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    tube flashes brightly on power-up

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    gravydb

    Posts : 193
    Join date : 2014-06-22
    Location : PA

    tube flashes brightly on power-up

    Post by gravydb on Thu Jul 02, 2015 8:17 am

    TSC indicates that all is well. When I turn the amp on, one of the power tubes (second from the left) gets really bright, just for a second. What does that mean? Does it indicate any sort of issue? The amps sounds fine, and never any weird noises. The tubes are a matched set of JJ's, fairly new (several months old)... this behavior has always been present with this set of tubes. I can't recall if it occurred with the OEM tubes...
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    mmiddei

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    Age : 56
    Location : Bethlehem, PA

    Re: tube flashes brightly on power-up

    Post by mmiddei on Thu Jul 02, 2015 9:47 am

    Hey Gravy,
    I've had my GM for now 31 days, tubes are originals, just checked mine for what you describe and it does not do that, all 4 power tubes light up exactly the same way.

    If you have another set of power tubes you could try installing them to see if this behavior happens with those.  If it does not I'd say you've probably got one weird tube, if it does you may have something else going on there...

    I do have a question; did you notice a significant difference in tone when you put in the JJ's?
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    gravydb

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    Location : PA

    Re: tube flashes brightly on power-up

    Post by gravydb on Thu Jul 02, 2015 10:41 am

    Hey Mike!
    That's good idea, one of these days (when I'm feeling ambitious) I'll put the OEM tubes back in, and see what happens. Or, play musical chairs with the JJ's and see if that particular tube behaves the same in different sockets, ya know? I'm not too worried about it, as the amp sounds fine and is working fine, but then again I don't want this to bite me in the ass at a gig.

    The main reason I have JJ's in there, is habit. It started many many amps ago, I think it was a Fender amp, I had a set of new OEM tubes go bad on me. I researched quite a bit for a set of replacement tubes and decided on JJ's, and I've stuck with them ever since because they have proven (to me) to be very reliable. I'm not a cork sniffer and I'm certainly not a tube expert by any stretch, but I am a "go with what you know" sort of guy, and I've been very happy with JJ's. I try to not talk about the sonic differences because it's so subjective and different people will have different perceptions, but yes I do notice a positive difference with the JJ's... more warmth... more richness... it's subtle but it's there...

    My main advice - IMO, there is something just as important as what brand tubes you choose, and that is who you buy them from. Do not buy them from a big box store. Instead, be sure to buy them from a place that does painstaking testing/matching/etc. I use eurotubes but there are other similarly reputable places. One time, I was in a pinch and ordered a "matched set" of JJ's from MF, and they failed right away. Otherwise I have always bought from eurotubes and I have never ever ever had a problem. Never a bad tube, never an unmatched set. They are an outstanding reseller.

    And hey we need to get together for a beer, we live nearby!
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    bordonbert

    Posts : 767
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    Age : 97
    Location : Southern England

    Re: tube flashes brightly on power-up

    Post by bordonbert on Thu Jul 02, 2015 5:31 pm

    Cold current surge at startup is a known phenomenon and is not a good thing.  I wouldn't have thought that it should happen in an amp of the quality of the GM as soft start can be built in.  In your case it might indicate that that particular valve is eventually going to turn up its toes before the others.  Do you allow plenty of time for the valves to warm up fully before kicking off the Standby?  If not you should.  Applying the Anode HT before the valve is heated up fully damages it by stripping material off the cathode.  Here is a simple read:

    http://koti.mbnet.fi/siliconf/JukkaTolonen/ga/amptimer/amptimer.html

    About one quarter of the way down see "Why Tubes Fail".
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    gravydb

    Posts : 193
    Join date : 2014-06-22
    Location : PA

    Re: tube flashes brightly on power-up

    Post by gravydb on Fri Jul 03, 2015 6:18 am

    Thanks bordonbert! That's a great read, I appreciate it. I am more suspicious of ending up with a premature failure of that tube. Like I said, the amp is operating perfectly and tsc indicates all is well... but apparently that tube is getting stressed on power-up and its days may be numbered...

    Yeah I always allow plenty of time before kicking off standby.... usually 5-10 minutes since I'm busy doing other stuff while the amp warms up.

    Some basic troubleshooting would be to relocate that tube to another socket and see if the issue follows the tube or does it stay at that same socket. I'll give that a shot this weekend and report back. And I'm all ears to any other suggestions. Thanks so much.

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    bordonbert

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    Location : Southern England

    Re: tube flashes brightly on power-up

    Post by bordonbert on Fri Jul 03, 2015 9:41 am

    Good plan to swap the valves around as long as you keep them in their pairs. Swap the outer pair with the inner pair. My money is on the valve doing it elsewhere, it's unlikely to be an issue with the heater supply.

    If you do find you need to replace it then you have a couple of options. You could just buy a matched pair and replace them both which would leave you with a working spare pair in your gig bag. Or you could use TSC and count the number of flashes for the remaining valve of that pair, look up the biasing requirement for that number of flashes, then source a valve with that characteristic. It's fiddly but it can be done. For myself, I would just buy a matched pair and have done with it, it would probably be almost as expensive for a single specifically selected valve.

    Do let us know how it turns out, this is all useful for future owners with problems.
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    gravydb

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    Join date : 2014-06-22
    Location : PA

    Re: tube flashes brightly on power-up

    Post by gravydb on Sat Jul 04, 2015 10:07 am

    OK so I put that tube in different sockets and guess what - the problem follows the tube - the sockets are all fine Smile

    I did notice that when I put that tube in the far right socket, that initial glowing is barely noticeable. Actually now that I'm paying closer attention, I see that the 2 right sockets seem to take an extra 1-2 seconds to glow compared to the 2 left sockets which start to glow immediately on power-up. I'd be curious to know if anyone sees this with their GM?

    So I think I'm ok for the time being... just to be prudent I'll order a spare pair of EL84's (which match my current ones) soon.

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