Sounds like people who max out power brakes and external attenuators and then wonder why their amp frys..... Gee, even if it isnt putting out "loads of volume" having all the controls maxed out is BAD. The amp just isnt made to be run on max power. But that pertains more to power brakes and attenuators.
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400+ Tube removal.
- Thread starter YL_Bass
- Start date
Sounds like people who max out power brakes and external attenuators and then wonder why their amp frys..... Gee, even if it isnt putting out "loads of volume" having all the controls maxed out is BAD. The amp just isnt made to be run on max power. But that pertains more to power brakes and attenuators.
well the guy who said it was ok also told you to use a power brake, even though you can't use one in such a high power amp. whereas the two guys who said it's not good for your amp are amp techs.
why is it that people who don't know anything about amps are the ones who most want to modify them?
I've been running my 400 at 2ohms for almost twenty years now (I use a 4ohm 215 and a 4ohm 1516 Mesa cabs).
Back when I bought it in 1991, the Mesa factory said it was okay, and even my owners manual copy says you can run two 4ohm cabs with no problems.
Even my D180 I ran for years also at 2ohms with the same cabs. That head is still going strong with it's three owners since my ownership.
Don't pull the tubes. Keep the volume down, reduce the number of speakers you're using or get a lower powered amp.
If the amp was designed to run on fewer tubes there'd be fewer tubes in there.
If someone didn't like suggestions of some guys from TB, just read what
Kevin O'Connor said in his tube amp faq about pulling tubes:
Q: In a magazine Q-A, a player wanted to pull tubes to reduce power, but the "expert" said this would cause a meltdown of the remaining tubes. Of course, it was suggested that the expert's attenuator product was the preferred way to go. Is any of this true?
A: This is a person who should know better!
Removing tubes from a multi-tube fixed-bias output stage is never a problem. You can remove any number of tubes, and yes, that means you can take one tube out of a two-tube amp; one, two, or three out of a four tube stage, et cetera. This sounds heretical to techs stuck in the mire of convention, but it is something that has been known since tubes were invented.
The even-number tube extractions reduce power symmetrically. Neither the tubes nor the transformer will be damaged. Power will be reduced and so will frequency bandwidth - you will lose some bass and some treble. This is the point that switching the impedance selector to a less-than-load setting is supposed to correct, but it is completely subjective whether you should. The only 'should' of the matter, is do I like it this way, or do I like it that way?
In the uneven tube extractions, asymmetric power reduction occurs. Conventional thought says "the one tube on one side of the circuit will be trying to match the output of the two tubes on the other circuit half". This is wrong. The single tube can only produce so much power, and that's all it does. It doesn't melt down. The transformer does not blow up.
So, what's missing from conventional thought? The realization that tubes are "self-limiting power governors", which was stated in The Ultimate Tone (TUT), and explored in more detail in TUT2 and TUT3. TUT4 explores all of this in great detail. Our "expert" should get a copy.
In the end, you can pull tubes to reduce power, unless the amp is cathode biased - then you have to split the bias resistor. In any case, you do not have to worry about the impedance selector either.
Invalid Link Removed
Kevin O'Connor said in his tube amp faq about pulling tubes:
Q: In a magazine Q-A, a player wanted to pull tubes to reduce power, but the "expert" said this would cause a meltdown of the remaining tubes. Of course, it was suggested that the expert's attenuator product was the preferred way to go. Is any of this true?
A: This is a person who should know better!
Removing tubes from a multi-tube fixed-bias output stage is never a problem. You can remove any number of tubes, and yes, that means you can take one tube out of a two-tube amp; one, two, or three out of a four tube stage, et cetera. This sounds heretical to techs stuck in the mire of convention, but it is something that has been known since tubes were invented.
The even-number tube extractions reduce power symmetrically. Neither the tubes nor the transformer will be damaged. Power will be reduced and so will frequency bandwidth - you will lose some bass and some treble. This is the point that switching the impedance selector to a less-than-load setting is supposed to correct, but it is completely subjective whether you should. The only 'should' of the matter, is do I like it this way, or do I like it that way?
In the uneven tube extractions, asymmetric power reduction occurs. Conventional thought says "the one tube on one side of the circuit will be trying to match the output of the two tubes on the other circuit half". This is wrong. The single tube can only produce so much power, and that's all it does. It doesn't melt down. The transformer does not blow up.
So, what's missing from conventional thought? The realization that tubes are "self-limiting power governors", which was stated in The Ultimate Tone (TUT), and explored in more detail in TUT2 and TUT3. TUT4 explores all of this in great detail. Our "expert" should get a copy.
