Princeton reverb trem issues

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JoshBernstein
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Princeton reverb trem issues

Post by JoshBernstein »

Hi all,
Im having some issues with my Princeton reverb's trem. It was working just fine, and then all of a sudden it went really weak. I tried swapping the tube from an rca 12ax7 to a known good tung sol and it doesnt work at all with that tube. When i shut down the amp with the rca in, the trem will go really deep as the amp quiets down. The sound clip attatched (pardon the quality) is with the depth control maxed, and i flipped the power off halfway through.
Any suggestions for me?
Thanks a bunch!
-Josh
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xtian
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Re: Princeton reverb trem issues

Post by xtian »

With amp off, measure the components attached to that tube socket. With amp on measure the voltages.
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tubeswell
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Re: Princeton reverb trem issues

Post by tubeswell »

Need to see the voltages. The LFO might be putting out a weak signal due to a bad triode in the bottle. Have you got a known good tube you can sub? (I know you said you subbed a tube, but how do you know whether it was any good in that triode?)

When the power goes off and you hear the trem kick in, that's probably because the output tube current is falling to the point where the weakened trem has enough output to begin modulating the depleting output tube current
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Re: Princeton reverb trem issues

Post by Stevem »

Not to bust your Ass, but this is a classic example of why when you build a amp , or work / repair a amp and it's working real nice you take 30 minutes and note down all the voltages for future reference!!
This can save you endless hours of trouble shooting!

On the Cathode of your tube do you have about 2.4 volts showing up with the foot switch unplugged indicating that the tube is idling as intended?
Is the Cathode bypass cap shorted ?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

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JoshBernstein
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Re: Princeton reverb trem issues

Post by JoshBernstein »

Stevem wrote: Wed Aug 09, 2017 10:46 am Not to bust your Ass, but this is a classic example of why when you build a amp , or work / repair a amp and it's working real nice you take 30 minutes and note down all the voltages for future reference!!
This can save you endless hours of trouble shooting!

On the Cathode of your tube do you have about 2.4 volts showing up with the foot switch unplugged indicating that the tube is idling as intended?
Is the Cathode bypass cap shorted ?
Here are the original voltages from right after i built it. I previously had an issue with the screen grid voltage, but it was just a resistor mixup. They now sit just below the past voltage. I havent had the opportunity to take more voltages since last night, but ill try to get them tonight.

Also i tried a couple other tubes that i pulled from my other amps and they don't do anything at all. The only one that has any effect at all is the rca.
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dorrisant
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Re: Princeton reverb trem issues

Post by dorrisant »

It Karma... Because you used a Jupiter cap for the trem speed... Just kidding. Did you check the cathode bypass cap?
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tubeswell
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Re: Princeton reverb trem issues

Post by tubeswell »

JoshBernstein wrote: Wed Aug 09, 2017 1:30 pm
Stevem wrote: Wed Aug 09, 2017 10:46 am Not to bust your Ass, but this is a classic example of why when you build a amp , or work / repair a amp and it's working real nice you take 30 minutes and note down all the voltages for future reference!!
This can save you endless hours of trouble shooting!

On the Cathode of your tube do you have about 2.4 volts showing up with the foot switch unplugged indicating that the tube is idling as intended?
Is the Cathode bypass cap shorted ?
Here are the original voltages from right after i built it. I previously had an issue with the screen grid voltage, but it was just a resistor mixup. They now sit just below the past voltage. I havent had the opportunity to take more voltages since last night, but ill try to get them tonight.

Also i tried a couple other tubes that i pulled from my other amps and they don't do anything at all. The only one that has any effect at all is the rca.
Can't see your HT voltages

Also I can't read V4 properly.

Did you take these just recently? You need recent voltages. Showing us the voltages when you built the amp doesn't tell us anything about the problem you are experiencing now.
He who dies with the most tubes... wins
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JoshBernstein
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Re: Princeton reverb trem issues

Post by JoshBernstein »

tubeswell wrote: Wed Aug 09, 2017 8:27 pm
JoshBernstein wrote: Wed Aug 09, 2017 1:30 pm
Stevem wrote: Wed Aug 09, 2017 10:46 am Not to bust your Ass, but this is a classic example of why when you build a amp , or work / repair a amp and it's working real nice you take 30 minutes and note down all the voltages for future reference!!
This can save you endless hours of trouble shooting!

On the Cathode of your tube do you have about 2.4 volts showing up with the foot switch unplugged indicating that the tube is idling as intended?
Is the Cathode bypass cap shorted ?
Here are the original voltages from right after i built it. I previously had an issue with the screen grid voltage, but it was just a resistor mixup. They now sit just below the past voltage. I havent had the opportunity to take more voltages since last night, but ill try to get them tonight.

Also i tried a couple other tubes that i pulled from my other amps and they don't do anything at all. The only one that has any effect at all is the rca.
Can't see your HT voltages

Also I can't read V4 properly.

Did you take these just recently? You need recent voltages. Showing us the voltages when you built the amp doesn't tell us anything about the problem you are experiencing now.
I intended to take more voltages last night but i got held up at work. Those were just the baseline of where i started. Will post current voltages after work
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JoshBernstein
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Re: Princeton reverb trem issues

Post by JoshBernstein »

Sorry for the long wait, i hope someone can still help. I got around to taking voltages tonight on the trem triode. Pin 1 of v4 is now at 240 volts and pin 3 is at 2 volts. This is much different than it previously was. The cathode cap seems to be okay but i can swap it out to be sure. Any thoughts?
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tubeswell
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Re: Princeton reverb trem issues

Post by tubeswell »

Really need to see the HT* voltages, as well as all the plate, screen and cathode voltages. Just knowing the plate and cathode voltages tells only part of the story. The HT voltage tells us what the overall supply is for that stage, so we can see what might be going on with the plate voltage etc

*HT='High Tension'
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Re: Princeton reverb trem issues

Post by Stevem »

You do know that you need to have a short across the Trem foot switch jack to get the Trem work right?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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Re: Princeton reverb trem issues

Post by sluckey »

Stevem wrote: Tue Aug 15, 2017 1:40 pm You do know that you need to have a short across the Trem foot switch jack to get the Trem work right?
That's true for the AB763 amps but not so for the PR.
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Re: Princeton reverb trem issues

Post by Stevem »

Yup, I just realized I had my Trem circuits crossed and I got back on the site to correct myself. Thanks !
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Firestorm
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Re: Princeton reverb trem issues

Post by Firestorm »

Bias mod trems on output tubes can be fussy about how the tubes are biased in the first place. If the bias is set hot, the trem will typically have less effect. Since it was working and then didn't, I'd guess the 6V6s have settled in and are drawing too much current. Try adjusting the bias circuit to get the tubes closer to 50% dissipation at idle.
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JoshBernstein
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Re: Princeton reverb trem issues

Post by JoshBernstein »

Firestorm wrote: Tue Aug 15, 2017 4:18 pm Bias mod trems on output tubes can be fussy about how the tubes are biased in the first place. If the bias is set hot, the trem will typically have less effect. Since it was working and then didn't, I'd guess the 6V6s have settled in and are drawing too much current. Try adjusting the bias circuit to get the tubes closer to 50% dissipation at idle.
I just realised that this occured right after another issue i fixed, i had originally had a 15k resistor feeding thr screen grids of the power tubes, and replaced it with the proper 1k. I didn't try the trem after this swap until the other day. Ill play with the bias and see what i get, will take voltages when i can. Thanks!
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