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Post subject: Re: Princeton Recording Amp
Posted: Sun Aug 04, 2013 2:53 pm
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I could not find anything in the schematic that showed an adjustment or a bias pot. Either way, I do not have the equipment for checking the bias.
I unplugged the amp., let every thing cool down, then removed the power tubes by pressing down on the releases ( wings) on each side at once, then pulled the tube out by slightly rocking it back and forth.
I then reinstalled the new tubes by reversing the process.
Bingo, the noise, popping, and static was gone.
This thing sounds better than ever. There may be a way to bias the tubes, but I am not worried about. It sounds killer!
If you need to change any pre amp tubes, push in slightly on the aluminun covers, rotate, and the bumps on the covers will line up with slots in the chassis, and come right out.

best of luck, please always remember that there are capacitors inside the amp that will knock the snot out of you ( a technical term!!!)

martin


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Post subject: Re: Princeton Recording Amp
Posted: Sun Aug 04, 2013 5:57 pm
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simonSP wrote:
martinwinder wrote:
I traded for this a while back ... Power Tubes went out last week, put GT 6V6 Red Med. Duet set in, and the amp sounded better than ever. ...


Hi Martin

I recently got a Princeton Recording Amp and I'm loving mine too. You mention that you changed out the Power Tubes in your amp and I was wondering if you could describe the process for me (this is my 1st valve amp in 25yrs and so I'm a bit nervous about screwing something up!).

When you installed the new valves did you have to bias them or did you just put in a matched pair? Any info you can pass on will be gratefully received. I have been looking around on-line for info re biasing (what is it, how do you do it etc.) but without much luck so far. Thanks.


Hobbyist,
I don't think the bias can be set on this amp. I could not find anything in the schematic.
To remove, unplug the amp. let the tubes cool, press down on the two arched retainers on the side of the power tube, rock back and forth gently while pulling up, it will come right out. Hold the retainers dawn while installing the new tubes. Biased or not, mine sounds better than ever, no more snap, crackle & pop!!!

If you need to change the preamp tubes, just slightly push down on the cover, and rotate it until the bumps line up with the gaps in the chassis. Remove the cover, rock thew old tube out , & install the new one, then replace the spring loaded cover.

Good luck, its easy, just please remember that there are fully charged capacitors in the amp, they will kick the snot ( a technical term) right out of you.

martin


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Post subject: Re: Princeton Recording Amp
Posted: Sun Aug 04, 2013 6:36 pm
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Martinwinder,

Well, as long as the 6V6GT plates are not red & the the amp isn't OD'ing too soon in the volume range --- you may avoid early failure.

Sure would be nice to have a BIAS KIT or some such adapter to measure the idle bias.

Good luck with the tubes! :mrgreen:


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Post subject: Re: Princeton Recording Amp
Posted: Mon Aug 05, 2013 5:17 am
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BMW2002Ti wrote:
Martinwinder,

Well, as long as the 6V6GT plates are not red & the the amp isn't OD'ing too soon in the volume range --- you may avoid early failure.

Sure would be nice to have a BIAS KIT or some such adapter to measure the idle bias.

Good luck with the tubes! :mrgreen:


Would be nice indeed. but oh well!!

thanks for the best wishes
martin :mrgreen:


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Post subject: Re: Princeton Recording Amp
Posted: Thu Aug 08, 2013 7:55 am
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Cut


Last edited by simonSP on Sun Sep 08, 2013 3:54 am, edited 1 time in total.

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Post subject: Re: Princeton Recording Amp
Posted: Thu Aug 08, 2013 8:01 am
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Quote:
Hobbyist,
I don't think the bias can be set on this amp. I could not find anything in the schematic.
To remove, unplug the amp. let the tubes cool, press down on the two arched retainers on the side of the power tube, rock back and forth gently while pulling up, it will come right out. Hold the retainers dawn while installing the new tubes. Biased or not, mine sounds better than ever, no more snap, crackle & pop!!!

If you need to change the preamp tubes, just slightly push down on the cover, and rotate it until the bumps line up with the gaps in the chassis. Remove the cover, rock thew old tube out , & install the new one, then replace the spring loaded cover.

