eHam
eHam Forums => Amplifiers => Topic started by: NU1O on March 21, 2023, 09:36:42 AM
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I just had a QSO with Tom, DK3EE. He needs a filament transformer for a TL-922. Anybody have one or know where he can get one?
Thanks,
Chris NU1O
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These days not too many people part out TL922 amps. When W0AKG passed away there went the parting out of these amps. Unlike most 3-500 based amps the 922 uses a 10v CT transformer and not a 5v. Size will be a major consideration since there is no extra room in those amps. I don’t know of any alternative transformer that will fit. The specs would be 10vac CT at 15amps.
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I think that transformer actually has 3 low voltage secondaries: 10 VCT winding for the filaments, another winding for cathode bias, and a third winding for the indicator/panel lamps.
Would need to find space for the transformer(s) to replace whichever winding(s) failed.
73, Ed
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Does Dahl or anyone offer a replacement?
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I had a MLA2500 converted to 3CX800A7's and the filament transformer was mounted externally on the back as well as a squirrel cage blower. Worked fine.
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Does Dahl or anyone offer a replacement?
I believe dahl / Hammond makes a drop in replacement.
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The schematic indicates not just filament, 0-10v CT, 0-80v (maybe bias) and 0-8v (meter lamps).
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now curious...sounds like the 2 i bought at sante fe park h f 35 ? yrs ago.! one is in my h b 2x 813 amp. i may have a look..
cant find the other..
might have sold an earlier amp??
id like one to lite up my spare 813's...!!
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The schematic indicates not just filament, 0-10v CT, 0-80v (maybe bias) and 0-8v (meter lamps).
The 80 v winding is for the +120 vdc for the TR relay..and also the cut off bias.
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The schematic indicates not just filament, 0-10v CT, 0-80v (maybe bias) and 0-8v (meter lamps).
The 80 v winding is for the +120 vdc for the TR relay..and also the cut off bias.
Amazing. I had one new in Hong Kong around 1991. Never used it, people used to come in and admire its cool looks, 'where are the speakers' was the typical comment..
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SB-220 filament transformer with modifications? Any reason the 3-500 filaments need to be wired in series?
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SB-220 filament transformer with modifications? Any reason the 3-500 filaments need to be wired in series?
Simply cuz kenwood, in it's infinite wisdom, decide to copy henry radio amps...and wire cathodes in series. The idea was the bifilar fil choke only has to handle 15 amps...and smaller ga magnet wire can be used. Small enough, like 14 ga wire, so they can get 22 uh so it will work on 160m.
If a 5 v @ 30 amp xfmr used, the fil choke would have to be replaced...with a 22 uh choke...wound with 10 ga wire. Ameritron only uses 12 ga wire on their '30 amp' fil chokes.
The other issue, with fils in series is...u then gotta use a 80 uh single layer choke for the B- return for cathode current ( sum of plate and grid current). Next issue is.... with one tube UN plugged, the other tube stays lit, with correct 5 vac across the cathode, BUT the return path is now via that 80 uh, fine wire B- choke they installed..which of course, burns out with 15 amps CCS flowing through it...back to the CT of their oem 10 vac @ 15 amp fil xfmr.
It's a goofy setup, as seen here in their manual. https://erikarn.github.io/kenwood/TL-922/TL-922_Service_Manual.pdf
It would take some work, but a 5 vac @ 30 amp SB-220 xfmr should work...provided it actually fits.
The 922 fil xfmr also has a 8 vac winding...to run the 6 x lamps, and each lamp has a drop resistor...and runs on AC.
The sb-220 fil xfmr, does not have the 8 vac winding. However, u can obtain almost 6 vdc, by rectifying the 5 vac from the cold end of the fil xfmr...through a FWB rectifier assy. Comes out to 7.07 vdc, but then u lose 1.4 vdc from the .7 v drop across 2 x diodes..... since only 2 of the 4 x diodes in the FWB are conducting at any one time.
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I'd be tempted to do the mod. Filament choke could be scrounged from a defunct SB-220 as well (fairly easy to compensate for the choke by modifying
the pi net values on the input network for 160.) My modified SB-220 works
well on 160.. pilot lamps could be handled in a number of different ways,
change lamps, live with lower illumination, go to LEDs. All not ideal, but how
should one spend on an unobtanium transformer which was used in a flawed
design?
Pete