Bassman jumpered compression and headroom question

htloren

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Hi everyone,

Just wanted to ask. It’s been a while since I played with my Fender ‘59 Bassman LTD reissue. Been using my Princeton Reverb and Deluxe Reverb more just because of the situations. Smaller events for the Deluxe and recording with the Princeton in a small room.

I pulled out the Bassman today. Been a really long time since I last jumpered the amp. I do it plugging the guitar into the Bright channel 1 and bridge Normal 1 to Bright 2. I then blend the normal and bright together.

I noticed the clean, no effects on sound is compressed. I guess I never noticed it before. I like it but don’t remember the jumper method ever compressing the sound before.

I plug into effects normally, 6 pedals, (buffered and the rest are true bypass pedals) and I also plugged in straight to make sure the pedals or cables were not an issue. I also tried different patch cables with the jumper. All fine here. I also switched around the jumper inputs where I am usually plugged into Normal, I plugged into the Bright channel.

Just wanted to check if this is normal? Also wanted to ask, is it true jumpering the two channels lowers the headroom? Might be a good idea to use then for this amp.

Thanks!

Loren
 
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Lowerleftcoast

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I like it but don’t remember the jumper method ever compressing the sound before.
I am not so sure the jumping is responsible for the compression. I would think the tube rectifier and primary impedance of the output transformer would be most likely reasons.
is it true jumpering the two channels lowers the headroom?
There may be a small increase in gain. The usual comments speak of a *thicker* type sound. Maybe a little more complex harmonics due to the *other* half of the tube interacting. Some tube rolling here may be beneficial because rarely are the two halves of a tube equal. This is not to say both halves of the tube should be equal. It very well may be more colorful when the tube does not have equal output. You sort of have some control over this harmonic effect with the volume knobs set at different levels.
Normal channel 1 and bridge Bright 1 to Normal 2. Just sounds better to me.
Plugging in like this results in ~roughly equal input on the two halves of V1. The bright channel has a bright cap (of course) which will be more noticeable on lower volumes and is progressively dialed out when the volume of the bright channel is turned up.
Idk if it would be perceptible but, it should retain a few more highs plugging guitar into Normal 2 then jump from Normal 1 to Bright 1. (It still provides ~roughly equal input on the two halves of V1.)
Always let your ears be your guide when trying this stuff.
 

htloren

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Hi Lowerleftcoast!

Thank you. I don’t know why I didn’t notice the thickening and compression before. It is a nice sound bit less open because of the thickening. Relaxed feel. I would say, if plugged into just the Normal channel, more open, spongy and jumpered is more tight but in your face, in a good way. More present?

Will continue checking it out, haven’t decided if I prefer blended over just plugging just into the Normal channel yet.

Any idea if there is a difference between plugging into the Bright Channel vs Normal channel when jumpering? The big card my Bassman came with said to plug into the Bright channel. On the Fender website, it said plug into either. Wondered if there was a difference?

Thanks again!

Loren
 

NTC

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Is the first preamp tube in the LTD a 12AY7 like in the original Bassman?
 

Lowerleftcoast

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haven’t decided if I prefer blended over just plugging just into the Normal channel yet.
I think I will recant my statement in the previous post:
"Idk if it would be perceptible but, it should retain a few more highs plugging guitar into Normal 2 then jump from Normal 1 to Bright 1."
On reflection, it probably retains more signal with plugging into 1 and jumping from 2 to the other channel 1. Like you originally had it.
Any idea if there is a difference between plugging into the Bright Channel vs Normal channel when jumpering?
The chosen channel will be supplied with the most signal. The signal sent to the other channel will be reduced by about 6%.
As mentioned before the Bright channel and the Normal channel circuits are equal when the volume is high. The only difference* between the two channels is the bright cap across the volume pot. As the volume is turned up, the cap has less effect.
The other part of the equation is the output of the two sections of the tube.

Fender assumes the volume will be lowish and the bright cap will be welcome when they say to plug into the Bright channel.

* I have discounted this but, another difference may come from the tolerance variable of the individual parts in each channel circuit.
 
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htloren

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Is the first preamp tube in the LTD a 12AY7 like in the original Bassman?
Hi NTC,

I did change the tubes and speakers so this amp is no longer stock.

v1 is a Tungsol 12ax7, v2 and v3 are Chinese tubes. Both 12ax7. Stock Rectifier tubes and the power tubes are TAD 6L6WGC.

