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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sat Feb 11, 2012 3:43 pm
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Blue, if you get that job, snatch ALL of the reverse-audio 3Meg and 25k-ohm pots they have in stock. Fender doesn't seem to use adjustable Intensity & a different Speed setup in the EC blessed VC. I can't get any straight answer on this from owners.

Boy, these puppies are getting hard to find.


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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sun Feb 12, 2012 11:07 am
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BMW2002Ti wrote:
Blue, if you get that job, snatch ALL of the reverse-audio 3Meg and 25k-ohm pots they have in stock. Fender doesn't seem to use adjustable Intensity & a different Speed setup in the EC blessed VC. I can't get any straight answer on this from owners.

Boy, these puppies are getting hard to find.


What's it worth to ya? Better yet, what's it worth to ME? :lol: :lol: :lol:

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sat Feb 18, 2012 7:35 am
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Been away from the Forum for a while and happened across this thread today...

Read all 13 pages!

Awesome build Sir!

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"You can't spend what you ain't got, you can't lose what you ain't never had" ~ McKinley Morganfield


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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sat Feb 18, 2012 8:07 am
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tyronne wrote:
Been away from the Forum for a while and happened across this thread today...

Read all 13 pages!

Awesome build Sir!


Thanks.

I'm planning on replacing the tone stack caps today with Orange Drops and Silver Mica caps. It will be interesting to see if it makes an audible difference. I am also going to change the cap in the bright channel to "thicken up" that channel just a bit as I find it a little too strident with the stock cap. I'll post more about these changes later today.

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sat Feb 18, 2012 4:14 pm
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Well, I ended up just replacing the bright cap, replacing the 100 pF cap with a 250 pF cap to give a little more gain in the upper mids.

I used the amp calculator found here to model the frequency response of the two different caps:

http://ampbooks.com/home/amplifier-calc ... ght-boost/

The output impedence of the preamp stage driving the bright channel (the output of the 12AY7 preamp) is 23 KOhms as calculated in "Circuit Analysis of a Legendary Tube Amplifier; The Fender Bassman 5F6-A, 3rd Edition by Richard Kuehnel".

I plotted the response using a 100 pF bright cap and a 220 pF bright cap (my cap is actually 250 pF, but close enough). The plots look like this:

100 pF Bright Cap
Image

220 pF Bright Cap
Image

As you can see, the gain at 10 KHZ is 0.75 dB greater for the 220 pF cap compared to the 100 pF cap, while the gain at 1 KHz is about 1 dB greater for the 220 pF bright cap compared to the 100 pF cap. The curve appears (and sounds to my ears) slightly smoother with the larger cap. Gain at 82 Hz is unchanged.

I set the two volume controls by setting the normal channel volume to the level I want first, then I turn the bright channel up until I am just able to hear it in the overall sound. Right now, the normal channel is set to "6" and the bright channel is set to "4". The sound has a nice sparkle on the high end while sounding slightly fuller in the mids without sounding harsh.

I was going to replace the tone caps with silver mica and Orange Drop caps, but then I looked at the parts list and Weber's website and discovered that they supply silver mica caps and their version of Orange Drops (though they are tubular shaped) in the kits already. I decided not to bother changing any of the other caps in the amp based on that discovery.

I also replaced the jumper cable that I was using to jumper from the low input of the normal channel to the high input of the bright channel (while plugging the guitar into the high input of the normal channel) with a Y-cable plugged into the high inputs of both channels. I realized that having the two cables plugged into the high and low inputs of the normal channel resulted in both inputs presenting a low impedance (136K Ohm vice 1M Ohm) to the guitar. You would need to jumper over to the low input of the bright channel to maintain equal input impedances in both channels. Using the Y-cable allows the guitar to see a 1M Ohm input impedance in both channels for maximum input level.

The amp sounds really nice in this configuration. :D

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Last edited by bluesky636 on Sat Nov 03, 2012 11:38 am, edited 2 times in total.

