[Amps] Titan Band Switch Arcing

[Wayne, W0ZW]

I am the owner of a Ten Tec Titan 425 amplifier (SN 1005) since about 2007.  It has been operating trouble-free on all bands 160 thru 10m.  The exciter is a Ten Tec Omni VII.  I utilize a Keying Loop circuit between the Titan and the Omni VII for QSK operation.  In series with the Keying Loop is an Array Solutions PowerMaster wattmeter which is configured to open the loop if an SWR greater than 2.5:1 is detected.  

<Long troubleshooting description follows... skip down to the end if you are just interested in my questions to the group.>

Description of the Problem

I recently fired up the amp on 10m (the band I had previously operated on).  I sent a series of test Vs and almost immediately the PowerMaster indicated an SWR fault and kicked the amp offline.  After placing the amp in Standby I repeated a series of Vs with just the exciter and the SWR was normal.  But retrying with the amp in Operate mode resulted in a repeat of the SWR fault.  I also heard the sound of arcing inside the Titan.  

Chasing Down the Cause

I suspected the RF vacuum relay (K4) as cause of the problem, even though energizing and performing DC continuity tests on the relay indicated low contact resistance on the NO and NC pins.  I replaced the original Jennings relay with an equivalent KiloVac vacuum relay from Nebraska Surplus Sales.  But when testing the Titan with the new relay installed I could hear the arcing sound again.  Interestingly, the SWR fault did not reoccur.  

Next I opened up the cabinet, defeated the interlocks and operated the Titan to see if I could locate the source of the arcing.  The source was immediately obvious.  It was arcing in one of the three sections of the Band select rotary switch (section S1C).  This particular section of the Band switch inserts or removes capacitors C14 and C15 in the tank circuit depending on the band.  The  rotating wiper on this switch is directly connected to the output of the finals (after the HV blocking caps).  

Next I attempted to clean the contacts on the Band rotary switch, focusing on section "C".  I liberally sprayed it with DeoxIT D5 contact cleaner and used lint-free cotton swabs and was able to remove some amount of black deposits.  Unfortunately, when I tested the amp again after the cleaning the arcing repeated.  In fact, I think it arced more energetically than before!

After much pondering, I realized that section "C" of the Band switch does not insert any capacitors in the circuit when 20, 15, or 10 meters is selected.  I decided to remove the wire connection between this switch section and the tank circuit.  Then I retested the amplifier on 10m to see if removing the switch section from the rest of the circuitry had any effect.  During this test no arcing occurred and the amplifier operated normally.  Apparently there is some defect in this switch section that is causing the arcing.  It is very difficult to see inside this part of the switch to try to eyeball the problem.  But it is apparent that something in there is not right.

So the next challenge is to repair/replace switch section S1C.  Given its location and the number of soldered connections, any repair is going to require some major disassembly.  

Questions

1.  It appears that each of the individual S1 switch sections (a, b, and c) can be disassembled from the other sections.  Is it possible to just remove and replace section "C" leaving "A" and "B" intact?  

2.  Whether just one section or the entire switch, what are potential sources for this switch?  Does anyone have a parts-only amplifier for sale?  Does anyone happen to have this specific Band switch available?  Where does one find a good Titan/Ten Tec boneyard?

3.  Ten Tec had this switch configured from some switch manufacturer when the amplifier was originally designed.  I would suppose a new switch or switch section can be specified, configured and purchased today.  Obviously this would be an expensive alternative.  Can anyone recommend such a manufacturer or supplier?

4.  Another possible solution is to rebuild the existing switch section.  I believe replacement switch components can be found.  This is probably the most tedious and labor intensive solution.  Also, I'm not sure if the HIPOT characteristics of the original switch can be guaranteed in a rebuilt switch.  Does anyone have experience with this solution?

I really love this old amplifier.  If this problem can be fixed I believe the amp still has a lot of life left in it.  Any help from the esteemed group would be greatly appreciated.  Thank you.

Wayne, W0ZW