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    Daily power-cycling of Mark III & ST-70...



    Posts : 103
    Join date : 2008-12-09
    Location : BC, Canada

    Daily power-cycling of Mark III & ST-70...

    Post by JunkyJan on Wed Sep 19, 2012 7:28 pm

    Hi Bob and all (long time no post!)

    I completed my ST-70 from Bob's kit back in 2009, and was so taken by the sound quality that a year later built a set of Mark IIIs as well. All these use the VTA board design (you'll find photos of my ST-70 and Mark III builds in the photos section).

    I work from home and my amps are on EVERY day of my life as I listen to music all the time while working.... I fire it up usually around 9:30 AM after my morning meetings and switch off only around 7 PM, sometimes it runs till 11 PM or 12 PM at night. So.... Many years ago in my dim distant past I used to be in the South African Air Force and involved in Early Warning Radar as well as mission control. IIRC I think we were running British Marconi radar systems at the time, and one day one of the radar Techies told me that with the radar systems running 24/7 it means that tubes last a lot longer than if the equipment were power-cycled every day (CRT tubes, transmitter and receiver amplifier tubes - all of of it - high-power Tactical Radar systems in the early 1970s were very much cavity magnetron + vacuum-tube driven).

    QUESTION: Would I be extending the life of my amplifiers tubes by leaving it on 24/7 ? Or as an alternative, I once read somewhere of a mod that puts the heaters in "standby mode" - dropping the heater current so that it stops conducting, but still high enough that the warmup time coming out of standby is a few seconds at most. Do anyone know of this mod?

    I rotate between my Mark III amps and my ST-70, to try and spread the Wear 'n Tear a bit. I favour the Mark IIIs over the ST0-70 for pure sound quality.... And after thousands of hours of continuous use I have had no problems whatsoever with any one of my amps (other than replacing the original set of KT88 tubes in my Mark IIIs - the Gold Lions I ordered originally must have been a bad batch, the subsequent set now have in excess of 1,500 hours on it).

    Your opinion on this is VERY welcome!
    -- JunkyJan, BC Canada

    Bob Latino

    Posts : 2464
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Daily power-cycling of Mark III & ST-70...

    Post by Bob Latino on Wed Sep 19, 2012 8:47 pm


    I don't recommend leaving tube gear on when you are not listening to music. The only exception that I personally make to this rule is if I know that I will be listening again within maybe 1/2 hour. If I know that I will be going "back to the music" shortly, I leave the amp(s) on.

    Tubes wear whether you are listening or not and whether there is a signal (the music) going through the amp or not. My recommendation is to shut the amp OFF when you KNOW you are done listening for the day - OR - you KNOW there will be a 1 hour or more lapse time when you will be away from your music system.

    Like you you, I cycle gear in and out of the three tube systems I have here so as not to get excessive wear on any one piece of gear.

    The sad truth is that all the tubes made today are made in China, Russia and the Slovak Republic and these tubes are made with less expensive materials and with less quality control. This all adds up to shorter tube life on the tubes made today. It is also one of the reasons why true NOS tubes go for so much money on "Epay". We all long for the USA, British and German tubes of yesteryear. Some are still around but the cost is high ..

    In conclusion - With the "life span" of todays tubes being as short as it is, shutting your tube amp or preamp OFF when you are not using it will milk a few more hours of usable life out of your tubes.


    Last edited by Bob Latino on Sat Sep 22, 2012 7:49 pm; edited 1 time in total


    Posts : 103
    Join date : 2008-12-09
    Location : BC, Canada

    Re: Daily power-cycling of Mark III & ST-70...

    Post by JunkyJan on Wed Sep 19, 2012 10:17 pm

    Hi Bob

    Thank you for the information! Very much appreciated. As to what those techies said back then, I guess it's a case of "Easy to talk when it's Government Money and not your own". Wish I could afford NOS power tubes, I use JAN (Philips) 12AT7 drivers which seems utterly bullet-proof.

    -- JJ


    Posts : 140
    Join date : 2012-03-19

    Re: Daily power-cycling of Mark III & ST-70...

    Post by wildiowa on Thu Sep 20, 2012 7:58 am

    Only slightly relevent to this discussion, but in moving back to tube gear I forgot how much heat is produced by our favorite old iron and how that impacts room temperature. I am using my ST70 to power a couple monitors in our rehearsal room and man that thing kicks off some heat. I also have a Citation II in my living room and after an hour or so there is a noticeable rise in the temps as the thing gets going. Running this stuff 24-7 would probably boost my air conditioning bill by at least $100 a month just to keep up, although it provides a warm and toasty source of heat in the winter months....

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    Re: Daily power-cycling of Mark III & ST-70...

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