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Post subject: 6G6B Build
Posted: Tue May 31, 2016 11:29 am
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This is my first try at an amp build. A 6G6B Bassman.

I decided to do a scratch build instead of a kit so I could pick the components I wanted to use, and with some careful shopping the amp was built for less than any kit I could find including a blackface Bassman kit that's available online. I'm sure that's not the case with all amp builds but the 6G6B seemed to be one of the better scratch build cost vs kit cost amps.
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The cabinets are finger jointed #2 pine.
The woodworking part wasn't difficult but the tolex corners and getting the grill cloth straight was the hardest for me. I still haven't mastered the later two.

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I used 5% carbon comps (except for MF input resistors), Malory 150 caps, CTS pots and Classis Tone iron.
I thought about using the Tone Clone transformers but the Classic Tone seemed to get good reviews so I gave them a try. They sound real good. I also added an adjustable bias pot and a switch for dual impedance (not shown) where the external speaker jack was. The OT I chose was 4 and 8 ohm output.

Grounding took more thought than I expected. Everyone has their own opinion on what works, and in the end I opted for something similar to a Fender grounding scheme. Instead of a brass plate I used a buss bar for all the circuit grounds and screwed it to the chassis near the input jacks. The preamp filter caps are also grounded at this point.

B+ filter caps, the rectifier, PT and output tube cathodes are tied together near the PT. All input and output jacks are insulated from the chassis. The output is grounded at the 4700 ohm presence resistor ground.
The amp is really quiet. Just a very slight hum which may or may not be normal.

At first power up, the amp had an awful hum. I was almost out of ideas when I noticed that I had screwed the ground bar to the chassis at both ends. I removed the screw at the far end of the bar near the rectifier board, powered up and the hum was gone. By securing the ground buss at both ends I had created a ground loop (a newbie mistake). It's hard to believe that one thing could cause such a hum.

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The finished amp. I'm not sure if the grill cloth lines are going in the right direction. The dark lines on my
66 Bandmaster head are vertical, but my 68 twin lines are horizontal.

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In the end, it was a great learning experience and a whole lot of fun. The amp sounds awesome even played through some cheap Yamaha test speakers I had handy.
When I hooked up a pair of C-Rex speakers from my twin the amp sounded even better. I thought there would be too much bottom end with those speakers but not so. With a Jazzmaster or strat plugged in there was plenty of high end with the presence and treble pushed up.

I follow the threads on this forum regularly which helped answer a lot of questions I had on different grounding techniques. Even though the amp is really quiet, any grounding tips would be appreciated for my next build (Deluxe Reverb).

I was also thinking of some Jensen RI C12N's or C12K's for this cab. Has anyone tried one of them with a Bassman?


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Post subject: Re: 6G6B Build
Posted: Tue May 31, 2016 12:08 pm
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Sorry I can't help with any of your questions, but I have to say, that is one sweet looking box you made there, and I imagine it sounds as sweet as it looks. I do have a question for you, how long did this project take.
enjoy it
mud


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Post subject: Re: 6G6B Build
Posted: Tue May 31, 2016 12:25 pm
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The grill cloth is incorrectly oriented (as you surmised). As well, the wrong side is facing outward.

Otherwise though, an excellent build.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: 6G6B Build
Posted: Tue May 31, 2016 1:31 pm
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mud wrote:
Sorry I can't help with any of your questions, but I have to say, that is one sweet looking box you made there, and I imagine it sounds as sweet as it looks. I do have a question for you, how long did this project take.
enjoy it
mud


I don't know how many hours I spent on it but the entire build took about a month in my spare time.


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Post subject: Re: 6G6B Build
Posted: Tue May 31, 2016 1:42 pm
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You do a geat job and I like you wires dress.

Congrat.

Just need a new grill cloth to be a perfect build


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Post subject: Re: 6G6B Build
Posted: Tue May 31, 2016 1:51 pm
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Retroverbial wrote:
The grill cloth is incorrectly oriented (as you surmised). As well, the wrong side is facing outward.

Otherwise though, an excellent build.

Arjay


I thought the grill cloth was going in the wrong direction but I never thought it was inside out.
I took some spare grill cloth and put the other side out and sure enough, the black lines are slightly broken up. Thanks Arjay. I will definitely be changing the grill cloth because it will drive me crazy every time I look at the amp

I just read on one of the forums that if the grill cloth has black lines, that side goes towards the baffle. Is that always correct?


