I Hate To Bring Up the Ugly Standby Switch Debate Again But...

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by schmidlin, Mar 1, 2015.

  1. schmidlin

    schmidlin Member

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    I think I found a snappy solution, if I understand this correctly. The Soft Switch. Ramps up your B+ slowly and could solve numerous problems, one being the big jolt to the system. I suppose you could even use fast fuses, offering faster protection. Anyone using these? Are they a good idea?

    Link here, about 2/3 down the page: http://www.kandkaudio.com/other-kits/
     
  2. mark norwine

    mark norwine Member

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    here's the thing, though...

    how many hundreds of thousands of amps...perhaps millions of amps.....have been built that don't have "numerous problems"?

    I suspect this is a solution in search of a problem.
     
  3. Diablo1

    Diablo1 Member

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    You can also use a $2 inrush NTC thermistor.
     
  4. schmidlin

    schmidlin Member

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    Did not know that. (rushes off to Google)
     
  5. telenut62

    telenut62 Member

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    "Cathode Stripping" does NOT happen in guitar tube amps.....so sleep easy.

    If you already have a standy switch....either don't use it or.....Improved standby switching....http://www.valvewizard.co.uk/standby.html
     
    Last edited: Mar 2, 2015
  6. pdf64

    pdf64 Member

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    Might that also be said of the standby function in general, for guitar amps?

    I don't think it's possible to quantify the number of power supply components that may have had their operational life foreshortened by use of this function.

    In some cases the standby implementation is so bad that it might have been devised purposely to induce failures! eg http://schems.com/schematicheaven.net/manu/marshall/jmp_lead_50w_100w.pdf

    The user may reasonably assume that a failed rectifier or power tube is due to it being a bad tube, rather than that the amp designer seems to have ignored good practice / common sense by subjecting various components to unnecessary stress, perhaps several times per power up cycle.

    Maybe a rough guesstimate could be made by counting the number of message board posts in which the writer has flipped standby and a fuse has blown, then put several zeros after it?
     
    Last edited: Mar 2, 2015
  7. teemuk

    teemuk Member

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    If you specifically need to interrupt the B+ supply, which is not that good idea, especially since standby switching schemes can be built by other means too. e.g. switch between open cathode and, say, 100K cathode resistance. No gigantic current or voltage peaks because cathode already resides in rather low potential, thus no need for "soft" anything, no cathode poisoning due to lack of plate voltage, etc.
     
  8. 2leod

    2leod Re-Member Gold Supporting Member

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    I must be out of touch - I had no idea there was a standby switch debate, let alone its homeliness!
     
  9. donnyjaguar

    donnyjaguar Member

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    What Diablo said. McIntosh used this back in the 1950s/60s and their bigger amplifiers were well known for being reliable.
     
  10. Otto Tune

    Otto Tune Member

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    I can't help but think that if manufacturers could do it cheaper AND better, they wouldn't.

    You're saying ALL these builders did it wrong?
    I'd like to hear from someone like Bruce Egnater on what he thinks.
     
  11. pdf64

    pdf64 Member

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  12. swiveltung

    swiveltung Member

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    My BFDR had RCA power tubes in it for 30 years before a failure. You think maybe the standby switch was OK? :>)
     
  13. schmidlin

    schmidlin Member

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    Stick around man, stick around.
     
  14. telenut62

    telenut62 Member

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    Exactly......it does nothing (unless you leave it on for hours)....it was originally put there to protect the filter caps from peak voltage start-up.
     
    Last edited: Mar 2, 2015
  15. Trout

    Trout Member

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    :agree

    Exactly Correct.

    In My MC240 I replaced the thermistor once!
    2 years ago.
    I did not replace it due to failure either, I actually broke it while fixing a bad cap.
    Dropped a darn screwdriver on it and cracked it.:bonk

    Lucky for me I had a whole card of exact replacements.
     
  16. ohiomatt33

    ohiomatt33 Member

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    A lot (most) of the info in this thread is over my head. I've just used the Standby switch like I was told to a few years ago when I got my first tube amp.

