Arcing Titan 425

[N3DRB The Derb]

the middle door knob has a huge zorch and I bet it runs all the way through the ceramic. Whomever did that work has not a clue of he nature of HV.

[flintstone mop]

I'm gonna try one thing before considering TenTec......I'll try to get a hot pencil type iron on the three doorknobs on S1B and get to the cold solder joints, THEN I'll get to the one dooknob, that I marked with red, on S1C, and solder the phillips screw term back on to the top. Can this cap get hot to melt solder?

I am familiar with the MFJ 'looking back' back into the tank. You have to disconnect the pubes and connect an equivalant value resistor to immitate the plate resistance.

Thanks for the tips. It will make RF one day.....well it does now, but with a little electrical show.

Fred

[Jim, W5JO]

I'm gonna try one thing before considering TenTec......I'll try to get a hot pencil type iron on the three doorknobs on S1B and get to the cold solder joints, THEN I'll get to the one dooknob, that I marked with red, on S1C, and solder the phillips screw term back on to the top. Can this cap get hot to melt solder?

I am familiar with the MFJ 'looking back' back into the tank. You have to disconnect the pubes and connect an equivalant value resistor to immitate the plate resistance.



Fred

You don't have to disconnect the tubes Fred.  Just hook the resistor across them to ground. 

If those doorknobs have been zorched or near one that has, then replacement of the zorched one is necessary.  A very thorough cleaning of the others is in order, including in all crevices.  Some of that zorch matter can be like the carbon tracks on ceramic switches.

When you finish, the thing should shine a much like a new baby's bottom as possible.

[WQ9E]

Jim is correct, the tubes need to be in so that their output capacitance remains in the circuit.  It doesn't make a whole lot of difference on the low bands where significant plate tuning capacitance is used but it will throw the results way off on the upper frequencies if you have tubes with a fair amount of output capacitance.

Given the price of 3CX800 tubes I would seriously consider getting those other door knobs out and getting them to someone who can "hipot" them.  When the zorch event happened you could very well have collateral damage and until you test you won't know whether hidden damage in one is likely to also cause damage to your new components.

I would also take a look at the RF choke on the output side (used to create a short to ground for DC appearing on the output tank) to make sure it wasn't damaged.  I have seen these chokes develop internal shorts across a number of their turns after other amp pyrotechnics and this will create some very odd tuning behavior.  They are pretty cheap so if there is any question replace it since it is also a safety device.

Rodger WQ9E

[flintstone mop]

Believe it or not I was able to get to the cold solder joints and soldered the philips terminal back onto the the doorknob cap. From my reading, the plate impedance for a 3CX800A7 is 2.7K. There are two in parrallel sooooo, take one half of that 2.7K?
I would like to connect the MFJ259 looking into the Plate Tank to investigate the fully unmeshed TUNE variable cap in the 160B for the upper end of Top Band. 1880 to 2.0Mhz

Thanks..I"m trying to take a stab at this before sending it to TenTec.

fred

[Jim, W5JO]

Believe it or not I was able to get to the cold solder joints and soldered the philips terminal back onto the the doorknob cap. From my reading, the plate impedance for a 3CX800A7 is 2.7K. There are two in parrallel sooooo, take one half of that 2.7K?
I would like to connect the MFJ259 looking into the Plate Tank to investigate the fully unmeshed TUNE variable cap in the 160B for the upper end of Top Band. 1880 to 2.0Mhz

Thanks..I"m trying to take a stab at this before sending it to TenTec.

fred

Plate load impedance is roughly 2 times the plate voltage Fred.  Or if you want, EP/2 X IP or as the old book say, EP/1.8 X IP

Be very sure everything is CLEAN and TIGHT before you fire it up.

[WQ9E]

Fred,

Are the tubes operated in Class B in the 425? If so then the load is voltage/1.57 times plate current.  For AB1 approximate value is voltage/1.4 times plate current.  This load is based upon the total current so just calculate this way rather than considering the number of tubes.

Rodger WQ9E

[Jim, W5JO]

Fred,

Are the tubes operated in Class B in the 425? If so then the load is voltage/1.57 times plate current.  For AB1 approximate value is voltage/1.4 times plate current.  This load is based upon the total current so just calculate this way rather than considering the number of tubes.

Rodger WQ9E

You are right Rodger, I am thinking AM (class C).  This isn't. 

[WQ9E]

Jim,

This is more of a class C board 

Rodger WQ9E

[flintstone mop]

The manual says class AB2.
I've had enough play-time. Contacting TenTec tomorrow. Everything looks better with some soldering but S1C still arcing under full power.
I did the MFJ259 looking into the Tank and it is happy. The TUNE cap is now about 3/4 mesh for tuning 1985.
Thanks for the great tips and reminders how to use tools already on hand.

Fred

[K6JEK]

Don't be so shy about calling TenTec.   Every time I've called them they've given me right on the money free advice.   They have a lot of experience with the 425.   When I had a 425E and blew it up by routing the output of my class E into the the input of the Titan and then keying everything up, there was a fellow (I can't remember his name) who on series of phone calls led me through diagnosing the damage.

I got it working again.  They sure made a fan out of me.