In the end, you can pull tubes to reduce power, unless the amp is cathode biased - then you have to split the bias resistor. In any case, you do not have to worry about the impedance selector either.
Invalid Link Removed
- May 9, 2008
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- Proprietor Springvale Studios
tubes have their own impedance and different tube sets require quite different matching transformers.
If you half the number of tubes you will need to half the impedance
of the loudspeaker relative to the secondary (loudspeaker) windings original spec.
From a strict engineering point of view Its not a great idea to do this,
as it is likely to be less reliable than when run with a reserve of power shared among well biased tubes of the right total impedance for the transformer design.
A suitable reliable Powersoak for an amp of this power is only available from Sequis to special order as far as I know.
And next Q from faq. Kevin O'Connor about impedance matching:
Q: I thought impedance matching was critical. Some designers say the output transformer must be changed if you want to use different output tubes. That seems awfully expensive.
A: It is awfully expensive, and awful that such things would be suggested. There are two issues here, though; one is the notion of "impedance matching", and the other is simple design preference.
As stated throughout the TUT-series, speaker load impedances and reflected loads to the output tubes are all "nominal". An 8-ohm speaker may actually look like anything from 6-ohms to 100-ohms, depending on the frequency, since the reactive impedance changes with frequency. This means that the reflected load to the tubes is varying widely over the frequency range.
A nominal 8-ohm load may reflect 4k to the plates of the output tubes with a given transformer. The amp might be designed to produce its maximum power into this load, with a designed frequency response. This is the "power bandwidth". If we change the load to 16-ohms, the reflected load doubles and the frequency response shifts upward. We lose bass but have a brighter sound, and also lose power. If we change to a 4-ohm load, the reflected impedance drops to 2k, into which the tubes produce less power, and the bandwidth is again narrowed.
The reason for the confusion, I believe, is that people think tubes will try to behave the same way transistors do. Into half the load impedance, a transistor will try to deliver twice as much current. The device may overheat and destroy itself in the process. Tubes, however, simply don't behave like transistors.
The design issue for impedance matching comes into play when a designer takes the approach that "everything is critical". In some circuits, this may be the case. Tubes don't really care. There is no optimum load for a tube unless you are going for minimum THD, and this then depends upon the other operating conditions. For guitar, criticality is purely aesthetic. The designer says "this is good", "this is bad" and in that decree believes it to be so. He is correct in his subjective impression, but should not confuse the subjective and objective.
Design approaches are dealt with in TUT4.
Q: I thought impedance matching was critical. Some designers say the output transformer must be changed if you want to use different output tubes. That seems awfully expensive.
A: It is awfully expensive, and awful that such things would be suggested. There are two issues here, though; one is the notion of "impedance matching", and the other is simple design preference.
As stated throughout the TUT-series, speaker load impedances and reflected loads to the output tubes are all "nominal". An 8-ohm speaker may actually look like anything from 6-ohms to 100-ohms, depending on the frequency, since the reactive impedance changes with frequency. This means that the reflected load to the tubes is varying widely over the frequency range.
A nominal 8-ohm load may reflect 4k to the plates of the output tubes with a given transformer. The amp might be designed to produce its maximum power into this load, with a designed frequency response. This is the "power bandwidth". If we change the load to 16-ohms, the reflected load doubles and the frequency response shifts upward. We lose bass but have a brighter sound, and also lose power. If we change to a 4-ohm load, the reflected impedance drops to 2k, into which the tubes produce less power, and the bandwidth is again narrowed.
The reason for the confusion, I believe, is that people think tubes will try to behave the same way transistors do. Into half the load impedance, a transistor will try to deliver twice as much current. The device may overheat and destroy itself in the process. Tubes, however, simply don't behave like transistors.
The design issue for impedance matching comes into play when a designer takes the approach that "everything is critical". In some circuits, this may be the case. Tubes don't really care. There is no optimum load for a tube unless you are going for minimum THD, and this then depends upon the other operating conditions. For guitar, criticality is purely aesthetic. The designer says "this is good", "this is bad" and in that decree believes it to be so. He is correct in his subjective impression, but should not confuse the subjective and objective.
Design approaches are dealt with in TUT4.
- May 9, 2008
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- Proprietor Springvale Studios
Too few loudspeaker ohms is not that dangerous to a tube amp in fact you can run a vintage marshall into a dead short without damage. it just reduces the power output the more mismatch you have, but you didn't notice because you picked up more volume in speaker coupling.
