SV: [AMPS] Band Switch arcing SB-1000/AL-80

[sm5ki]

I remember I had a destroyed 160 meter switch contact in the SB 1000 I built
years ago because of arcing. Maybe the fault is built in in this linear?

By the way, whats wrong running the 3-500Z in IVS for 1000 watts out in this
amplifier?  How much are the distorsion products increasing when overdriving
the 3-500Z slightly for 1000 watts out? Has anyone measured this? I believe
most transistorized exciters ( not the ones using 28 volt transistors I
think ) still determine how much distorsion you get? I remember Rich did not
like the idea but they are running many amps using 8874, 8875 and 8873s in
IVS and exceeding the maximum anode current of, isnt it, 0.35 amps/ tube. 

Prosit de Hans SM5KI

>Från: measures <measures@vcnet.com>
>Till: "Jim" <jdc@ieway.com>, "AMPS" <amps@contesting.com>
>Ämne: Re: [AMPS] Band Switch arcing SB-1000/AL-80
>Datum: tor 25 nov 1999 00.47
>

>
>>
>>I know there was a thread about this a bit ago........But.......
>>
>>
>>The arcing that I am having is in the front wafer of the switch.  This wafer
>>just switches the tuning cap padder for 160 meters. 
>
>This usually indicates a stability problem or spilt coffee.  .If you have 
>a dipper, it might be fun to look for resonances between 150 and 160 MHz 
>in the lead to the open switch.    
>
>>
>>The cap is 170 Pf.  The open contacts arc when in the 80 meter position.  I am
>>not sure if it is a parasitic or not.  I would say not.
>>
>>Rich's special plate suppresser is installed in the plate lead.  The gap
>>that arcs is almost 3/4 inches wide!  Why does the tune cap itself arc ?
>>
>3/4 inch is an incredible air gap, Jim.  This feat should take more than 
>4x the anode supply potential.  To find out if it's a vhf parasitic, try 
>increasing the inductance in L-supp.  in order to decrease VHF-Q in the 
>anode resonant circuit.  /  One method of reducing feedback is VHF 
>cathode loading.  We use this in our 3CX1200A7 suppressor retrofit kit 
>due to its extraordinarily high feedback C.  .  For starters, connect 
>25pF to 36Pf in series with a 10-ohm MOF resistor.  The R and C should 
>have low intrinsic L.  .   (we use a Matsushita resistor. ).  Use short 
>leads and a new ground lug at the site if it will reduce L.  The RC combo 
>goes from one or both filament pins to ground.  
>
>>Did Ameritron re-design this portion of the switch ?
>
>doubtful.  /  The stock bandswitch tests at over 5000v on a high-pot.  
>The peak RF potential in the amp. is about 2100v less.  The bandswitch 
>should not arc.
>
>Photos of AL80 bandswitches are on my Web site.  See Figure 15.  
>>
>>I really do not want to replace an $ 80.00 switch. Let alone the fuss of
>>replacing it.
>>
>cheers, Jim
>
>-  Rich..., 805.386.3734, www.vcnet.com/measures.  
>
>
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