6G6-B blonde Bassman mods?

JohnnyCrash

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I built a 6G6-B clone this year. It’s not a vintage piece, all new parts. It has a few tweaks, but I’d like to hear your mods for this circuit.

Originally I only made one change, swapping the 2200pF across the 100k plate resistor on the second stage (the treble shunting cap) to a 680pF.

This was WAY too bright! For anyone listening to people on the internet who tell you to clip that cap entirely, do not listen to them. The amp isn’t “dark,” especially once you start goosing the Treble control for added gain.

I replaced the 680pF for the stock 2200pF cap. Sounds glorious with any of my guitars and has plenty of treble on tap. I suspect this cap was more for controlling oscillation since the Treble control also acts as a second gainstage (if you’ve ever cascaded gainstages, you know you have to control very high frequencies or you end up with noise and squealing!).

So in its current state the amp is built to spec/schematic, except:

1. I used a mid-60s black faceplate era Bassman dual 80uF filter cap setup for the first B+ node (actually two 100uFs). It really tightened up some of the loose bass these things can sometimes get when fully cranked.

2. I removed the Presence control and instead I simply hardwired the Negative Feedback control to a 3-way switch in the rear panel. The options are 1) Stock NFB resistor; 2) raw or no NFB; and 3) JTM45 type high NFB, for an ultratight bass response and more cleans on the volume dial. I generally leave it in stock NFB mode.

3. In the old Presence control knob I put a dual 250k pot PPIMV Master Volume control.

The preamp has two pull switches for some optional mods.

1. In the Normal channel (uses the tapped Treble pot, like the original early 60s Bassmans) the Bass knob pulls out to swap the original midrange resistor from 6.8k to 15k. I put this switch on a lot of my Fender style VTB tonestacks to give me a second mid setting option. On this 6G6-B it sounds great, like it does on all of my VTB stacks. Shimmery slightly scooped Fender, to fat barking Marshall with the pull of a knob.

2. The second switch I’m ambivalent about, which is why I’m asking for your favorite mods…

On the already Marshally sounding stock Bass channel I installed a pullswitch on the Volume control. When engaged it throws a huge plexi style 4700pF bright cap across the volume pot. On my 1987x plexi clone, this has always been what I consider the plexi’s secret weapon (why people clip this or shrink it to 100pF-500pF is beyond me, it almost acts as Rangemaster style treble booster!). However on my 6G6-B it doesn’t give me much more immediate gain and it doesn’t need a Rangemaster style treble boost… in fact, even with the 2200pF across the second stage plate resistor, it still almost gets too bright when I turn up the treble and engage this “bright” cap.

I previously tried a cathode bypass swap on this switch — changing the stock 25uF when pulled with a more Marshally 0.68uF cap to tighten bass and boost midrange. And again, the awesome Bass channel didn’t really need it — it didn’t really give me much “more” of anything.

What switchable mod would you consider replacing this with? Why?


1AFC4B95-C526-4112-9689-CC30569BA93F.jpeg
 

schmee

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I did mine with a tube rectifier. I didn't find anything I liked that much for the Bass circuit so just put it back to the original. Although I thought about using it for a Vibrato....
BssmnFrontFinal.jpg BssmnRearFinal.jpg
 

JohnnyCrash

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OK, I think I found my mistake…

The Marshall plexi uses a 1 meg pot with that massive 4700pF cap across it.

The 6G6-B’s Bass channel’s Volume pot is 250k.

Am I calculating this correctly?: if I want that same high shelf Marshally midrange action from a 250k pot (instead of a 1 meg) I should use a bigger cap in the range of 0.022uF?

I’m about to open the amp up again and try a 0.022uF on the switch.
 

JohnnyCrash

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I did mine with a tube rectifier. I didn't find anything I liked that much for the Bass circuit so just put it back to the original. Although I thought about using it for a Vibrato....
View attachment 1019240 View attachment 1019241



I really like both channels for cranked rock sounds.

