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4-125A'S x 2 in a TL 922??




 
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Author Topic: 4-125A'S x 2 in a TL 922??  (Read 5276 times)
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xe1yzy
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« on: December 12, 2009, 11:51:08 AM »

Hola Amigos,

Well, come to my hands  one TL 922 with a severe glitch damage in one tube, so I wondering... I don´t want to spend more than 350 USD for a new set of 3-500Z, (at least not for the moment ),  Looking into my junk box I found a couple of NOS 4-125 A tetrodes, and a couple of 2 813 with bases, So I can make 3 things...

1.- Install the 2, 4-125A tetrodes tubes in push pull AB2, and pray to have at least 500W in the output , right?
2.- Change the filament transformer an bases, an install the 2 803 in push pull, but this requieres more "wiring" and modifications for fix the tubes inside the linear, ( And the risk of be killed for some kenwood fans hehe).
3.- Left only one 3-500Z in operation.

I plan to use this linear in CW, so 500W its a good power for this mode, what do you think?, (no, I not in drugs hehe)

Thanks in advance

Pedro XE1YZY
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Ralph W3GL
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« Reply #1 on: December 12, 2009, 12:14:27 PM »

Pedro,

If only one of the 3-500's was damaged, just remove it and fire that rig up on the remaining 3-500, it will work that  way and you will achieve plenty of RF output on CW...

Only difference is the tuning will change a bit and of course, you  will not be able to load the amplifier as heavy as with both tubes in there...

No need to modify the TL-922, keep it Kenwoody... 
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73,  Ralph  W3GL 

"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other"     Ed Morrow
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« Reply #2 on: December 12, 2009, 12:49:58 PM »

I agree that the one 3-500Z is the best of the options.  If you do decide to use different tubes later, the Russian GI-7B triodes are probably one of the better choices when modifying for lower cost tubes. It appears sockets can be homebrewed fairly easily.

Rodger WQ9E
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Rodger WQ9E
WA1GFZ
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« Reply #3 on: December 12, 2009, 01:21:59 PM »

Sell the 4-125s to someone with a T368 and use the money to buy the right tube.
They will beg for mercey unless you run low power.
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ke7trp
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« Reply #4 on: December 12, 2009, 01:51:18 PM »

Agreed. Use one 3-500.  I ran this way for a while on an SB220.  It made an easy 500 to 600 watts. I did not push it much past that.  I got some new tubes later and put them in.  Make sure to isolate that now hanging Plate cap!!!

C
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xe1yzy
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« Reply #5 on: December 12, 2009, 04:37:52 PM »

Ok guys, well thanks for your answers and advice, I got the idea...

Best Regards!

XE1YZY
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KM1H
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« Reply #6 on: December 15, 2009, 10:51:46 AM »

Why not a pair of 4-400A's, C's? Readily available at low cost and they use the same socket.  Remove the grid chokes and ground all grid pins. They will require a bit more drive to equal 3-500Z output but still capable of 1000W+ with 100W.

The 4-125's will be stressed way too much IMO.

Carl
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Ralph W3GL
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« Reply #7 on: December 15, 2009, 11:45:06 PM »


Carl,

4-400's are not a solution for the TL-922 Amplifier due to the height difference
between the 3-500 and 4-400... Different base.  The 400 is slightly more than
an inch taller...

Actually, without serious chassis modification of the TL-922, none of the "4-"
series tubes (125, 250 or 400) will set in there!


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73,  Ralph  W3GL 

"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other"     Ed Morrow
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« Reply #8 on: December 16, 2009, 02:49:10 PM »

Where there is a will there may be a way looking at a 3-500 and 4-400 here.

The 3-500Z with the usual 4 row heatsink cap (Eimac HR-6 or clone) is taller than the 4-250/400. The 3-500  metal tube cap is held on by an Allen set screw and can be put on a 4-400. Then use the 2 row heat sink from Ameritron. I dont have a TL-922 here to do any measuring so dont know if it will fit without punching a clearance hole in the top cover shield.

There is also considerable room below chassis to drop the socket on a spacer.

The 4-125A seated height is 5/16" shorter than the 4-250/400. However using it in the TL-922 raises other issues.

Carl
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Carl WA1KPD
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« Reply #9 on: December 16, 2009, 07:32:39 PM »

Hey Pedro
Best of holidays to you. Are you still in QTO? I will be back in MX in Jan. Any chance for another eyeball?
73 and best wishes to you and yours for the holidays
Carl
/KPD
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