Again on Triple Rectifier used pulling tubes

[DS-1]

I've noticed that seems to be a lot of confusion about using Triple Rectifier pulling out tubes. On some posts I've found that it couldn't be done, but according to this post: http://forum.grailtone.com/viewtopic.php?t=6998&highlight=triple+rectifier+half+power , it seems to work. So please can anyone tell me if it can be done, as on Dual, without problems? In this case what tubes should I pull out to reduce the power? Thanks in advance.

 

[nathan28]

Yes you can pull the outer tubes and drop your triple down to 100 watts, but you have to pull out one of the rec tubes as well. You can pull the same tubes out on a dual and make it 50 watts. You cannot pull two pairs of power tubes out and make your triple 50 watts. At least that is what mesa told me when i called them.

 

[warped]

Be carefull pulling tubes on a triple rectifier.

Pulling out 2 of the 4 tubes on a Dual rectifier means you also need to half the impedance (ie, plug your 8ohn Mesa cab into the 16 ohm speaker output, as with all 4 power tubes, your 16ohm speaker out expects 16ohms, however pulling 2 tubes will mean your 16 ohm speaker output is now expecting 8ohms).

Pulling 2 tubes on a triple rectifier kinda leaves you in limbo with impedances - your 16 ohm speaker output expects 16 ohms with 6 power tubes, but if you pull 2 tubes your 16 ohm speaker output expects 16 x 2/3 = 10.6 ohms, and your 8 ohm speaker output expects 8 x 2/3 = 5.333 so you don't have a matching cab with this impedance to use.

Mismatching impedances can be safe in some cases, but I wouldn't recommend it.

Just my 2 cents - I'm sure some more technically minded people can explain it better (I might even have this mixed up myself)..

 

[JW123]

I have the inner tubes pulled in mine and 1 rec tube. I did try pulling 4 for a while but the amp sounded real thin. It could have been an impedence issue with cab. I also have some THD Yellowjackets that Ive put in with 4 EL 84s. It does lower the volume or sound pressure level some but sounds kind of ice picky to me. I use a Weber Mass for home practice to lower the volume, for recording I prefer turning it up and isolating the cab in another room.

 

[Sustain]

first off it doesnt matter which rectifier tube you pull

secondly, you are to remove the INNER 2 tubes on a dual recto, not the outer.

 

[Sustain]

Be carefull pulling tubes on a triple rectifier.

Pulling out 2 of the 4 tubes on a Dual rectifier means you also need to half the impedance (ie, plug your 8ohn Mesa cab into the 16 ohm speaker output, as with all 4 power tubes, your 16ohm speaker out expects 16ohms, however pulling 2 tubes will mean your 16 ohm speaker output is now expecting 8ohms).

Pulling 2 tubes on a triple rectifier kinda leaves you in limbo with impedances - your 16 ohm speaker output expects 16 ohms with 6 power tubes, but if you pull 2 tubes your 16 ohm speaker output expects 16 x 2/3 = 10.6 ohms, and your 8 ohm speaker output expects 8 x 2/3 = 5.333 so you don't have a matching cab with this impedance to use.

Mismatching impedances can be safe in some cases, but I wouldn't recommend it.

Just my 2 cents - I'm sure some more technically minded people can explain it better (I might even have this mixed up myself)..

mesa engineering has indicated to me that is it NOT an even change for impedance. yes it does change in the direction you have indicated, but it is not a "half the tubes went so half the impedance went too" scenario.

I was told that it does not half the impedance when you remove 2 tubes it only lessens it some. therefore if you operate as per the usual standard as indicated in the manuals, its safer to run the one direction than the other, but it is not a direct half for half change.

to be clear, just because you remove half the tubes you only move some, not a full half of impedance, giving yourself a guaranteed mismatch, but they are durable and can withstand a partial mismatch.

 

[DS-1]

Thanks all for the replies. I have a 16 ohm Marshall cab on my Triple. Pulling out two power tubes and a rectifier one, what impedance should I use for my cabinet?

 

[JW123]

I know the techies on here will flame me, but I would try it on 16 and then try 8. I would let my ears be the guide. I dont think you are making a big enough change that you will hurt anything. When I pull a set out of my amp I plug in the 8 ohm for my 8 ohm Mesa cab. Why cause it sounds better there.

