National company HRO 500 how adjust VFO top and bottom ranges for gross linearity after VFO changes
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- Опубликовано: 13 сен 2024
- Why was I adjusting VFO linearity you ask?
The HRO is good down to 250 cycles with the dial markings.
Well I was mucking with the VFO.
I removed the cover of the VFO to put a crease in the cover to allow passage of the AGC knob / rod.
I had tried to put in an aluminum switch rod. Long story and a MISTAKE.
Leave the fiberglass rod alone - if the rod is still intact.
DO NOT remove the copper cover from the VFO for any reason.
Because?
The VFO is a hand assembled unit and a hack at that.
There is a coil assy which is installed at an ODD angle and HITS the copper cover.
You have 1/2 mm to get the cover on correctly. Too much pressure on the cover
trying to get the 4 screws in and the VFO will quit and the receiver is non-operative.
IF the VFO is working LEAVE IT ALONE. PERIOD.
I wasted 8 hours at least on changing the fiber glass rod and FXING the VFO from me goofing
it up.
I was moving parts around on the VFO. BIG MISTAKE.
The VFO is factory calibrated.
So after mucking with the VFO and FINALLY getting the VFO running again the
VFO was not lined up correctly with the dial and the markings were not on at all.
Off by 10 to 15 Khz.
And the offness got worse the higher in frequency I went.
SOLUTION.
Read the manual.
Wow.
They had a VFO adjustment section.
Repeat this 10 times:
1) Go to 500 on the dial. Adjust the COIL near the VFO topside for 0 beat on calibrator.
2) Go to 0 on dial. Adjust the variable capacitor underside under the copper lid for 0 beat.
Now do this 10 times or more.
Eventually the 0 and the 500 will be smack on.
But in the middle - you may be off 1 to 2 Khz.
This part is the linearity adjustment. Which I skipped.
You need to BEND fins on the variable capacitor.
Beyond my pay grade for now.
Owning 3 HRO-500 your videos are Top Notch!!!! Learned a lot about the internal workings... Need to change the dial lights so that will help a lot... Working on a Collins 51S-1 receiver at this time.. Trust me, in the end your level of satisfaction will bring High Rewards! 90% of hams would have given up hours ago!!! Robert, San Diego, Ca.
HI Robert. There are NO videos on RUclips.com on repairing the HRO 500. Well at least were were none. Now there are many videos on repairing of this beast of a radio.
@@moviestudioland but yours are the best
Worthy radio to restore. But can you get new transistors today?
Sure, you can get transistors on eBay and I’ve been using a few silicon from Bojack on Amazon for BI stable circuit and they seem to work