Too many ohms or open circuit is a transformer and tube killer.
The quotes by Kevin O'Connor may or may not be the god's honest truth, but it sounds to me like he is saying "whatever, do anything you want with your tube amp it will just sound different". Or as a drugged out British metaphysical writer once said, "do what thou wilt shall be the whole of the law". Which, speaking subjectively, hasn't been my experience at all. When I just plugged my cabinets in any old way and blasted them, it would end up blowing amps, cabs or both. When I stay within correct impedances (printed on the back of the amps in most cases) and then blast them, it doesn't blow up. We aren't talking about "can an amp do this", sure it can. We are talking about can you do this with this amp and then crank it until it gets overdrive in the power section. Which obviously puts some stress on the system.
Otherwise all you would have to do is turn the master down.
MR Caca? Really? I have been told the exact opposite by Mesa and my tech. I used to work across the street from there and grill those fellas on my lunch break (if I caught them at the cafe). Are you talking about the 400 or the 400+?
I personally run two 4 ohm cabs on a 400 as well. I run them in series to make an 8.
Otherwise all you would have to do is turn the master down.
MR Caca? Really? I have been told the exact opposite by Mesa and my tech. I used to work across the street from there and grill those fellas on my lunch break (if I caught them at the cafe). Are you talking about the 400 or the 400+?
I personally run two 4 ohm cabs on a 400 as well. I run them in series to make an 8.
you can pull 1,1 or 2,2 etc. the front row are all one side of the circuit, the back row is the other, so you could pull one from the front, one from the back. Don't trust me? Pop the bottom cover off and have a look for yourself. Don't be grabbing anything in there, but do have a look.
Pulling tubes is safe to do, But, you will shorten the usable life of the remaining tubes, in the same manner that you would shorten the life by running the amp wide open with all the tubes in.
The closer you operate components toward their maximum limits, usually, the faster they wear out.
Pulling the tubes will change the way the amp sounds, to a certain extent, you may like this, you may not. Give it a try, make your own descision.
Calaverasgrande said:MR Caca? Really? I have been told the exact opposite by Mesa and my tech. I used to work across the street from there and grill those fellas on my lunch break (if I caught them at the cafe). Are you talking about the 400 or the 400+?
I personally run two 4 ohm cabs on a 400 as well. I run them in series to make an 8.
The original 400.
I have an original owners manual, and of course in the 80's their 215 cabs were only available in 4 ohm, and it says in there you can run two of them just fine. Then also in that manual they also go into saying Michael Anthony played his original 400 and multiple 215 cabs night after night.
And yeah it also says you can also (re)wire the 4 ohm cabs to be an 8 ohm load together.
You are quoting Kevin as an expert source. Kevin is a GUITAR player. What you can get away with in a guitar amp is not necessarily applicable in a BASS amp. If a tapped secondary was immaterial why would manufacturers go to the trouble of adding them? Just 'cos someone writes a book doesn't make everything he says gospel.
A tube amp is happiest when it is working with a load matched to the output tubes plate impedance. Less is to some extent tolerable but will shorten tube life, more can cause tube damage which could lead to a costly repair.
Paul
+1
why are you using a 300watt valve head if you want power amp distortion?
get a Bassman or marshall superbass there similar amps with less power.
you mean this part?
They dont list a 400 non plus manual at the boogie site, only a 400+ manual that refers alternately to 400 and 400+ depending on whether they are talking about a feature that is unique to the 400+ (7 band graphic, 2 ohm tap) or the same on both (channel one and two, pull treble, bass etc).
If its kosher to run the amp at 2 ohms that would be great for me, I could forgo using a series box, but all my sources say no.
6L6 is a GUITAR tube))
If OP wants overdrive from output section, than even with matched impedance there will be damage to output tubes. Because that is the only way to get overdrive (exceed max cathode current) from them, it is not the same case as class A in preamp.
Tube can be damaged in two major cases:
a) exceed cathode max current;
and/or
b) exceed anode max power dissipation.
So, if you pull some tubes and do not want to cause abnormal operation for the remaining tubes you need to draw loadline and see what happens. In most cases you just need to be careful with vol knob.
But you have to forget about overdrive from output section)
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Its the other way round actually, less speaker ohms than the nominal impedance of the transformer winding is safer in all tube amps.
But safest of all by far is running your amp correctly.
If it has too much power for the tone you want to create at the volume required get one exactly the right size or a reliable tube friendly power soak like a motherload and run it in place of one 8 ohm cab thus it only has to deal with 150 odd watts.
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