Fender 6G2 Re-Build As Pre-Amp

PLX

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rrgpWdt.jpg
 

PLX

MENSA member, Astronaut, Dated Your Mom Once
Messages
15,120
Op6xWrO.jpg


:rolleyes: Changing original AC power scheme to modern 3-prong grounded outlet, chassis ground.
:rolleyes: Changing AC power switch to DPST switch and change location in circuit to de-energize power transformer when switch is off.
:rolleyes: Change location of 2 Amp fuse
:confused: Add stand-by switch
:rolleyes: Add bias adjust circuit
:rolleyes: Remove tremolo circuit
:confused: Add Presence control
:rolleyes: Upgrade output transformer to Classic Tone CT-40-18045
:rolleyes: Replace speaker with resistive load (8Ω 200W) and adjustable line out
:rolleyes: Replace filter cap can with 3 board mounted 30uF 500V caps
:rolleyes: Remove grounding switch and death cap
 
Last edited:

pdf64

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To mitigate the risk of hum from mains ground loops, I suggest to keep the circuit's 0V common isolated from the chassis ground; see how Fender do this on the RI standalone with R23/CR5/CR6 https://el34world.com/charts/Schematics/files/Fender/Fender_63_reverb_manual.pdfreverb
Note that the range of control from the presence will become much less when there's a resistive load (ie less boost available).
Have you considered implementing a full tone stack (or at least T&B), and making up the consequential loss in signal level with the spare 12AX7 section?
 
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Rockinrob86

Gold Supporting Member
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I use this circuit to fix ground loops in gear like this -
screen-shot-2018-06-14-at-7-32-35-pm-png.522123


It safely makes the ground of whatever you put it in just a bit higher than the other things, so the amp becomes the main grounding point and avoids the loop, but the other piece of gear is safely connected to ground. It's a must have for 6g15's! You have to isolate the input jacks and not ground anything to the backs of the pots, i.e. use a star ground design.
 

PLX

MENSA member, Astronaut, Dated Your Mom Once
Messages
15,120
To mitigate the risk of hum from mains ground loops, I suggest to keep the circuit's 0V common isolated from the chassis ground; see how Fender do this on the RI standalone with R23/CR5/CR6 https://el34world.com/charts/Schematics/files/Fender/Fender_63_reverb_manual.pdfreverb
Note that the range of control from the presence will become much less when there's a resistive load (ie less boost available).
Have you considered implementing a full tone stack (or at least T&B), and making up the consequential loss in signal level with the spare 12AX7 section?
Thanks for bringing that up - I have a very real concern about ground loops based on my experience with running one amp into another previous to this experiment.

Appreciate the link. I'll spend time reading it and trying to learn something. :aok

I did consider using the unused half of the 12ax7, but I wanna try it like this first and see how it is.

I've done this with a 50W Music Man and the results were exactly what I'm looking for. Want this to be a dedicated all-in-one-box solution tho'
 

PLX

MENSA member, Astronaut, Dated Your Mom Once
Messages
15,120
To mitigate the risk of hum from mains ground loops, I suggest to keep the circuit's 0V common isolated from the chassis ground; see how Fender do this on the RI standalone with R23/CR5/CR6 https://el34world.com/charts/Schematics/files/Fender/Fender_63_reverb_manual.pdfreverb
Note that the range of control from the presence will become much less when there's a resistive load (ie less boost available).
Have you considered implementing a full tone stack (or at least T&B), and making up the consequential loss in signal level with the spare 12AX7 section?
That link is broken.

Can you re-post ?

Thanks :aok
 

PLX

MENSA member, Astronaut, Dated Your Mom Once
Messages
15,120
I use this circuit to fix ground loops in gear like this -
screen-shot-2018-06-14-at-7-32-35-pm-png.522123


It safely makes the ground of whatever you put it in just a bit higher than the other things, so the amp becomes the main grounding point and avoids the loop, but the other piece of gear is safely connected to ground. It's a must have for 6g15's! You have to isolate the input jacks and not ground anything to the backs of the pots, i.e. use a star ground design.
So, this is a monolithic grounding scheme then ?

You have one instance of this circuit, and all your chassis grounds (except the incoming AC) ground via this ?

