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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Mon Feb 18, 2013 7:14 am
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Sohara1111
Your exactly right.
Without aclemapoppi, Arjay, Beemer and others with years of real repairs, forums like this would be a waste of time !
One of the reasons i wanted to share all of the ups and downs was to shed light on some of the tactics used by these guys to trouble shoot.
There was a lot of personal e-mails that made this happen too.

and hopefully to get more guys to understand their amps better so they can make it sound the way they want it to and at least know how to talk the talk with their local techs.

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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Mon Feb 18, 2013 7:23 am
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blues bondsman wrote:
The 67 I have has baffle issues, the sawdust and glue board is literally coming apart from moisture damage.

the board is like 4 7/16" tall by 20" and a real 1/2" thick
Problem is I don't have a table saw and don't want one !!!
Mine won't hold screws any more it just crumbles.

I should re name this thread our fender projects :lol:

Image


Oh, the baffle on the head is fine. It was the VT-15 cabinet. And those baffles are in dado's and are part of the cab structural integrity. (CBS was cost cutting.) So I had to install all the braces and cut a new board to install after cutting out the old and a LOT of sanding. Thank goodness for power tools. :lol:

Looks great now, but I still don't take her out. I think the corners are lap joint rather than finger joint. And without the baffle glued in those dado's I just don't think the strength is there.

Art


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Mon Feb 18, 2013 7:51 am
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Yes sir
I'm with Arjay on that subject
Floating baffles were the stuff ! and really what needs replacing on cabs ?
Usually the baffle is a mess.

I sure am looking forward to finding another mid 60's or earlier small 2x12
or two :mrgreen:
Hey I have two bassman heads now and my precious Bandmaster Reverb.
The ear candy cabs I have sound great, just don't have "the look" for the vintage Fender heads.

I'm getting kinda amp heavy here 8)
So if we ever have the first annual Fender guys jam, you guys can travel light !

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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
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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Mon Feb 18, 2013 6:18 pm
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Chris,

Did you try some NOS 5881s in the amp? My experience with these mil spec tubes, is they take a LONG time to break-in. Longer than the RCA 6L6GC.

Be interested. I like my Tungsols in the 1962 Pro.

BTW... I have a BF VC on the way. Gonna try some mods, as soon as my work schedule settles down.


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Tue Feb 19, 2013 7:02 am
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Sweet a Vibro Champ is fun too !
I got the three prong cord installed on the new Champ last night.
I guess I'll most likely do the sig Weber in it.
The speaker (a replacement) sounds decent but it had a broken tab thats is still rattling even after a JB weld fix by me.

The bassman is back on the bench, after lengthening that wire from the Output Transformer and installing some Blue molded .047's it reverted back to oscillation.
:(
What can we learn here ??? If it aint broke, don't fix it !!!
The tubes are back to flashing.
I went back to the brown bomber caps and shortened the wire again, cleaned out and re soldered and it still isn't back to the fantastic sound I had prior to this last "fix"
I've never seen such a fickle critter in all of my life !!!!!
Well except maybe Mrs C (hope she doesn't read this) :mrgreen:

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Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
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1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

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Cmatmods Signa Drive


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Tue Feb 19, 2013 7:11 am
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Go back and solder in those brown drop 0.047mfd caps.

See what happens.


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Tue Feb 19, 2013 7:21 am
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I had replaced them soon after the trouble re appeared, so ya I'm thinking it's a solder joint problem or back to the sockets again.
Last time I pulled v-5 out of the chassis completely cleaned it and installed the resistors while out of the chassis, I did all of this while installing the NFB circuit.
So who knows if it was the completely cleaned up socket or the NFB ???
Or both.
I think I'll pull V-6 and give it the same treatment.
Just placed my AES order, gonna stink if I need sockets and have to pay additional shipping !

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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: Tue Feb 19, 2013 7:48 am
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Chris,

Try a 22k-ohm resistor in place of a 47k-ohm in the feedback circuit. This should add more feedback voltage & change the noise issue. If not.... it's not your GNFB newtwork.


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Tue Feb 19, 2013 7:57 am
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I can tell in an instant that I'm going to have early nasty sounding OD and oscillation.
When I flip the standby to play the 6L6's flash across the top, there is also some crackle (bad something) in the circuit
Sensitive little creep !

I have a 26K metal oxide , no 22K and I live in a ghost town when it comes to electronic supply.

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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: Tue Feb 19, 2013 8:22 am
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Chris,

Try the 26k-ohm resistor. You are doing this to rule-out GNFB issues. Really sounds like you have a hinky connection(s) or ground point(s) -- somewhere in the amp.

The amp makes the funky-ass noise with the old brown 0.047,fd caps in place?


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Tue Feb 19, 2013 10:03 am
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I cleaned out the entire stage where the bais supply feed is, i pulled the 1/2 watt 100K's and replaced them with 1 watt 100K's
Removed every bit of solder I could without pulling the board.
carefully re soldered the board, shortened a couple of leads on some resistors.

Result:
80% better
The 6L6 tubes still seem pushed a bit too hard, still flash when off standby and pulse at very high volume or if i push the signal with boost from my Compressor at mid to high volumes.

It still sounds a bit bright to me and well, lacks warmth

I had replaced the 100pf across the resistor last night also
I may take the NFB apart and re build it carefully !

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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: Tue Feb 19, 2013 11:16 am
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Good work, Chris!!! Would it be possible to post a recent photo of the chassis interior, maybe a shot of the power side and the preamp side? Just want to make sure I'm still up to speed. Thanks, Art

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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Tue Feb 19, 2013 1:03 pm
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Will d0 I'm at the jail right now.

_________________
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
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Tue Feb 19, 2013 2:53 pm
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here is the requested picture.
Notice the brown bomber caps are back.
I'm afraid to touch this amp with a soldering iron :oops:
But mallory 150's in .022 and .047 are on the way

You'll also notice that the NFB is sandwiched between the boards

Image

_________________
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


Top
Profile
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Tue Feb 19, 2013 4:02 pm
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Ah the practice room !
Sweet sounds of Fender goodness 8)
I switched to a smaller soldering tip to keep my work easier to see and control solder flow better, no more pregnant solder joints !
I did as you can see from the last picture decrease the size on the NFB to 26K and used a metal oxide resistor.
Sounds excellent again !

The kid's bass rig dwarfs my stuff, mine is cooler ! :mrgreen:

Image

_________________
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


Top
Profile
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