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Heathkit DX-40 Plate question




 
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November 24, 2017, 05:07:48 PM *
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KC3GMQ
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« on: September 08, 2017, 09:05:46 AM »

Hi all,  I just got done rebuilding a Heathkit DX-60 and a DX-40.  Did them at the same time.  Pretty much the same transmitter in a different case.  So everything tests fine, both transmitters are putting out about 55 ish watts CW so all is well there. Plenty of grid to play with and i am setting it to 2.5 instead of the 3 ma the book says.

  My questions is, on the DX-40, when I key down, the plate spikes to about 175ma (50ma higher then the setting of 125 ma), then settles back down to  to 125ma. The DX-60 does not do that.  Is this ok?  or do I have an issue to find?

Thanks

Dave
KC3GMQ
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W1ITT
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« Reply #1 on: September 09, 2017, 05:28:12 AM »

If I recall correctly, the meter on the DX40, along with the DX20 and DX35 was a cheap undamped movement.  The DX60 has a better meter and was damped.  The result is that the spike you are seeing is the result of ballistics rather than actual current spikes.  It's a mechanical overshoot, rather than an electrical phenomenon.
The meter in the older Heath transmitters looked a lot like the Emico product line.  Their saving grace was that they were affordable, and you see them on homebrew projects of the era constructed by hams who couldn't afford the more desirable componentry.
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KC3GMQ
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« Reply #2 on: September 09, 2017, 05:45:13 AM »

Thank you
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N3GTE
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« Reply #3 on: September 09, 2017, 08:52:17 PM »

The DX-40 had a meter like the DX-60 not the iron vane type like it's old brothers. Does the cw note sound ok? Pretty chirp free?? I'd look in to it a bit further.

Terry N3GTE
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KA2DZT
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« Reply #4 on: September 09, 2017, 10:12:35 PM »

Could be the drive is not there in the first few seconds for some reason
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KC3GMQ
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« Reply #5 on: September 10, 2017, 05:29:32 AM »

The CW tone is fine, using a VFO with it also. Should have said earlier, the DX-40 iron was replaced with DX-60 iron .  The modulation section is a full upgrade. This is how I received it.I recapped it and changed a few resisters and repaired the broken xtal switch. The electrolytics were replaced with over double the capacity as the originals from the book. I inturn matched what the previous Ham had used. I am now wondering if these are too big. (The 40uf caps have 120uf caps now) I thought they were big but I wasn't sure with all the mods in this unit.
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N3GTE
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« Reply #6 on: September 10, 2017, 09:48:44 AM »

Interesting. I have a DX-40 that the pt failed and caught fire. Replaced it with one from a HW-16. Got it working but it has a wicked chirp on 40mtrs and above. Have yet to sort that out.

You may be able to see the hv spike w/an analog volt meter. What you are looking for is the hv not to drop for a split second when you key up.

Is there any sort of bleeder resistor across the p/s output? If not I'd try adding something around 60K @10w. That will give you abt 10ma of load. Will help bleed off extra voltage that the large filters charging up.

GL
Terry N3GTE
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AJ1G
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« Reply #7 on: September 16, 2017, 04:07:10 PM »

The one I currently am using (no pun intended) has had a similar current surge in CW mode for the first few dots and dashes then settles down.  Also shows heavy sparking on the key contacts on break on those first dots/dashes.  The thing sounds very good note-wise. 
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Chris, AJ1G
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AC0OB - A Place where Thermionic Emitters Rule!
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« Reply #8 on: September 16, 2017, 06:04:36 PM »

Hi all,  I just got done rebuilding a Heathkit DX-60 and a DX-40.  Did them at the same time.  Pretty much the same transmitter in a different case.  So everything tests fine, both transmitters are putting out about 55 ish watts CW so all is well there. Plenty of grid to play with and i am setting it to 2.5 instead of the 3 ma the book says.

  My questions is, on the DX-40, when I key down, the plate spikes to about 175ma (50ma higher then the setting of 125 ma), then settles back down to  to 125ma. The DX-60 does not do that.  Is this ok?  or do I have an issue to find?

Thanks

Dave
KC3GMQ

The DX-40 has poorer Power Supply regulation than does the DX-60.

Due to the poorer PS regulation, the DX-40 power supply voltage simply drops voltage faster at KeyDown than does the DX-60.

Nothing to really worry about.

There are a number of Improvement/Enhancement mods down here:

http://amfone.net/Amforum/index.php?topic=43002.0


Phil - AC0OB
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"What kind of Koolaid do they make you drink in the Physics Department?" Charlie Epps to Dr. Larry Fleinhardt, NUMB3RS   Smiley
KC3GMQ
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« Reply #9 on: September 18, 2017, 10:43:05 AM »

Thanks all
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