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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Tue Oct 08, 2013 7:37 pm
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Roadie
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It's a 100w non-ultra-linear model. I don't believe the .01 cap and 220K resistor were in it originally when I bought it. Since it was hacked up, I followed the schematic for the 100w Twin on ampwares. The eyelet the cap and resistor connect to was never soldered. Should I remove the cap and resistor?


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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Tue Oct 08, 2013 7:42 pm
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Roadie
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BTW, this is a Twin Reverb, not a Bandmaster.


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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Tue Oct 08, 2013 9:33 pm
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Rock Star
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Think it's UL.

135watt UL schemo:

http://ampwares.com/schematics/twin_reverb_sf_135.pdf


100watt non-UL schemo:

http://ampwares.com/schematics/100W_Mas ... in_Rev.pdf


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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Tue Oct 08, 2013 10:21 pm
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Negative. The UL model has a line out / recording jack on the rear panel as well as a "hum balance" pot.

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: Best replacement for Blue Blob Paktron caps
Posted: Wed Oct 09, 2013 12:09 am
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Rock Star
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So his Twin Reverb does not have the 0.1mfd and 2.2k-ohm resistor network in the GNFB? Or it does? Guess it could be transition model between the non-UL and UL? With the eyelets for the cap and resistor-- but not populated.

In any event, UL amps tend to have more complicated feedback and anti-parasitic devices in the circuitry.

Sorry for the confusion. :( :?: :(


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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Wed Oct 09, 2013 12:18 pm
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Roadie
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I used the 100w non-linear schematic from ampwares.com
However, the eyelet where the .01 cap and 220K resistor, coming off the top leg of the .1 bias cap, was never populated. In the pic I posted, you can see the .01 cap between the right bias cap and the feedback cap. I would agree with Arjay that it could be a transition model and was more like the AA270 chassis than a UL. I originally played it without the .01 cap and 220K resistor. It had a tad more midrange, low-end and volume. I'm thinking of taking out the cap a resistor. Thoughts.


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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Wed Oct 09, 2013 12:36 pm
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Rock Star
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Krankster, if you decide to pull the cap-resistor, keep an eye on the bias. If it jumps around, you may want to keep this in the feedback circuit.


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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Wed Oct 09, 2013 12:57 pm
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Roadie
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Will do. Thanks Beemer. Would there be any theoretical tone benefits from taking out the cap and resistor, or should I leave them?


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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Wed Oct 09, 2013 1:02 pm
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Rock Star
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Perhaps earlier onset of OD. But, at a risk of an unstable amp.


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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Fri Oct 11, 2013 6:21 pm
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Roadie
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Took out the the .01 cap and 220K resistor. The amp sounds great and is very stable. It actually increased the voltage a tad. It's a bias balance circuit. With the cap and resistor I was getting about 33.5 ma. After I removed them, it's 34.6 ma. The layout and schematic don't always refelect the way the amp was made. Damn the schematic. In my case the clue was the eyelet for the cap and resistor was not populated. The more I get into working on old Fender amps, the more I realize there are many variations and transition circuits. That's why they all sound a little different. I'll give her a workout tonight. Keep learning and Rock On!


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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Fri Oct 11, 2013 8:22 pm
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Rock Star
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" The more I get into working on old Fender amps, the more I realize there are many variations and transition circuits. "

Boy, ain't that the truth. But, it beats Ampeg. I have yet to find an amp that has exactly what the schematic shows. I've done plenty of V4 and V22 with extra circuit BOARDS ---- let alone resistors and caps.


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