The Bass channel is very Marshall sounding when really cranked… though it’s LOUD at that point :D
 

mountainhick

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Not sure what you are after. And, these are not mine, but I dug out my notes from a youtube vid by psionic. IMO, he essentially marshallized, maybe takes it a bit far,

Smaller cathode and coupling cap values and possibly eliminating bypass cap on V2A. You can make switchable cathode with anti pop resistors

He uses these values for tone stack: treble bypass 330pf, bass and middle .022uf, and 100K-L bass pot.

He increased V2B cathode resistor to 10K.

Bypassed plate load R with 500p to bleed off highs
 

JohnnyCrash

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Not sure what you are after. And, these are not mine, but I dug out my notes from a youtube vid by psionic. IMO, he essentially marshallized, maybe takes it a bit far,

Smaller cathode and coupling cap values and possibly eliminating bypass cap on V2A. You can make switchable cathode with anti pop resistors

He uses these values for tone stack: treble bypass 330pf, bass and middle .022uf, and 100K-L bass pot.

He increased V2B cathode resistor to 10K.

Bypassed plate load R with 500p to bleed off highs


Saw that vid when I started building mine.

That 500pF on the plate resistor is absurd. That repair guy treats the unusual 6G6-B preamp as if it’s all cathode follower Marshall… but it’s not.

I started with a 680pF there since so many people seemed to think clipping it off entirely was something good. Way too bright and harsh. Snipping or even reducing that cap is just ill-advised.

After spending about a year building and tweaking mine, I realized that guy was off his rocker. Then again, wasn’t he working with someone’s strange kit? I wasn’t about to turn this circuit into something it wasn’t.

The stock 6G6-B is an awesome sounding amp. I didn’t want to Marshallize it, just tweak the blonde sound a bit…

That said, I just swapped the 4700pF for two 0.010uF caps in series (0.020uF) to get a similar cutoff shelf frequency of the plexi (the 6G6-B’s Bass channel volume pot is 250k). It gains it up earlier on the knob, which is good when I’ve got the PPIMV turned all the way up. When using the PPIMV though, it sounds better (fuller) with the cap switched out of the circuit.

I think I’m done tweaking.

I am very happy with my 6G6-B’s sound!

Thanks for indulging me everyone :)
 

mountainhick

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Saw that vid when I started building mine.

That 500pF on the plate resistor is absurd. That repair guy treats the unusual 6G6-B preamp as if it’s all cathode follower Marshall… but it’s not.

I started with a 680pF there since so many people seemed to think clipping it off entirely was something good. Way too bright and harsh. Snipping or even reducing that cap is just ill-advised.

After spending about a year building and tweaking mine, I realized that guy was off his rocker. Then again, wasn’t he working with someone’s strange kit? I wasn’t about to turn this circuit into something it wasn’t.

The stock 6G6-B is an awesome sounding amp. I didn’t want to Marshallize it, just tweak the blonde sound a bit…

That said, I just swapped the 4700pF for two 0.010uF caps in series (0.020uF) to get a similar cutoff shelf frequency of the plexi (the 6G6-B’s Bass channel volume pot is 250k). It gains it up earlier on the knob, which is good when I’ve got the PPIMV turned all the way up. When using the PPIMV though, it sounds better (fuller) with the cap switched out of the circuit.

I think I’m done tweaking.

I am very happy with my 6G6-B’s sound!

Thanks for indulging me everyone :)

I appreciate your POV. I wasn't advocating anything for you, just passing on what I observed there. Interesting to know your outlook, and like I said I thought he took it too far as well. I'm on the road to completing a 6G6B micro, and will keep your input in mind for the future. Thanks!
 

JohnnyCrash

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I appreciate your POV. I wasn't advocating anything for you, just passing on what I observed there. Interesting to know your outlook, and like I said I thought he took it too far as well. I'm on the road to completing a 6G6B micro, and will keep your input in mind for the future. Thanks!


