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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Feb 09, 2013 6:05 pm
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Chris,

You know what that "plop, plop.. fizz, fizz" sounds like (besides Alka-Seltzer)? :lol:

You have some resistors that have gone bad --- prolly due to absorbing moisture over time. If you do a WOODEN chopstick test on ALL board components, pots, and ground & solder points, etc --- my bet is you'll find the culprit(s).

Worth a try. REMEMBER! KEEP THE FREE HAND OFF THE CHASSIS DURING "HOT TESTS."

Good luck!


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Feb 09, 2013 6:37 pm
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I'm absolutely sure your right !!!

I don't know if you recall but you guys got me through my very first bassman re-cap
it was a 65 Blackface or 66 ???
any way we got her re-capped (safely) you guys taught me how to discharge caps (build a discharge tool etc...)
then I had a sizzle, no chop stick on earth could find the little monster making that noise.
Far right side of the board was a Carbon Comp hiding under a couple of Tone caps and it tested OK or within spec, but it had absorbed humidity and was cooking that humidity every time the amp warmed up.

I'll try hard to resist any more questions till I've checked some more components on the board.

That wire going nowhere just looked like an invite for interference !

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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Feb 09, 2013 7:38 pm
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OK
here is the very best description of the sound of the amp when it gets into OD AKA Louder volumes.

Overly Bright and VERY !!! Grainy sounding OD

There I said it, the amp sounds warm and sweet till about 2.5 to 3 then it gets way too bright and if you get into OD levels its grainy OD no smooth at all !!!

Its an epiphany :lol: :idea:
For the life of me i could not properly explain what was wrong with the sound till i read it on another forum.
That says it exactly !

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1968 Bandmaster with 2X12 cab C-rex speakers
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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Feb 09, 2013 8:07 pm
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Chris, does that map have a BRIGHT switch? [I'm at work --- no access to my handy-dandy schemo dBase].

If so, may want to try off-on and see if there is any change in tone.

Good luck!


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Feb 09, 2013 8:15 pm
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Glad you mentioned that.
It makes very little difference and
Almost sounds warmer in the up
Position.
Weird !

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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: Sat Feb 09, 2013 8:32 pm
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Chris,

Clean the switch with De-Oxit. May want to think about that disc cap in the BRIGHT circuit. A good silver mica is a good way to go.

Just another crazy thought, amongst the many....

:mrgreen:


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Feb 09, 2013 8:51 pm
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Yeah, the remedy on the other amp was the plate load resistor. You could just change all of the 100K ohm plate load resistors with 1watt CC's. BTTW this condition is on both channels? And that bum pot is history for sure! And what's happening with the deep switch on the bass channel? Art

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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Feb 09, 2013 9:11 pm
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I need to switch out that pot on the Bass side before i can answer that, its real noisy !!!!!

The wafer I burned ? yes I know .01 silver mica's ? what voltage ?
I didn't see a voltage designation for those.
Edited:
(sorry I see what your talking about now the little 120pf on the bright switch)

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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: Sun Feb 10, 2013 2:24 am
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Chris,

At least 600VDC. A good ceramic cap is fine. 1KV would be the best.


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sun Feb 10, 2013 4:25 pm
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Ceramic disc .01 500volt is all i can find

Mallory .01 150's are only 400 volts

Orange drops are 600 volts , bright ????

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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: Sun Feb 10, 2013 6:38 pm
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Chris,

You know, SBE 716P (Orange Drops) aren't all that bad. Esp for the price. If you really want to go "brown" --- The Russian mil spec PIO K40Y-9 (600 or 1KV) maybe the way to go.

http://www.ebay.com/itm/0-01uF-1000V-10 ... 20b52efc83


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sun Feb 10, 2013 8:51 pm
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Yep!!! Used those PIO's in my '55 Valco rebuild. Very cool caps!!! Art

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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Mon Feb 11, 2013 1:31 pm
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firing out an order tonight.

and getting some filter caps for the 67 too 8)

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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: Mon Feb 11, 2013 5:54 pm
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Chris,

Sorry late for this post --- two more nights of GY shifts.

If Bluesy, creamy OD tone is what you are after ---- PIO is the way to go in the input and PI stages. Don't change all of the coupling caps to PIO or you get a little to "creamy" and unfocused. Like the photo. Heaven forbids!

:lol:


Image


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Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Mon Feb 11, 2013 7:49 pm
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I have that JTM-45 with the under rated (for its power) scumback and Weber P12B in it and running three 12AX7's plus a pair of 6L6GC's
Gets that sorta overwhelmed speaker blues sound, its very similar to the 20112 Victoria I had with a bit more headroom, more controlled crunch I guess.
Should really try to match output volume and run it and the Bassman together on my ABY switch.
Why didn't I think of that before ?

What I like out of my fenders is piano lows, so cleaner really !

I'm pretty sure my brite cap switch is shot, it makes little if any difference up or down, and with it obviously direct in the tone signal path, maybe its affecting the whole thing ????
Still waiting on soldering tips, should have just bought a new weller and been done !

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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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