This is a commom problem with TT QSK amps.
You can replace the Kilovac K41C234 relay with a RJ1A relay. The RJ1A is
available on surplus market for as little as $35. I can supply .JPG photos
of the relay replacement in a Titan Amp, which may assist you with your
Centurian. Replacement will require reconfiguration of the relay driver
board for 26 volt operation by removal of a resistor.
Alternatively, you can affect a short term repair of the K41C234 relay by
removing it from the amp., wiring the coil in series with the NC contact,
and applying 12 VDC to the series combination for a short period of time.
This will cause the relay to oscillate and pass current through the 'RECV'
contacts (NC) and cleanse them. This is only a temporary cure...see the
explanation below. The following is an explanation, which I have posted to
this reflector several times.
Relay Contact Failures:
Relay manufactures design the contacts of their relays for specific
applications. Relays generally carry an application rating such as 'Make &
Break Load Switching', 'No Load Switching', 'Make Only Load Switching',
etc. The selection of the proper relay for a specific application is
crucial to the life of the relay and it's performance in the circuit.
Relays rated as 'Make and Break Load Switching' depend upon current flow
through BOTH the normally closed AND normally open contacts in order to
maintain a specified minimum contact resistance over the specified life of
the relay. Use of such a rated relay in a circuit where no current flows
through either the NC or NO contacts can cause contact resistance to
increase over time and the relay will eventually fail to provide circuit
continuity through the contacts. This is sometimes misinterpreted to be a
sticking relay armature problem.
Use of such a relay in an QSK amp where "hot switching" is prevented by
circuit design but also no current flows through the NC contacts (on
receive) will eventually cause these symptoms to occur, usually identified
as "no signal or a greatly attenuated signal on receive". Rapping the relay
may cause the symptom to disappear (for awhile) and is often interpreted as
a sticking solenoid versus a contaminated NC contact. A better choice for
such an application would be a relay whose contacts are rated as 'No Load
Switching'.
The specifications on the K41C234 and RJ1A relays may be obtained from the
Kilovac www site at: http://www.hv-relays.com/home.htm. Pay attention to
the ratings for the K41C234, which is rated as 'Make & Break Load Switching'
while the ratings for the RJ1A are for 'No Load Switching', a far better
choice for the application in TT amps. since no current flows thru the NC
contacts during receive.
73, Dave, K1FK
Fort Kent, ME
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