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I would like to try common mode chokes right at the output tube sockets. (I have a couple rated for Buddha’s power line conditioner from wayback) The Welborne lab star chief schematic shows this being done….My modded Tulip amp uses 45‘s, fixed bias and there isn’t a lot of room under the chassis. The filament is AC voltage, and not DC. I’ve measured 0.5 ohm resistance across each leg of the choke (it looks like 20 gauge uninsulated wire) and wonder if that will decrease the filament voltage too much?
Can the choke actually increase AC hum from local pick up?
Is this safe to just solder tack it in and try?
Thanks in advance
Jerry
Follow Ups:
I heard from a star chief builder, that there is no CMC in current production. I have to assume that it was initially used or considered, but dropped for good reason. I am not going to pursue the use of a CMC because the filament voltage would drop too much, as suspected. Anyone else know of a commercial or diy design using CMC on an AC filament? I have seen them used successfully in DC filament supplies. Thanks for the discussion.
Jerry
Jerry,I don't know if the DRDs (including the Star Chief) use a standard DRD power transformer. But if they do, you might have a solution if you want to try a CMC.
What I am thinking is this:
My DRD 45s were tube rectified. Thus they have a 5volt 2 amp tap for the 5ar4. I am in the process of upgrading them to Star Chief (solid state rectified and regulated) so the 5 volt secondary won't be needed anymore. It could be used instead of the 2.5 volt secondary to heat the 45 tube. Currently I just have those leads taped off.
A 1 ohm choke drop + a few drop resistors could fine tune the voltage. It could also cause extra heat in the chassis so be aware of that.
Now I don't know if your amps have the 5 volt secondary, but if they do you would have enought headroom to try a few interesting heater approaches.
I am also going to try a pair of Tentlabs regulated current source Heater Supplies that I have in my parts drawer forever on my DRDs.
In the meantime I added a few drop resistors to fine tune my heater voltage to 2.45 volts AC.
Here is where I get my CMCs:
http://www.coilws.com/toroidal/CM_Series_toroidal_c_choke.php
Used them for my DC on my 12B4 PreAmp.DanL
Dan: thanks, I'm going to try themJerry: whoops, reread your post and noticed you don't have DRDs.
Adding 1 ohm total to the heater circuit would drop the heater voltage well below 2.5 volts. Down to 1 volt!
Mike
At least not that I see. The Terraplane shows a CMC in a DC supply for the 300B
My copy of the 45 STAR CHIEF does show a CMC (L3) in the schematic, but as you say, the current schematic on line does not show it.Is the CMC not recommended for AC filaments? I'm glad I posted the question, and would really like some feedback. Thanks again.
Jerry
Jerry,I can't tell you if the choke will make the sound better since I don't have 'em in my Welborne 45 DRDs. However, it certainly could. I've read favorable reviews of CMCs on heaters.
Can you tell me the size and type of the choke? I'd like to try this myself. Thank, Bill
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