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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Thu Feb 14, 2013 6:07 am
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Yep we play bass through all of them at home volume levels.

for the stage My son the touring bass player uses this

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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Thu Feb 14, 2013 8:30 pm
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I must say I'm kinda shocked nobody here caught my mistake.
I'll air it here to save someone else the trouble.
When i installed the replacement Output Transformer from Art I ran all of the wires through the grommet at the front of the Transformer, and so that is why it seemed as if the wires were short.
another directly related issue is the resulting hum from running the speaker outs right alongside the power section.
9:30 pm or I would fire it up to see what difference rerouting that mess made in noise reduction.

Hey Art, the wires were plenty long :oops:

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1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Thu Feb 14, 2013 10:35 pm
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Glad you caught that one, Chris!!! Your younger eyes are way sharper than mine. Took a look at my Bassman, and yeah, the OPT primary and secondary leads have dedicated paths. Hope this helps with some of that pesky noise!!! Art

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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Fri Feb 15, 2013 6:19 am
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For whatever reason we all just skipped by the fact that I had to add wire to reach the red and brown wire connections.
Live and learn :D

Its a snowy cold day and hopefully I'll get my load of parts, A good day to solder and watch the birds at the feeder.

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Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
2017 50's Baja Telecaster BSB

1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

Visual Sound Route 66
Cmatmods Signa Drive


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Fri Feb 15, 2013 7:35 am
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Early analysis (not too loud)
Fixing the routing of the Transformer wiring certainly helped eliminate more noise
it also cleared up the signal enough to get a better perspective of the other noise.

If I play a bar chord in the key of G at the third fret just before clipping volume, I get very ugly distortion sounds along side the notes and the tubes pulse.
If I slide down to say a C bar chord, all I get is the notes and it sounds great.
the overall sound is bass and i have to turn the bass down to 5 or under on the amp.
So........ Vibration issue ?
Only the V-5 pulses until you really crank the amp the V-6 does a little.
Whatever is happening its within the bass frequencies or is caused by them.

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Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
2017 50's Baja Telecaster BSB

1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

Visual Sound Route 66
Cmatmods Signa Drive


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Fri Feb 15, 2013 2:46 pm
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Parts arrived !
Those 25/25uf 25volt F&T's are huge by the way !!!!
eliminated nearly all of the unwanted noise and the tubes are stable even at higher volumes.
The amp has a much cleaner voice further up the volume dial too.

So what do I think about the Silverface bassman ???
What a huge pain in the keester !!!
and after all of that ,the lows are woofy and the highs are shrill and its very hard to get a good EQ balance out of it at stage volume.
All caps were kept to stock spec and that may indeed be the problem.
at low levels and using my compressor, it sounds pretty good, close to the Bandmaster.
It may just need some break in too, nearly the entire board has new components and the filter cap board is all new so........

Image

Image

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Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
2017 50's Baja Telecaster BSB

1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Fri Feb 15, 2013 6:52 pm
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Chris, I never used those dual section 25/25 F&T's. They are actually like multi-section cap cans --- two 25mfd sections with a common negative.

I replace all bypass caps with individual 25mfd/50VDC Sprague Atoms. You should definetly have better bass and transient response with those new bypass. Old, dried out caps really affect the frequency response of those tubes.


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Fri Feb 15, 2013 7:02 pm
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Now that all the noises are mostly gone I can clearly hear extra notes when i play through this amp like a very bad pitch shifter attached to it somehow.

Ghost notes ??? an out of sync sound that is destroying the "first tone" that I hear, it wants to sound good, its just extra out of tune notes that are there, it is more pronounced in the lower sounds, but its there across the board !

And that zbbbt buzz sound still appears and affects the bias for a second or two then stabilizes, it only pushes it up one ma then settles back ????

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Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
2017 50's Baja Telecaster BSB

1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

Visual Sound Route 66
Cmatmods Signa Drive


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Fri Feb 15, 2013 10:19 pm
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Chris, if you're confident that those power tubes are solid, I'd R&R the diode and cap(or bridge the cap) on the bias section. BTTW what's happening on the B+ supply from the main diode string, when the noise occurs? Usually, the "zbbbbt" would be attributed to a faulty tube. I don't know if an old diode could cause a momentary interruption! I use hexfred diodes in my Bassman. But Shimmy didn't seem to think that was of any advantage. Like Beemer suggested, the power and bias supply must be rock solid. Art

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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Feb 16, 2013 4:34 am
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Chris,

If you go to new diodes -- use ultra-fast (UF4007). Much quieter and just as cheap as 1N4007.


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Feb 16, 2013 9:34 am
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I'll post my voltage readings here
all measurements are DC volts

V-1 pin #1 228
pin #6 234

V-2 pin #6 267

V-3 pin #1 210
pin #6 256

V-4 pin #1 244
pin #6 243

Bias test point -44.5 till the Bzzzp sound then -45.7 for a second or two then back to a stable -44.5

I tried a 12AY7 in V-2 and V-3, it did offer clean headroom up to 2.7 on the volume pot, then back to nasty distortion.

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Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
2017 50's Baja Telecaster BSB

1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

Visual Sound Route 66
Cmatmods Signa Drive


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Feb 16, 2013 9:40 am
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Chris,

You have mail! That PI section may not be setup correctly, with your mods. Go back to original AC568 layout and see if that helps the OD issue.

Remember, change BOTH plate loading resistors back to 47k-ohms AND the coupling caps off the PI to the 6L6GCs to 0.047mfd/600VDC caps.


Good luck!


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Feb 16, 2013 10:26 am
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Putting a 12AY7 in V-4 did add headroom and smooth out the OD some, still too strong for me.

I'll revert the .1 to .047 and the 100K back to 47K and see how it reacts.

Now a tiny bit or crackle sound when I first take it off standby.

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Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
2017 50's Baja Telecaster BSB

1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

Visual Sound Route 66
Cmatmods Signa Drive


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Feb 16, 2013 10:29 am
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Chris,

Try changing ONLY the 0.1mfd coupling caps to 0.047mfd/600VDC caps. Try may help the excess OD, without modding the anode plate resistors.

This may do it...

:D


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Feb 16, 2013 10:38 am
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Soldering Iron is heating up !
ALL I have at hand are the old .047's
I'll get new stuff later

This is fun !!!
Long distance repair :mrgreen:

You have the patients of Job my friend !

I am however very glad that were sharing this here were hopefully many others will benefit from our fun !

_________________
Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
2017 50's Baja Telecaster BSB

1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

Visual Sound Route 66
Cmatmods Signa Drive


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Profile
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