I’m excited to see a micro version!
 

NTC

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That said, I just swapped the 4700pF for two 0.010uF caps in series (0.020uF) to get a similar cutoff shelf frequency of the plexi (the 6G6-B’s Bass channel volume pot is 250k)

Caps add in parallel, not in series. Your total value for the two 0.01 uF caps in series is 0.005 uF, or 5000 pF. If that is really what you did, you are right at 4700 pF. Plus 6.4%.

I am looking at the 6G6-B circuit and don't see a 4700 pF. Where is it?
 
Last edited:

JohnnyCrash

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Caps add in parallel, not in series. Your total value for the two 0.01 uF caps in series is 0.005 uF, or 5000 pF. If that is really what you did, you are right at 4700 pF. Plus 6.4%.

I am looking at the 6G6-B circuit and don't see a 4700 pF. Where is it?



I caught my second mistake last night.

I essentially put the same value I tried earlier by mistake!

The only problem is, this amp’s namesake, my daughter Daphne, is on her way. My wife’s water broke this morning.

I’ll have to replace this cap later.

In any case, it’s not in the 6G6-B schematic. It’s on mine as a pullswitch as an option. I like what large bright caps do to the midrange on Marshalls, so I’m putting it on a switch to try it in this amp.
 

JohnnyCrash

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If this doesn’t tell you my current mental state… I’ve been building amps for, what, fifteen years? And my brain treated capacitors as resistors in-series!

I was hoping to finish this amp before my daughter arrived, but that’s not going to happen now :D
 

ruger9

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The only mod I've heard of for these is making the bass channel more suitable for guitar... probably a cap change? But other than than, Nocturne makes the Blondeshell, which is a 6G6B with onboard spring reverb... it's also got a switch for "hollowbody" or "plank", not sure what that is

 

rschiller

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I built a 6G6-B clone this year. It’s not a vintage piece, all new parts. It has a few tweaks, but I’d like to hear your mods for this circuit.

Originally I only made one change, swapping the 2200pF across the 100k plate resistor on the second stage (the treble shunting cap) to a 680pF.

This was WAY too bright! For anyone listening to people on the internet who tell you to clip that cap entirely, do not listen to them. The amp isn’t “dark,” especially once you start goosing the Treble control for added gain.

I replaced the 680pF for the stock 2200pF cap. Sounds glorious with any of my guitars and has plenty of treble on tap. I suspect this cap was more for controlling oscillation since the Treble control also acts as a second gainstage (if you’ve ever cascaded gainstages, you know you have to control very high frequencies or you end up with noise and squealing!).

So in its current state the amp is built to spec/schematic, except:

1. I used a mid-60s black faceplate era Bassman dual 80uF filter cap setup for the first B+ node (actually two 100uFs). It really tightened up some of the loose bass these things can sometimes get when fully cranked.

2. I removed the Presence control and instead I simply hardwired the Negative Feedback control to a 3-way switch in the rear panel. The options are 1) Stock NFB resistor; 2) raw or no NFB; and 3) JTM45 type high NFB, for an ultratight bass response and more cleans on the volume dial. I generally leave it in stock NFB mode.

3. In the old Presence control knob I put a dual 250k pot PPIMV Master Volume control.

The preamp has two pull switches for some optional mods.

1. In the Normal channel (uses the tapped Treble pot, like the original early 60s Bassmans) the Bass knob pulls out to swap the original midrange resistor from 6.8k to 15k. I put this switch on a lot of my Fender style VTB tonestacks to give me a second mid setting option. On this 6G6-B it sounds great, like it does on all of my VTB stacks. Shimmery slightly scooped Fender, to fat barking Marshall with the pull of a knob.

