Replacing power tubes, need advice.

Discussion in 'Glowing Bottle Tube Amp Forum' started by Voyevoda, Jul 13, 2020.

  1. Voyevoda

    Voyevoda TDPRI Member

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    Hello all! This is my first post on this forum!. I just got a Ampeg GVT52-112 today and it showed up with a weird sound on certain notes that ended up being a microphonic power tube. Now I have to replace them and I am not sure what kind to get. it is a 25/50w amp. I do not need it to be that loud honestly so I was wondering if I could get a pair of 6v6s and lower the wattage a bit or if that would hurt the amp, thanks!
     
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  2. Dacious

    Dacious Poster Extraordinaire

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    No. You can't just fit lower power tubes. The power and output transformer specs are related to the power specified for the output wattage.

    You need to get some 6L6GC tubes. JJ appear to be tough tubes. Buy a matched pair - that means someone has actually run them in a test rig and checked the tube is mechanically and electrically reliable.

    It would be good to get an amplifier technician to fit and check them in operation in the amp.

    If you do fit them yourself check them on standby, then on operate keep an eye on them to ensure you don't get redplating.

    images (1).jpeg

    The tube on the left is redplating, which is destructive if allowed to continue.

    If the amp sounds OK and makes no thunderstorm sounds, bad loud hums or similar you're good to go.

    A tech is still recommended to.ensure all is well.
     
  3. Voyevoda

    Voyevoda TDPRI Member

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    Okay thanks, on reverb there is a set that says that the JJ 6v6S can be used in this amp, and another option I was looking at was the JJ 5881 which seems to be a 6L6 but a little weaker.
     
  4. Dacious

    Dacious Poster Extraordinaire

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    5881s have roughly the same operating parameters but some are only good for 23watts each in push-pull and might need a different bias point. That's a tech job. You'll probably notice negligible difference in volume.

    The 6L6s have a plate-plate resistance of around 3500-4000 ohms and your output transformer will have a winding ratio to convert that to 8ohms at the speaker taps.

    6V6s expect to 'see' roughly double, 6500-8000 ohms on the output transformer primary.

    Running 'out of range' is possible but again - it's still likely to be very loud and possibly your tubes may not live that long. It may also sound a bit strange. Really the issue is 50 watts with am efficient speaker like the Celestion 7080 is bloody loud. You could try an attenuator, that 'losds down' the power section letting you crank it without deafening volumes.

    You could try an Eminence Maverick soeaker. That has adjustable sensitivity, it can act like an attenuator to drop volume, as it adjusts from 93 to 99 db which basically halves perceived volume.
     
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  5. Voyevoda

    Voyevoda TDPRI Member

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    Okay thanks! I was looking at a Jensen 12-50 which is less efficient than the 7080(and also way cheaper than a maverick)
     
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  6. Dacious

    Dacious Poster Extraordinaire

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    That would work. An attenuator might be a good option though. There's even models with headphone out, which means you can use the amp as a quiet practice unit.
     
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  7. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

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    I have installed 6V6 tubes in a 6L6 type amp. It can be done but you must change the bias voltage. Generally the bias adjustment pot will not have enough range so resistors have to be replaced to use the 6V6 tubes. You will need a tech. You do not have the option to swap tubes anytime you want. It must have the bias changed whenever the tube type changes.

    The Ampeg has 4, 8, and 16ohm speaker jacks. To overcome the output transformer primary mismatch, you simply use the next lower jack. If you have an 8ohm speaker it will plug into the 4ohm jack when you use the 6V6.

    The JJ 6V6 is a rugged tube. It sounds very much like a 6L6. It is not much quieter.

    The amp will be a little quieter but it will still be very loud. If a volume reduction is what you are after. Take the advice of the others here and get an attenuator. Keep the 6L6.

    Changing to the 5881 again does not change the volume much. The main difference is, you may get a different tonal variety than the 6L6 sound. OMMV.

    Best of luck on your quest.
     
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  8. KC

    KC Friend of Leo's

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    I would just get it up and running with the 6L6 tubes & see if you like the thing. Sounds like it might be more amp than you need. I'm always suspicious of hacking an amp to turn it into something it's not. A 2x6L6 amp is kind of a beast in my book -- but a proud beast.
     
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  9. Voyevoda

    Voyevoda TDPRI Member

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    Ye
    Yeah I was looking at attenuators with headphone outs but they are hella expensive. The amp isn’t really too loud as the master volume works great and I can still get some good preamp drive at apartment levels. I was just looking at ways to open up the power section a bit more at the same volume.
     
  10. Ed Storer

    Ed Storer Tele-Holic Silver Supporter

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    Changing tube spec (e.g. 6L6 to 6V6) is a waste of time and money. The change won't give nearly the volume reduction you seek. A good attenuator is what you need.

    Another option is a Peavey Impulse personal monitor. 8 Ohm impedance, 80 Watt power handling, includes an L-pad, two 2x5-1/4 speakers. There is a huge reduction in volume even with the L-Pad on 10.

    PM me if you're interested.
     
  11. zook

    zook Friend of Leo's

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  12. jrblue

    jrblue Friend of Leo's

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    Most of the suggestions made on this thread are unrealistic, oddball, or worse. Don't change your power tube type, period. The power tube type is the basis for the amp's design. If you don't like the kind of power tube or overall output, you need a different amp. Trying to re-engineer this one is, IMO, silly. A low-efficiency speaker will make a real difference in output without changing the amp. Using lower-power preamp tubes will reduce output somewhat, too, and can even be an improvement in headroom and feel depending on your preferences. Those Ampegs are loud amps -- too loud for most applications. I would not go with attenuators, etc.; I'd get a more appropriate amp. Period.
     
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  13. Milspec

    Milspec Poster Extraordinaire Silver Supporter

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    i have to agree with those observations, it is sage advice. As my Father used to say, you buy the shoes that best fit your fit, and the same goes for amplifiers. Trying to make the wrong amp sound like what you really need is never going to end well. Find the amp that fits your needs better and sell off that Ampeg to somebody who is also trying to find the right amp for them.
     
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  14. Voyevoda

    Voyevoda TDPRI Member

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    I also have a vox ac4tv so I already have the tiny amp covered and I got this one for way less than a blues jr so I’m not too worried about having to have the master down low for now. I was just looking for little things I could do for fun so I could see what it’s like opened up a little more
     
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