Speakers are 4x10 Eminence GA10-SC59 alnicos. I absolutely recommend these speakers! No fizz when overdriven. High’s are chimmey and sweet. Mids focused. Focusing on frequencies 5khz and below. But if you need brighter, then you can EQ. The high’s never hurt. Bass is great too. No flub. Tight but big. Pretty balanced speaker for guitar amps. I have the 10” ceramic version of this speaker in my Princeton Reverb and a 12” version in my Deluxe Reverb. Fantastic!

I did consider a 12ay7 and may try it in the future but cannot find a decent 12ay7 tube from where I am at so I went with the best 12ax7 tube for the amp for me. I do have NOS but I do like current productions for certain amps. The TAD 6L6WGC are amazing. TAD’s 6v6 GT STR are also great. I use them in my 2 Blackface amps.

I like to maintain records on my tube replacements. Since this whole pandemic began, I hardly used the amp. So the last v1 replacement was on September 2020.

Loren
 
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htloren

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I think I will recant my statement in the previous post:
"Idk if it would be perceptible but, it should retain a few more highs plugging guitar into Normal 2 then jump from Normal 1 to Bright 1."
On reflection, it probably retains more signal with plugging into 1 and jumping from 2 to the other channel 1. Like you originally had it.

The chosen channel will be supplied with the most signal. The signal sent to the other channel will be reduced by about 6%.
As mentioned before the Bright channel and the Normal channel circuits are equal when the volume is high. The only difference* between the two channels is the bright cap across the volume pot. As the volume is turned up, the cap has less effect.
The other part of the equation is the output of the two sections of the tube.

Fender assumes the volume will be lowish and the bright cap will be welcome when the say to plug into the Bright channel.

* I have discounted this but, another difference may come from the tolerance variable of the individual parts in each channel circuit.
Hi Lowerleftcoast,

Fender on the amp card suggested plugging into the bright section and after your explanation made absolute sense! But I do now prefer plugging into Normal over the Bright for jumpering. I have always preferred the Normal channel somehow when not jumpered. But when jumpering, it really does take a blending of the Normal and Bright channels for the whole tone come out.

Been jumpering this early morning and am starting to really dig it. The added thickness and come forward tone. More muscular. Knowing more about the background definitely helps make it more fun!

Thanks!

Loren
 

charlie chitlin

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Not sure about compression, but definitely more gain.
I've been using tweed amps for almost 40 years (current #1 is a 5F6A Bassman), and every time I jumped the channels it sounded great at home and every time I did it at a gig, I was yanking the jumper out by the middle of the first tune.
Whatever it does, it does a thing that makes the amp retreat into the mix.
 

htloren

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Not sure about compression, but definitely more gain.
I've been using tweed amps for almost 40 years (current #1 is a 5F6A Bassman), and every time I jumped the channels it sounded great at home and every time I did it at a gig, I was yanking the jumper out by the middle of the first tune.
Whatever it does, it does a thing that makes the amp retreat into the mix.
Hi Charlie Chitlin,

Ahh. The last time I used my Bassman in a gig was a so long ago I cannot remember and the last time I jumpered it was longer than that. I do remember my friend telling me to put more treble. Adding treble at the time did add life at that gig. At the time, I just thought it was the room. The bar was a dark & reverby sounding room. But maybe it was that. Sounds great in the room and lost in a band mix. I will observe that the next time I go out with my Bassman.

Thanks!
Loren
 

ballynally2

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You might want to try a 5751 preamp valve. Allows for bigger voltage swing. Kind of a cleaner sounding 12ax7. My 63 Vibroverb is happy with those.
You can try one 5751 in V1 coupled with a 12ay7 in V2..
 

htloren

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You might want to try a 5751 preamp valve. Allows for bigger voltage swing. Kind of a cleaner sounding 12ax7. My 63 Vibroverb is happy with those.
You can try one 5751 in V1 coupled with a 12ay7 in V2..
Hey Ballynally2,

I have tried both 5751 and 12ay7. Have NOS Sylvania 5751. The 12ay7 I didn’t care for but the 5751’s were nice. But I still preferred the 12ax7. Happy with the Tungsol 12ax7 in v1
 




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