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sat Feb 18, 2012 4:19 pm
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Bill...Wow you certainly channeled your inner Engineer there :lol: Glad you are digging that fine looking amp...now quite messing with its guts, go crank it and channel your inner Duane, Eric, Jimi, Jeff... :lol:

T2

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sat Feb 18, 2012 4:22 pm
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T2Stratman wrote:
Bill...Wow you certainly channeled your inner Engineer there :lol: Glad you are digging that fine looking amp...now quite messing with its guts, go crank it and channel your inner Duane, Eric, Jimi, Jeff... :lol:

T2


I ..... can't ..... help ..... it. Addicted ..... to ..... the ..... smell ..... of ..... rosin ..... core ..... solder. :lol: :lol: :lol:

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sat Feb 18, 2012 4:54 pm
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So you actually increased gain with a larger cap? Hmmm.. without messing up the overall freq. response.

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"You can't spend what you ain't got, you can't lose what you ain't never had" ~ McKinley Morganfield


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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sat Feb 18, 2012 5:01 pm
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tyronne wrote:
So you actually increased gain with a larger cap? Hmmm.. without messing up the overall freq. response.


Actually, I decreased loss. :lol: This was a bright cap, not a coupling or bypass cap although they exhibit a similar response. Gain is affected above the crossover point of the circuit.

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sun Feb 19, 2012 9:44 pm
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Switched back to the 100 pF bright cap from the 250 pF I installed. After playing for awhile I found that the background hiss was accentuated more with the 250 pF cap. Guess it shows that it doesn't always pay to second guess Leo. He usually got it right the first time. :lol:

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sun Feb 26, 2012 6:12 am
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I found that the preamp tube shields were resonating and making a slight buzzing noise with certain notes at higher volumes (>6). I pulled them off and installed these on all the tubes (Yes, even the GZ34. Looked funny without one. :lol: ). No more buzzing and no problems with noise pickup by the unshielded tubes. I use these in my BDRI also. Well worth the price.

https://ssl.eurotubes.com/cart/index.ph ... ory_id=200

I have also found that using a Y-cable instead of a simple jumper to bridge the inputs works better. I plug into input #1 of the normal channel and input #2 of the bright channel and set the volume knobs to the same position on the scale. This drops the bright channel 6dB below the normal and gives a nice chime without harshness.

I continue to love this amp. I have it set up for my Fenders with stacked noiseless pickups and my BDRI is set up for my guitars with PAF type humbuckers. Works great that way as the tone settings are completely different. :D

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sat Mar 10, 2012 4:14 pm
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Well, time to wrap up my build thread. The speakers have broken in nicely and the amp just gets better sounding each time I play it.

I decided I needed a few finishing touches to make the amp complete. I have already shown the logo I had made for the amp:

Image

I decided I also needed a tube chart on the inside, so I made this one up on my computer and glued it in with a little Elmer's:

Image

The ink smeared a little as I smoothed it down, but I figure that adds a little to the "mojo". :lol:

Finally, I went back to the company that made the logo plate and had a "manufacturer's plate" made up:

Image

I named the amp a "Bluesman 5F6A/C" for "clone". Seemed fitting.

Anyway, that about wraps it up. I'll be back if I decide to do any mods to the amp or if there are any questions. I hope everyone enjoyed reading about my build as much as I enjoyed building and posting about it. Thanks again for reading and putting up with me. :D

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Last edited by bluesky636 on Sat Nov 03, 2012 11:42 am, edited 1 time in total.

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sat Mar 10, 2012 5:05 pm
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Fantastic build Bill!!

Love the final touches you gave the amp.
And Yes, the smudge will add Mojo. :lol:

Hoping you have many years of enjoyment with it!

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"You can't spend what you ain't got, you can't lose what you ain't never had" ~ McKinley Morganfield


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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sat Mar 10, 2012 6:16 pm
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tyronne wrote:
Fantastic build Bill!!

Love the final touches you gave the amp.
And Yes, the smudge will add Mojo. :lol:

Hoping you have many years of enjoyment with it!


+1

That's how Retroverbial Productions, Inc does it.

RAWK......ON!

8)

Arjay

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sat Mar 10, 2012 6:21 pm
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tyronne wrote:
Fantastic build Bill!!

Love the final touches you gave the amp.
And Yes, the smudge will add Mojo. :lol:

Hoping you have many years of enjoyment with it!


Thanks. :D

I did do one final mod that I forgot to mention. I have been experimenting with different value caps in the bright channel. Since I am just a home player, I found the factory 100 pF bright cap to be just a tad too bright at lower volumes. I have replaced it with a 68 pF cap which seems to smooth things out a little bit while still retaining a good bite. Of course, on those few occasions when I am able to crank the amp, it doesn't matter what the value of the bright cap is. :shock: :lol:

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