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> About Pulling Tubes
MickeM
post Oct 13 2008, 01:41 PM
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Please discuss the following and sort out what's right and what's not. I've recieved different advice from people that I would concider experts in the respective area.

For the record, I've pulled 2 tubes in my H&K Switchblade getting 50w from a 100w amp.


A) Tube guy with plenty of experience told me that I should set the head to half of the cab.


B ) Product specialist at H&K said in theory (A) is correct. But since I was aiming for a softer and less a loud sound in the first place I would still have to match the impedance, same from amp into cab.


I'm a slave under the old device "speak too high and your head will fry" so got to be careful about imedance wink.gif
I'm puzzled about what goes here and my theory knowledge about this isn't strong so I hope we (your guys) can come to a conclusion in the end wacko.gif

This post has been edited by MickeM: Oct 13 2008, 08:39 PM


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blindwillie
post Oct 13 2008, 02:25 PM
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Trial and error always works.
You'll know when you are smoked tongue.gif

Hmmm I'm off to Stockholm now so please don't try this until I'm back home. *fear the revenge*


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Ivan Milenkovic
post Oct 13 2008, 06:25 PM
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I'm not really familiar with the subject mate, but I think pulling tubes out of amps in order to cut down power can work, but I never heard that is a good thing to do. It may damage the amp, cause amp is built to send certain amount of power to all the tubes.
On the other hand, maybe your amp is resilient to this kind of issues, so I cannot say it can be true in that case mate.
If you wanna cut down the power, wouldn't some kind of attenuator maybe be a better solution?

PS Even if you get the attenuator, I think you will have to get a 50W cab in order to get a good sound.


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Noangels
post Oct 13 2008, 07:48 PM
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I pulled the mid tubes out on my blade and and kept the speaker ohm as normal briefly when I had a powertube fail on me,and it sounded just the same

In my manual for my Mesa Boogie Dual Rec they actualy tell you to pull out the two mid tubes and one rectifier if you want to half the power!It wont damage the amp in the slightest.I am not sure on the speaker ohm but If i remember right it wasnt mentioned on pull tube threads I googled before trying with the blade ages ago

I keep meaning to pull out the centre tubes in my blade again and keep the other two as spares


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MickeM
post Oct 13 2008, 09:11 PM
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QUOTE (blindwillie @ Oct 13 2008, 03:25 PM) *
Trial and error always works.
You'll know when you are smoked tongue.gif

Hmmm I'm off to Stockholm now so please don't try this until I'm back home. *fear the revenge*

Thanks, I'll make sure to take your good advice in concideration. laugh.gif I've sent my good friends to meet you at the station, you'll easily recognise them since they are all muscles and hands large as fryingpans and they will be wearing skimasks over their heads. So if you see them please approach them smile.gif *hihihi*

QUOTE (Ivan Milenkovic @ Oct 13 2008, 07:25 PM) *
I'm not really familiar with the subject mate, but I think pulling tubes out of amps in order to cut down power can work, but I never heard that is a good thing to do. It may damage the amp, cause amp is built to send certain amount of power to all the tubes.
On the other hand, maybe your amp is resilient to this kind of issues, so I cannot say it can be true in that case mate.
If you wanna cut down the power, wouldn't some kind of attenuator maybe be a better solution?

PS Even if you get the attenuator, I think you will have to get a 50W cab in order to get a good sound.
Yes I agree, it feels like walking through a minefield but since I now even got an OK from H&K product specialists I tend to think that with this model there's not a problem.
I've got an attenuator, it's set to handle 50w so pulling a couple of tubes (or be caeful on the output wattage) was neccessary anyway. But the problem I felt when I had the attenuator plugged in was that I lacked som "force", don't know what better word to use. I could push the amp into saturation but still I felt like the speakers didn't get to work as hard as they should. I don't get that since the signal from the attenuator would be the same to the speaker, if not better even.
Yeah, I agree fully, a 2x12 cab would be the way to go now when I'm trying to play at a lower volume, there's no use for a 4x12 vintage 30.

