[BC] CCA still Low modulation CHanges made

[Lewis Munn]

Werner,
   
  High hum level sounds like one side of your audio feed is open.  Check that out carefully.  Espeically if the audio tht remains is "tinny" in sound.
   
  I am not familiar with the lower level audio on the unit, but you have made improvements obviously from what you had before.
   
  Verify both sides of the audio line comming in have equal signal.  At the transmitter terminals.  And you might disconnect the lines and verify that the transformers are continuous in their windings.  Sometimes transformers open on one side and cause hum and low levels.  Wires break too!  Or mice bite them!!
   
  Do you have a 'scope to carefully follow audio signal thru the transmitter lower level stages?  
   
  I presume with the changes you have made you should now have balanced readings on the tubes...and the PA plate amps should be normal for a KW operation, along with the antenna or common point current.
   
  I'd chec the lower-level audio, possibly a bad capacitor.  Scope if possible.  All the way to the modulator grids.  Watch the higher voltages at some points...DC voltages.
   
  I presume you have checked the lower level audio tubes, if any.
   
  And verified that the PA grid drive is ample. Low grid drive makes it hard to modulate heavily.  Be sure the low level RF components are are good and the PAs are getting ample RF drive, as shown by the grid 1 current being normal...or a little higher...than book.
   
  A 60 Hy choke will have a fair amount of resistance...and high is not likely to be a problem, tho that really seems very high.  Check to see if it is hot to the touch.  It should be only warm.  And verify the 80 ma figure...800 ma is more reasonable for a modulation reactor.  But if you are making normal efficiency and RF output, the choke is probably OK as far as resistance goes.
   
  Did not get the attachment of the schematic; would be helpful!!
   
  I'd go after tho the reason for the audio hum.  Sounds liike a problem in some low level area, like an open side on the 600-ohm feed.  
   
  Question:  Do the two modulators show equal deflection upwards with modulation on their plate currents, or cathode currents, whichever is metered?  This can be important information.
   
  If you have a good test oscillator with high output, see if it will give you more modulation by itself hooked directly to the transmitter audio input.  Could even be a bad output transformer in the console line amplifier. 
   
  Also, have you used a scope on the modulation monitor RF sample to see what the envelope waveform looks like?  This can tell a lot.
   
  You can take a digital cam photograph and attach it to an e-mail so we can see what you have going there.
   
  Good luck.
   
  Looey Munn
  Roundup, MT
  
"wernerl at tutopia.com" <reader at oldradio.com> wrote:
  
Dear friends

After changing the tube V1 , the tube V3( smoked one) and changing 
resistor all 1 Mohm network , I didn't get more that 2 or 3% 
increase in the modulation ,, Rigth Know reach as 20% of total 
modulation and a lot of HUMM
			
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