So I know about pulling v1 in a bf fender...

cerebralpaul

Member
Messages
271
but if I'm using the vibrato/reverb channel without actually using the vibrato/reverb- can I pull v3 and v5 too? Any reason not to? Does the current increase or something like when v1 is pulled?
 

Diablo1

Member
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620
Pulling tubes is not a good idea. If you pull V1, it changes the bias setting on the other tube that shares the bias resistor with V1. It runs the other tube at a very hot bias. I can't see any benefit.
 

drbob1

Gold Supporting Member
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28,577
It's supposed to increase the voltage on V2 slightly making it "hotter" and yielding more gain.
 

Silent Sound

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5,342
I believe the OP was refering only to V1..
I tried it yesterday on my vibrochamp but it didnt seem to help the gain much.
Vibrasonic got my joke.

Although, I would like to say one thing to the OP, on a serious note. It might help to know which amp exactly you are talking about. There are a lot of similarities between all of the Blackface amps, but if we're going to start pulling tubes, we may want to specifically identify which tubes (reverb driver, phase inverter, etc.) instead of just V1, V2, etc, or specify exactly which amp we're talking about. V4 isn't the same in every Blackface Fender.
 

Diablo1

Member
Messages
620
It's supposed to increase the voltage on V2 slightly making it "hotter" and yielding more gain.
That may be what some believe is happening, but they are wrong.
Voltage increase?...No.

Biasing the paired tube much hotter?.....Yes.
 

cerebralpaul

Member
Messages
271
It might help to know which amp exactly you are talking about. There are a lot of similarities between all of the Blackface amps, but if we're going to start pulling tubes, we may want to specifically identify which tubes (reverb driver, phase inverter, etc.) instead of just V1, V2, etc, or specify exactly which amp we're talking about. V4 isn't the same in every Blackface Fender.
I use a bf Super Reverb. As far as v1, it's a common "mod"(to the extent that pulling out a tube can be called a mod;)) that is referred to on many resources(i.e., here: http://www.kcanostubes.com/content/fender-amp-preamp-tube-layout-and-recommendations) and some threads here which are hard to search for because the search function doesn't look for "v1". Anyway I've been pulling the v1 tube for years, it works as advertised.

But it got me thinking, what happens if you pull v3(reverb driver), or v5(vibrato), or both? (hint: I tried it- amp still works :) and sounds fine… buuut I put them back in.) Figured I'd check in here and see if there's any technical reason for not messing with those too much.
 

xtian

Gold Supporting Member
Messages
2,502
Yes, pulling preamp tubes from a two channel Fender style amp is a way to increase overall voltage and gain a little headroom and power. When you pull the tube out, the circuit is placing less demand on the power transformer, and overall voltage will go up slightly. This is especially true of amps with marginally spec'd power transformers, like the Band Master.

No, the bias won't be a problem, because it will scale along with the rest of the voltages. We're talking about preamp tubes here, and there is no "paired" tube to worry about. Do not attempt this with power tubes.
 

Diablo1

Member
Messages
620
Yes, pulling preamp tubes from a two channel Fender style amp is a way to increase overall voltage and gain a little headroom and power. When you pull the tube out, the circuit is placing less demand on the power transformer, and overall voltage will go up slightly. This is especially true of amps with marginally spec'd power transformers, like the Band Master.

No, the bias won't be a problem, because it will scale along with the rest of the voltages. We're talking about preamp tubes here, and there is no "paired" tube to worry about. Do not attempt this with power tubes.
I was wrong about blackface Fenders. I had the Tweed Twin schematic in my head. Pulling V1 in this amp does screw up the bias on V2, because they share a single bias resistor and cap. Lookee here.
http://www.webphix.com/schematic heaven/www.schematicheaven.com/fenderamps/twin_5e8a_schem.pdf

But, I would check the schematic of your amp before pulling any tubes.
 

xtian

Gold Supporting Member
Messages
2,502
@Diablo: Thanks for the schematic! That's an interesting case. Not many examples of shared cathode resistors for FOUR triodes! Wow.
 

donnyjaguar

Member
Messages
4,194
Typical Fender amp "modification". Pointless in my view, but I suppose if you don't use channel 1 it'll save you wear on one tube.
 




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