QUOTE (Noangels @ Oct 13 2008, 08:48 PM) *
I pulled the mid tubes out on my blade and and kept the speaker ohm as normal briefly when I had a powertube fail on me,and it sounded just the same

In my manual for my Mesa Boogie Dual Rec they actualy tell you to pull out the two mid tubes and one rectifier if you want to half the power!It wont damage the amp in the slightest.I am not sure on the speaker ohm but If i remember right it wasnt mentioned on pull tube threads I googled before trying with the blade ages ago

I keep meaning to pull out the centre tubes in my blade again and keep the other two as spares

*ignored*

laugh.gif just kidding
I've also pulled the mid ones. Next rehearsal I will put it at 8->8 Ohms and see how that affects the sound. Bringing my spare tubes just in case wink.gif
Just keeping my fingers crossed it won't break. But I suppose like you mention Mesa Boogie would mention that it's important to change the Ohmage when pilling tubes. Like H&K would too if that was of highest importance. They couldn't just leave that information out, right?


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jer
post Oct 13 2008, 09:26 PM
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If you pull tubes to drop power, then adjust impedance ALSO, arent you adjusting the power even further?

100 watts at 16 ohms for example with 4 tubes.

Take out 2 tubes = 50 watts at 16 ohms.

If you take out 2 tubes and adjust ohms to 8 arent you back to 100?


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MickeM
post Oct 13 2008, 10:11 PM
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QUOTE (jer @ Oct 13 2008, 10:26 PM) *
If you pull tubes to drop power, then adjust impedance ALSO, arent you adjusting the power even further?

100 watts at 16 ohms for example with 4 tubes.

Take out 2 tubes = 50 watts at 16 ohms.

If you take out 2 tubes and adjust ohms to 8 arent you back to 100?

Just guessing but I belive the capacity of a EL34 tube at a certain plate voltage and current will add up to 20-30 Watts, I usually simply stick to 25W a piece where four of them = a 100W amp.

Pulling two and while the plate voltage doesn't change isn't affects gives a maximum of 25+25 = 50 watts (surely a 50W amp can peak a lot higher but I rather keep it simple since this is rocket science to me)
But usually it's said that an amp puts out this or that many watts @ this or that impedance, f.ex 100W at 16Ohm.

And for calculating the effect the impedance isn't calculated straight in relation to current or voltage but is deminished by a factor. Don't know how well Ohms law applies to calculation amp power though but just to put digits to what I'm raving about... Yes, I do belive the selected Ohm has an affect on the effect, but not that many percent.
P (watt) = U^2(Volt)/R(Ohm)

But I surely would like to hear from someone who stayed awake during these lessons in school laugh.gif


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Ivan Milenkovic
post Oct 14 2008, 02:02 AM
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Just a suggestion mate - possibly you can tweak your 4x12 VIntage 30s cab to have another wiring setup for 50W. You can wire only two upper speakers and make separate input on the cab for this kind of power rating and build in a switch. It is fairly easy to do with a bit of soldering, and it will definitely bring the speakers into nice overdriven punchy state.

This post has been edited by Ivan Milenkovic: Oct 14 2008, 02:05 AM


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MickeM
post Oct 14 2008, 07:42 AM
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QUOTE (Ivan Milenkovic @ Oct 14 2008, 03:02 AM) *
Just a suggestion mate - possibly you can tweak your 4x12 VIntage 30s cab to have another wiring setup for 50W. You can wire only two upper speakers and make separate input on the cab for this kind of power rating and build in a switch. It is fairly easy to do with a bit of soldering, and it will definitely bring the speakers into nice overdriven punchy state.

I never thought of that, I'll look into it smile.gif


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Noangels
post Oct 14 2008, 08:07 AM
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Just had a look in my mesa book and it says this

NOTE: On the Dual Solo Head it is possible to run two 6L6 or EL34 tubes pulling the two center tubes, leaving far left and far right tubes intact. This procedure reduces the power by approximately 50%. Remove one of the Rectifier tubes if you are using the TUBE RECTIFIER setting to assure a correct match.


There is NO mention of changing the speaker OHM,so I take it you shouldnt?


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MickeM
post Oct 14 2008, 09:24 AM
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QUOTE (Noangels @ Oct 14 2008, 09:07 AM) *
Just had a look in my mesa book and it says this

NOTE: On the Dual Solo Head it is possible to run two 6L6 or EL34 tubes pulling the two center tubes, leaving far left and far right tubes intact. This procedure reduces the power by approximately 50%. Remove one of the Rectifier tubes if you are using the TUBE RECTIFIER setting to assure a correct match.