2. The second switch I’m ambivalent about, which is why I’m asking for your favorite mods…

On the already Marshally sounding stock Bass channel I installed a pullswitch on the Volume control. When engaged it throws a huge plexi style 4700pF bright cap across the volume pot. On my 1987x plexi clone, this has always been what I consider the plexi’s secret weapon (why people clip this or shrink it to 100pF-500pF is beyond me, it almost acts as Rangemaster style treble booster!). However on my 6G6-B it doesn’t give me much more immediate gain and it doesn’t need a Rangemaster style treble boost… in fact, even with the 2200pF across the second stage plate resistor, it still almost gets too bright when I turn up the treble and engage this “bright” cap.

I previously tried a cathode bypass swap on this switch — changing the stock 25uF when pulled with a more Marshally 0.68uF cap to tighten bass and boost midrange. And again, the awesome Bass channel didn’t really need it — it didn’t really give me much “more” of anything.

What switchable mod would you consider replacing this with? Why?


View attachment 1019191

I built a 6G6-B clone this year. It’s not a vintage piece, all new parts. It has a few tweaks, but I’d like to hear your mods for this circuit.

Originally I only made one change, swapping the 2200pF across the 100k plate resistor on the second stage (the treble shunting cap) to a 680pF.

This was WAY too bright! For anyone listening to people on the internet who tell you to clip that cap entirely, do not listen to them. The amp isn’t “dark,” especially once you start goosing the Treble control for added gain.

I replaced the 680pF for the stock 2200pF cap. Sounds glorious with any of my guitars and has plenty of treble on tap. I suspect this cap was more for controlling oscillation since the Treble control also acts as a second gainstage (if you’ve ever cascaded gainstages, you know you have to control very high frequencies or you end up with noise and squealing!).

So in its current state the amp is built to spec/schematic, except:

1. I used a mid-60s black faceplate era Bassman dual 80uF filter cap setup for the first B+ node (actually two 100uFs). It really tightened up some of the loose bass these things can sometimes get when fully cranked.

2. I removed the Presence control and instead I simply hardwired the Negative Feedback control to a 3-way switch in the rear panel. The options are 1) Stock NFB resistor; 2) raw or no NFB; and 3) JTM45 type high NFB, for an ultratight bass response and more cleans on the volume dial. I generally leave it in stock NFB mode.

3. In the old Presence control knob I put a dual 250k pot PPIMV Master Volume control.

The preamp has two pull switches for some optional mods.

1. In the Normal channel (uses the tapped Treble pot, like the original early 60s Bassmans) the Bass knob pulls out to swap the original midrange resistor from 6.8k to 15k. I put this switch on a lot of my Fender style VTB tonestacks to give me a second mid setting option. On this 6G6-B it sounds great, like it does on all of my VTB stacks. Shimmery slightly scooped Fender, to fat barking Marshall with the pull of a knob.

2. The second switch I’m ambivalent about, which is why I’m asking for your favorite mods…

On the already Marshally sounding stock Bass channel I installed a pullswitch on the Volume control. When engaged it throws a huge plexi style 4700pF bright cap across the volume pot. On my 1987x plexi clone, this has always been what I consider the plexi’s secret weapon (why people clip this or shrink it to 100pF-500pF is beyond me, it almost acts as Rangemaster style treble booster!). However on my 6G6-B it doesn’t give me much more immediate gain and it doesn’t need a Rangemaster style treble boost… in fact, even with the 2200pF across the second stage plate resistor, it still almost gets too bright when I turn up the treble and engage this “bright” cap.

I previously tried a cathode bypass swap on this switch — changing the stock 25uF when pulled with a more Marshally 0.68uF cap to tighten bass and boost midrange. And again, the awesome Bass channel didn’t really need it — it didn’t really give me much “more” of anything.

What switchable mod would you consider replacing this with? Why?


I built a 6G6-B clone this year. It’s not a vintage piece, all new parts. It has a few tweaks, but I’d like to hear your mods for this circuit.

Originally I only made one change, swapping the 2200pF across the 100k plate resistor on the second stage (the treble shunting cap) to a 680pF.

