Re: Wicked intermittant Amplifone (Ampliphone) issue

----- Original Message -----
From: Cinelabs Info <cinelabs.info@gmail.com>
Date: Wednesday, May 11, 2011 9:29 am
Subject: Re: VECTOR: Wicked intermittant Amplifone (Ampliphone) issue
To: vectorlist@vectorlist.org

> P.S. To answer your other question, after a few hours under
> normal operating
> conditions, it's normal for the flyback core to be warm. Unless
> by "warm",
> you mean it was glowing orange.
>
>
>
> On Wed, May 11, 2011 at 11:24 AM, Cinelabs Info
> <cinelabs.info@gmail.com>wrote:
> > The most common cause of the symptom your described is the
> screen and/or
> > focus wires fraying, oxidizing or breaking underneath their
> boots on the
> > focus assembly.
> >
> > For starters, I'd pull back the boots, cut, strip and *TIN*
> the focus and
> > screen connections, then re-terminate them on the focus
> assembly. I would do
> > this, even if the "look" good. Ensure there are no sharp
> points left after
> > your final cut.
> >
> > You might do one wire at a time, just to ensure they don't
> accidentally get
> > swapped.
> >
> > Also check the connection to the flyback, but this is usually
> ok, as it was
> > re-terminated during the most recent installation of the
> flyback itself.
> >
> > After that, you would need to supply voltage readings (i.e.
> anode, screen
> > and focus) for further diagnosis.
> >
> > I don't think I caught your name, or you forgot to sign your
> post. What's
> > you name again?
> >
> > Thanks,
> > -Mark
> >
> > On Wed, May 11, 2011 at 12:39 AM, pj pj
> <pj1@shaw.ca> wrote:
> >
> >> Hi All,
> >>
> >> I have an interesting one that makes you go "OH $%#&".
> >>
> >> Having been awhile , I flashed up my starwars and after a few
> hours of
> >> running normally, I glanced at the screen, and found a super
> bright,>> swollen, out of focus and light greenish game display,
> with the game
> >> running.
> >>
> >> Since the tube had a deflection loss sometime in the past,
> there already
> >> was a small burn spot, but now its' a lot worse
> (<1/4"). I installed a
> >> Cinelabs transformer in the past to replace a dead/red, which
> I checked
> >> almost right after I powered the game off, and found the
> ferrite core warm.
> >>
> >> Cautiously restarting the game with the screen down, I slowly
> brought the
> >> control up with a cross hatch, and it did the same behaviour
> again, with the
> >> brightness up.
> >>
> >> I'm wondering if I have a bad rectifier in the transformer, a bad
> >> focus/screen resistor block (connections are fine), or a tube
> with an
> >> intermittent H-K short. The 24V regulators are fine and
> have mil-spec metal
> >> power resistors replacing (as in Andre's rebuild) the
> regulator bypass ones
> >> now mounted to the main heatsink and the board was fully rebuilt.
> >>
> >
> >
>

I was thinking warm like not lukewarm but warm like uncomfortably core being heated by some inductive heating issue oversaturation warm. I'll tear into the drive waveform this weekend and snap a pix.

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).

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.

I'm wondering has anyone ever seen what a heater/cathode or heater to grid short would on an Amp look like? One thing that came to mind was that when it did this, the deflection sensitivity was much higher, which likely meant that the HV during the episode was probably way low.

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Received on Wed May 11 15:28:44 2011