8950 / 6LF6 / 6MH5 / 6LB6 / Etc

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w4bfs:
Anyone know the input impedance of one of the sweep tubes common to the CB linears in grounded grids / cathode driven service?  My plan is to put the pair of 8950s in service.

input Z (grounded grid) = 1/ Gm

example: a 4-1000 has Gm = 10000 x 10E-6 mho

so: 10000 x 10E-6 mo = 1 x 10E-2 mho = .01 mho --> Z = 1/.01 mho = 100 ohms

hope this helps

W1GFH:
Putting a converted tube-type CB on 10 is a fun project, I think you'll enjoy it. My only observation is that 350W PEP is a bit overkill for 10 meter AM work when that band is truly "open." There is no QRM to speak of in the AM segment of the band, and atmospheric noise and static levels are quite low. During the last sunspot cycle, I had almost daily QSO's from W6-land with WB9GKZ in Green Bay, WI that featured 40 over S9, full-quieting signals on both ends. We experimented by lowering our power outputs down, from 50 watts to 3. No difference in signal strength. The ionosphere does all the work.

WBear2GCR:


It might be that the sweep tubes are worth more than making the amp work... see what they go for on ebay??

Just a thought...

           _-_-WBear2GCR

KD6VXI:
Quote from: W1GFH on October 23, 2009, 09:54:24 AM

Putting a converted tube-type CB on 10 is a fun project, I think you'll enjoy it. My only observation is that 350W PEP is a bit overkill for 10 meter AM work when that band is truly "open." There is no QRM to speak of in the AM segment of the band, and atmospheric noise and static levels are quite low. During the last sunspot cycle, I had almost daily QSO's from W6-land with WB9GKZ in Green Bay, WI that featured 40 over S9, full-quieting signals on both ends. We experimented by lowering our power outputs down, from 50 watts to 3. No difference in signal strength. The ionosphere does all the work.


I aggree wholeheartedly.  I traveled for years with my grandparents and one of the 25 watt 10 meter rigs in the truck (they pulled a 5th wheel and traveled the last 20 years of Grandpas life)...  25 to 30 watts was the word of the day.

I made international contacts with that thing on the East Coast, and on the West, I could talk pretty much to anyone I could hear.  Slopbucket of course.

My plan on the linear is just to get it up and operational, and when I NEEDED it, be able to use it to drive the SB220.  The Johnson will drive my Harris RF-103 nearly to full output (only needs 65 watts), but the Heath is another story.

On another note, anyone tried converting one of these to another band?  Shouldn't be too hard, just wondering if I'd just be reinventing the wheel, getting a Messenger on 75 :)

BTW, my math led me to 62 ohms on the cathode, it had 16,000 mho on the datasheet listed.  SO, off to build a Pi net.  I'd also like to be able to drive this thing with the multimode radios here...  I've got about 3 or 4 of them.  The L works, but I'd rather play with pI.

And thanks to the gentleman that posted the formula....  I for the life of me, could not find or remember it.


--Shane

KD6VXI:
Quote from: BEAR on October 23, 2009, 12:11:20 PM



It might be that the sweep tubes are worth more than making the amp work... see what they go for on ebay??

Just a thought...

           _-_-WBear2GCR


I thought of that...  If I decide this isn't worth it, after I'm done, I'll build a monoband tuna out of the linear and sell the tubes.

I'm sure a PAL collector (if they exist) would LOVE to have darn near NOS 8950s, labeled with the PAL logo on them....  If anything, they look neat on the mantel next to the 4-400s and 4-1000 dud.

--Shane

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