[BC] Tips to repair a CCA AM 1000D

[Lewis Munn]

Werner,
   
  There are general procedures for transmitters.  I am not specifically familiar with this transmitter, but most of the older tube-type transmitters are similar.
   
  First, check to be sure audio is reaching the transmitter OK, of course.
   
  The V1, V2 unbalance sounds like replacing them might help.  There should be controls to balance the modulators.
   
  A "smoked" tube inside is not a good sign, but be sure you are not confusing "smoke" with the normal gettering, or with electron bombardment inside the envelope, which can happen and does not necessarily destroy the tube.  If a tube does not show somewhere tho the silvery getter flash residue, it is likely gassy or will be soon, and should be replaced.
   
  The resistors being low in the feedback ladder, as I think you were commenting on, is a serious matter.  If they are low it curtails the modulation.  And it can go down fast.  And in some circuits the unbalance of values can unbalance the modulator tubes seriously.
   
  You should probably look at the audio driver tubes too.  They can go...or components in the audio amplifier if it is solid state,  Bad audio driver tubes can kill modulation and unbalance the idle currents.
   
  Look at the plate colour of the tubes.  The RF tubes should likely show some plate colour if running at full power, and it should be equal.  The modulators will usually show significant plate colour variation with modulation.  Brighter when modulating more heavily.  They should show about the same plate colour and variation.   In general, if the RF tube pair and the modulator tube pair do not show good colour balance, the less-red tube should be connsidered for replacement as not carrying its share of the load.
   
  IF a mopdualtor tube tsht is good shows a very bright colour, it is possuible you have a shorted winding on the modultion transformer, also, which will kill the modualtion fast, while working one tube to death.  Shorted modulation transformers, or modulation choke, or an open PA blocking capacitor off the modulation transformer are potentials.
   
  But the one thing tht really stands out is that the 1 meg resistors in the feedback ldder should not be backed down to 600K!  They need to be 1 meg +/- the specified tolerance, which is not going to be 40%!!
   
  You need to replace them with the correct value AND POWER. And tolerance...some might be 1% resistors.  I have seen modulation vanish as the resistors bake down, and the feedback rises and wipes out the incomming audio.
   
  I would be glad to offer help further, if I can be of help.  I can talk on the phone also to help.  (406)323-2599.
   
  Best wishes.
   
  Looey Munn
  Roundup, MT

"wernerl at tutopia.com" <reader at oldradio.com> wrote:
  I just want to get some tips on the reparation of one CCA AM 1000D. 

		
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