Re: Wicked intermittant Amplifone (Ampliphone) issue

On Wed, May 11, 2011 at 2:28 PM, pj pj <pj1@shaw.ca> wrote:

>
> I was thinking warm like not lukewarm but warm like uncomfortably core
> being heated by some inductive heating issue oversaturation warm.
>

>From your description, it sounds normal. In operation, it's normal to get
very warm to hot.

> JR suggested running the heater off an isolation transformer, so I'll try
> that at the same time using a separate adjustable supply that I can ease the
> filament voltage up a bit to see if that will trigger the event (I had such
> an issue back with a G07 on a really bad tube).
>

That's ok if you have an H-K short, which is the most likely if you have any
short in the kine. You mentioned a short to a grid. Rodger can comment on
how likely that is, but if that's what you have, depending on which grid it
is, isolating the heater will raise all of the heater circuit to the grid's
potential. If it happens to be the focus grid, it could get messy. Be
careful.

> The 3 focus block connections were redone when I overhauled the board,
> wrapping the leads around the terminals. I used Ag/Sn/Cu solder I use for
> high power RF joints on these specifically since I felt it couldn't hurt.
>

It never hurts to check. No need to re-terminate if you've already done it,
but just pull the boots back for grins.

> the deflection sensitivity was much higher, which likely meant that the HV
> during the episode was probably way low.
>

That's logical. The question is, is it low because the (HV) power supply is
putting out too low a voltage (bad PS), or is it low because the tube is
drawing too much current from the supply (bad tube). The PS can only source
a very small current, on the order of uA's, so it wouldn't take much to drag
it down. The easiest way to check is measure the voltages, disconnect the
anode and the kine and measure the voltages again.

If you disconnect the kine, be sure to disconnect the anode. Legend has it
that leaving the anode connected can damage the tube. Again, Rodger can
editorialize.

Your subject includes the word "intermittent". How often does this happen,
and for how long?

Still didn't catch your name.

Thanks,
-Mark

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Received on Thu May 12 03:23:32 2011