 

[DS-1]

What tubes should I pull? The outer or the inner?

 

[Elpelotero]

It does not matter which you pull as long as they are matched, as in working in the same push-pull configuration pair.

Like this:

X Y Y X

Y X X Y

In the first example, the X's are the outer and Y is the inner. This is what is meant by outer or inner pair.

 

[DS-1]

Thanks a lot, Elpelotero.

 

[ANIMATED SUSPENSION]

You can only do this with the Dual not the Triple !!! I can't really see the point of pulling tubes, it makes very little difference to the volume anyway ??

 

[R_ADKINS80]

You can only do this with the Dual not the Triple !!! I can't really see the point of pulling tubes, it makes very little difference to the volume anyway ??

Completely wrong....you CAN do this with a Triple. Mesa told me this directly and that it is perfectly safe. They described it in a scenerio that if you're playing out and experience a failing power tube, you can pull it, it's mate and a rectifier tube and play on as you normally would.

 

[AdmiralB]

You can certainly pull tubes on a triple. It will affect the load that the amp wants to see - pull one pair, and the jacks will want to see loads of 6, 12, and 24 ohms instead of 4, 8, and 16, respectively. Pull two pairs, and it becomes 12, 24, and 48 ohms.

You could run either a 4- or 8-ohm load on the '6-ohm' tap. I'd probably only run an 8-ohm load on the '12-ohm' tap, and a 16-ohm load on the '24-ohm' tap. The '48-ohm' situation is, of course, fairly useless.

Contrary to what appears to be nearly universal opinion, you don't have to pull a rectifier tube. In fact, on a Dual, you should NOT pull one, unless you take a very specific precaution.

If you don't pull a rectifier, the amp will feel more like it's SS rectified. In fact, it'll feel that way to a degree anyway, since by pulling power tubes you've lightened the load on the power supply and it'll sag less under any circumstance.

However, there's a parameter related to rectifier tubes that I've never seen mentioned in these threads, and that is maximum input capacitance. When used in a capacitor-input circuit (which includes 99.9% of all guitar amps), there is a maximum amount of capacitance that tube rectifiers are rated to 'see'. This is because at the instant you take the amp off standby, the first filter cap looks like a dead short to the tube, and it is asked to provide an infinite amount of current for an instant. The time over which that stress occurs is affected by the size of the first filter cap (or caps).

For the 5U4 family, that maximum size is 40uF.

The Rectifier amps use a pair of 220uF caps in series, for an effective input capacitance of 110uF.

It's clear that the pair of 5U4s wants to see around 80uF (the current capacity is additive, when rectifiers are connected in parallel), so the stock Dual circuit is already stressing them somewhat. The stock Triple circuit, with 120uF of 'capacity', is fine.

So, if you pull one rectifier from a triple, you're showing the remaining pair of tubes a load that's higher than they'd like to see, but not critically so.

However, if you pull a rectifier from a Dual, you're showing the remaining tube almost three times the maximum load for which it was designed.

Happily, there is a way around this - power the amp up set to use the SS diodes, then after charging the filters (i.e. taking the amp off standby), switch to the tube(s). This will let the caps charge from the SS rectification (which effectively has no limit on input capacitance), and then the tube(s) can take over afterward.

 

[ANIMATED SUSPENSION]

You can only do this with the Dual not the Triple !!! I can't really see the point of pulling tubes, it makes very little difference to the volume anyway ??

Completely wrong....you CAN do this with a Triple. Mesa told me this directly and that it is perfectly safe. They described it in a scenerio that if you're playing out and experience a failing power tube, you can pull it, it's mate and a rectifier tube and play on as you normally would.

I was referring to the example above which shows only 4 tubes, the Triple has 6 ! Why does it specify to remove the inner tubes ONLY in a Dual Rec then ? From what you're saying you can pull any pair out of the 6 in a Triple ? I'm guessing this is only as a temporary fix and not recommended long term ? I'd ask for it in writing personally !!

