[Central-Electronics] CE-200V progress/problems - Status update 6/03/10

[George Maier]

Nice bit of detective work Paul, congratulations!

Not sure what else you've looked at or replaced at this point, but with
regard to the LSB only problem, I'd check the mod caps and diodes in the
removable octal plugs as a starting point.  

Hope you get to use it on the air soon.

73, George - W1LSB

-----Original Message-----
From: central-electronics-bounces at mailman.qth.net
[mailto:central-electronics-bounces at mailman.qth.net] On Behalf Of Paul
Sent: Thursday, June 03, 2010 11:11 AM
To: central-electronics at mailman.qth.net; boatanchors at mailman.qth.net
Subject: [Central-Electronics] CE-200V progress/problems - Status update
6/03/10



Finally got back to work on the CE-200V this weekend (my weekend is Tues/Wed
due to my work schedule). Too hot to work outdoors so decided to spend some
time in the cool shack.
 
When I last left the 200V, I had obtained full CW output on all but 10
meters and was starting to work on the audio problems,  where I now had good
carrier suppression but considerable noise and very weak audio.
 
First, at Nick Tusa's suggestion I used a lot of deoxit on the tube sockets
as there was lots of corrosion as I had noticed elsewhere on the rig during
the RF stages debug. Then I started following thru the audio stages, tracing
thru a 1000cps injected signal at the mic connection. Found good audio
amplification and little noise until I got to checking V7 the audio phase
inverter. Found a drastic drop in audio and huge amounts of noise injected.
Started a resistance check and found a suspicious resistance reading on pin
1 of V7, a very low reading to ground, a few hundred ohms. A visual
inspection showed the V7 tube socket ground lug, which was mounted along
side pin 1 of V7, was actually touching pin 1 and a large amount of carbon
had built up between the two points, apparently due to arcing over time at
that point, and resulting in the low resistance reading rather than a
complete short. Also, I'm guessing that the low resistance short caused
 excessive current flow over a long period of time thru R153 in that
circuit, a 1% precision 7k resistor, because that resistor was now reading
48k. I replaced the original resistor and bent the ground lug down so it no
longer came close to pin 1. Finished the resistance and visual checks and
fired the CE-200V back up. Wow! What an improvement!  
 
I now had a decent 1000cps waveform output on the external scope, although
with some ripple, and the trapezoid waveform on the 200V actually looked
good. I performed the suppression steps from the manual and was able to
pretty much eliminate the ripple.
 
With evrything looking good on the scopes, I gave a listen to the signal on
my receiver and it sounded really good, a nice LSB signal on 75 meters.
Switched to USB and gave a listen and....oops, it's still an LSB signal!. So
I have something still not adjusted right, doesn't matter whether the 200V
is in LSB or USB mode, I get a LSB signal. So still have to look further
into that, but at least LSB sounds good, although I haven't actually gotten
the rig on the air to make a contact yet.
 
Oh, also checked AM and that sounded good as well, showing about 25 watts
output.
 
Won't get back to the rig for at least another week (my next weekend) but at
least some more significant progress has been made. Here are a few pictures
of the rig in operation:
 
http://www.w2ec.com/CE200V-LSB-1000cps.jpg
 
http://www.w2ec.com/CE200V-CW.jpg
 
 
______________________________________________________________
Central-Electronics mailing list
Home: http://mailman.qth.net/mailman/listinfo/central-electronics
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Central-Electronics at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

__________ Information from ESET Smart Security, version of virus signature
database 5170 (20100603) __________

The message was checked by ESET Smart Security.

http://www.eset.com


 

__________ Information from ESET Smart Security, version of virus signature
database 5170 (20100603) __________

The message was checked by ESET Smart Security.

http://www.eset.com