Tube amp question

[metalchurch]

I've heard that you can cut your wattage in half just by removing half of the powertubes.
Ive read that in order to do this, you MUST remove either the inner pair, or the outer pair in sets.
Also you must cut your ohms in half also.
ie: if you're running @ 16ohm mono, it must then be set @ 8ohm mono.

So my first question obviously, is this true?
Is this safe?
Has anyone done this?

I know that Mesa's will continue to run if you blow a power tube, and I guess it has a warning light that comes on when this happens.

I've been thinking about building another rack setup that's less than my 100w that I'm using now.
Been thinking about a Marshall EL84 20/20 (20w) or a Marshall 9100 50w tube poweramp (little brother to my 9200 100w)

So if I can use this tube removing thing effectively on my Sdie B without harming the amp, I think it would be a much cheaper alternative for now.

What do you guys think about this?
I'll post a schematic of my Marshall 9200 if that would help?
Would it be wise to have it re-biased if this is in fact possible?

Thanks alot!

[metalchurch]

Here's the owners manual in pdf:
http://www.drtube.com/schematics/marshall/91009200.pdf

Here's the wiring and output schematic:
http://www.drtube.com/schematics/marsha ... -65-02.pdf

Here's a photo of the innards:

[onegunguitar]

I did that with my 5150 before Joe,I didn't have any problems but I only tried it out for a few minutes.Like you said, just pull the inner two or outer two and cut the ohms in half.

[metalchurch]

I was gonna, but I was scared to try it even though my poweramp is essentially 2 amps in 1, and the Side B is a seperate unit, so it wouldn't affect Side A (which is my main side).

I'm gonna give it a shot here in a little bit and see what it does.
What was the difference when you did that to your 5150? Did you play it long enough to hear if it breaks up and distorts faster?
Thanks Scott.

Here's a picture that I used paint to show what I mean, and which tubes to pull out.
Yellow = Inside tubes / Blue = Outside tubes

[metalchurch]

One more thing I want to know is which preamp tube should I pull?
Each side has one 12AT7, and one 12AX7 for the preamp side.
When I had this tubed my tech said that "it must have an AT7 per side, because it was equipped that way from factory."
But of course he was speaking of the amp functioning as a 'whole unit' not like what I'm trying to do here.

Not sure why?
So should I pull the side with the AT7, or the AX7?
Thanks

[onegunguitar]

I don't think you would pull any of the preamp tubes,without them it's not gonna push the signal into the power amp section. I don't know Joe,I think it's time you sell everything and just buy a PowerBall-problem solved.Hahaha!! (See avatar):D

[metalchurch]

On the front of the 9200 there's a 'Voicing' toggle switch (A/B)

Which changes the output from a warm 'Vintage Tone' (A), to a 'Modern High Output Tone' (B)

What exactly does this do? Does it take one of the preamp tubes out of the equation for the "A" Voicing (Vintage Tone), or is something more complex than that?

Sorry for all the questions, hope yins are followin me on this. I just dont wanna screw anything up.

[metalchurch]

I don't think you would pull any of the preamp tubes,without them it's not gonna push the signal into the power amp section. I don't know Joe,I think it's time you sell everything and just buy a PowerBall-problem solved.Hahaha!!

Ok, so LEAVE the preamp tubes in??

Believe me bro, as soon as I get the money for that, I'm gonna have one.
It's not that my tone sucks, I am just tryin to find a Low Watt practicing sound, and just to experiment a little bit.

It would be tits to have a 9100 50w version, cause then I could cut Side B down to 25w of screaming Marshall.
I'd love to have an EL84 20/20 poweramp for another rack.

Thanks Scott!

[metalchurch]

I found this article on an amp forum about the subject that I was talking about:
http://plexipalace.com/plexiboard/viewt ... ling+tubes

It says to pull these tubes:


It's also recommended to change the main and HT fuses to a lower value, because they are running at a lower current.
It's suggested to buy the fuses for the Marshall 9100 50w poweramp, which are:
T3.15A (115v main fuse)
T315mA for the HT fuse

One guy has done the mod without changing the value of the fuses yet, and he hasn't experienced any problems yet.
Another guy has done this to a Marshall 1987X non master volume amp, and it caught fire because the fuses were too large and never blew, therefore it got too hot for whatever reason and caught fire

[orangekick]

What are you trying to accomplish by pulling tubes?

[metalchurch]

Basically it allows the amp to break up sooner because there's not all of the tubes there.
Essentially it lowers the output wattage, but in reality it only drops the sound about 3db.
It's the "cheap bastard's attenuator". It's hard to explain, but if someone has the right description...