    SO a friend recently sent me this after he got a Dr. Z amp. This is from Dr. Z himself, via Humbucker Music, about how to use a standby switch. Which is not how I've been using one.

    "I'm a bit confused about the Standby Switch. Exactly when do I use it?

    Many people still don't know how and when to use the stand by, and it's completely understandable since just about everyone has a different opinion on how to use it. Well, in the Dr. Z Official Forum, Dr. Z himself confirmed the following for use on his amps:
    Always check to make sure the amp Standby is on before you power up.
    When powering the amp up, have the Standby switch already on.. Switch the power on, wait a minute, and turn Standby off.
    When taking a short break, put the amp back on Standby.
    When powering down, DON'T put the amp on Standby. Just turn it off.
    Now, if you just turn it on without using Standby, it'll be okay. Standby just warms the Tubes up a little slower, so they will last longer
    When plugging in/unplugging effects or switching speaker cabs, It's always best to turn the Standby switch on."


    Anybody care to elaborate on this? Does it sound correct? Or is the good doctor a hack and needs to stay of the interwebs.
     
  17. Chris Scott

    Chris Scott Silver Supporting Member

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    Now THIS is something that should be more widely disseminated throughout the amp community - I really like how you can, quite simply and cheaply, utilize an existing standby switch to implement TWO different improvements that actually can help prolong component life, rather than just perpetuating an old myth.

    Sticky - worth, at least imo.
     
  18. pdf64

    pdf64 Member

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    Just in case of any doubt, see p65 of http://www.tubebooks.org/tubedata/tt4.pdf for the RCA technical manual reference that Merlin cites.

    Mike makes some very nice amps for a reasonable price and has managed to survive and even grow his business in a tough economy, so massive kudos to him for that.
    He's even provided a helpful response to a query about implementing UL in guitar amps that I (as a non customer) made, so an all round good guy.
    But I can't make sense of the above!

    And the one example of so-so design that I found in my buddy's EZG50 was that the standby switch was between the rectifier and reservoir cap, which would result in 'hot switching' surge currents when used. It may have been done that way due to the 500V rating of the B+ caps, as described by Merlin.

    Mike's key competencies may probably be as an engineer and a business man.
    An engineer shouldn't waste resource re-inventing the wheel, rather if a known working solution is available then that should be the first choice.
    A business man should ensure that customers expectations are at least met.
    As Alan Philips explains in the previously linked thread, customer expectation is that a high spec / quality tube guitar amp should have standby, and trying to re-educate them away from that is too hard, those 'amp power up' rituals are just too ingrained.

    As previously mentioned, the best way to use standby is not to use it; rather just power the amp up with the main power switch, and find alternative means to mute it during breaks, if required.

    The DR standby is about the least 'bad' of the Fenders, with only 16uF reservoir and no 'hot switching' like the 5F6A Bassman, certainly way better than that Marshall.
    My long lasting tube story is that I got my 1963 JMI AC30 in 1982, and its Brimar GZ34 looked like it had been in place a good while even then; it may have been original to the amp.
    The Brimar is still going strong, I suspect it may outlast me and the spare I got will stay NOS.
    As a protective measure for the PT, I added a B+ CT - ground fuse inside the amp, same as an AC50. To assess what value of fuse to fit, I monitored the B+ current as the amp powers up and under various signal conditions.
    The B+ current comes up smoothly (without any surge as the rectifier begins to conduct) (32uF reservoir) to a static level of about 200mA, and the amp has been running fine for about 3 years on a 250mA fast blow B+ fuse.
    So although anecdotal evidence is no substitute for a real data set, it may be seen that the 'no standby' AC30, despite the continuous high current demand on its rectifier and oven like conditions, provides it with a fairly stress free life.
     
  19. telenut62

    telenut62 Member

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    Ha :aok....I'm going use that the next time someone mentions Harvey bloody Peavey.
     
  20. schmidlin

    schmidlin Member

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    While we are on the topic, I don't think I've shared this concept with you yet. It should be self explanatory:

    [​IMG]

    [​IMG]
     
    Last edited: Mar 5, 2015

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