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Post subject: PRRI midrange
Posted: Wed Oct 29, 2014 9:24 am
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Aspiring Musician
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Joined: Sun Oct 27, 2013 7:11 am
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I've been experimenting with 12's in a recently acquired PRRI and the mid's seem to disappear, maybe the added bass response is responsible. 60's C12NA and a Tone Tubby 12" alnico red. I can change R52, or are people liking the idea of adding a mid pot over just changing resistors. I know, personal preference, but I'm just wondering before I tear into it and order a 25K pot. Maybe an Allen TO20 is in order as well.

Of the reissues I've tried I like this Princeton the best. The reverb on these reissue amps sure varies from amp to amp as far as noise/hum is concerned, swapping tubes doesn't cure it either.

Thanks for any input.


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Post subject: Re: PRRI midrange
Posted: Thu Oct 30, 2014 5:28 am
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Amateur
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Joined: Sun Jul 13, 2008 5:37 pm
Posts: 171
I liked the mid pot mod- alot. I usually had it full up all the time after I installed it, which means I could have just changed the resistor. If I did it again, I would just change the resistor, but I wouldn't have known that had I not installed the pot first.

Install the pot temporarily- on 2 leads- and let it hang out of the chassis, you can then use it for awhile, decide where you like the pot set, remove it, and measure it with a multimeter to find out what the resistance reading is, then install a resistor closest to that value.

I also installed a TO20, and it made a -subtle- difference. The biggest difference, insofar as tightening up the low end, was adding a filter cap. That made the biggest difference of all, besides replacing the speaker (altho I stuck with 10" speakers).


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Post subject: Re: PRRI midrange
Posted: Thu Oct 30, 2014 5:48 am
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Aspiring Musician
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Thanks for the reply. Did you replace C28 with a higher value?

UN


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Post subject: Re: PRRI midrange
Posted: Thu Oct 30, 2014 6:10 am
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Well, I would have replaced it [mids resistor] with a 25K, because I liked that 25K pot wide open, but instead I removed the pot, put the 6.8K back in, and sold the amp.

Only because I bought a SS22, and the vintage channel on that gets me close enough to the PRRI tone that I didn't need both amps. However, if I had unlimited space to keep amps, I would have kept the little PRRI, it was one of the sweetest amps I've ever owned. Reverb to die for.

As for C28... that's the filter cap. I didn't replace it with a higher value, I just piggybacked another one on top.... because capacitors add in parallel.... let me see if I can find a pic....

Image


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Post subject: Re: PRRI midrange
Posted: Thu Oct 30, 2014 6:44 am
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Aspiring Musician
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I've got some 47uf/500's that I can use for the cap change and I think I'll add a switch to the back for switching the mid between a "tweedish" sound and the stock scooped PR. Shimmilou helped me out a while back by suggesting a switch in parallel for a NFB loop to eliminate an open circuit. The same could apply for a "mid Switch".

Thanks for the info. Did you just parallel another 22uf?

UN


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Post subject: Re: PRRI midrange
Posted: Thu Oct 30, 2014 8:51 am
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upnorth wrote:

Thanks for the info. Did you just parallel another 22uf?

UN


Yup!


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