Pulling out V1 tube?

[kavalero]

Anyone experimented with this and are there any bad implications to the amp>

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If you are like most players and only use the Vibrato channel (reverb, tremolo, the brigth cap and the extra gain stage), you should pull out the V1 tube. This is the preamp tube for the normal channel which you are not using. Vice versa; If you’re using the Normal channel, you can pull out the V2 tube. All AB763-similar circuits (Deluxe Reverb, Super Reverb, Pro Reverb, Twin Reverb, Vibroverb, Vibrolux) are designed so that signal is leaking between the two channels. The amp will play louder at the same volume knob setting when pulling the V1/V2 tube that you’re not using. The stronger signal will push the second gain stage (V4 tube) harder and give you increased sustain, compression and harmomics. This mod does not change the amp’s clean headroom.
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[gridlock]

I've tried this in a few of my Fender amps and could not really tell a lot of difference. I wanted earlier overdrive but I guess that my volume needs were lower than this semi-mod can handle. I currently have V1 in place in all four of my Fender amps. Pulling V1 is not supposed to hurt the amp but I am not a tech or an expert. The Fender Amp Guru website has some pretty good information on this and other mods for most BF or SF Fender amps. Check it out and keep us posted to your findings.

http://fenderguru.com/amps/deluxe

 

[Johnny Cache]

Won't hurt anything, but I doubt much of the claim is realistic.


[If you are like most players and only use the Vibrato channel (reverb, tremolo, the brigth cap and the extra gain stage), you should pull out the V1 tube. This is the preamp tube for the normal channel which you are not using. Vice versa; If you’re using the Normal channel, you can pull out the V2 tube. All AB763-similar circuits (Deluxe Reverb, Super Reverb, Pro Reverb, Twin Reverb, Vibroverb, Vibrolux) are designed so that signal is leaking between the two channels. The amp will play louder at the same volume knob setting when pulling the V1/V2 tube that you’re not using. The stronger signal will push the second gain stage (V4 tube) harder and give you increased sustain, compression and harmomics. This mod does not change the amp’s clean headroom.]

Never heard this called a mod before. And if someone with better knowledge could explain how the signal is leaking between the two channels I would like them to explain this.

 

[rokdog49]

I did it. There is a little more volume even at lower settings and quicker break up as well. I think the greatest benefit would probably be in a live band scenario. Since I never use the "Normal" channel, I just leave ithe V1 out. It won't hurt your amp.

 

[Wally]

Johnny Cache wrote: "Never heard this called a mod before. And if someone with better knowledge could explain how the signal is leaking between the two channels I would like them to explain this.[/QUOTE]

Johnny, the pin 8 cathodes of V1 and V2 in these two channel Fender guitar amps...BF/SF...are tied together. The bypass resistor for those cathodes is 820 ohms...versus the 1.5K that is used on the other individual cathodes in those two tubes...the pin 3's.
That 820 ohm resistor serving two cathodes yields the same biasing /gain result as does a 1.5K on one cathode. When you pull V1, the pin 8 cathode is then biased 'hotter'. I like to separate those two cathodes---pins 8---so that I can manipulate gain separately. I maintain a 'stock' biasing on V2--Vibrato channel--by using a 1.5K cathode bypass(biasing) resistance. I use the 820ohm on the other cahnnel....biasing it hotter. This is more than likely what FEnder is doing on those two -channel '68 Custom amps---if they are on the market...like the Deluxe REverb version. They are also modifying the slope resistance and tone cap values.....tweedy thing in that channel....which is what a lot of techs have been doing for a long time.

Is pulling a tube a mod?? I can't say I have heard it called that either...or a semi-mod. But....since the circuit is being changed by pulling that tube, it is a modification of what the amp was built to do, right?

 

[fenderguru.com]

Hi guys. Jens from fenderguru.com here. Thought I should just clarify a few things.

1) Pulling the other channel's preamp tube on blackface Fender amps won't hurt the amps. It has stood the test of time and been been done by players in 50 years.

2) Johnny Cache is right about "Signal leaking between channels" is not a technically precise description of what actually happens. We have used simple explanations on the web site so that more people can understand. The content on fenderguru.com is targeted for mucisians, average guitar players and amateur amp techs eager to learn. It is not meant for amp builders or people with electrical engineering degrees. It is more important to me to explain the basic concepts of Fender amps to thousands of musicians and players than telling experienced amp gurus something they already know.



This is by the way my first post here. I love this forum.

Best.

Jens, Norway.

 

[Wally]

Hi guys. Jens from fenderguru.com here. Thought I should just clarify a few things.

1) Pulling the other channel's preamp tube on blackface Fender amps won't hurt the amps. It has stood the test of time and been been done by players in 50 years.

