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Post subject: Replacement Tubes for Vintage Amp
Posted: Sat Mar 07, 2015 7:32 pm
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I have a 1973 silverface princeton reverb I purchased recently and had some work done on it which included replacing the 6v6’s. It sounds great but the tremolo seems a little weak now. I am considering replacing the other 12ax7’s and the 12at7 also. Good idea or not. Since I changed the 6v6’s I thought it may be a good idea to start over with fresh tubes. Should I replace the rectifier (5U4GB) also? I replaced a worn out 1993 eminence speaker with a new 10a125 weber 20 watt with no dope. Sounds great. Any suggestions would be appreciated.

Joe in Mobile, AL


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Post subject: Re: Replacement Tubes for Vintage Amp
Posted: Sun Mar 08, 2015 1:44 am
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Joe in Mobile wrote:
I have a 1973 silverface princeton reverb I purchased recently and had some work done on it which included replacing the 6v6’s.
Did you check bias ?


It sounds great but the tremolo seems a little weak now. I am considering replacing the other 12ax7’s and the 12at7 also. Good idea or not.
If they are bad , / resistor , capacitor , reverb transformer , the amp to reverb

Since I changed the 6v6’s I thought it may be a good idea to start over with fresh tubes. Should I replace the rectifier (5U4GB) also?

Probably not , need a voltage reading to know . These old tube are very good
I replaced a worn out 1993 eminence speaker with a new 10a125 weber 20 watt with no dope. Sounds great. Any suggestions would be appreciated.
Replace all filters caps ; in the power supply , bias circuit

Joe in Mobile, AL


Last edited by stratele52 on Sun Mar 08, 2015 2:15 am, edited 1 time in total.

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Post subject: Re: Replacement Tubes for Vintage Amp
Posted: Sun Mar 08, 2015 2:12 am
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The Princeton Reverb's tremolo circuit operates via a simple RC oscillator which varies the bias-supply voltage to the plates of the power tubes. As such, it's inextricably linked to the bias supply itself and a tremolo issue may be indicative of a developing problem there. The bias-circuit voltage is fixed -- hence, there's nothing there that's easily adjustable. If you have not already done so, I'd urge you to have the filter-cap can replaced and inspect the power-rail resistors for any evidence of thermal fatigue. Overhauling the power supply might in fact cure the weak tremolo. If not, then it may very well be the 12AX7 in your V4 position (or a component within that tube's circuit array).

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: Replacement Tubes for Vintage Amp
Posted: Sun Mar 08, 2015 2:15 am
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Retroverbial wrote:
The Princeton Reverb's tremolo circuit
Arjay



Ooppss tremolo :oops:


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Post subject: Re: Replacement Tubes for Vintage Amp
Posted: Sun Mar 08, 2015 7:13 am
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If you need a 5U4GB, look of for a good NOS US made one. Any brand is better than what is available now. Black plate versions seem to have best life.

A strong testing 12AX7 may help the tremolo/vibrato section. Of all the new brands, the Gold Lion B759/ECC83 seems the closest to the original RCA in tone and power.


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Post subject: Re: Replacement Tubes for Vintage Amp
Posted: Mon Mar 09, 2015 2:19 am
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BMW2002Ti wrote:
If you need a 5U4GB, look of for a good NOS US made one. Any brand is better than what is available now. Black plate versions seem to have best life.


+1

They remain plentiful and reasonably priced, and treated respectfully will last a decade or more.

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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