100 ohm resister vs heater center tap

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john t
Junior tube assistant
Posts: 86
(7/24/03 9:49 pm)
65.230.54.161
Reply | Edit | Del All  100 ohm resister vs heater center tap
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 I am building my second Hoffman style 5e3. I went with the 100 ohm resister artificial tap for the heaters on my first build. I was thinking of just using the heater center tap for the second build. Any opinions on this one.
Thanks John T.
 
GroundhogKen
Moderator de forumus
Posts: 1724
(7/24/03 10:29 pm)
66.67.155.173
Reply | Edit | Del  Re: 100 ohm resister vs heater center tap
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 Either way is fine, but I lean towards the 100 ohm resistors. If a tube shorts to a filament, it takes out the 100 ohm resistors rather than a transformer winding.

I suppose you could get the same result and protection by connecting the CT through a single 100 ohm resistor to ground. I've never tried that.

For me, Murphy's Law dictates that if you don't make provisions for the 100 ohm resistors, then you can guarantee the transformer you select for the project will not have a center tap.  


Ken
 
mrr3000gt
Hey get your own solder
Posts: 275
(7/24/03 10:36 pm)
148.78.245.13
Reply | Edit | Del  Re: 100 ohm resister vs heater center tap
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 This thread occasionally pops up: which is better.

I have built several amps and tried both heater CT and 100 ohm 'tap', and I have yet to hear a difference.

The Hoffman boards do a good job of incorporating 100ohm resistors into the board design, and I have only not used it on my Plexi-50 (only because the Hammond PT supplies a CT for the heaters and I chose to use it).

For what ever it is worth, I would use the CT if your PT has one and use 100ohm resistors is the CT is not present. Now, I am willing to buy a new PT if there is a screw-up, but for posterity I like to use the CT if it is there (a Karma thing??).
 
 
john t
Junior tube assistant
Posts: 87
(7/25/03 10:53 am)
24.93.29.9
Reply | Edit | Del  heater tap
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 Thanks for the info. The transformer I have has the center tap. I thought one method might reduce hum more efficently then the other. My first build is very quite.It sound like either way would be fine.
Thanks again.
john T.
 
Lucid Alice
Junior tube assistant
Posts: 63
(7/26/03 9:16 am)
209.94.180.173
Reply | Edit | Del  Re: heater tap
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 I prefer the Doug's method as stated by GHK. I feel the protection of an expensive piece of iron is worth the few cents in resistors. I would not expect you would hear any difference at all. The resistors create an artificial center tap and perform a fuse type function in the event a tube shorts. If you have the bucks to replace your PT if it smokes the point is irrelevant. But if your replacement PT doesn't have a center tap you are back to square one. Better to plan for the two resistors to begin with... even if you don't use them.
 
bartman
Junior tube assistant
Posts: 24
(7/27/03 11:41 am)
64.12.96.238
Reply | Edit | Del  Re: heater tap
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 Question:

If I use the 100 ohm resistor method and my PT has a center tap, should I simply cap off the c/t wire?

Thanks,
Bart

 
mrr3000gt
Hey get your own solder
Posts: 276
(7/27/03 12:49 pm)
148.78.245.13
Reply | Edit | Del  Re: heater tap
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I wouldnt: if you leave it you can always use the CT later if you wanted to. Just tape it off.
 
GroundhogKen
Moderator de forumus
Posts: 1733
(7/27/03 8:57 pm)
66.67.155.173
Reply | Edit | Del  Re: heater tap
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 I think:

Cap equal Tape.

Cap not equal Cut

Ken
 
bartman
Junior tube assistant
Posts: 25
(7/28/03 10:25 pm)
64.12.97.6
Reply | Edit | Del  Re: heater tap
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 Thanks for the clarification Ken.

I meant 'to wire nut and tape' the conductor end of ct off, then wire tie it out of the way.

See ya...
 
 
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