2) Johnny Cache is right about "Signal leaking between channels" is not a technically precise description of what actually happens. We have used simple explanations on the web site so that more people can understand. The content on fenderguru.com is targeted for mucisians, average guitar players and amateur amp techs eager to learn. It is not meant for amp builders or people with electrical engineering degrees. It is more important to me to explain the basic concepts of Fender amps to thousands of musicians and players than telling experienced amp gurus something they already know.



This is by the way my first post here. I love this forum.

Best.

Jens, Norway.

Welcome, Jens. Thanks for joining in the discussion.

regarding that 'signal leaking between channels' phrase....I don't know where that came from...and I didn't address its use in this thread because ...well, because I was caught in a rare moment of saying to myself..."Why bother?"...right? (;^) Hey everyone else....Jens doesn't know me...let him know that there is a laugh due for that last statement, okay?!? LOL
But...with that in mind, if this phrase is incorrect technically then from my point of view the phrase should never be used...especially by anyone who wants a layman---and I am a layman in essence--- to understand much of anything at all. Ime, misinformation leads to misunderstanding....and this is never so true as in this internet age.....widlfires spread quickly....but the internet is worldwide instantaneously, right?
From my point of view, a simple explanation that is tecnically correct is a much better way to convey information. Here is how I would express it IF I wanted someone to gain some basic understanding of what is going on....and I beleive that too much information is better than misinformation...

" The gain structure of V1 and V2 are tied together. The tubes do not intereact or leak signal across this connection, but removing one or the other from the circuit increases the gain of the remaining channel preamp tube."

That is simple, understandable and accurate. This statement may or may not spur the person to delve into understanding the technical side of these amps, but it will accurately inform them that if they want to increase gain in one of those channels, they can pull the other channel's preamp tube and achieve that gain in a very simple manner.
I predict that from now on there will amp owners claiming that those two channels are interactive--that signal leaks between these two channels.

from a song by The Band...

"Now when the rumour comes to your town,
IT grows and grows;
And where it started
No one knows!"

Ya'll have a good one....

 

[Josey]

Here's how a local tech once tried to explain it to me...

"Think of it like this... You know how you can close the air vents on the passenger side of your pickup in order to get more air blowin in your face?? Well that just like pulling the V1/V2 tube of the channel you aint using."

Great guy and knew his stuff but he made Gerald Weber sound like an English Professor.

 

[Wally]

Josey, that is not a bad analogy. When considering how much information to reveal to someone who doesn't know anything about a subject, I remember one suggested response to 'awkward' questionsfrom one's children as to certain subjects.....Reveal all that you know in a truthful manner. IT will be of value to them someday even if they don'tnderstand it all at the timef revelation.
analogies are cool...I use them a lot. But...soemtimes, the truth is more useful....adn might spur investigationa dn thought, imho.
At any rate...good analogies or straightforward simple explanations are much better than misrepresentation.

 

[fenderguru.com]

I agree with you all. I think I will re-phrase this explanation.
Thanks for the input.

 

[gridlock]

Hi guys. Jens from fenderguru.com here. Thought I should just clarify a few things.

1) Pulling the other channel's preamp tube on blackface Fender amps won't hurt the amps. It has stood the test of time and been been done by players in 50 years.

2) Johnny Cache is right about "Signal leaking between channels" is not a technically precise description of what actually happens. We have used simple explanations on the web site so that more people can understand. The content on fenderguru.com is targeted for mucisians, average guitar players and amateur amp techs eager to learn. It is not meant for amp builders or people with electrical engineering degrees. It is more important to me to explain the basic concepts of Fender amps to thousands of musicians and players than telling experienced amp gurus something they already know.



This is by the way my first post here. I love this forum.

Best.

Jens, Norway.

Hi Jens,
Glad you here and I have learned a lot from your website and visit it every time I get an new (to me) vintage Fender amp. You mentioned that pulling V1 will not hurt a blackface Fender amp, any problem with doing the same on a siverface Fender amp? Just for clarification.

Thanks,
Gridlock

 

[Wally]

Gridlock, and two channel BF FEnder guitar amp is wired this way...stock....except for the new '68 Custom things. I believe...adn Jenns can either confirm or correct this...that the cathodes are separated on those amps in order to manipulate gain in the separate channels. At lesat, that is how techs have been doing it for years/deacades out here in the working world.

 

[gridlock]

Gridlock, and two channel BF FEnder guitar amp is wired this way...stock....except for the new '68 Custom things. I believe...adn Jenns can either confirm or correct this...that the cathodes are separated on those amps in order to manipulate gain in the separate channels. At lesat, that is how techs have been doing it for years/deacades out here in the working world.

Wally, Are you saying that pulling V1 in my Silverface 72 TR and 74 DR will not work the same as in my BF 65 VR? Thanks Grid

 

[Wally]

No, Gridlock, I am saying that all vintage two-channel Fender guitar amps from the vintage BF/SF era have the pin 8 cathodes tied together...and pulling V1 in your '72 SFTR and your '74 SFDR work just the way your BFVR does....if all amps are still wired as they left the factory back in the day.

