Pulling Tubes From Fender Amp Channels That You Don't Use

[Tal_175]

Do you pull tubes permanently from your Fender (or other) amps that power channels/effects that you don't use?
The linked Fenderguru page recommends pulling tubes from blackface/silverface Fenders if you don't need them.
Is there any long term harm to the amp in doing that? Does that enhance the remaining channel or features in any way.
Tubes explained in AB763 amps | fenderguru.com

I don't use the virbrato channel on my Deluxe Reverb, I wouldn't mind disabling it completely and reduce hum/noise and possible future maintenance problems. Is there a risk in pulling out v2,v3, v4, v5 permanently from a deluxe reverb?
Note even if you turn off the effects with the foot switch, there still is idle current flow through the unused tubes that gradually deteriorate them. Also possibly causing noise or being prone to causing noise in the long term as well as wasting good tubes.

[vintagelove]

Well, I can guarantee that the majority of surviving 50 year old amp did not have tubes pulled, so, will it “hurt” anything? No

it could be a bit gentler on the power Transformer, and not wear out the tube socket pins.

This is is different from pulling v1 to intentionally change your tone.



In your case, it will certainly make retubing cheaper!!!

[KirkP]

There’s no harm in pulling the tubes suggested by the fenderguru site. If you don’t ever use the reverb/tremolo channel, pulling those tubes reduces the current draw on the power supply so might give you a little extra headroom in the normal channel. It’s also true that the reverb recovery tube is a potential noise source. But the normal channel has a different sound than the effects channel since it lacks both the tremolo’s optocoupler and the extra triode. If you prefer the tone of the normal channel and have no need of the effects go for it.

[Tal_175]

There’s no harm in pulling the tubes suggested by the fenderguru site. If you don’t ever use the reverb/tremolo channel, pulling those tubes reduces the current draw on the power supply so might give you a little extra headroom in the normal channel. It’s also true that the reverb recovery tube is a potential noise source. But the normal channel has a different sound than the effects channel since it lacks both the tremolo’s optocoupler and the extra triode. If you prefer the tone of the normal channel and have no need of the effects go for it.

Would removing V2 affect the voltage/bias on V1?
V3-V5 are I guess more straight forward, but removing V2 might affect the tone/gain perhaps?

[KirkP]

After reading the fenderguru post more carefully I noted that he mentions two alternatives: disabling the normal channel or the vibrato/reverb channel. Your needs for effects and your preferences between the tones of each channel (they do differ) would drive your decision. Here are some marked up schematics of each alternative.

Disabling the Vibrato/reverb channel:


Disabling the Normal channel (and the Tremolo/Reverb functions):


Note that for the latter you can’t pull V4, since half of it is in the signal path. The opto-coupler in the vibrato circuit attenuates the gain of the Vibrato channel and I think alters the tone a bit, so sometimes people snip its connection (circled in blue). It’s more invasive than pulling tubes, but easily reversed. The opto-coupler doesn’t affect the Normal channel.

The preamp tubes are all cathode biased, so removing a few shouldn’t mess up the biases of those that remain. The output tube bias should be fine too.

[Tal_175]

If I remove v2, v3, v4, v5 and disable the vibrato channel, is it safe to just unplug the reverb tank from the chassis? Do I need to jumper the input jacks?

[KirkP]

If I remove v2, v3, v4, v5 and disable the vibrato channel, is it safe to just unplug the reverb tank from the chassis? Do I need to jumper the input jacks?

If V3 is removed as in the 2nd figure, the reverb tank can be disconnected or left in. It doesn’t matter. Don’t replace it with jumpers. And to eliminate any noise from what remains of the reverb circuit, keep the reverb knob at the minimum.

I’d miss the reverb so would never disable it for myself. I do find Fender reverbs to be too bright though. I’ve considered putting a treble control in a small box and routing the reverb return through that on it’s way back to the chassis. No mods to the amp would be required. The Princeton-based amp I’m using lately has some treble rolloff in the circuit so I have no need for more rolloff, but I may try it in my Twin.

[Tal_175]

I find the normal channel to be a bit fatter and rounder. Nicer for jazz. Vibrato channel has a bright cap and tremolo neither of which I need. I use reverb occasionally. But when I use it, I like to set it so it's very subtle. Subtle enough that I can't really tell the difference between the amps reverb and hall of fame pedal reverb. In louder situations, I don't use reverb. Good amps with larger cabinets sound good without reverb IMO.

[sgosnell]

The Fender amplifiers are not new designs, and have a long history. If a mod has been used for 50+ years, it's probably safe. And none of the mods on Fenderguru are new.

[icr]

I spend so much time getting special functions to work on vintage amps, I'm not sure I'd disable special functions on purpose. I'd use an amp with no special functions in that case.

[Tal_175]

I'm not sure what you mean by special functions. But DR has a normal channel and a vibrato channel. Both channels are voiced differently. Normal channel is more "pure" so to speak. It has only 2 preamp tubes (preamp and PI). Vibrato has bright cap, reverb, tremolo and an extra gain stage (5 preamp tubes). So they are different.
My understanding is most people either only use the normal channel or only use the vibrato channel (more common) virtually all the time. Many people never seem to use the tremolo function. Also it's quite common that people just clip the bright cap on the vibrato channel.
So I think people don't buy DR because they need and use all it's features, they buy it for it's cleans for the most part. If Fender offered a single channel no-effect version of it, I'd have bought that one happily.

[KirkP]

By the way, here’s the most detailed road map of a Deluxe Reverb I know of. You can trace the signal through the Normal and Vibrato channels and see how they differ.
How the AB763 Works
The Vibrato channel has the bright cap, a resister to send a signal to the reverb tank and to mix the reverb back in with the dry signal, the tremolo pot (which attenuates the signal even with the tremolo turned off), and an extra triode which recovers the gain lost in the reverb and tremolo resistors. Besides the added gain, I think that extra triode stage adds another bit of nonlinearity to the signal chain. I don’t have a Deluxe, but on my other Fender amps the Vibrato channel seems to roll off the highs and lows a bit and the Normal channel seems a bit more hi-fi.