[Vintage-Audio] Scott Amp Goes Pop!

Sun Sep 1 05:50:05 2002

Also, Duane,  when they threw the box containing your precious tubes into
numerous trucks and bins, well...  I am not gloating just giviing my 2 cents
worth.
RR
----- Original Message -----
From: "Duane Fischer, W8DBF" <[email protected]>
To: <[email protected]>
Sent: Saturday, August 31, 2002 6:48 PM
Subject: Re: [Vintage-Audio] Scott Amp Goes Pop!


> Rudy,
>
> It is possible that the rectifier tube did receive enough natural (ins
pite of
> excellent packing) vibration during transit to cause an internal short.
However,
> I may be in error here, but because the tube had only a maximum of three
seconds
> of power I doubt it had adequate time to even be a factor in this
equation. I
> suspect the resistor itself simply failed without outside assistance.
>
> There are enough technically gifted people on this list to know for sure
if the
> time power was present was sufficient for a shorted rectifier tube to
cause this
> resistor to explode.
>
> Gentlemen?
>
> Duane W8DBF
>
>
> ----------
> From: Rudy Rutenber <[email protected]>
> To: [email protected]
> Subject: Re: [Vintage-Audio] Scott Amp Goes Pop!
> Date: Saturday, August 31, 2002 9:30 PM
>
> Duane,
> I am quite sure the rectifier tube is shorted.  If you have not fixed it
> yet.  I would just replace the resistor and the tube, then bring up the
> power slowly with a variac.  Sorry I am not in MI.
> Rudy
>
> ----- Original Message -----
> From: "Duane Fischer, W8DBF" <[email protected]>
> To: <[email protected]>
> Sent: Saturday, August 31, 2002 5:05 PM
> Subject: [Vintage-Audio] Scott Amp Goes Pop!
>
>
> >
> >
> > Hi All,
> >
> > I am in Glint, MI Genesee Township. I have a H. Scott LK-72b stereo
> amplifier.
> > It was just recapped and completely gone through by a friend in CA. He
> burned
> > her in for four or five days with no problems.
> >
> > It was very well packed, padded and cushioned when UPS made the transit.
> No
> > problems there. All of the tubes were shipped in a separate box.
> >
> > Everything appeared fine. I plugged the four 7591a into the proper
sockets
> being
> > certain to match the correct tube to the correct socket. The bias was
> already
> > sset. I plugged the rectifier tube in. I checked all other tubes to be
> sure they
> > were properly seated. Everything was as it should be.
> >
> > I plugged the H. Scott LT-110 FM tuner into the unswitched power outlet
on
> the
> > back of the amplifier. I did not turn the tuner on! I connected the
> speakers,
> > being certain that the jumpers were set for 8 ohms. Speaker polarity was
> > correct.
> >
> > I connected the FM tuner output to the FM tuner input on the amplifier
> input
> > side. I connected an antenna to the FM tuner.
> >
> > I then plugged the amplifier into the wall outlet. I turned it on.
> >
> > I heard a soft hum immediately from the right rear of the chassis. The
> amplifier
> > and tuner have no cases, by the way. The big power transformer is
located
> here.
> > This hum was NOT from the speakers, some six feet away. It was
immediate,
> no
> > warmup time involved.
> >
> > About two seconds after I turned the amplifier on, I heard a sharp pop,
> heard a
> > sizzling sound and instantly shut the power off. (I still had my left
hand
> on
> > the on/off switch). I was bent over the amplifier.  I smelled burne
> components
> > at this time.
> >
> > I immediately disconnected the line cord, unplugged the tuner, unplugged
> the
> > tuner input cable from the amplifier and disconnected the speakers.
> Although I
> > smelled no smoke at this time, I still carried it outside and set it on
> the
> > concrete sidewalk just in case.
> >
> > The fuse did not blow.
> >
> > The only visible damage was a large resistor to the right of the
rectifier
> tube.
> > The side was blown right out of it.
> >
> > As far as I know, there was insufficient time for B+ to be present, as
the
> > rectifier tube had not even warmed up. This blew in no more than two
> seconds
> > after power was turned on.
> >
> > I need somebody in MI with experience who is willing to examine the
> amplifier,
> > determine the problem and repair it. I have the service manual and
> schematic.
> >
> > If you are willing and able, please contact me by e-mail. Thanks!