Sorta OT: Removing power tubes?

[blueduck577]

I have a Peavey Classic 50 and I've heard of people removing a pair of power tubes to get the amp to distort more easily at lower volumes.  I don't know if this is safe or not, and I know next to nothing about amps or tubes, so I did some googling and got inconsistent answers.  Some people say that I can remove a pair and be fine, others say that it changes the impedances so I'd have to use a different speaker output.

A lot of you guys really know your stuff, and a lot of you love tube stuff.  So tell me, would this be a safe thing to do?  Will I blow up my output transformer?

[R.G.]

For (1) a class AB fixed bias amp and (2) an amp that's not on the edge of some other problem, it's safe. The PC50 qualifies on (1), don't know about the design or your particular amp on (2).

However,  you simply must remove one tube from each side of the output transformer, not two from one side. If that statement is mysterious, don't be messing with your amp.

While we're at it, this dodge *may* reduce your amp's output power by half. That will NOT reduce the output volume by half, or make a huge difference in the sound level where it starts to distort. A little, but not huge.

The human ear does perverse things, hearing quiet sounds easily, but "compressing" the louder sounds logarithmically, so you need about 1/10 the power to sound half as loud subjectively.

The real answer to getting overdriven amp distortion more easily at lower volumes is to get a smaller amp.

[blueduck577]

Thanks, RG.  So I'm not going to have to plug my speakers into a different output?

I wont mind if there is a no perceptible difference.  It's an easy mod to do and an easy one to reverse, so I have nothing to lose by trying it.  If I don't like it, I'll just put the tubes back in.

[.Mike]

To add a bit to what R.G. said (I can't believe I can add anything... heh), some Peavey amps, like the Classic 30 / Delta Blues, run their heaters in series. That means that if you do pull two tubes, you also remove the power to the heaters in the other tubes, and the amp won't work at all.

I've read that you can get around this by taking a couple of old tubes, clipping all of the pins except the heaters, and reinstalling them. Sounds risky to me, having a tube held in by just two pins.

Mike

[R.G.]

To add a bit to what R.G. said (I can't believe I can add anything... heh), some Peavey amps, like the Classic 30 / Delta Blues, run their heaters in series. That means that if you do pull two tubes, you also remove the power to the heaters in the other tubes, and the amp won't work at all.

If I'm reading the schemo I found on line correctly, they're all parallel in the C50.  And you'd pull (V4 and V5) as a pair OR (V6 and V7) as a pair.

If the schematic I found is any good.

If.

[PRR]

> I'm not going to have to plug my speakers into a different output?

If you needed "exactly Half", yes.

Since you just want "less", no. It may be a third, but so what?

Note that half third or quarter power is NOT a lot less loud. If the neighbors are complaining, you should be thinking tenth power to get less complaints, and I think many situations call for 1/100th the Watts of a typical stage amp. Yes, Part-Watt.

> It's an easy mod to do and an easy one to reverse... just put the tubes back in. ...I know next to nothing about amps or tubes

Note that tubes do not come out real easy, and on Octals (base under the glass) there is a plastic center nub which is much too easy to bust-off. Without the nub, an Octal will go in the socket 8 different ways, only 1 works right, and 3 or 4 of those wrong-ways will burn-up expensive parts.

Miniatures (pins come right out of glass; most small tubes) are harder to put in wrong, but it can be done.

I do feel you should know how to change your own tubes. That's a Basic Skill, or used to be.

Ideally a tube comes out with a straight up yank. In fact you can't get all 7, 8, or 9 pins going all at once. You end up rocking it. The Octal's center nub may break before you think you are over-stressing. Miniatures will take more rocking, no nub and the pins bend nice, but it is still possible to over-bend pins and crack the seal, let the vacuum out.

On poorly-made or over-cooked Octals you can also pull the glass off the base.

Grip the base. If it is slippery, use a rubber grippy. Pull up, and wobble the top in very small circles while pulling up.

[blueduck577]

Thanks PRR.  I've changed the tubes before, so no worries.  When I said I knew nothing about amps I meant the circuitry.

I'm not too fond of the drive channel on my amp, but I absolutely love when the clean channel starts to get crunchy.  I'm just trying to get some more breakup without having to crank my amp up to 11 and then drowning out my bandmates 

[PRR]

> I've changed the tubes before

Cool.

Someone else may benefit. Some of us grew up fixing (tube-replacing) tube radios and TVs, but there's a younger generation which has not yet learned all the mistakes, tricks, and tips.

[zombiwoof]

Thanks, RG.  So I'm not going to have to plug my speakers into a different output?

I wont mind if there is a no perceptible difference.  It's an easy mod to do and an easy one to reverse, so I have nothing to lose by trying it.  If I don't like it, I'll just put the tubes back in.

Removing two power tubes changes the output impedance of the amp.  If you were previously plugging into the 8 ohm ouput, you are supposed to plug into the 4 ohm output after taking out the two tubes, or set the impedance selector one position lower if you have one (I don't know how your amp is set up).  Or put a load of twice the impedance on the amp (guys with Twin Reverbs would sometimes pull two tubes and disable one of the two speakers).

Al

[R.G.]

Removing two power tubes changes the output impedance of the amp.  If you were previously plugging into the 8 ohm ouput, you are supposed to plug into the 4 ohm output after taking out the two tubes, or set the impedance selector one position lower if you have one (I don't know how your amp is set up).  Or put a load of twice the impedance on the amp (guys with Twin Reverbs would sometimes pull two tubes and disable one of the two speakers).

