apache problems

[w30kc]

I bought an apache that was D.O.A. when I got it, I finally got it to load up on the dummy load after finding a bad tube.  After getting it to load up I tried to put a mic on it when I would speak into the mic the output on the watt meter would decrease with voice peaks instead of increasing. I watched the grid current and it drops on voice peaks. I am new to ham radio but am interested in learning and love the old boat anchors can anybody steer me in the right directions.

Thanks
Steve

[WB6NVH]

Did you review the manual, in that the mic gain control is hidden behind the panel and has to be accessed through the key jack, while what appears to be the mic gain on the front panel is actually the clipper?  That may have nothing to do with the issue you have but I thought I would bring it up. 

[KX5JT]

With an average reading meter, AM up to 100% modulation will show as a 'wiggle'.  A peak reading meter may show some forward swing.  You may be seeing what is normal but the BEST ADVICE ANYONE can give  you right now is to get a SCOPE!  THEN you will know what's going on.

[W2PFY]

Sounds like your not driving the final grid current high enough. I think it should be around 5 mills. Downward modulation is usually a sign of lack of grid current. There, I said it twice, two different ways!

[WQ9E]

How much grid current do you have with no modulation?  Be careful as 6146 tubes are easily damaged by excessive grid current and anything over 8 mils (for a pair) is excessive.  6 mils is the desired level and should be at this level when properly loaded for normal output.

Pay close attention to NVH's suggestion as this is a common problem with TX-1 setup.  I believe that Heathkit with the hidden audio gain was competing with Johnson and their "intuitively reversed" clipper control on the Valiant to see who could design a transmitter most likely to be improperly adjusted by the user.

As I recall,  the modulator screen supply in the Apache comes from the B+ supply.  I suppose that severely degraded filter caps in the B+ supply could result in the B+ dropping on peaks with reduced grid drive.  I would expect this condition would result in noticeable hum on the carrier.

[w30kc]

I have the proper grid current of 6 mil, but I was monitoring the signal with another reciever and did noticed a hum in the audio.

[KA2DZT]

A weak LV PS will sag with modulation due to the higher screen current pulled by the modulator tubes.  This can cause a dip in grid drive.  I added a regulated 300V PS for my 6550 mod tubes in my 6146 HB rig.

Fred

[WBear2GCR]

Also, make sure you have the plate dipped properly, and the current when dipped not higher than spec'd in the manual for AM operation! If you have the plate current too high, you may see downward modulation... and how much downward change?


                      _-_-bear

[w30kc]

Around 30 watts, how much should I be seeing on the watt meter for am carrier full output?

[WQ9E]

A healthy Apache should produce 100 watts carrier output on 80 and 40, a bit lower on the higher bands.  30 watts is well short of normal.

What is your plate current and how does it react as the loading is increased.  It sounds like you may not have it loaded properly and as you increase the loading you will also have to increase the drive to keep it at the proper level.  Alternatively, you may have the loading far too advanced if the plate current is close to normal dipped where you have the loading set.  In this case the final is operating with very low efficiency due to improper loading.

[KA2DZT]

Around 30 watts, how much should I be seeing on the watt meter for am carrier full output?

I think probably around 100 watts.  Rig has two 6146s

Fred

[flintstone mop]

I think he meant that there was a 30 watt dip under modulation........
The P.S. caps might need changing out. That's a beginning. If it's been sitting a long time or if they are original, then there will be a lot problems with the TX.
A 'Scope would be so helpful to you. The metering on an Apache is useless for setting the audio level from the microphone.
Take your time with it. They are nice TX's. Do you have a schematic??
Keep us posted.
Fred

[w5gw]

I'd replace power supply filter caps, and also check the rectifer tubes as well. Since you have a hum on modulation perhaps there are some issues with caps in the speach amp and driver section as well.

I really don't need anything beyond 5 ma grid drive on my Apache.

Soft 6146s may also cause negative modulation.

In the Apache manual that I got there was an eratta sheet from Heathkit with common problems causing negative modulation - a bunch as I recall.

73

Gary

[w30kc]

I think my problem with the downward modulation was to much plate current and I was stressing the powersupply.  I sent an email to Frank K3SQP and he was nice enough to email me a step by step tuneup procedure  with meter readings and when I did it the way he instructed me the downward mod was gone and output was around 100 watts. I still seem to hear a hum in my audio, guess it is time to put it on the air and get some feedback on my audio. I really appreciate all the help as you can tell I am new to the old AM boatanchors and have alot to learn. I heard Frank on 7.190 and hope to get on soon. I also have a BW 5100B that I need to get up and running but that comes after the apache.

Thanks
Steve

[WU2D]

Mine did 100 Watts with the tube power supply and 110W when solid stated.  MM

[KX5JT]

I think my problem with the downward modulation was to much plate current and I was stressing the powersupply.  I sent an email to Frank K3SQP and he was nice enough to email me a step by step tuneup procedure  with meter readings and when I did it the way he instructed me the downward mod was gone and output was around 100 watts. I still seem to hear a hum in my audio, guess it is time to put it on the air and get some feedback on my audio. I really appreciate all the help as you can tell I am new to the old AM boatanchors and have alot to learn. I heard Frank on 7.190 and hope to get on soon. I also have a BW 5100B that I need to get up and running but that comes after the apache.

Thanks
Steve

Do put it on the air!  I was hearing a hum on my Viking II when monitoring on an R-75 but it was not coming from the signal.  It was being induced into the radio somehow.   The transmitter was not putting hum on the signal.