This was WAY too bright! For anyone listening to people on the internet who tell you to clip that cap entirely, do not listen to them. The amp isn’t “dark,” especially once you start goosing the Treble control for added gain.

I replaced the 680pF for the stock 2200pF cap. Sounds glorious with any of my guitars and has plenty of treble on tap. I suspect this cap was more for controlling oscillation since the Treble control also acts as a second gainstage (if you’ve ever cascaded gainstages, you know you have to control very high frequencies or you end up with noise and squealing!).

So in its current state the amp is built to spec/schematic, except:

1. I used a mid-60s black faceplate era Bassman dual 80uF filter cap setup for the first B+ node (actually two 100uFs). It really tightened up some of the loose bass these things can sometimes get when fully cranked.

2. I removed the Presence control and instead I simply hardwired the Negative Feedback control to a 3-way switch in the rear panel. The options are 1) Stock NFB resistor; 2) raw or no NFB; and 3) JTM45 type high NFB, for an ultratight bass response and more cleans on the volume dial. I generally leave it in stock NFB mode.

3. In the old Presence control knob I put a dual 250k pot PPIMV Master Volume control.

The preamp has two pull switches for some optional mods.

1. In the Normal channel (uses the tapped Treble pot, like the original early 60s Bassmans) the Bass knob pulls out to swap the original midrange resistor from 6.8k to 15k. I put this switch on a lot of my Fender style VTB tonestacks to give me a second mid setting option. On this 6G6-B it sounds great, like it does on all of my VTB stacks. Shimmery slightly scooped Fender, to fat barking Marshall with the pull of a knob.

2. The second switch I’m ambivalent about, which is why I’m asking for your favorite mods…

On the already Marshally sounding stock Bass channel I installed a pullswitch on the Volume control. When engaged it throws a huge plexi style 4700pF bright cap across the volume pot. On my 1987x plexi clone, this has always been what I consider the plexi’s secret weapon (why people clip this or shrink it to 100pF-500pF is beyond me, it almost acts as Rangemaster style treble booster!). However on my 6G6-B it doesn’t give me much more immediate gain and it doesn’t need a Rangemaster style treble boost… in fact, even with the 2200pF across the second stage plate resistor, it still almost gets too bright when I turn up the treble and engage this “bright” cap.

I previously tried a cathode bypass swap on this switch — changing the stock 25uF when pulled with a more Marshally 0.68uF cap to tighten bass and boost midrange. And again, the awesome Bass channel didn’t really need it — it didn’t really give me much “more” of anything.

What switchable mod would you consider replacing this with? Why?


View attachment 1019191 Where the preamps join are 470k resistors before going into the .0005 CC on the Phase Inverter grid. You can use 220k which will be slightly higher in gain and clearer in tone and likely go to a .001 CC.

Not sure what you are after. And, these are not mine, but I dug out my notes from a youtube vid by psionic. IMO, he essentially marshallized, maybe takes it a bit far,

Smaller cathode and coupling cap values and possibly eliminating bypass cap on V2A. You can make switchable cathode with anti pop resistors

He uses these values for tone stack: treble bypass 330pf, bass and middle .022uf, and 100K-L bass pot.

He increased V2B cathode resistor to 10K.

Bypassed plate load R with 500p to bleed off highs
The 6G6-B is what it is and great for that particular tone. The Normal channel is essentially the later 2 stage AB763 circuit though here uses that odd tapped volume control. The Normal channel and Bass Channel (3 stage with 1st stage cathode follower) mix with 470k resistor at the .0005 CC into the phase invertor grid. Leave the preamp values alone though you might experiment with a 10k midrange resistor or wired in 10k pot. You might also like the slightly fatter tone of a .022uf mid-range resistor and use polyester-film and not polypropylene-film like Orange Drops. So in a replica build I would try 220k mix resistors for slightly more clarity with a .001 CC into the PI grid.

But I would certainly never do this to a vintage amp - see attached.
 

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