Fender's new series of two channel reverb amps...the '68 Customs....do NOT work this way IF I understand what they have done. Maybe Jenns can either confirm this or straighten me out....but in order to best manipulate gain separately in these BF/SF guitar circuits, one would do best to separate those pin 8 cathodes, ime....and therefore one would 'undo' this relationship that is established with the shared pin 8 cathodes that your Fender amps had when new...and probably still have today. Maybe Fender went about things in a different manner in these new '68 Custom amps that have two channels.....but separating those cathodes to manipulate gain separately in those channels is one way to get to that goal. You see....as I expalined above...when you pull that tube...either V1 or V2, you are in effect chagning the gain in the remaining channel...taht is the effect that is ocurring when you pull that V1...you are rebiasing the other channel due to the effect of lifting the other channel---the one whose tube you removed---from that shared cathode bypass circuit...teh 820ohm resistor now is yielding a hotter bias because it is carrying only one load on it rather than the shared load. When that 820 ohm resistor had two loads on it, each of thoose cathodes was 'seeing' the exact same thing as they would IF one ran them separately with a 1.5K resistor there.

 

[gridlock]

Got it Wally. Thanks for the clarification.

 

[old goat]

I've tried on a BFSR and a BF Tremolux, made no difference

 

[Wally]

I've tried on a BFSR and a BF Tremolux, made no difference

old goat, it made a difference; but the difference is something that you simply missed. The change is not liek the difference between night and day....but those who apply their ears and develope some sensitivity for small changes/differences in voluem and tone do hear the chagne...it is an honest increse in gain..it exists....it yield a difference.

Same thing happens wtih tube changes...sometimes one can install a different 12Ax7 in a preamp, and the difference is dramatic. The difference bgetween two other 12AX7's might be more difficult to discern....but those who apply themselves can hear differences that others do not...and some times cannot...hear.

 

[rokdog49]

old goat, it made a difference; but the difference is something that you simply missed. The change is not liek the difference between night and day....but those who apply their ears and develope some sensitivity for small changes/differences in voluem and tone do hear the chagne...it is an honest increse in gain..it exists....it yield a difference.

Same thing happens wtih tube changes...sometimes one can install a different 12Ax7 in a preamp, and the difference is dramatic. The difference bgetween two other 12AX7's might be more difficult to discern....but those who apply themselves can hear differences that others do not...and some times cannot...hear.

+1 It does make a difference in gain. As I stated earlier in my post. The amp will break up sooner and you will get a small volume bump. You will.

 

[kavalero]

+1 It does make a difference in gain. As I stated earlier in my post. The amp will break up sooner and you will get a small volume bump. You will.

+1

I have experimented excessively with my BF amps, and its exactly as described above.

Earlier break-up and bit more volume.

Also, I have noticed that puling out the V1 makes my DR gets a bit more of a sonic definition.

Again, the differences are subtle, but still there, and I like them.

It is an improvement.

 

[SRVYJM]

Bump for a pretty old post- but I have to chime in here. Just bought a Fender Custom '68 Deluxe Reverb (2018)- I actually thought they were brand new designs- but I believe that's the one mentioned on here because mine shares reverb and tremolo with both channels. Because I pulled V1 in my '67 Super Reverb and loved the results- I tried it today on my new Deluxe Reverb. Same result- the amp is louder at a lower setting and not more "gain" to my ears- but more "growl", very noticeable- nothing subtle about it. Since I just bought the amp today I was a bit underwhelmed by it's tone initially- until I removed V1 (just like I was with my BF '67 Super) and suddenly all the stuff I love about listening to SRV is just there. I think of it as more growl (again- not really gain- just something in the mids that is missing otherwise I think)- kind of like putting a TS808 in front of the amp without having to do that- I also think the tone becomes much more 3D and alive. I can also say the sustain and bell-like chime all increase too. I don't use the "custom" channel in mine so far so won't miss V1 at all. It's like the perfect Super Reverb El Mocombo tone and sustain at bedroom friendly volumes- but I can take this amp out to gigs and cut through any drummer- but still not hurt anyones ears with ice pick harshness. Just by removing V1. With it back in- Ice Pick is back and it's painful- with it out- Tonal Nirvana! I have to shout out to Jens from Fenderguru too- love your website and YouTube Channel- been a subscriber for some time. This new '68 Deluxe Reverb sounds like Amund Maarud's beast you built him. The "something magic" in that beast that everyone talks about in the comments is in this amp too with V1 out! It's weird how much of a difference it makes to my ears and the feel of the guitar. Just an awesome amp. It's like kavalero says- it has more "sonic definition" for sure- and more of that SRV awesome GROWL!