With the parts I have on hand, I can build this - perhaps on a small perf-board:

JG5Ztgg.jpg
 
Last edited:

Tron Pesto

Silver Supporting Member
Messages
920
So time out - what's the goal here? Whatcha aimin' to do with this?

Obviously, all the tech tips for the circuit itself are awesome, but the overall picture might help frame the direction - nah'mean?
 
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Tron Pesto

Silver Supporting Member
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BTW - why include a standby? I'm kinda ambivalent about them. I'll remove them if they're stupid (like a switch on the secondary center tap) if the opportunity represents itself and on the other hand, I'll leave them if they are wired "correctly" (there are some bad positions to have a standby).

But if I'm designing/building an amp that has ANY tube rectifier (direct or indirect cathode/heater), I'm not going to waste the real estate/time on it.

BUT - I'm not going to knock anyone who would include one, especially if they know how to use it properly, but I'm just CURIOUS why you would go through the trouble?
 

PLX

MENSA member, Astronaut, Dated Your Mom Once
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15,120
So time out - what's the goal here? Whatcha aimin' to do with this?

Obviously, all the tech tips for the circuit itself are awesome, but the overall picture might help frame the direction - nah'mean?
According to a guy who grew up with Ed, who I have bought some tubes from, and who I've been asked not to name..

The signal chain for VHI was an EP-3 => Fender Bandmaster w all controls on 10 => ext. speaker jack into stock a Marshall plexi.

I've tried this with a Badgerplex AC into a Music Man 50W loaded down with resistive load into my 2203 clone and it is very convincing.
 

PLX

MENSA member, Astronaut, Dated Your Mom Once
Messages
15,120
BTW - why include a standby? I'm kinda ambivalent about them. I'll remove them if they're stupid (like a switch on the secondary center tap) if the opportunity represents itself and on the other hand, I'll leave them if they are wired "correctly" (there are some bad positions to have a standby).

But if I'm designing/building an amp that has ANY tube rectifier (direct or indirect cathode/heater), I'm not going to waste the real estate/time on it.

BUT - I'm not going to knock anyone who would include one, especially if they know how to use it properly, but I'm just CURIOUS why you would go through the trouble?
Not 100% sure I'm going to put the standby switch in the circuit yet.

Was already leaning against it.
 

Tron Pesto

Silver Supporting Member
Messages
920
The signal chain for VHI was an EP-3 => Fender Bandmaster w all controls on 10 => ext. speaker jack into stock a Marshall plexi.

Sounds like an awesome thing to try - and with your chops, it could be epic.

JUST KEEP IN MIND - without naming names - all of these guys that were there are FRIED. LOL!!! There are more rumors about what Eddy did with what, it seems like there could have been 673 different people with 1,072 different interpretations about what he did on VH1 (and 2 for that matter).

BTW - I'm not immune to the hype - today I literally finished a bucking transformer from parts I had laying around for a Hammond amp I just converted. I created two taps from the transofrmer, and one is dropping the voltage to the low 90s and IMMEDIATELY I thought - HELLS YEAH, THAT'S WHAT EDDY WAS RUNNING HIS VARIAC AT - TONE GOLD MUTHATFECKER!!!!
 
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PLX

MENSA member, Astronaut, Dated Your Mom Once
Messages
15,120
Sounds like an awesome thing to try - and with your chops, it could be epic.

JUST KEEP IN MIND - without naming names - all of these guys that were there are FRIED. LOL!!! There are more rumors about what Eddy did with what, it seems like there could have been 673 different people with 1,072 different interpretations about what he did on VH1 (and 2 for that matter).

BTW - I'm not immune to the hype - today I literally finished a bucking transformer from parts I had laying around for a Hammond amp I just converted. I created two taps from the transofrmer, and one is dropping the voltage to the low 90s and IMMEDIATELY I thought - HELLS YEAH, THAT'S WHAT EDDY WAS RUNNING HIS VARIAC AT - TONE GOLD MUTHATFECKER!!!!
A guy on MetroAmp did this with a Bassman a decade ago.

He actually ran the signal out of the ext. speaker jack into a plexi clone - which is crazy.

His recording methods were haphazard, and his playing ability was not up to par.. but there was definitely something there.
 




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