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Turn the amp (EMP) off for tuberolling?

post #1 of 15
Thread Starter 
I'm used to turn my EMP off and wait at least 30 seconds before removing any tubes and replacing them. This seems to be reasonable. But is it really necessary to turn the amp off? I'm worrying each time about shortening the tubes' lifetime by doing this (at least of the one[s] remaining). Is this a dumb question? I'm a relative noob with tubes... (as far as theory and technical background are concerned).

JaZZ
post #2 of 15
Definitely turn the amp off before changing tubes. Otherwise you could fry something. Unplugging the power is a good idea too, just to minimize the shock hazard. It doesn't hurt to give the tubes a few minutes to cool off too, before handling them.

You wouldn't swap out a card in your PC while it's running, right?

KJP
post #3 of 15
Thread Starter 
Quote:
You wouldn't swap out a card in your PC while it's running, right?
Of course I wouldn't... I'm not dumb! But I wouldn't mind swapping CDs in my player without turning it off...
post #4 of 15
Erm, a CD is kind of different it doesn't have any volts pumped through it.
post #5 of 15
Quote:
Originally posted by Kevin P
Definitely turn the amp off before changing tubes. Otherwise you could fry something.
KJP

More specifically: YOURSELF!!
post #6 of 15
The plate voltage of a 6922 is rated at about 220 volts. Not a good idea to pull a glass device with that kind of voltage running around without turning the power off first.
post #7 of 15
I always turn my EMP off before I roll tubes. I guess the most danger for the tube's lifespan comes from powering it up when cold and from moving it when hot.

BTW, I use a 12AU7 at the moment, not the recommended 12AT7 as the input tube, a Philips ECG 5814A to be specific. I figured my source had so much output voltage that less gain would be sufficient. The 12AT7 and 12AU7 have the same pin-out and the same heater current and heater voltage, their specs are fairly close, but the 12AT7 has a gain of about 60 and the 12AU7 has a gain of about 20. If anyone thought the EMP had a lush midrange before - the 12AU7 transforms it. It now offers utterly relaxing musicality. I guess the 12AU7 might make the EMP to tubey sounding for some, but I am very pleased so far.
post #8 of 15
Thread Starter 
That's what I expected. The high voltage is reason enough to turn the amp off. Thanks!
post #9 of 15
Tomcat I assume you would get the same result if you used attenuated cables or plugs on the EMP input rather than a tube with a lower gain?
post #10 of 15
Rob,

That's not necessarily true. Using a tube with lower gain is akin to using a flea-powered SET amp instead of high-powered Solid State amp. 12AU7 and 12AT7 are different tube families with a different sonic character. Adding something to the signal path with the intention of limiting the voltage (and probably the dynamics) - that's not what I tried to achieve. I just thought less gain might mean more music. The 12AU7's sound is so relaxed, soft and free of any edginess that it's hard to say whether the amps dynamic impact has been compromised or whether the sonic signature is just less busy, whether there is simply less artificial high-lighting of transients. At this point, I'm leaning toward the latter explanation, but my impressions aren't definitive.

And there might be another tube to try: the E80CC which looks like the 12AT7 on steroids, it's a lot taller. Pin-out and heater voltage are identical to the 12AU7/12AT7/12AX7 group, but it has twice the heater current. As far as I know, anyone at Audio Asylum who replaced his preamp's 12AU7 with the E80CC has reported improvements. With its gain of 27, the E80CC might have a slightly more dynamic sound than the soft-spoken 12AU7. I don't know.
post #11 of 15
Tomcat,How far do you have to turn the volume knob using this tube?
post #12 of 15
The volume knob's range is from 7am to 5pm. With the 12AT7, the knob is usually bewteen 8 and 8:30am. With the 12AU7, it's between 9 and 9:30am.
post #13 of 15
Tomcat have you tried any other types of ECC82/12AU7 tubes?

I've found these 3 :-

GE 5814 military dated 4-66

Sylvania 6189 military dated 5-64

RCA 12AU7A commercial box with side getter probably 60's or 70's



I haven't tried any of these yet.Are they any good?
post #14 of 15
No, I haven't tried any other brands. But as far as I know, The design of the Philips 5814A and the GE 5814 is identical and they sound very similar.

I have tried the 12AU7-substituted EMP with high-impedance, low efficiency phones now. My Beyer 770 Pro is rated at 250 Ohms and 96dB/mW. It's not a good combination. The EMP seems seriously underpowered with the Beyer. I guess if one wants to try the EMP with the 12AU7 and reduced power and reduced voltage swing, a high-efficiency and low-impedance headphone is mandatory.
post #15 of 15
I'm currently waiting for a set of Telefunken tubes to arrive (1 x ECC801S and 2 x ECC88) and also a set from the UK distributor,The Audiophile Club.This is a special set which they 'test and match performance and the actual sound to create more gain less microphony, better imaging, and soundstage.'
They take upto 14 days to supply because of this.
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