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Old 2nd October 2009, 04:03 PM   #11
pjanda1 is offline pjanda1  United States
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Do you have carrier options? My AT&T (GSM) phone used to cause all sorts of commotion in my system. Heck, it'd cause noise in pretty much anything with a speaker (like my fancy metronome). My new Verizon phone doesn't seem to create any problems, but then my tube amp also seems less susceptible than the chip amp was.

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Old 2nd October 2009, 04:34 PM   #12
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Originally Posted by whitelabrat View Post
Of course RF may get in through the speaker wire. Cellphones will operate at short wavelength so all sorts of things can act as an antenna, but with a cellphone in close proximity I'd guess what we hear are the harmonics from the signal generated that are in the audible spectra. Speaker wire could be a nice antenna for frequencies in the Mhz and Khz ranges if tuned to the right length.
The cell-phone does not transmit continuously. They transmit information in packets, one system transmits packets 217 times per second. If this signal gets into your unit it causes bias shifts at that 217 times per second which is very audible.
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Old 5th October 2009, 10:15 PM   #13
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Thanks for all the responses.
What I've done to the WL25:
The Input is a 6N2P SRPP with global feedback to the cathode of the lower triode.
1) I put a RF bead in the feedback line to cathode to block RF pickup in the speaker cables.
2) I added 10K + RF bead grid stop to the lower triode
I haven't touched the driver (6N6P diff amp) or output stage (cathode biased Ultralinear 6C3P).
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Old 6th October 2009, 08:25 PM   #14
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cathode biased Ultralinear 6C3P
Don't you mean the 6P3S or 6N3C?

I'm curious what that amps sounds like since I ordered a couple of those 6P3S or 6N3C to build something with oneday.
If you can see the speaker cone's not hifi.
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Old 6th October 2009, 10:20 PM   #15
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I meant 6P3S, sorry. The amp sounded OK, not in the league of my Baby Huey but then I've yet to hear a commercial offering that is. I fitted NOS Mullard EL34 matched pairs in place of the 6P3S and that improved the sound quite a bit, particularly the top end.
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