|
Tubes Asylum Questions about tubes and gear that glows. FAQ |
|
|
|
Tubes Asylum Questions about tubes and gear that glows. FAQ |
|
In Reply to: RE: Tube Life- Power Cycling posted by Escobar on October 4, 2010 at 12:54:14:
Is your switch marked "standby" or just "speakers ON/OFF" like on my Scott 350B? If it is the later it's not a "standby" switch instead what it does is kill the speakers so that you can use the headphones without disturbing others by switching the power output from the speaker terminal strip to an internal 20 ohm resistor. While this will reflect a tad more impedance back to the output tubes and you'll probably turn down the signal level so as not to fry your ears (truly dependent on modern listening levels and phone efficiency) but the output tubes will still draw "most" of the current that they would under normal low room listening levels (If I can remember to - terrible memory these days - I'll measure the current flow in this state the next time I rebias my 350B - I set it up with individual cathode current monitoring resistors/7591 and individual bias).
Since the purpose of "standby" isn't to preserve output,or other, tubes but instead to provide an "instant on" environment the way standby is accomplished can kill tubes as easily as not having the standy and simply turning down the amp or having no signal (assuming the theoretical noiseless environment). Those schemes that either removed B+ or lift the cathode from ground do preserve tube life but some circuits do things like short the control grids together on a push-pull output or remove screen grid voltage or, in at least one amp, short the PI control grid to ground. In all of these cases the amp may be subject to "sleeping sickness" and output tubes with very few hours on them simply lose emission. The control grid shorting scheme I've noted in particular is more likeley to cause this but still the best way is to turn the dang thing off - the "off" part of the cycle isnt' doing any damage - and install some sort of ramp-up "soft start" turn on that doesn't thermally shock the heaters/filaments and in this day and time there are tens if not hundreds of ways to accomplish this. And if one is an obsessive purist concerning devices in the line side it would be easy to have a ramp up device that is switched totally out of circuit using a "make-before-break" switch once the tubes are hot.
Rob
"Monoblocks" = "monoblockheads" - it's "monaural amplifier"; "power output tubes" not "power tubes" & "patch cords" not "interconnects!" "Passive preamp(lifier) is oxymoronic!
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- RE: Tube Life- Power Cycling - R. Mercure 11:54:53 10/07/10 (1)
- RE: Tube Life- Power Cycling - Escobar 05:46:35 10/08/10 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
