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Dirty-South Blues Harp forum: wail on! >
Pulling 1 6L6 ?
Pulling 1 6L6 ?
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Littoral
1240 posts
May 02, 2015
3:45 PM
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Anybody do this with a 4-10 that runs on 2 tubes? I know it sounds awesome but does anybody REALLY know how realistic is damage?
Thanks!
Last Edited by Littoral on May 02, 2015 3:46 PM
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5F6H
1875 posts
May 02, 2015
5:00 PM
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On a push-pull, fixed bias Fender amp, like a bassman, super reverb, twin, it's pretty safe. Plate voltage will rise a tad, but typically not by an amount that will cause damage. The bias won't shift dramatically either. The impedance mismatch is tolerable. I can't recommend it for other brands without more info, nor for the above amps with non-standard speaker wiring (running into 3x10" or less, like a 3x10" bandmaster for example).
For some smaller amps like BF & SF Deluxes & Princetons, it's probably not such a great idea.
For cathode biased amps, it will kill the remaining tube. Don't do it, always run them with all power tubes, unless the builder advises otherwise (most factory builds don't allow it).
There are concerns that the OT can become magnetised...I honestly don't know how much study has been made into this beyond theoretical assumptions relating to air gaps in single ended OTs, one suggestion is to periodically switch the socket being used.
I don't really recommend it just because I don't like the sound, others do though, so go with your preference. Anecdotally, I have heard of players running amps like this for many years, Victoria amps offer a mod on their amps where the amp keeps both power tubes installed but one can be switched out.
If you have a bias balance pot, you can reset this to mismatch the bias between the 2 installed tubes, monitor both and don't set the hottest tube outside of spec. A 12DW7 tube in the phase inverter of long tail PI amps can also give a more single-ended type tone too, with both tubes fitted, but the low gain side can stress PI plate resistors. If it burns out a resistor, it's still a relatively safe option as long as you go into it with your eyes open.
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www.myspace.com/markburness
Last Edited by 5F6H on May 02, 2015 5:05 PM
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Bilzharp
61 posts
May 03, 2015
8:28 AM
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5F6H,
For my benefit, what is a long tail phase inverter? Can the 12DW7 PI be used in both fixed and cathode biased amps?
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5F6H
1876 posts
May 03, 2015
11:51 AM
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@ Bilzharp "5F6H,For my benefit, what is a long tail phase inverter??"
5F6 & 5F6-A Bassmans (earlier "5E"s are not)
5F8-A Twin
All fixed bias, tolex Fenders with 2 or more 6L6/5881 power tubes. Pro Jr, Blues Jr. Other models, just ask.
You can still fit a 12DW7 in other designs, but it may not have the same effect re. making the amp act more like (but not exactly like) an amp with 1 power tube, sometimes it just drops some gain.
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www.myspace.com/markburness
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