[Amps] repair of older Command Tech VHF-2000 amp

[Carl]

I didnt say it wasnt. Ive no idea what temperatures are encountered in those 
crammed USAF equipment racks. My 432 amp has a 2700W Pd tube in order to get 
1000W as an AM linear; all that heat goes somewhere and the manual doesnt 
indicate what the external coax should be.

My relay, feed and antenna system cant handle close to what that tube can do 
on CW/SSB !
The most Ive pushed it is 1200W and normally run 800W which is 3dB above the 
AM-6155.

Carl


----- Original Message ----- 
From: "Mark Bitterlich" <markbitterlich at embarqmail.com>
To: "Carl" <km1h at jeremy.mv.com>; <amps at contesting.com>; "Louis Parascondola" 
<gudguyham at aol.com>
Sent: Monday, October 14, 2013 4:46 PM
Subject: Re: [Amps] repair of older Command Tech VHF-2000 amp


> When subjected to external heat, the best coax to use is a teflon 
> dielectric.
>
> Mark
> wa3jpy
>
>
>
> ----- Original Message ----- 
> From: "Carl" <km1h at jeremy.mv.com>
> To: "Mark Bitterlich" <markbitterlich at embarqmail.com>; 
> <amps at contesting.com>; "Louis Parascondola" <gudguyham at aol.com>
> Sent: Monday, October 14, 2013 2:40 PM
> Subject: Re: [Amps] repair of older Command Tech VHF-2000 amp
>
>
>> Teflon is very prone to cold flow as are some foam cables.
>> Neither should be subjected to sharp bends and the manufacturers specs 
>> should be followed.
>>
>> RG-213/214 type dielectrics are much less prone to cold flow but are very 
>> susceptible to heat flow from the center conductor.
>>
>> Use of the correct cable and installation procedure for the job usually 
>> works.
>>
>> Several VHF amps use a coax stub filter to meet FCC requirements. If the 
>> end isnt properly finished corona can develop and eat away the 
>> dielectric, even Teflon.
>>
>> My 432 amp is ex military and was used as a 1000W output AM linear and 
>> the internal interconnects to the Type N output connector have no sharp 
>> bends, just a few gentle swoops.
>>
>> Carl
>> KM1H
>>
>>
>>
>> ----- Original Message ----- 
>> From: "Mark Bitterlich" <markbitterlich at embarqmail.com>
>> To: <amps at contesting.com>; "Louis Parascondola" <gudguyham at aol.com>
>> Sent: Monday, October 14, 2013 12:44 PM
>> Subject: Re: [Amps] repair of older Command Tech VHF-2000 amp
>>
>>
>>> Louis,
>>>
>>> This phenonamom used to be seen quite regularly in certain military 
>>> aircraft where coax types such as RG-214, RG-213, RG-217 were used.  Any 
>>> kind of medium to sharp bend at all, co-located with a heat source 
>>> caused it as you mentioned.  Typically around turbine compartments or 
>>> bleed air lines.
>>>
>>> All of these coax runs  were eventually replaced with Teflon dielectric 
>>> types, such as RG-142 & RG-393.    That lesson learned, all of my amps 
>>> have been re-plumbed with the same teflon type coax. :-)
>>>
>>> Mark Bitterich
>>> wa3jpy
>>>
>>>
>>> ----- Original Message ----- 
>>> From: "Louis Parascondola" <gudguyham at aol.com>
>>> To: <amps at contesting.com>
>>> Sent: Monday, October 14, 2013 12:17 PM
>>> Subject: [Amps] repair of older Command Tech VHF-2000 amp
>>>
>>>
>>>>I performed what seemed to be a rather odd repair on an older Command 
>>>>Tech VHF-2000.  I thought I would share this since it could possibly 
>>>>affect the HF models.  This particular amp like most has a piece of coax 
>>>>that comes off the output of the tank circuit and goes over to the 
>>>>antenna relay. In this case a harmonic filter.  The coax was affixed to 
>>>>the side of the wall and dove down to the bottom and over to the relay. 
>>>>Filter in this case. There was what seemed to be a soft arc to the coax 
>>>>as it bent over the edge and down.  The amp exhibited no output 
>>>>whatsoever and acted like there was not antenna connected.  I tracked 
>>>>down the problem to that coax being internally shorted.  An autopsy of 
>>>>the piece of coax was amazing. Apparently the owner of this amp operated 
>>>>digital modes like JT65 so I would think there were many  periods of 
>>>>heavy duty cycles.  Apparently over time the dielectric center conductor 
>>>>heated up and little by little the wire migrated to the outer edge and e
>>>> ventually broke through at the "arc" strain point and shorted to the 
>>>> braid.  Several inches of the center wire was way far away from the 
>>>> center of the dielectric.  Go figure.
>>>> _______________________________________________
>>>> Amps mailing list
>>>> Amps at contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>>> _______________________________________________
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>>>
>>>
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>>
>
>
>
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