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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 11:36 am
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vinyl wrote:
The electrolytic "fluid" dries up over time. The ESR rises and the capacitors ability to do what it is supposed to do diminishes. Useful life of an electrolytic capacitor is about 15 to 20 years or less. Yours are 52 years old. The amp will sound better when the power and bias supply have fresh caps for filtering. Fresh bypass caps will ensure the gain and frequency response of the preamp stages are working as designed.

.


I desagree with that.

Electrolytics caps life is longer than 20 years.
20 year ago it is 1998 , how many guitar amps or electronic gear bought before 1998 are always working with all original caps ?


I have a many amps with all original filters caps . I can repair any amps so I can replace caps by myself.

Brand new capacitors may give you more punch at high volume but it is a case by case


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 11:41 am
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[quote="sfceric64" No problem w/ a 50ufx50vdc or 50ufx100vdc. The bias voltage is about -33 depending on tubes and such.
The 3- 25ufx25vdc cathode capacitors should be replaced w/ the same usually unless your trying to alter the tone somewhat and 25ufx50vdc is also not a problem.
.[/quote]

Bias voltage at the filter caps could be -50 volts , -33 volts is a the pot's wiper. A 100 MFD at 100 volts give better filtering ( less noise ) and good safety margin.


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 11:45 am
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stratele52 wrote:
vinyl wrote:
The electrolytic "fluid" dries up over time. The ESR rises and the capacitors ability to do what it is supposed to do diminishes. Useful life of an electrolytic capacitor is about 15 to 20 years or less. Yours are 52 years old. The amp will sound better when the power and bias supply have fresh caps for filtering. Fresh bypass caps will ensure the gain and frequency response of the preamp stages are working as designed.

.


I desagree with that.

Electrolytics caps life is longer than 20 years.
20 year ago it is 1998 , how many guitar amps or electronic gear bought before 1998 are always working with all original caps ?


I have a many amps with all original filters caps . I can repair any amps so I can replace caps by myself.

Brand new capacitors may give you more punch at high volume but it is a case by case


We're not talking about twenty Y/O caps, slick......they're over fifty years old. A HALF CENTURY.

Who wants to risk a $300 power tranny because they were too fu¢king cheap to spend thirty bucks on new caps?

Get a grip!

:roll:

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: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 11:48 am
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Retroverbial wrote:


Who wants to risk a $300 power tranny because they were too fu¢king cheap to spend thirty bucks on new caps?



Arjay


It could happened only if you have the wrong fuse,

Reassure yourself, with your comments to scare, our friend Lammchop93 will replace these pieces no matter what I will add


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 11:58 am
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His pictures tell a story, NO Fuse or cap & a horrible PLUG. Repair immediately!!
As far as the caps go, I don't see anything that looks bad. But I don't recommend looking to determine voltage fluctuations. Replace as soon as possible if voltage irregularities are present.


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 12:14 pm
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stratele52 wrote:
I have a many amps with all original filters caps . I can repair any amps so I can replace caps by myself.

those of us who end up on stage from time to time would rather do a little preventative maintenance BEFORE we are standing in front of an audience.


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 12:53 pm
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That Mallory can was made (edit) 26th week of 1966. The new CE 30/20/20/20 at 525VDC fits fine. Even with most aftermarket speakers.

https://www.tubesandmore.com/products/c ... 30202020uf

"Bias voltage at the filter caps could be -50 volts , -33 volts is a the pot's wiper. A 100 MFD at 100 volts give better filtering ( less noise ) and good safety margin."

The Princeton and PR of this era do not have OEM bias pots. It doesn't appear that anyone added one to this amp. Adding one would be nice. However, you can adjust bias by means of changing the fixed 22 (or 27k-ohm) C-minus-to-ground resistor. Usual range is around +/- 5k-ohms.

Good luck with this amp! Worthy of proper R&R.

:mrgreen:

Image


Last edited by BMW2002Ti on Tue Jun 05, 2018 6:49 am, edited 1 time in total.

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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 1:17 pm
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sfceric64 wrote:
His pictures tell a story, NO Fuse or cap & a horrible PLUG. Repair immediately!!
As far as the caps go, I don't see anything that looks bad. But I don't recommend looking to determine voltage fluctuations. Replace as soon as possible if voltage irregularities are present.