 

[DS-1]

You can certainly pull tubes on a triple. It will affect the load that the amp wants to see - pull one pair, and the jacks will want to see loads of 6, 12, and 24 ohms instead of 4, 8, and 16, respectively. Pull two pairs, and it becomes 12, 24, and 48 ohms.

You could run either a 4- or 8-ohm load on the '6-ohm' tap. I'd probably only run an 8-ohm load on the '12-ohm' tap, and a 16-ohm load on the '24-ohm' tap. The '48-ohm' situation is, of course, fairly useless.

Contrary to what appears to be nearly universal opinion, you don't have to pull a rectifier tube. In fact, on a Dual, you should NOT pull one, unless you take a very specific precaution.

If you don't pull a rectifier, the amp will feel more like it's SS rectified. In fact, it'll feel that way to a degree anyway, since by pulling power tubes you've lightened the load on the power supply and it'll sag less under any circumstance.

However, there's a parameter related to rectifier tubes that I've never seen mentioned in these threads, and that is maximum input capacitance. When used in a capacitor-input circuit (which includes 99.9% of all guitar amps), there is a maximum amount of capacitance that tube rectifiers are rated to 'see'. This is because at the instant you take the amp off standby, the first filter cap looks like a dead short to the tube, and it is asked to provide an infinite amount of current for an instant. The time over which that stress occurs is affected by the size of the first filter cap (or caps).

For the 5U4 family, that maximum size is 40uF.

The Rectifier amps use a pair of 220uF caps in series, for an effective input capacitance of 110uF.

It's clear that the pair of 5U4s wants to see around 80uF (the current capacity is additive, when rectifiers are connected in parallel), so the stock Dual circuit is already stressing them somewhat. The stock Triple circuit, with 120uF of 'capacity', is fine.

So, if you pull one rectifier from a triple, you're showing the remaining pair of tubes a load that's higher than they'd like to see, but not critically so.

However, if you pull a rectifier from a Dual, you're showing the remaining tube almost three times the maximum load for which it was designed.

Happily, there is a way around this - power the amp up set to use the SS diodes, then after charging the filters (i.e. taking the amp off standby), switch to the tube(s). This will let the caps charge from the SS rectification (which effectively has no limit on input capacitance), and then the tube(s) can take over afterward.

Thanks a lot, man. I have a 8 cab cabinet, so I can run it thru my 8 output, without changing nothing...right? In what way, in your opinion, this can change the sound of the beast? I also would like to try EL-34 in my Triple, trying to "open" a bit the hi-mid, so I think I'll buy a matched couple. Do you think is it a good try?

 

[AdmiralB]

There's no reason you'd have to pull a specific pair (or, in the case of the Triple, a specific quartet). As long as you take the same number from each side of the OT primary, it'll work.

In the case of a Dual:

A B C D

You can pull A or B, AND C or D. They don't have to 'appear' symmetric.

On a Triple:

A B C D E F

You can pull one or two from the A, B, C set, and one or two from the C, D, E set - as long as you pull the same number from each side and observe impedance effects.

 

[AdmiralB]

I have a 8 cab cabinet, so I can run it thru my 8 output, without changing nothing...right? In what way, in your opinion, this can change the sound of the beast? I also would like to try EL-34 in my Triple, trying to "open" a bit the hi-mid, so I think I'll buy a matched couple. Do you think is it a good try?

Yeah, if you pull a pair from a Triple, you can leave the cab where it is, from an impedance perspective.

I doubt it'll change the tone significantly, though.

If you mean trying just a pair of EL34s in your amp, that'll be fine but do remember the impedance issues I mentioned above. And of course you can't mix EL34s and 6L6s without 'cherry picking' tubes that all idle properly with the same bias setting.

 

[DS-1]

Ok, thanks to all. Today I'll try pulling 2 tubes to ear if there are differences in the sound. Then I'll try with 4 EL-34, to try to set the Triple a bit more "open" in the sound. What EL-34 do you think I should use? I can take some Electro Harmonix with a good price. Should I try it, or do you think it's better to use Mesa's tube? Do I need to buy 2 matched pairs?

 

[Gtr_Pkr]

I would try the EH 6CA7. It's a rugged tube and sounds great in my Marshalls. I would suggest getting a matched quad. Try and get the EH's matched to the same mA as the Mesa tubes. That should work.