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Author Topic: T368 with 4-250s  (Read 29157 times)
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ke7trp
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« Reply #50 on: April 24, 2012, 12:22:48 AM »

Random pics of my T3 with the oil slick cleaned up and the New non PCB 12.5 MFD 4KV cap in the PS. The pics also show the new Fil transformer installed in the open location on the modulator deck and of course the larger modulator tubes.  Pictured is 4-400s.  I later swapped back to 4-250s.  The 4-400s needed more idle current to hit the same power and since I was not going to run over 1500 anyways, I thought it was a waste.   

C


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ke7trp
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« Reply #51 on: April 24, 2012, 12:23:09 AM »

last one.


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ke7trp
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« Reply #52 on: April 27, 2012, 12:00:20 PM »

Update.  More complaints from the peanut gallery.  Hum on the signal.  WTF???

This time I called W8QBG and had him listen. He said there was a slight 60hz signal with some FMing. I cant even see it here. I could hear the Beat change a bit while using the BFO on a reciever to get a steady tone.  waw waw waw as I could modulated.

I started pulling tubes in the audio section. Then all the way back to the exciter. It was in fact comming from that exciter unit. I could even yank the intermediate PA tube (6000) out and still here.  I got down to the two PTO tubes.  I pulled one, Still there.  I pulled the last one and of course, I lost the signal.  I noticed that some FORKING $*($&# E*(#_)(*$ #_)(#!!!!!  put a 6ah6 in the left side PTO!  FORK!!!! I was SOFA KING pissed I missed that the other day! when I checked all of this.

I got a new 6ba6 out and installed it. The dials off. I had to then realign exciter.

Why do hams rig things up?  I mean really.  WHY?  A 6ba6 is $2.  Why not get one and put it in the PTO rather then just insert some incorrect tube and then Realign the Exciter to make it work? 

FMing is gone.  Hum is cut in half or better.  Keyed up 500 watt carrier on 1885 and QBG said its so low that he would not notice it. 

Hooked up the Audio tubes again and found some hum return with the insertion of the first and second preamp tubes. 

Zoomed in using Spec AN and see a blip at 60hz that is over 52 DB down from carrier.  I think thats pretty good right?  I mean is some band cop complains at a 52DB down Hum on my signal, Fork him  Cheesy

I believe the only way to get this lower now is to DC the filiments on the speach amp.  I can vary the slight hum with the audio gain control.  Kinda like on a PA system or audio amp. Turn up the gain, The hum gets louder. I am going to make a new post about this so we can start a new discussion on common practices for filiments on Triodes.

Learned alot.  Kept me busy.  I think I got this rig running decent now. These issues bugged me for 4 years now and needed to be dealt with.

Thanks for all the help my fellow AM'rs


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KC2TAU
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« Reply #53 on: April 27, 2012, 12:15:17 PM »


It's certainly something how a transmitter (and many other types of both electrical and mechanical items) can carry on and operate quite well even with a number of problems present. We think everything is okay until we really go through it and make sure everything is according to spec. I know it's nowhere near as complicated but that reminds me of my HQ-129X. I've had it for years and it has always worked very well. I've finally decided to go through it with a very fine tooth comb and I've found a few resistors that have gone 50% high!
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ke7trp
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« Reply #54 on: April 27, 2012, 12:30:53 PM »

Thats a very good point TAU.  These old rigs are very robust when it comes to things like this!

C
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