I pulled the tubes and set the poweramp to 8ohms, and after talking to Scott (onegunguitar) we decided that the cab should be left alone @ 16ohm mono, as opposed to 4ohms. (which would be half of the poweramp, as suggested for this mod)

Anyway, I got it hooked up, and powered it up and let it sit for about 15 minutes because I haven't used Sde B for over 1 year, and I heard that the transformers should be given time to get up and runnning after sitting. I might have been alright otherwise, but I was just being safe, in order to keep the variables to a minimum.

I could hear the difference right away, and it does exactly what it's said to do, which is break up sooner @ lower levels. I wasn't able to really crank on it, because I live in town and it was 10pm.
But I was able to dial in some great low gain 80's tones that I would never have been able to get.
In fact, just about every sound I messed with, I wouldn't have gotten otherwise.
It was so cool to be able to mess with something else! I found a nice Warren DeMartini and Jake E. Lee sound. I even got some really cool ZZ Top/ Classic blues, and Classic tube overdrives.
I really liked the clean sounds that I was getting. They were like a warm jazz type cleans that broke up with moderate-heavy picking, yet it had an almost glassiness to it. Hard to explain.
I never mess with clean stuff that much, and I know that Side A @ 100w would have driven the cleans too much.

I played it for about 45 minutes to an hour and I had no problems or unusual noise, so I guess it's "so far so good"
Very cool for sure, I'm so glad that I did this, I cant wait for tomorrow! I'm like a kid before Christmas!

Thanks for your help Scott!

[VENTGtr]

Joe,

I ran the Carvin like this for a while. Worked great. I went back to all the
tubes (Just so I'm running the single 8ohm speaker at , but am goin' to
give it another try since I'm back to a single 12. Just to try out.

If the amp is self-biasing, not much else to do. Others, I believe, may need
need biased/re-biased.

The downside is, of course, if you're now running the amp at half power,
are you running speakers that will be running at their optimal ability.

The idea being that you can get a "better" sound without having to have
the volume as high, it is the case. However, the volume isn't actually half,
as it would seem. Some guy on a site recommended by Carvin's forum
did a breakdown. I can't remember what he found the ratio to be...but it's
not quite down to half. Regardless, if it's working in a way you like and
is safe, cool nonetheless.

[metalchurch]

Yeah it wasn't quite down to 50w in my opinion, it was more like 70w maybe a tad higher, but still less than 100w.
My amp is not self biasing, but everyone says that if your amp is biased correctly to begin with, then it would be ok to do.
I just had my amp serviced this past June with new tubes in Side A, and Side B biased and gone over, and I have never even used Side B until last night.
In fact when I got the amp about a year and a half ago Side B never worked until this past June.
I'm lovin the variety in tone that I'm able to get by simply yankin out a couple of tubes.
Neer thought I'd see the day when I'd ever mess with anything but in your face all out metal, but it's nice to try and come up with riffs and stuff using a different sound.
Like I said, so far so good but I'll definitely be keeping and eye and ear out for anyting bad.

[orangekick]

There are a few of the newer amps from Mesa that allow you to choose how many tubes you can run on each channel. They usually suggest that you run the clean channel at 100 watts so that you get a really clean, hard to break up sound and then the gain channel is run at 50 watts so that the power tubes come into the gain sound earlier and the break up is sooner.

[VENTGtr]

Joe,

That's cool man. I do have to admit getting a bit of a kick that you never
use the clean. 'At's jes funny man.

Is interesting how tichanges the tonal character. Thought that just might
be something I thought I was hearing since didn't really see it mentioned.
I mean...mebbe it still is...but at least I'm not the only one that's nuts.

"They usually suggest that you run the clean channel at 100 watts so that you get a really clean, hard to break up sound and then the gain channel is run at 50 watts so that the power tubes come into the gain sound earlier and the break up is sooner."

Interesting. Makes sense, and it's cool that they're thinking of it. The built
in attenuator's a cool idea, and I guess as a pseudo-something-similar, you
can run 12AYs in the cleans pre (What I do) and something like a TungSol
12AX, or somethin' that breaks up sooner in the dive chan.

Either way, pretty cool.

[metalchurch]

Dave, I have TiungSol's planned for the pre side of the Marshall and also for the Engl asap.

Right now the Marshall has TungSol powertubes, and EH pre tubes in SideA, and Sovtek power, Marshall pre tubes in Side B (stock).

The Engl has (3) 12AX7 GT's in it, and I'm not even sure how old they are really. They were in it when I got it, and I've had it for about 1-1/2 yrs now.

The only time I ever use clean is for the intro to Slayer's "South of Heaven", "Seasons in the Abyss", "Behind the Crooked Cross", Ozzy "Killer of Giants", and Iron Maiden "Remember Tomorrow".

Other than those couple of songs I never use clean, in fact usually, I get lazy and roll the volume down and palm mute those parts.

