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June 05, 2020, 02:10:42 AM *
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 on: Today at 12:18:07 AM 
Started by K1JJ - Last post by K1JJ
No screen by-pass caps.   That's my guess.

Nope.  Good guess though.   Each screen has a 500 pF bypass cap.

Hint: The rig was basically working - but not very well. The screen meter showed more current when driven harder, but only about 1/10th of normal. It acted like the screens had big holes in them and were not pulling their loads.  

I just fixed the finals and working on the modulators now...  Power test later tonight.


 on: Today at 12:07:48 AM 
Started by K1JJ - Last post by KA2DZT
No screen by-pass caps.   That's my guess.

 on: Yesterday at 11:31:41 PM 
Started by k7mdo - Last post by k7mdo
Built a replacement lock but on the lathe with a little piece of brass bed rod....  Pressed it on with a C clamp!  Works fine.

Got the set aligned on band 1 but dead on others...!! However the process is encouraging!

 on: Yesterday at 10:40:20 PM 
Started by K1JJ - Last post by K1JJ
Suppressor grid pin 5 left floating?

Wow!  So close but no cigar, Tom.   The exact root cause is not an easy one to figure out.

 on: Yesterday at 10:25:27 PM 
Started by K1JJ - Last post by Tom WA3KLR
Suppressor grid pin 5 left floating?

 on: Yesterday at 09:37:41 PM 
Started by K1JJ - Last post by K1JJ
Now that the GFZ MOSFET audio driver is finished and working, for the last two days I've been testing, ironing out problems and generally going thru the new homebrew pair 813s plate modulated by a pair.  This is "Hollywood" as seen in a different thread. Everything is generally working except for one baffling problem...

It seems that the screen current is as dead as a doorknob.  Grid current rises way up past 40 mA under normal drive, but screen current, even with 350 volts on will not go over 5-10 mA.  Using 3KV, the pair of 813s will not go past 150 watts output.

How can this be? The screen supply is putting out plenty of voltage and the grid current is strapping and the plate current is 75 mA with a nice dip of the final tank. But the screen acts like it is blown out.

Walking Yaz today it suddenly dawned on me what was wrong. I made some simple measurements and found the problem. It was not bad parts.   I have yet to make the change, but without a doubt, the symptoms told the story.

I'll give it a day to see who can come up with the answer and may give some hints later...    It's one of those really dumb specific situations that may have happened and will probably happen to others too, so I want to highlight it.

BTW, hint: The SAME problem independently affected the two modulators too.


 on: Yesterday at 02:05:05 PM 
Started by SA2CLC - Last post by W1RKW
I looked at the HC12 as an option and even bought a few for my project but then I came across some arduino shields based on the RFD21733 module. It works as a wireless RS-232 connection with error handling/correction and plugs right into the Arduino Mega. Just 2 serial commands in the code and you're off and running as if using a pair of wires for the serial connection. A little more expensive but totally idiot proof. 

Some easy-to-use RF link modules are HC12 ...  look on ebay, less than $4 and they work great. I have used 6 of them with arduinos in telemetry.

 on: Yesterday at 12:47:54 PM 
Started by SA2CLC - Last post by SA2CLC

what is the main coil diameter ?


It's 2 3/4" (or around 70mm here on the metric side of the lake)

 on: Yesterday at 08:28:47 AM 
Started by KC4VWU - Last post by KC4VWU
Need a power transformer and function switch. I'd consider a parts set as well. What 'ya got?


 on: Yesterday at 12:04:32 AM 
Started by Pete, WA2CWA - Last post by Pete, WA2CWA
Did screen grab around midnight June 3 of a great opening.

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