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Title: 4-125A'S x 2 in a TL 922?? Post by: xe1yzy 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 donīt 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 Title: Re: 4-125A'S x 2 in a TL 922?? Post by: Ralph W3GL 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... Title: Re: 4-125A'S x 2 in a TL 922?? Post by: WQ9E 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 Title: Re: 4-125A'S x 2 in a TL 922?? Post by: WA1GFZ 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. Title: Re: 4-125A'S x 2 in a TL 922?? Post by: ke7trp 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 Title: Re: 4-125A'S x 2 in a TL 922?? Post by: xe1yzy on December 12, 2009, 04:37:52 PM Ok guys, well thanks for your answers and advice, I got the idea...
Best Regards! XE1YZY Title: Re: 4-125A'S x 2 in a TL 922?? Post by: KM1H 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 KM1H Title: Re: 4-125A'S x 2 in a TL 922?? Post by: Ralph W3GL 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! Title: Re: 4-125A'S x 2 in a TL 922?? Post by: KM1H 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 KM1H Title: Re: 4-125A'S x 2 in a TL 922?? Post by: Carl WA1KPD on December 16, 2009, 07:32:39 PM Hey Pedro AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
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 |