I need to do some reconfiguring with my setup, so that I have some sort of lead boost.
Like either use the "vintage" voicing switch on my 9200 for the rhythms, and the "modern" voice for the leads, because I just recently discovered that the voicing switch (toggle) on the face of the '92 is footswitchable, so I need to find a cheap A/B footswitch for an amp.

You got an old 'pos' switch lying around?

Either that or I could invest in an EMG PA-2 preamp, but I would need one for every guitar, or atleast the ones that I play the most.

I'll figure it out I guess.

I know it is funny that I use only 1 volume/ 1humbucker, no cleans, and no effects.
Pretty one dimensional now that I think about it.
I'm surprised that I've amused myself for this long w/out getting bored with it.

[metalchurch]

There are a few of the newer amps from Mesa that allow you to choose how many tubes you can run on each channel. They usually suggest that you run the clean channel at 100 watts so that you get a really clean, hard to break up sound and then the gain channel is run at 50 watts so that the power tubes come into the gain sound earlier and the break up is sooner.

Thats a good idea too!
I've thought about using 2 preamps, 1 going to each side of the head, with 1 cab for each side, and an A/B switch, that way I could use the 100w side for the cleans, and the "50w" side for the rhythms.

I'd like to try either a 1936 2x12 cab, or a 1960A cab loaded with V30's or something that would break up sooner.
And an ADA MP-2 preamp, because they have one of the most beautiful, and natural clean's in all of the rackmount world.
I'm curious to see if there will be an ADA MP-3 coming out soon. There's rumours about it, but you all know how rumours are....

I'd love to have an Engl E670 preamp ($2,200) Mesa Triaxis ($1,200), or a Recto preamp($1,100). I've never had any Mesa gear before, so it is all new to me.

Lots of ideas and wishes, but I gots to have the $$$ to play the game!

[metalchurch]

I went to Terry's Guitars-N-Stuff today and bought (3) Tung Sol 12AX7's for my Engl preamp to replace the old an worn Groove Tubes that were in it.

I noticed an immediate difference as soon as I turned it on and hit the first chord.
They are tighter and the notes are more pronounced. There's a tad bit more gain than the GT's, but it's a crisp/smooth gain.
They are alot quieter and have a better low end.
Great product all around, I'm impressed that's for sure.

Terry hooked me up with some old 12AX and AT7's today, so I also did some preamp tube swapping on the 9200's B side.

Here's a list of the 12AX7 preamp tubes that I had:
(2) Groove Tube 12AX7
(1) Groove Tube 12AX7R (slightly less gain, and quicker compression than the GT-12AX7)
(1) Marshall 12AX7
(2) Sovtek 12AX7
(1) Unlabeled no name 12AX7 (probably Chinese)
(2) Unlabeled no name 12AX7-A (probably Chinese)

Here's the 12AT7's:
(1) Ruby 12AT7
(1) GrooveTube 12AT7
(1) Marshall 12AT7
(1) Unlabeled no name, no size or anything at all (I'm calling this one the Generic Tube)

Well I left only (2) of the Sovtek 5881 power tubes in Side B as I left it the other day and I messed with different combo's of preamp tubes this evening.

*I kept the volume and amp settings the same throughout the test so everything remained consistent.

Out of all of them the Sovtek 12AX7's seemed to be the most consistent and better sounding of the bunch.
However when using both of the Sovtek 12AX7's I thought it was too bright and sounded like dog shit.

So I left one of them in and swapped out the other side, which is recommended that it has an AT7 in that side anyway.
So I used the Sovtek with every AT7 that I had and then tried every possible combination imaginable using all of the tubes.

Here's the ones that I thought were the most impressive combinations:
(Best combo)
#1 - Sovtek / "Generic"
#2 - Sovtek / 12AX7 "No name"
#3 - Sovtek / Groove Tube 12AX7R
#4 - Sovtek / Ruby 12AT7

The best sounding pair were the Sovtek / Generic combo. I dont know what it is, but it was nice and had alot of gain and was medium-bright sounding with a nice low end. It really added alot to the sound and I'm really starting to like Side B with (2) Powertubes and those preamp tubes.

The #2 best sounding was again the Sovtek and the other "No Name", but that one is labeled as a 12AX7. It was very comparable to the "Generic" tube.
I had a feeling that those unlabeled tubes were gonna be a surprise, but I had no idea that they sounded this good.
When I put the "Generic" tube in and turned it on I thought I accidentally bumped the volume because it was louder and had more gain than the other tubes.

You know I just thought of something; I didnt try both of the no name's together, so I'm gonna do that tomorrow.
But I know that each of them paired up with a Sovtek were sweet sounding.

And what really surprised me is that everyone of these tubes were used, but I heard sometimes it's the old and used ones that have that "tone".

I had alot of fun with this and I'd like to try out some more soon. I cant wait to check out Orangekick's Yellow Jackets!