Horrible static bursts from my BF PR clone - any ideas?

rexterrexter Frets: 369
edited November 2017 in Amps tFB Trader
I have a hand wired BF Princeton Reverb type amp made by Klone, a German company. 

Sounds fantastic, but definitely needs looking at. I've always been a bit suspicious of one of the power tube sockets as it seems to get very hot around here and one of the Tung Sol 6V6s it came with was blue arching and there was quite a bit of hum. Switched these to Brimar 6V6s really fattened up the sound - this was early last year. I know I should have had it rebiased when I did this but it looks to me like the only amp guy I've heard good things about round here (Pete at SonicFix) has stopped working - or at least website down for months.

When i play through the amp for more than 10/15 minutes now I start getting these crazy static bursts. Thought I had a bad 12ax7 which i switched out tonight - still the same problem...

Any ideas people? I seem to be able to trigger it with lower notes and also touching the power cable where it plugs into the back of the amp.

Here's what it sounds like!

https://drive.google.com/open?id=1vcESJYz2_X0y5KhjTgEEdI18S8QbsLP8

I know the answer is 'take it to a good tech'... just wondering if anyone has experienced this kind of thing and it's possible causes.


If there could be a simple solution, I'm not adverse to poking around in amps and checking out solder joints etc as have done some basic stuff on Silverfaces before, but did give myself a bit of a shock on a Kalamazoo Reverb the other year so am a bit more wary now!

Thanks!
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Comments

  • ICBMICBM Frets: 71951
    The clip doesn't seem to want to work for me, but if it does it when you touch the mains cable, a break in the cable - most likely where it goes through the chassis clamp, if one has been used - is a strong possibility.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • rexterrexter Frets: 369
    tFB Trader
    Hey thank you, definitely does trigger it when i touch the connecter from the power cable into the amp when it’s in operation and the static bursts have started.

    Would a problem in that area potentially lead to excessive heat possibly damaging power tubes? 

     It’s been shipped internationally a couple of times since I’ve owned it so that probably hasn’t helped it!
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  • rexterrexter Frets: 369
    tFB Trader
    Custom colours, vintage restorations, high end guitar finishing
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  • DJH83004DJH83004 Frets: 196
    Managed to get the audio clip to play, and it's definitely something arcing internally, could either be a break in the mains cable or the HT tracking somewhere, possibly a valve base. I would strongly suggest you don't use it anymore until it is properly checked out by a competent person.
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  • rexterrexter Frets: 369
    tFB Trader
    DJH83004 said:
    Managed to get the audio clip to play, and it's definitely something arcing internally, could either be a break in the mains cable or the HT tracking somewhere, possibly a valve base. I would strongly suggest you don't use it anymore until it is properly checked out by a competent person.
    Thanks very much, wise advise you're right. I tend not to dare to fire it up often because of this. I just checked out your website and I don't bloody believe it but you're based literally 5 minutes walk from my folks' house! I was planning to drive up in a week or so to pinch my dad's drill press - might have to pay you a visit, would love to be able to use this amp without fear!
    Custom colours, vintage restorations, high end guitar finishing
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  • DJH83004DJH83004 Frets: 196
    Absolutely no problem at all, you would need to leave it with me for about a week or so though, due to my backlog.
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  • rexterrexter Frets: 369
    tFB Trader
    DJH83004 said:
    Absolutely no problem at all, you would need to leave it with me for about a week or so though, due to my backlog.
    Brilliant, I’ll drop you a PM here or on Facebook!
    Custom colours, vintage restorations, high end guitar finishing
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  • rexterrexter Frets: 369
    tFB Trader
    After a trip to Nottingham to visit family and a short stay at Dave's place (the amps, not me!) I've revelling in the joys of having a Princeton Reverb clone that sounds amazing and no longer emits terrifying bursts of static. Also the tube bias vibrato is now slowed to a more usable rate and stronger than ever! And other small issues fixed.

    As an added bonus, I can now experience my Bandmaster Reverb/Vibrolux style combo working correctly for the first time in the six/seven years that I've owned it. It had a very weird problem with the treble pot having no effect which others could not diagnose or fix. But Dave tracked down the issue and fixed it, sorting out some other issues along the way too. It's a strange situation, but now I have to re-learn the amp, as I suppose I had got used to it operating incorrectly! But it's sounding great and Dave turned things around in a week for a price that was far more reasonable than I'm used to. Great to have found such a good amp tech!

    Taking my amps in is kind of like going to the dentist for me - I worry about it, so put it off for as long as possible fearing the worst - and a massive bill at the end ... this experience seems to change finally that, cheers Dave!


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  • DJH83004DJH83004 Frets: 196
    Thank you for the kind words Jon, you have two really nice amps there. I am still amazed that your parents live just around the corner from me! 
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  • rexterrexter Frets: 369
    tFB Trader
    Not at all Dave, thank you. Yeah a really big coincidence that made me take the leap and glad I did.

    Yep, they are really great amps... not sure the neighbours back here will agree though!
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  • ChalkyChalky Frets: 6807
    Good news! So what was the official diagnosis and corrective actions?
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  • rexterrexter Frets: 369
    tFB Trader
    The main problem of the scary static noises was being caused by a loose solder joint - "HT centre tap ground connection badly soldered to earth tag making intermittent connection". Promptly re-soldered. Dave did a very thorough investigation by the looks of the report he gave me. There were other minor niggles that Dave sorted too, alongside slowing the vibrato rate and increasing its intensity, he tightened the reverb cable connectors which solved the problem of intermittent reverb, checked and corrected bias for the NOS Brimar 6V6s I have in there and gave all sockets etc a thorough clean. Probably the best spect £50 of 2017 for me!

    Side note: this amp has WGS ET65 speaker in it, which I know strays from the 10" format so maybe not for purists, but it sounds excellent!

    One thing I've just noticed is that previously the back of the chassis around the power supply input was insanely hot and almost burning to touch even just a few minutes after powering the amp up. Now it's cool to the touch. I'm wondering how I didn't manage to fry myself over the last couple of years!


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  • ICBMICBM Frets: 71951
    rexter said:

    One thing I've just noticed is that previously the back of the chassis around the power supply input was insanely hot and almost burning to touch even just a few minutes after powering the amp up. Now it's cool to the touch. I'm wondering how I didn't manage to fry myself over the last couple of years!
    Sounds like it was running *way* too hot. Not only does that shorten the life of the valves, it reduces the tremolo intensity on a bias-trem amp because the swing doesn't go close enough to cut off, as Dave said. There is a fashion for biasing right up to - or above - the 70% of maximum dissipation mark, apparently in the belief that it sounds better for the amp to run very hot, but it really isn't a good idea usually.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • rexterrexter Frets: 369
    tFB Trader
    Probably so. It did get crunchy at around 4 on the volume and by 5/6 pretty gnarly. Haven't had the chance to push it that far since getting it back yesterday, so will be interesting to see if that's changed.
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  • DJH83004DJH83004 Frets: 196
    As IC quite rightly says everything was running hotter than it needed to be including the rectifier, and the IEC socket was basically sandwiched in between the rectifier and one of the output valves, so the whole area was starting to cook.
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