Preamp tube shields.

Discussion in 'Glowing Bottle Tube Amp Forum' started by Dr Improbable, Jun 6, 2019.

  1. Dr Improbable

    Dr Improbable Tele-Meister

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    The little metal things. Do you folks leave them on? Leave them off? If so, why?
     
  2. Ricky D.

    Ricky D. Poster Extraordinaire

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    It's good to leave them on. Those tubes are very sensitive because they amplify low level signals. The shields block RF interference.
     
  3. theprofessor

    theprofessor Friend of Leo's

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    I leave them on now, but I used to keep them off and use tube damper rings. Yes, leaving them on can help prevent radio frequency interference. But those shields can rattle, too. They rattle on my 5f4, and I wish they didn't.
     
  4. beninma

    beninma Friend of Leo's Silver Supporter

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    I have them on my Orange.. they are very tight and would be very hard to vibrate. I left them on. They are a bayonet mount type design, slide on, push the spring down (pretty heavy spring) and twist to lock them in.

    I find it interesting the power tubes don't work that way at all. The power tubes have some kind of rubber/cloth strap with an eyelet that goes over the top of the tube, then a larger cage that bolts down covering both power tubes.

    Who likes RF interference? My amp is really quiet, even compared to some of the SS amps I've owned, and I would normally expect transistors to pick up way less noise.
     
  5. 3-Chord-Genius

    3-Chord-Genius Poster Extraordinaire

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    Honestly, I've never heard of anyone taking them off. Is that a thing?
     
  6. Bob M

    Bob M Tele-Afflicted Ad Free Member

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    Leave them on. For the best reason-Is that not what Leo intended?
     
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  7. Dr Improbable

    Dr Improbable Tele-Meister

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    Yeah, I'm leaving them on. Thanks!
     
  8. Greg_L

    Greg_L Tele-Holic

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    I leave them on if they're there. If they're missing and the amp isn't noisy then I don't worry about it.
     
  9. teletimetx

    teletimetx Doctor of Teleocity

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    I'm hoping, for the sake of all humanity, that a professor can figure out how to fix that rattle...I mean, if you can't, what hope do the rest of us have? :):D (...or maybe try: http://www.tdpri.com/threads/tube-rattle-problem-help.253032/page-2 - see post #24...)
     
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  10. King Fan

    King Fan Friend of Leo's Ad Free Member

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    Heh, I'm gonna think different here. I had an amp with tubes upright inside a perf metal cage — you can bet I ran shields off for the gorgeous glow playing in a dim room. In fact, I'm gonna guess the large majority of 'tubes-up' amps don't run shields. On mine, I got the Belton socket version without the shield-mount collar. This looks nicer, and better yet, exposes the shoulders of the bottle, which makes it easier to pull and replace tubes without damaging their lettering.

    Then consider that on tweak-y hi-fi amps you seldom see shields (maybe so you can read the 'Telefunken' tube labels?)

    I had no RF issues on mine with the cage, and many hifi guys don’t cage. So I think the shield is somewhat for RF but even more to suppress vibration and discourage microphonics. Tweak-y hifi amps seldom get carried to gigs or (gasp) dropped. Still, I guess, if shields were really important for vibration *or* RF, you might not see so many bass amps run like this...

    [​IMG]

    You can hear that shields decrease thermal shock on heating / cooling, but I have no idea if this is true.

    All this makes me think, Professor, you may want to check the springs and mounts and sockets and socket mounting bolts in your 5F4. As above, I have to push fairly hard to get my shields in place when the springs are fresh and centered.
     
    Last edited: Jun 6, 2019
  11. schmee

    schmee Poster Extraordinaire

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    I leave them on. On some amps they help reduce noise a bit. Others not so much so.
     
  12. theprofessor

    theprofessor Friend of Leo's

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    Thanks, KingFan! Will do. I've determined it's not the socket but definitely the shield, at least on one of the preamp tubes, maybe two. I have the Belton tube sockets that have the integrated shield mount. It may be that the spring inside the shield is looser than it should be, and it certainly does not seat very snugly like many of my other tube shields do on preamp tubes. It's perhaps misaligned, leading the inside of the shield to touch the tube or something. I'll give it a look again. I think it's only one of them, but sometimes that's enough to be quite annoying!
     
  13. Silverface

    Silverface Poster Extraordinaire Ad Free Member

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    I leave them on - except in a few cases where I like the tone or gain qualities of a specific tube and it's microphonic with the shield - but not with one of two types of tube rings I use at times - a large red one that doesn't fit under the shield. Small black rings fit but don't always work.

    But understand I have a ton of amp (plus work on others daily) and hundreds of tubes. For 99% of the players out there I just advise leaving the shields on.
     
  14. StoogeSurfer

    StoogeSurfer Tele-Afflicted

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    Since they're sprung, they're also going to help hold your tube in its socket. This is not a metaphor.
     
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