You can do this, but in spite of the flame wars on alt.guitar.stuff.and.nonsense, you don't have to. Changing impedance 2:1 won't harm your amp or speakers, although it may change the tone slightly.

[zombiwoof]

Removing two power tubes changes the output impedance of the amp.  If you were previously plugging into the 8 ohm ouput, you are supposed to plug into the 4 ohm output after taking out the two tubes, or set the impedance selector one position lower if you have one (I don't know how your amp is set up).  Or put a load of twice the impedance on the amp (guys with Twin Reverbs would sometimes pull two tubes and disable one of the two speakers).

You can do this, but in spite of the flame wars on alt.guitar.stuff.and.nonsense, you don't have to. Changing impedance 2:1 won't harm your amp or speakers, although it may change the tone slightly.

I think that depends on the amp, that's fine with Fenders for instance, but with Marshalls the advice is to always match impedance exactly, as they are less tolerant of mismatches.  I just don't know if Peaveys like the OP's are tolerant of mismatches or not, so that's why I posted that.  You could be absolutely correct in this case.

Al

[mac]

The real answer to getting overdriven amp distortion more easily at lower volumes is to get a smaller amp

+1.
Laney, Marshall, Epiphone and others have released low wattage amps, some cheap some not.
I bought a VJ for this reason. But 5 watts are still a lot of noise if you live in a building. I had to make a power attenuator for my VJ.
Some small amps have built-in power attenuators.

mac

[jacobyjd]

I can still say that the most useful purchase I've ever made for allowing my amps to be on pretty much the same playing field in [most] situations is my Weber attenuator.

I have the 50w version, and it's unbelievably useful for amps in the 5-40w range. There are a few compromises, but nothing that is unacceptable.

The only thing better would probably be power scaling, but this is far less intrusive

[tubelectron]

Well,
IMHO of nearly 30 years of building and servicing tube amps, I am merely tempted to say "if it works, don't fix it" : let your amp factory stock, with it's 4xEL84/6BQ5. Yes, your amp will sound (bad or good ?) with 2 tubes removed, but how long before failure or roasted remaining power tubes ? Of course, it's up to you to decide the use or abuse of your amp, but... stay wise !
A+!

[DougH]

I pulled two tubes in my modded 100W windsor and set the impedance switch to compensate and it sounded fine. In this particular case there was a slight increase in high freq response when I did that. I eventually went back to running it with all 4 output tubes and use an attenuator, which I prefer. People pull two tubes all the times in amps like this and it works fine. The volume drop will be noticeable but it will still be very loud.

[trjones1]

I bought a VJ for this reason. But 5 watts are still a lot of noise if you live in a building. I had to make a power attenuator for my VJ.

Do you think you could link to a power attenuator project?  I recently bought a Valve Junior and it is incredibly loud for just 5 watts.  It blows away the Kalamazoo Model 2 I have which is rated around the same power level.  And by blows away I mean the Epi on 5 is louder than the Kalamazoo on 10.

[R.G.]

I think that depends on the amp, that's fine with Fenders for instance, but with Marshalls the advice is to always match impedance exactly, as they are less tolerant of mismatches.  I just don't know if Peaveys like the OP's are tolerant of mismatches or not, so that's why I posted that.  You could be absolutely correct in this case.

I should have given my standard warning/disclaimer with this. I normally say "if there is nothing else wrong with the amp, then changing..." and follow up with a note that most Marshalls are on the edge enough by design to make any tinkering chancy.

You are correct - it depends on the amp. I would put it another way: for almost all amps which don't have some other almost-ready-to-fail condition, it will do no harm. All classic Marshalls are almost ready to fail. 

[mac]

Do you think you could link to a power attenuator project?  I recently bought a Valve Junior and it is incredibly loud for just 5 watts.  It blows away the Kalamazoo Model 2 I have which is rated around the same power level.  And by blows away I mean the Epi on 5 is louder than the Kalamazoo on 10.

http://www.diystompboxes.com/smfforum/index.php?topic=84633.0

I still have to try coils which might sound better.

mac

[DougH]

Go to Amp Garage, register, and get their plans for an "Airbrake". They have a Mouser parts list included. With Mouser parts it will run you a little under $100. I built one with mostly surplus parts for about $35. It took me about a half hour to build. When you are finished you will have a fine sounding attenuator that handles 4, 8, 16 ohm loads and will work with up to 100W amps. IOW, it will pretty much cover everything for all your amps.

One of the issues with impedance mismatches with vintage amps is their output xformers may not have the extra current capacity if you stress them.

[Cliff Schecht]

Go to Amp Garage, register, and get their plans for an "Airbrake". They have a Mouser parts list included. With Mouser parts it will run you a little under $100. I built one with mostly surplus parts for about $35. It took me about a half hour to build. When you are finished you will have a fine sounding attenuator that handles 4, 8, 16 ohm loads and will work with up to 100W amps. IOW, it will pretty much cover everything for all your amps.

One of the issues with impedance mismatches with vintage amps is their output xformers may not have the extra current capacity if you stress them.

Yes, yes and YES!! I use an Airbrake live with my Express build when I'm playing small bars or at band practice when I don't want to cut peoples heads off. Cost me all of nothing to build too, I had everything I needed on hand (I knew my rheostat collection would come in handy!). The files are available from TAG but you have to do some digging to find them.

Here are some pics of mine (you have to sign in to see them I think):
http://ampgarage.com/forum/viewtopic.php?t=10802&start=0&postdays=0&postorder=asc&highlight=attenuator