Is there a way I can test the capacitors before knowing if I actually need to change them?


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 1:28 pm
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ghost_of_strings wrote:
stratele52 wrote:
I have a many amps with all original filters caps . I can repair any amps so I can replace caps by myself.

those of us who end up on stage from time to time would rather do a little preventative maintenance BEFORE we are standing in front of an audience.


+1000!

"Hope" is not a strategy.

Periodic routine maintenance is the only way to prevent catastrophic amp failures. Anything less is a FOOL'S ERRAND.

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: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 1:41 pm
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BMW2002Ti wrote:
That Mallory can was made 22nd week of 1966. The new CE 30/20/20/20 at 525VDC fits fine. Even with most aftermarket speakers.

https://www.tubesandmore.com/products/c ... 30202020uf

"Bias voltage at the filter caps could be -50 volts , -33 volts is a the pot's wiper. A 100 MFD at 100 volts give better filtering ( less noise ) and good safety margin."

The Princeton and PR of this era do not have OEM bias pots. It doesn't appear that anyone added one to this amp. Adding one would be nice. However, you can adjust bias by means of changing the fixed 22 (or 27k-ohm) C-minus-to-ground resistor. Usual range is around +/- 5k-ohms.

Good luck with this amp! Worthy of proper R&R.

:mrgreen:

Image


This is probably an easy question for my amp tech, but just out of curiosity, if I go with the 30/20/20/20 525v cap, do I have to change any of the bias like you said? or is it just plug and play?

I have good experience working with guitar electronics, but all of this amp talk is confusing as heck to me. I'll get there one day! I want to keep this amp as original as possible, as I love the sound, so I may just replace with the exact same value parts if I can.


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 1:48 pm
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The new B+ should be checked after every PSU cap or rectifier tube change. You may need to adjust the idle bias current draw to get the output tubes into proper working range.


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 8:52 pm
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Quote:
Is there a way I can test the capacitors before knowing if I actually need to change them?

W/O power, pull them out of the circuit(lift [de-solder] one side + or -) and test them on an IC meter.
A good DVM w/ a capacitance feature will show max capacitance.
W/ power in circuit, you can test for voltage loss to ground.
W/ a good DVM you could run for a period of time and get a good sense of the fluctuation.
Basically it comes down to how you feel about your amplifier running on 52 year old re-chargeable batteries.

Supposing you paid under $1200 at auction, $50-200 in maintenance is small change to preserve the amp for another 20-25 years.

What BMW suggests is true also, a 20+% increase in capacitance in the 1st stage from 40(20/20/20/20 or 40/20/20) to 50(30/20/20/20x525vdc) will reduce ripple current(60 cycle hum) and increase bass response slightly.
A key point is the size of the cap-can, diameter of the chassis opening and the clearance between the cap-can and the speaker.
The regulating resistor for bias adjustment is the 27k on the schematic BMW posted(the first one up from the bottom right, above the letters "AL" in FMIC Logo & address).
Any component change to the output section(tubes), Power supply section or rectify and you should check & adjust the idle bias.

Overall, replacing the capacitors will refresh the amplifier electronically speaking and enhance frequency response, perceived loudness, etc.


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Post subject: Re: Auction find: '66 Princeton
Posted: Tue Jun 05, 2018 12:39 am
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sfceric64 wrote:
Quote:
Overall, replacing the capacitors will refresh the amplifier electronically speaking and enhance frequency response, perceived loudness, etc.


Poor filtering PSU caps can not only affect bass and transient response --- but can also cause many oddball problems. Like motorboating, "ghost note" tones, odd coupling between stages. A new can will give you that OEM clean Fender tone, again.

:)


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Post subject: Re: Auction find: '66 Princeton
Posted: Tue Jun 05, 2018 4:53 am
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This is great info! Thank you!


Last edited by Lammchop93 on Mon Jun 18, 2018 12:34 pm, edited 1 time in total.

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Post subject: Re: Auction find: '66 Princeton
Posted: Tue Jun 05, 2018 8:40 am
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I would heed the recommendations given concerning the caps. I shake my head when people check their oil and it's so black they can't even see the dipstick. It's full and they call it good. Yeah, it's still oil, but no longer doing it's job.

UN


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