Tube testing South UK

Discussion in 'Amp Central Station' started by 52BIGSBY, Sep 6, 2013.

  1. 52BIGSBY

    52BIGSBY Tele-Meister

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    Hello Telers,
    I am based near Portsmouth in the South of England, and have recently purchased a Vox AC30 hand wired head. Although new, and I do not expect the valves to fail in the short term, I am aware of the need to have spares just in case.
    I note that it is advised that valves should be replaced in matched pairs, (inner two and outer two I think?). I cannot afford to buy a replacement set as one sees advertised, however I do see many mullard EL84 and similar on thEBay that go for sums I can afford.
    I have no means of testing these valves in order to match them in whatever way they are matched, and the ones that are sold as such seem to fetch more £'s per valve. So two questions:
    Is there anyone near me who can test valves for a reasonable price?
    If I just carried one EL84 and 12AX7 or similar would that suffice until I found a matched pair, and what difference would it make in the "real world"?
    Thank you for any help,
    Richard.
     
  2. Captain Bb

    Captain Bb Tele-Holic

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    The 12aX7 pre-amp valves are okay to just swap out as you like.

    Only the power valves need to be matched (ideally) - although it isn't strictly essential if the valve tolerances (current draw) are close enough.

    A quick and dirty method for checking a new power valve is to just swap it for one of the old valves in the amp and watch the new valve (once it has warmed up) while you are playing it. If it doesn't red plate then the valve will be safe to use as an emergency spare. Never use a valve that is showing signs of red plating.

    This is what red plating looks like:

    [​IMG]
     
  3. leebman

    leebman Tele-Meister

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    It is probably more efficient to find a good amp tech in your area get your gear serviced regularly and only get tubes when you need them.
     
  4. backline

    backline Tele-Afflicted

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  5. Captain Bb

    Captain Bb Tele-Holic

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  6. leebman

    leebman Tele-Meister

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    I will give a thumbs up for Karltone he sorted me some valves when hotrox kept sending duff ones.
     
  7. bananafist

    bananafist Tele-Meister

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    I live not far from you and have only found one guy in Hove with the knowledge and equipment to test valves and modify/repair tube amps. He is a guitarist, and does quite a bit of studio stuff (repairs/servicing too). If you want his name send me a pm.
     
  8. jefrs

    jefrs Doctor of Teleocity

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    Watford Valves does test his valves

    If your HW AC30 was Made in England then the valves in it probably came from there, otherwise OEM valves tend to be shoddy and don't last all that long.

    When you do eventually re-valve then do so with 'better' valves.
    One of the best methods is to email Derek Rocco at Watford and ask what he recommends from his current stock, expect a concise answer. It's a one-man show, he's very busy and not very talkative, but he is competent, reliable and gives good service.

    You can swing all sorts of changes by swapping the ECC83 individually as different makes and models have varying characteristics. Most ECC83 try to copy Mullard or Telefunken, but Brimar were better. Some copy American NOS 12AX7 models, but the AC30 is a Brit-amp ;) Do Not ever pay silly money for NOS, there are some good new ones better than the cheap NOS available.

    There is a huge variation in gain and current on EL84 models, and they have to be changed en-bloc, all four. Whilst high-gain, high-current versions are the loudest ime they are perhaps not the most musical. Unlike their ECC83, Mullard EL84 were never the best-in-class. I did a little "review" of some odd-ball EL84 in a recent thread on here. (qv)

    Have a look here - http://www.watfordvalves.com/home.asp
     
  9. jefrs

    jefrs Doctor of Teleocity

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    I have never needed to get valves tested.

    I /can/ get them tested because I know a man I can ask a personal favour but even he will tell you that the amp is the best tester. No, I cannot offer his services.
    How do you know when a valve is dead? it stops working, or sounds bad.

    The AC30 is cathode/self-biased so no messing about adjusting the grid-bias, so you can pop any EL84 in, but best if they are at least same make/model on either side, two pairs even if they are not 'matched', replace in pairs, or a 'matched' quad.

    The ECC83 PI-driver probably best if it is 'balanced'.
    The VI ECC83 probably best if it is a 'low-noise' type.
    ECC83 are available in various gain (from testing data), high-gain is not always most musical.

    Once you have re-valved a few amps, you tend to end up with a few known-good used bottles to use as spares. Don't keep the dead ones ;(
     
  10. 52BIGSBY

    52BIGSBY Tele-Meister

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    Thank you all for the useful replies. Things are financially very tight for me at the moment. I have seen some used mullards go for about £8, and if I find two out of three that balance then I am on to a good thing? Good picture of red plating.
    Thank you all again,
    Richard.
     
  11. jefrs

    jefrs Doctor of Teleocity

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    Used valves are used valves.

    I have some genuine Mullards in use, both ECC83 and EL84. The Harma-Retro are close copies.

    Mullard only ever came in Mullard boxes even to the military, so if it is in a white box then it has been re-boxed and you gotta ask why.

    You do not need to hold spares until you can afford to re-valve because the delivery from Watford is that fast. You would be sans amp only for a day or two if you break down.
     
  12. Ron Garson

    Ron Garson Friend of Leo's Silver Supporter

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    Another place you can check out is http://vyseamps.com/ as Barry Vyse does know a thing or two about valves! :)
     
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