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Post subject: Re: 6G6B Build
Posted: Tue May 31, 2016 2:07 pm
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The grill cloth should not touch the baffle, did you put some pieces ( framing ) of wood between the grill cloth and the baffle ?


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Post subject: Re: 6G6B Build
Posted: Tue May 31, 2016 2:14 pm
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stratele52 wrote:
The grill cloth should not touch the baffle, did you put some pieces ( framing ) of wood between the grill cloth and the baffle ?


Yes. I built a small frame all around the baffle.


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Post subject: Re: 6G6B Build
Posted: Tue May 31, 2016 2:15 pm
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strat98 wrote:
I thought the grill cloth was going in the wrong direction but I never thought it was inside out.
I took some spare grill cloth and put the other side out and sure enough, the black lines are slightly broken up. Thanks Arjay. I will definitely be changing the grill cloth because it will drive me crazy every time I look at the amp

I just read on one of the forums that if the grill cloth has black lines, that side goes towards the baffle. Is that always correct?


The "black lines" are actually chocolate brown on the wheatstraw cloth.

This is the correct orientation......

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And as Stratele mentioned, there should be a grill frame at the perimeter of the baffle board, made of 1" x ¼" poplar or pine strip. A trapezoidal logo shelf of ¼" poplar or pine plank belongs at the upper left corner.

Arjay

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Post subject: Re: 6G6B Build
Posted: Tue May 31, 2016 2:22 pm
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strat98 wrote:
stratele52 wrote:
The grill cloth should not touch the baffle, did you put some pieces ( framing ) of wood between the grill cloth and the baffle ?


Yes. I built a small frame all around the baffle.



+1 :D


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Post subject: Re: 6G6B Build
Posted: Tue May 31, 2016 4:20 pm
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Very nice build! Good layout and soldering. Like the use of wire-wound resistors on the screens. This will definitely help the stability issue. What trannies did you finally use? They look like very close knockoffs of the original Schumacher. At least from bottom and sides.

Very smart idea to put in a bias pot. That way you can use various makes of 6L6GC and not have to juggle resistors. How do you like those JJ tubes? Tone, strength, & longevity seems to vary the most with JJ output tubes. If you get a good pair, they may last years. Bad pair may go "poof" in a month or two.



I loaded my Bassman cab (silverface) with one Celestion Vintage 30 and one Weber 12A150. Combo actually makes a nice, powerful tone. With pretty good midrange.


:D


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Post subject: Re: 6G6B Build
Posted: Tue May 31, 2016 5:16 pm
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BMW2002Ti wrote:
Very nice build! Good layout and soldering. Like the use of wire-wound resistors on the screens. This will definitely help the stability issue. What trannies did you finally use? They look like very close knockoffs of the original Schumacher. At least from bottom and sides.

I loaded my Bassman cab (silverface) with one Celestion Vintage 30 and one Weber 12A150. Combo actually makes a nice, powerful tone. With pretty good midrange.


:D


Thanks BMW.
I used the Classic Tone transformers made by Magnetic Components.
Very reasonably priced and the sound is great. I know a lot of people swear by the Mercury Mag transformers but they were out of my price range. The output transformer alone was 3 times the price of the Classic Tone.

The JJ's sound good. I use them in my 68 Twin and they seem to have more bottom end but sound is subjective. I just ordered a pair of JJ 5881's to see how they sound.

I never thought of 2 different speakers. That's something to keep in mind.


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Post subject: Re: 6G6B Build
Posted: Tue May 31, 2016 5:32 pm
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Very nice build! Can't believe it only took a month of spare time!

As for speakers, might I suggest a pair of Kendrick black frames? They have a bit of that old Jensen C12N charm to em and even though a bit pricey, they are worth it especially when broken in. The Jensen C12N's where a great speaker choice for an OEM speaker in the Bassman.

http://www.kendrick-amplifiers.com/mm5/ ... ry_Code=12

Enjoy the 6G6!

T2

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Post subject: Re: 6G6B Build
Posted: Tue May 31, 2016 6:09 pm
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T2Stratman wrote:
As for speakers, might I suggest a pair of Kendrick black frames? They have a bit of that old Jensen C12N charm to em and even though a bit pricey, they are worth it especially when broken in.


+1

Definitely worthy of consideration.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: 6G6B Build
Posted: Tue May 31, 2016 8:03 pm
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I have the Kendrick Black Frame in my princeton Reverb and like it.

I've also found Warehouse Speakers G12C or the G12C/S pair nicely with Fenders; I have the G12C in my bandmaster cab, and the G12C/S in my 2x12 Bandmaster combo.

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