Good luck, its easy, just please remember that there are fully charged capacitors in the amp, they will kick the snot ( a technical term) right out of you.

martin


Thanks for that info, I'm thinking now that I might do it myself, as per your instructions. If I hit any snags I can always find a tech to sort it. Thanks again :)


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Post subject: Re: Princeton Recording Amp
Posted: Thu Aug 08, 2013 8:31 am
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According to the info I've found, the Princeton Recording Amp is fixed bias with a bias adjustment pot.

http://ampwares.com/amplifiers/fender-p ... rding-amp/

If you don't know how to bias an amp, have a tech do it. The outcome if you don't know what you're doing can be very costly including cooking your tubes and other components as well as electrocution. You need to know how to measure the plate voltage and know the some info about the tubes you're installing too as well as what you're even looking at component wise.

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Post subject: Re: Princeton Recording Amp
Posted: Mon Aug 19, 2013 1:12 pm
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I've had a PRA since January 2007, and it has truly been a go-to do-it-all-and-then-some tool for me.

I've played the royal snot out of mine -- blues, jazz, rock, etc. I think I need new power tubes.

The tubes currently in there are GT-rebranded EHX 6V6s, painted white. No other rating or color code are found on the tubes.

It sounds like even if I go with medium-range Groove Tubes, rebiasing will be necessary.

martinwinder wrote:
I traded for this a while back, know about the attenuator problems ( it has never cut out on me) , and was not expecting alot. Wrong! This little amp can sound very clean and sweet, and can be nasty an hell!!! I have tried to tell my self that I need a better / bigger / newer / lodouder amp. but I always come back to this amp.

It loves the Hwy. 1 Tele, Amer. std. HSS Strat, and the Les Paul Special.

Power Tubes went out last week, put GT 6V6 Red Med. Duet set in, and the amp sounded better than ever.

Pre amp 12A7T went out this week, put in a GT Silver 12AT7, and the amp just screamed at both clean and dirty.

I don't think this amp is ever going to let me move on to something else.
If I don't need to buy another guitar, and don't need another amp, what the hell am I going to buy now???

thanks for letting a forum newbie on here!

martinwinder


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Post subject: Re: Princeton Recording Amp
Posted: Fri Dec 08, 2017 11:54 pm
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Hey guys I know this is a bit old but I want to just update the individuals on the tube matching. There are two options I’ve found that provide the tubes that the RCA uses.

(1)

https://reverb.com/item/2508102-tube-se ... amp-doctor

(2)

https://reverb.com/item/2508103-tube-se ... lectronics

Personally I am going to go with option #2 because it’s cheaper and I read in-depth on the “Apex Tube Matching” system they use to match them....I’m sure you gentlemen would like to see the depths and lengths that they go to to guarantee this, so I’m posting the link below.

https://www.apexmatching.com/how-apex-matching-works


NOW!!! On to a few (two) questions of my own for all you awesome intelligent people! So as we are all aware, the PRCA has known issues with the attenuator. This leads me to ask/inquire about information I read on another site about the pre-amp stage in concerns to the built in attenuator: I read that basically if ANY bit of the attenuator is used then what the amp is essentially doing is taking the power tube signal and running a pre-amp tube directly before it...thereby defeating the purpose of a pure Princeton tone...if this is accurate then my question is...If I run the PRCA without any attenuation, meaning I turn the knob completely clockwise to the right, does this mean that all of the pre-ampe tones are essentially void of the signal?

The second question I have is about the reverb. Is it a tube driven reverb tank? Or is it electronic, as in like solid stateish? Only Asking because I just snagged a reallllly good deal on a PRCA for $250!!!! The tone is excellent but the reverb is non existent so I’m gonna order those new tubes and replace them and I will update everyone...but I just wanted to tackle that because I’m a gear nut, but at the same time I hope that one of those tubes fixes the reverb! (Sorry I’m not very accurate with my terminology regarding amps! But I hope y’all can get the question i’m conveying!)


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