Pulling Tubes

[se3k4life101]

I'd like to try pulling 2 of the tubes in my dual rec. From quite a bit of searching, it seems like it needs to be either the 2 inner or 2 outer ones, i'd have the 16 ohm jack running 8ohms which i guess means i'd just need to put in the other jack of my cab, and then do i have to pull a rectifer tube or not? if so, which one? i've seen it mentioned once or twice but most threads on the subject haven't brought it up. Anyway, I just want to make sure before I do something dumb and fry my amp. Thanks.

 

[Gamera]

perhaps you should make a new topic with the headline:

Which tubes do I remove to convert 100 watt amp to 50 watts?

or

What must I do to convert 100 watt amp to 50 watts?

 

[mystidream]

perhaps you should make a new topic with the headline:

Which tubes do I remove to convert 100 watt amp to 50 watts?

or

What must I do to convert 100 watt amp to 50 watts?

Or someone will just see the title, check out the post and help the guy out. :lol:

 

[ANIMATED SUSPENSION]

You pull the inner two power tubes and one (either) of the rectifier tubes. The speaker output must still match the impedance of the cab though !

 

[MikeK]

I'd like to try pulling 2 of the tubes in my dual rec. From quite a bit of searching, it seems like it needs to be either the 2 inner or 2 outer ones, i'd have the 16 ohm jack running 8ohms which i guess means i'd just need to put in the other jack of my cab, and then do i have to pull a rectifer tube or not? if so, which one? i've seen it mentioned once or twice but most threads on the subject haven't brought it up. Anyway, I just want to make sure before I do something dumb and fry my amp. Thanks.

I asked the same thing, you might want to check out the responses here ...
http://forum.grailtone.com/viewtopic.php?p=173677&highlight=#173677

The short of it is ...
1) pulling either pair will work (outer or inner set, manual says pull the inner)
2) use a half value fuse of the same type. (if stock is 4amp slo-blow, go to a 2amp)
3) you can pull one of the rectifier tubes but you don't have to.
4) cut the impedance in half (if you use an 8ohm cab, put it in the 4ohm out)

... I was a little skeptical about #4 until I tried it. Big difference, the tone opened up. Better presence and it didn't sound as restrictive as it did with the 8ohm out... but I only knew that after I switched it to 4. Worse case it would be a safe mismatch. I've been using it this way ever since with no apparent ill effect. I also like it better with both rectifier tubes left in.

Hope this helps you as much as it did me.

 

[se3k4life101]

thanks, that clarifies things quite a bit but i'm still a little confused.

so i'm going from the 16 ohm output to my cab's (1960a) 16 ohm input. that means i switch to an 8ohm output or an 8 ohm input?

how dangerous is it to do this without changing the fuse? i don't have easy access to a place where i can get a new one so if i can live without it then i'll give it a shot.

 

[JW123]

Ive been pulling tubes out of my recs for years and never changed the fuse. Just pull inner or outer and one rectifier tube. Mesas are pretty tough when it comes to ohm mismatches. I ussually plug mine in and find which ohm load sounds better.

 

[se3k4life101]

Ok, I'm still confused about this ohm thing. So normally, I just run from the 16 ohm output to the 16 ohm input in my cab. It's a Marshall 1960A, so it's got two inputs, 16 and 4 ohm when switched to mono and 8 and 8 when switched to stereo. I've tried different set ups and I can't hear much of a difference, so what should I have it set to when 2 of the tubes are pulled?

 

[RR]

If you pull out two of the power stage tubes, and pull one rectifier tube (assume the switch is set to the 'tube rectifier') your output transformer taps are double the impedance. (if I'm not mistaken)

The 8 ohm impedance tap is now a 16 ohms tap, the 4 ohm impedance tap is now 8 ohms.

So you should set your impedance to 8 ohms for you 16 ohms cabinet.


Side Note:
I tried this setting, personally, I prefer the full 100 watt, all tube in.

The output transformer remains a 'clean' 100 watt transformer, not a 'saturated' 50 watt transformer like the mojo we hear from a cranked up smaller lower power tube amp.

But personal preference may vary.

 

[Sustain]

Ok, I'm still confused about this ohm thing. So normally, I just run from the 16 ohm output to the 16 ohm input in my cab. It's a Marshall 1960A, so it's got two inputs, 16 and 4 ohm when switched to mono and 8 and 8 when switched to stereo. I've tried different set ups and I can't hear much of a difference, so what should I have it set to when 2 of the tubes are pulled?

