>
>Hi there.
>
>I have a TL922 by Kenwood and the folowing happend to it:
>
>On Standby-Mode (after some minutes operation) I heard
>a loud "bang" . As I looked on the panel the IP-Meter was
>showing 500mA. Remember the Amp is set to STANDBY
>not to operate nor the PTT is hit.
The 922 occasionally oscillates at c. 120MHz. The oscillation
temporarily causes the tubes to conduct, thereby arcing the contacts of
the cathode bias relay. . Since the tank is a LPF, there is essentially
no load for the 120MHz energy - which runs amok and typically causes a HV
arc to chassis-gnd.
- note - see p. 14 of owners manual regarding ''normal arcing''.
Since the 3-500Z/8008s have high Mu, the grid current is large during the
intermittent oscillation. It is not uncommon for the emf produced by the
burst of grid current to bend the filament helix, thereby causing a
filament to grid short. If you find a damaged filament choke, this is
the likely reason. // Back to back 3A diodes across the meter movements
prevents the meters from taking a one way trip to Kaputsville. //
Changing the 922 to from V-cutoff bias to R-cutoff bias can save your
filament transformer from a meltdown in case one of the tubes shorts. .
>
>My guess was maybe a missreading so I pushed the PTT
>and sended out a short burst via mike. The Power meter
>showed that the AMP is delivering about 1000 watts as
>normal. Back to standby - the IP reading is still 500mA.
Weird science?. . If you have output, the tubes can not be shorted, so
there should be no Ip on standby.
>I turned the thing off.
>
Good news.
>Any Ideas what happend ?
>Anyone had a simular problem in the past ?
>I am also seeking for a Service Manual to
>download or faxpoll.
>
Thanks to Skipp, I have s 922 service manual. The ''troubleshooting
section'' is one page. .
cheers, Helmut
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