3V/390ohms is 11mA, giving a plate power dissipation of 181*0.011 or 2W.

The other triodes have essentially no plate power dissipation.

Now factor in the heater power.  Each 5814 receives 6.3V*0.45A or 2.8W .
Therefore V509 is dissipating 4.8W while V506 and V507 are dissipating 2.8W, so it is perfectly normal for V509 to be significantly hotter than the other two.

Dave Wise

>-----Original Message-----
>From: r-390-bounces at mailman.qth.net 
>[mailto:r-390-bounces at mailman.qth.net] On Behalf Of Robert Young
>Sent: Thursday, February 24, 2011 8:49 PM
>To: r-390
>Subject: [R-390] V509 runs hot
>
>
>Hello all again,
>
>I'm on a quest to find the intermittent volume jumps in my 
>R390A and finally got around to getting some of my stuff from 
>my storage space and pulling the radio out of it's cabinet. A 
>list member suggested it may be a cathode to filament short in 
>one of the 5814A's. I find that V509 runs MUCH hotter than the 
>other 5814A's in the IF deck, I subbed another tube for the 
>one that was there and it too got very hot quickly, is this 
>normal? The intermittent is quite difficult to isolate, at 
>first it was constant after warm up, it is now very sporadic 
>and only lasts a few seconds, for ex. it has only occurred 
>twice tonight in about 4 hours. If this question from a 
>beginner at trouble shooting an R390A is beneath you or you 
>think I am wasting band space please ignore it. (I had to add 
>that after my last controversy generating post).
>
>Thanks,
>
>Bob
>KB1OKL