There is NO mention of changing the speaker OHM,so I take it you shouldnt?

Thanks for the effort, so now things really point towards not changing the impedance.

Great by the way that Mesa puts that in their manual and H&K keeps a FAQ about how to go about (no mention of impedance there either). It used to be such hush hush about pulling tubes before and manufacturers didn't really recommend or provide the information on how to do it, which tubes to pull etc.
Maybe it's because the old amps had more problems handling being tampered with like that?


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OrganisedConfusi...
post Oct 14 2008, 09:31 AM
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On my old amp when I pulled 2 tubes I put the Impedance selector to half also and I had no problems.

This post has been edited by OrganisedConfusion: Oct 14 2008, 09:57 AM


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OrganisedConfusi...
post Oct 14 2008, 09:56 AM
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But I do that because I prefer how it sounds that way. If you drop the amount of tubes you don't have to do anything with impedance but you may not like the sound at that impedance with half the tubes. If that is the case then drop the impedance to 4 ohm. Also NEVER drop the impedance below 4 Ohm as most amplifiers can't handle it. There are some that can but most can't. You can up the impedance to 16 Ohms and this wont damage the amp either. It's down to what sound you want. But you don't have to lower impedance when pulling tubes.

This post has been edited by OrganisedConfusion: Oct 14 2008, 09:57 AM


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Noangels
post Oct 14 2008, 10:50 AM
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Yeah mesa go into a lot of detail in their manuals,you get a lot more info than you realy need!

Hnk's manual is rubbish!lol just a few pages and no mention on pulling tubes

heres more from the manual

IMPEDANCE: Wiring up speakers to provide the most effective load and making sure that all of them are in phase will help in creating the best sound possible. This is not too difficult, as long as you understand a few things about loading and how to connect your speakers to provide an optimal resistive load.
MESA/Boogie amplifiers can handle 4 and 8 ohms effectively. Never run below 4 ohms in a tube amplifier unless you are absolutely certain that the system can handle it properly; this can cause damage to the Output transformer. A few amplifiers can handle 2 ohms effectively without damaging them (for example the MESA’s Bass 400+). You can always have a higher resistance (16 ohms, for example)
without damaging results, but too low of a resistance will likely cause problems.

MIS-MATCHING: When running a higher resistance (for example: 8 ohm output into 16 ohm cabinet), a slightly different feel and response will be eminent. A slight mismatch can provide a darker smoother tone with a little less output and attack. This response is a result of the amplifier running a bit cooler. Sometimes when using more than one cabinet a mismatch will be the only option.


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post Oct 14 2008, 10:56 AM
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QUOTE (Noangels @ Oct 14 2008, 10:50 AM) *
Yeah mesa go into a lot of detail in their manuals,you get a lot more info than you realy need!

Hnk's manual is rubbish!lol just a few pages and no mention on pulling tubes

heres more from the manual

IMPEDANCE: Wiring up speakers to provide the most effective load and making sure that all of them are in phase will help in creating the best sound possible. This is not too difficult, as long as you understand a few things about loading and how to connect your speakers to provide an optimal resistive load.
MESA/Boogie amplifiers can handle 4 and 8 ohms effectively. Never run below 4 ohms in a tube amplifier unless you are absolutely certain that the system can handle it properly; this can cause damage to the Output transformer. A few amplifiers can handle 2 ohms effectively without damaging them (for example the MESA’s Bass 400+). You can always have a higher resistance (16 ohms, for example)
without damaging results, but too low of a resistance will likely cause problems.

MIS-MATCHING: When running a higher resistance (for example: 8 ohm output into 16 ohm cabinet), a slightly different feel and response will be eminent. A slight mismatch can provide a darker smoother tone with a little less output and attack. This response is a result of the amplifier running a bit cooler. Sometimes when using more than one cabinet a mismatch will be the only option.

Yeah. That's pretty much what I said I guess just with a bit more info. Cheers for getting this information from Mesa Manual smile.gif


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Noangels
post Oct 14 2008, 11:08 AM
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No probs mate.you can download most of their manuals in pdf format,as there are BIG sections in those on speaker settings!

anyway I am going to yank out those two mid powertubes on the blade,while I still remember and see what it sounds like with rehearsals tonight


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