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Pulling two power tubes? Lets put this one to bed. Makers spill the beans please.

john l

Silver Supporting Member
Messages
3,059
Can we all agree one way or another if this is a good idea or if this turns your big amp into a lack luster hi fi deal due to the other components in the amp (OT/PT) being designed put out more juice?

...Discuss

Edit and obviously I meant when done with the impedience being set correctly to compensate for the lack of tube tubes before you techies jump me. lol
 
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Blue Strat

Member
Messages
30,319
No need to agree on anything. It's all about personal preference...like everything else here;)
 

fenderpro

Member
Messages
377
i did it recently with a silverface twin reverb. i also installed new speakers...one 12" Weber Signature Alnico and one 12" Mojo Ceramic. it's like having a different amp. i was initially concerned with impedance mismatch, but so far, no problem. i love the sound...
 

rockon1

Platinum Supporting Member
Messages
13,509
Can we all agree one way or another if this is a good idea or if this turns your big amp into a lack luster hi fi deal due to the other components in the amp (OT/PT) being designed put out more juice?

...Discuss

Edit and obviously I meant when done with the impedience being set correctly to compensate for the lack of tube tubes before you techies jump me. lol
My Ultra plus disengages two tubes at a flick of the switch on the front panel.It doesnt compensate for the mismatch. I do prefer it on full power but honestly I think its a mental thing. Bob.
 

riffmeister

Silver Supporting Member
Messages
16,701
My Tone King Meteor goes from 4x6V6 to 2x6V6 at the flick of a switch (along with a flick of the impedance switch) and lo and behold, the amp breaks up a little earlier. Some slight readjustments of the tone controls are needed to maintain the same sound as full power.
 

john l

Silver Supporting Member
Messages
3,059
Itd be nice if some makers would chime in here wouldnt it? Ill edit the tittle. I was reading in one of Gerald Webers books where he goes through some mods for more head room for old fenders and he actually recomends swapping trannies with higher wattage fenders of the same era to go about getting there. Combine that with Myles Rose's "Power Modelling" article in the TAB and its pretty easy to end up on the fence ya know? I thought this would make for a good discussion on a Saturday morning. Thanks for the replies so far.
 

JJman

Member
Messages
994
Pulling 2 tubes and adjusting impedance should result in output-tube-breakup at the same position on the volume knob as with all 4 in. However, that should now be at about half the wattage coming out the speaker(s.) Half the wattage is not half the volume. It's more than half the previous volume. I forget the "perceived" volume reduction from the human perspective.

Other variables also matter, like a SS vs tube rectifier since the "sag" differs there.
.
 

rockon1

Platinum Supporting Member
Messages
13,509
Pulling 2 tubes and adjusting impedance should result in output-tube-breakup at the same position on the volume knob as with all 4 in. However, that should now be at about half the wattage coming out the speaker(s.) Half the wattage is not half the volume. It's somewhat lower volume. I forget the "perceived" volume reduction from the human perspective.
.
Yeah its noticable but not much at all. Technically its a 3 db reduction. Most people can percieve a 2 to 3 db increase/decrease but not less than that. Bob
 

john l

Silver Supporting Member
Messages
3,059
:bumpbump
For the afternoon crowd
I think its pretty clear to everyone that loudness and wattage arent the same thing. What Ive noticed from the lower wattage amps Ive owned and played is that its more of a tone and feel thing. However all those amps were designed that way not converted to it.
 

Jackie Treehorn

Silver Supporting Member
Messages
2,223
Let's clarify something, though. If it's four tubes cathode biased through a single resistor (AC30 style), you can't pull two tubes.

For fixed bias bias 4 power tube amplifiers, it's fine to pull a pair (not two on the same side) then mismatch downward, 16 ohm cab into 8 ohm tap, 8 ohm cab into 4 ohm tap, etc. In addition to the drop in power, there will be less miller capacitance so it's a bit brighter. I suppose voltages will be a bit higher. It's a matter of taste, of course, but I think the overrated transformers run this way sound very good.
 

Leftyman

Gold Supporting Member
Messages
1,651
I have been running My Fender Twin Reverb Reissue with 2 tubes for many years now with no problem. My local tech said it should be fine. No problems thus far. This is esentially what is being done to a lot of amps which have a half power option like Jubilees and Ecstasys. They are just shutting down two of the tubes without you having to pull them out.
 

Primakurtz

Member
Messages
2,311
Please elaborate. Did that extra 3 db allow you to turn up much more?
A little more - not a ton. Basically, it gave me a little more overdrive, a little less volume, a bit less of that huge low-end "thunk" for which the V4 is famous, and made it sound just a tad sweeter. Much like the difference between 50 & 100 watt Marshalls.

Not dramatic, but useful. Also, it allowed me to use a 16 ohm cab, since the Ampeg only had 2, 4, and 8 ohm speaker output.
 

torquil

Member
Messages
1,636
Can we all agree one way or another if this is a good idea or if this turns your big amp into a lack luster hi fi deal due to the other components in the amp (OT/PT) being designed put out more juice?
You won't find agreement on that one. People have differing tastes.

I do it on my amp (which has a Hiwatt-ish power section).
 

Laced Senses

Double Platinum Member
Messages
431
I have sometimes pulled two power tubes and halved the impedance on my '74 and '78 Hiwatt DR103 amps. The sound is a tad louder and definitely more ballsy will all four EL34 tubes pushing 100 clean RMS watts.
 

groovetube

Member
Messages
900
I have a Peavey Classic 50 watt 2x12 combo with vintage 30's in it. I pulled out the two inner tubes because I live in an apartment where I can't get the volume up as much as I want.

It seems to break up earlier and I recommend doing it if you don't need to use all of your wattage/headroom
 




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