First I'd have concern that using a Variac to bringing the voltage up slowly
would also bring the heater voltage up slowly and the blower voltage up
slowly. In summary, not good as far as circuit tests go, but might identify
a direct short such as a bad diode string or a shorted filter cap.
The bang was/is most likely caused by a HV flashover. Generally, not in the
tubes. In general, if the tubes are tetrodes, then removing anode voltage
and not removing screen voltage can cause instant tube failure.
Open the case, be sure all HV is discharged safely and then look for black
charred lines on circuit boards, around transformer terminals, burn spots
and burn marks between any two points. A good visual inspection is
required. I've seen and heard transmitters go BANG when a bug flew into the
system and landed across a HV terminal (fatal on the bug) or even a build
up of dirt caused a flashover. In general , no harm caused, just time for a
good cleaning.
A simple in circuit check of all HV capacitors with a ohm meter might give a
clue. Also a check of all diodes using the diode test mode of a DVM is also
worth the time. With everything in place measure from the anode of the
tubes to ground. Should see the bleeder resistance, what ever that value
should be. Anything lower will require further investigation.
Good luck
73
Bob, K4TAX
----- Original Message -----
From: "Bill Turner" <wrt@dslextreme.com>
To: "ON4MA Marc" <marc.wullaert3@pandora.be>
Cc: <amps@contesting.com>
Sent: Saturday, October 18, 2003 12:53 PM
Subject: Re: [Amps] a BANG in the AMP ?
On Sat, 18 Oct 2003 13:52:33 +0200, "ON4MA Marc"
<marc.wullaert3@pandora.be> wrote:
>My question is ,wat caused
>the bang ?
>bad tubes ? How could you check the tubes ?
_________________________________________________________
Start by removing the tubes, or by disconnecting the anode connectors.
If the "bang" no longer happens, re-connect the anodes one at a time.
When the bang reoccurs, you have your answer.
If you have a variac, use it to bring up the AC mains voltage slowly
while monitoring the current. Saves fuses. :-) You don't have to use
a 240 volt variac either; a 120 volt one should give you enough
voltage to answer the question.
I have a Commander too, and one thing to beware of is a replacement
fuse holder. The original fuse holder is pretty short, and if was
ever replaced with a longer one, one of the end terminals can touch
the frame of a nearby transformer when it is reassembled, and that
will also give you a "bang". This problem could be intermittent if
the terminal is just barely touching.
Don't ask me how I know. :-)
--
73, Bill W7TI
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