I would like to point out there is no mention in the owners manual anywhere about halfing the impedance. Only removing two tubes, and how it will cut power by half. Nowhere does it say the impedance is changed.

I am referring to the 2channel, not teh 3 channel dual head. I do not know if there is a difference in this regard, but the except below and my statement above is based on the owners manual for the 2 channel dual and triple heads, and refers specifically to the DUAL only below.


=======================================
from the manual:
NOTE: On the DUAL Solo Head it is possible to run two 6L6 or EL34 tubes by pulling the two center tubes leaving the 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.

========================================

I am still running my 2ch dual recto w/ 2 tubes only, (50 watt). I still run my marshall cab @ 4 ohm mono, plugged into a 4 ohm jack on the back of my head.

 

[RR]

...
I would like to point out there is no mention in the owners manual anywhere about halfing the impedance. Only removing two tubes, and how it will cut power by half. Nowhere does it say the impedance is changed. ...

C'mon amp technician, doesn't pull out two power tubes and a using rectifier tube changes the output transformer's tap? :?

The reason the manual does not mentioned about doubling the output taps on output transformer, these transformer do allow impedance mismatch with little or no ill-effects.

 

[MrMarkIII]

Ok, I'm still confused about this ohm thing. So normally, I just run from the 16 ohm output to the 16 ohm input in my cab. It's a Marshall 1960A, so it's got two inputs, 16 and 4 ohm when switched to mono and 8 and 8 when switched to stereo. I've tried different set ups and I can't hear much of a difference, so what should I have it set to when 2 of the tubes are pulled?

If you're pulling tubes, the safest thing to do is set the cab at 16 ohms and plug it into the 8 ohm jack on the head. All should be cool as long as the cab ohms are higher or match the head ohms.
As a rule of thumb. don't go lower, for example, plug a single 4 ohm cab into an 8 ohm jack on the head. Even that will not blow a Boogie, though.

 

[Sustain]

...
I would like to point out there is no mention in the owners manual anywhere about halfing the impedance. Only removing two tubes, and how it will cut power by half. Nowhere does it say the impedance is changed. ...

C'mon amp technician, doesn't pull out two power tubes and a using rectifier tube changes the output transformer's tap? :?

The reason the manual does not mentioned about doubling the output taps on output transformer, these transformer do allow impedance mismatch with little or no ill-effects.

if this is the case I would be glad to know this for sure before I do something hurtful, I suppose I will call Mesa tomorrow to confirm this.

and I am hardly an amp technician or I would not be so worried to do as the manual says

 

[RR]

...
I would like to point out there is no mention in the owners manual anywhere about halfing the impedance. Only removing two tubes, and how it will cut power by half. Nowhere does it say the impedance is changed. ...

C'mon amp technician, doesn't pull out two power tubes and a using rectifier tube changes the output transformer's tap? :?

The reason the manual does not mentioned about doubling the output taps on output transformer, these transformer do allow impedance mismatch with little or no ill-effects.

I'm actually calling all the amp technicians of this board to confirm what i just said. :wink:

MESA has really durable transformer I don't think you would hurt it so long there's a load whether its a speaker(s) or a dummy power resistor.

 

[MikeK]

... I'd be really interested to hear what Mesa says about this impedance issue, too.

So Sustain, if you get a chance, please post what The Factory says?
Thanks in advance!

The fuse thing was suggested by a few people and it seems logical from my layman's point of view. It doesn't hurt anything and the lower value fuse works fine and is safer.

 

[mikey383]

Two things here.

I've been running on two tubes for about 4 years, on 2 different DRs. I've yet to change the fuse, but that doesn't mean it's ok not to.

I've been running my 8 ohm cab from the 4 ohm tap, and have had no ill effects. It sounds better that way, as opposed to the 8 ohm tap.

 

[Sustain]

I was too busy at work today to call mesa, i will ring them now, probably wont get anyone til tomorrow tho.

 

[Sustain]

****, they called while I was at my kids graduation.

I will likely hear from them tomorrow afternoon.

 

[MikeK]

... still interested to know about that conversation

 

[se3k4life101]

now i'm running 2 power tubes and 1 rectifier tube. 8 ohm output to 16ohm input on my cab. it sounds much better. i'm getting less low end flabbiness and better chunk out of my palm muting. exactly the tone i was looking for. i didn't change the fuse, but it seems to be working fine. i guess running this way will also save a lot of money on buying new tubes too.