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UNPLANNED DOWNTIME: 12th Oct 23:45

One for Valve Technology experts

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mattacjonesmattacjones Frets: 472
in Amps
Hi - I just wondered why it is that a reasonably expensive set of TAD 6v6gt 69 specials that are in my Imperial MKii should suddenly start doing this (see below). The amp doesn't get used a great deal, I'm not gigging, home use primarily and I have a second amp which I tend to use far more, or the PC.. Anyway - it's a bomb proof amp, suddenly started making this noise when using the trem. Replaced various valves and finally popped a spare pair of 6v6's in. Noise goes away. So, now looks like another set of power valves, but my question is, how can this happen or is it just tough, that's valves for you!? Cheers
(43) Imperial mk ii trem noise - YouTube
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Comments

  • PALPAL Frets: 465
    Did you re bias the amp ! On some amps like Fender Princeton amp biasing can have an effect on the trem .
      
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  • ecc83ecc83 Frets: 1488
    That amp uses something called "Bias modulation tremelo" and although I have some idea how that works I have not come across it nor seen a schematic. From the clip it seems to me that the valves could be being cut off and thus producing that 'click'?

    ICBM or someone else will have met that amp. I suspect that there is some form of 'DC balance' adjustment or it might just be that the original valves have drifted and need re biasing?

    Dave.
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  • RickLucasRickLucas Frets: 353
    edited August 2023
    Ticking tremolo is a common problem. I'm no expert, but I think it can be fixed by moving some wires around and/or putting a cap in there somewhere. Loads of info online about this.
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  • mattacjonesmattacjones Frets: 472
    The amp is cathode biased so apparently no rebias needed on tube swap. Tubes been in there at least 12 months fwiw
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  • mattacjonesmattacjones Frets: 472
    But way of an update, I refitted the offending 6v6s and it's gone away now. WTF?!
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  • Danny1969Danny1969 Frets: 9752
    I was going to say earlier it was unlikely to be a valve, sounds more like the switching noise of the tremolo getting into the audio path. Dodgy cap would be my guess 
    www.2020studios.co.uk 
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  • ICBMICBM Frets: 69426
    mattacjones said:
    But way of an update, I refitted the offending 6v6s and it's gone away now. WTF?!
    Did you put them back in the same positions, or swap them?

    "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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  • mattacjonesmattacjones Frets: 472
    Didnt think to check. I'll swap them and see
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  • mattacjonesmattacjones Frets: 472
    No difference
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  • ICBMICBM Frets: 69426
    I would guess a bad connection between the valve and the socket - a small amount of oxidation/corrosion - causing one valve not to be working, or not working very well, and the tremelo then 'chopping' the waveform into cutoff, as Dave said. Taking the valve out and then putting it back has probably cleaned the contact and fixed it.

    "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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  • mattacjonesmattacjones Frets: 472
    well I'll be. Thanks for the thoughts and guidance. I'll know what to do it it pops up again. I asked Tone King but haven't had an opinion yet. Cheers
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  • marxskimarxski Frets: 201
    edited August 2023
    If the circuit is the same as the classic Fender vibrato  then the ancient service bulletin that was released suggested 1) lead dress 2) putting a capacitor (forget the value) in the bulb circuit.

    the ‘78 Deluxe I got last weekend does it although not as loudly as your video.

    EDIT - just saw someone has a likely cure to this particular case. 
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  • Alex2678Alex2678 Frets: 909
    marxski said:
    If the circuit is the same as the classic Fender vibrato  then the ancient service bulletin that was released suggested 1) lead dress 2) putting a capacitor (forget the value) in the bulb circuit.

    the ‘78 Deluxe I got last weekend does it although not as loudly as your video.
    Looks like the imperial uses bias tremolo, the Fender issue with ticking is with their optocoupler trem
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