Princeton in a Champ

[jojokeo]

Brian, all it takes is a couple uf4007 diodes soldered on the rectifier tube’s pins and pull the tube. No need for the Weber stuff.

[purpletele]

Brian, all it takes is a couple uf4007 diodes soldered on the rectifier tube’s pins and pull the tube. No need for the Weber stuff.

Thanks Joe,

This Princeton in a Champ seems to perform to its upgraded potential with the Voltage Divider trick. 

I don't see a need to change the rectifier and re-bias, etc.  I'm going play the heck out of it all around my house, all 28 lbs of it.


I'm down in a hole on the other Princeton as discussed off line. 

Time to set it aside and play my amps that work for a while.

 

[Ed_Chambley]

Hey Joe,  Love doing that!
If you think, and I agree since the results show, he has too much signal.  If this signal is simply from pickups plugged into the amp without anything like a booster or active pups, wouldn't you think raising the PI voltage and checking for some balance would be in order.  What I am saying is it will scream a bit more

Shhsh Ed, these kind of things are secrets of the ninja! Ha! 😉


I will do a lot of things like this on my own stuff or on others but it gets complicated quick and time consuming over the net without being there. Plus Brian was already doing a lot of stuff which is trying and frustrating, didn’t want to add more just give him a solution.


I have emphasized to him that just because an amp is working after being built doesn’t mean its done or performing optimally and to embrace this aspect. Besides, after his unlucky deluxe build issues he needed some confidence building blocks from these and think he got it. Well deserved too.

Makes sense.  Get it working as it, however, and you know what however is, you know how I really like this phase inverter.


I am not speaking of whart is Called the Stokes Mod either.  That is shootong in the dark, but generally works.  I have not posted a lot lately.  I have been off in Acoustic and Solid State land for a while, but I am now back to tubes and building a geetar.  Got my hands on the original wood of a 53 telecaster, with neck.  Building a nitro booth.


And learning to Crosspick, which is hard for me since I have not used a pick regualrly since the Day the Music Died.

[PRR]

> just because an amp is working after being built doesn’t mean its done or performing optimally and to embrace this aspect.

Say I write a song. Is it "optimally finished"?

Even if you don't know the process from write to first demo to "finished" track, all of us can think of records that were OK, then later covers (or self-covers) improved them.

Clapton screams "LAYLA!", yawn, Eric wants pussy. The producer was not satisfied and added the piano movement that the studio gofer stole from his girlfriend with scrap Eric-wails over. Now an icon of his work. And THEN, couple decades and 6 pounds of smack later, he took Layla as a waltz pace, contemplative, and that worked real well also. (Let's hope your amp does not need THAT much aging.)

The Dead released a 3-min 45 called Dark Star. Sank like a stone. They played it longer live. Worked on it off/on for 26 years until Jerry left. It's been said it never stops. Certainly changes each time. (Like bringing your parts-stash and iron to every gig, modifying while you play?)

Dylan's "..Watchtower" is perhaps more optimal by Hendrix. And his "Tambourine Man" was re-worked by the Byrds. Sometimes a song just needs a slight re-word: "There's a bathroom on the right", "This is the dawning of the Age of Asparagus."

[purpletele]

Hey guys,

I hope everyone is doing well. 

I haven't been tinkering with amps in quite a while, but this Princeton in A Champ came back for some service and something interesting happened while I had possession.

I ended up trading this amp for some various guitar work that I needed.  My friend Dave Lynch in Sacramento owns Guitar Workshop.  This has been his main bench amp since 2018.  He has used it at 2 gigs with a three-amp set up.

1. When I picked up the amp it had some serious static.
        a. I suspected a tube at first, but after an unsuccessful tube rolling routine, I suspected a cold joint somewhere.
        b. I found a cold joint at V2 & V7
            A. I cleaned up that connection and re-soldered it and everything was back to normal
                The amp sounded great as expected.
            B. I let the amp run while I was playing another amp.  It was probably an hour of idle time.
        c.  I heard a pop and then smoke came out of the cabinet.  I shut everything down and walked away.

        d.  When I came back to the amp and reviewed the event, I noticed that the board was really messy with flux.
        e.  I found that the 22/50 cap and the 2.2 K 3 watt coming from V2-3 to be toasted!
        e.  The only thing that I can think of is that when I let this amp run for more than an hour the heat may have caused the flux to be conductive and
             create a short.

I spent some time cleaning up the board, I would not consider that as a potential shorting potential at this time.

Let me know what you think would cause a V2-3 and 8 to be toasted.

Thank you,

Brian V

[AlNewman]

The amp worked, and now it doesn't.
Replace filter caps, test and replace any components that don't fall into spec.

[tdvt]

Let me know what you think would cause a V2-3 and 8 to be toasted.

I don't have an answer & will be as interested to see what the more knowledgeable have to say.

I know those tubes run hot, but doing the math, I think that cathode resistor is ball-parking around 29mW (8V X .0036A), yet Doug has a 3W resistor specified in that position.

I asked about that being a 3W once & even Sluckey wasn't sure why that hi-watt was there, other than Doug having seen failures in that position over the years.

[mresistor]

Tubeswell once said this;
"SF and BF reverb driver tubes are the most overstressed dual triodes in the pre-amp world. They will naturally run way hotter than other tubes, and the best thing to do is find a tube that can handle it. Or lower the B+ voltage"


There had to have been more K current sufficient to burn that resistor.  Replace the 12AT7.  Lowering the plate voltage isn't a bad idea.

[mresistor]

Read through this   https://el34world.com/Forum/index.php?topic=15729.0

[tdvt]

Not really addressing the OP's issue, but tangentially related, is this thread...   https://el34world.com/Forum/index.php?topic=31718.0

I have also tried a few of the ideas mentioned in the earlier linked thread; different tubes, larger cathode resistor (4K7) as well as a much larger bypass cap (200uF) mentioned in the thread I just linked.

The last one I built uses a 12AT7 & was quietest with the larger bypass cap & larger Rk.  It has not overheated...yet.

[purpletele]

Not really addressing the OP's issue, but tangentially related, is this thread...   https://el34world.com/Forum/index.php?topic=31718.0

I have also tried a few of the ideas mentioned in the earlier linked thread; different tubes, larger cathode resistor (4K7) as well as a much larger bypass cap (200uF) mentioned in the thread I just linked.

The last one I built uses a 12AT7 & was quietest with the larger bypass cap & larger Rk.  It has not overheated...yet.


Thank you, I'll try the larger cathode resistor and larger bypass cap.

[purpletele]

Update on the Princeton in a Champ

I had replaced the Cathode Resistor to 4K7 as well as an upsized 220 uF bypass cap.  The amp was up and running so I played it on and off multiple times.

I thought I had it back on track until I went to set the bias.  I found that the readings were wonky, and the Intensity Pot was not working.

I caused a rectifier to light up and a fuse blew while probing voltages.  I had touched the bias point and that caused the fuse to blow.

I replaced the fuse, started up the amp and let it run as I chop sticked for pops and such.  Turned the amp on and off multiple times during the day to see what noises might arise.  I went to turn on the amp and a fuse blew.  Down to one fuse tonight, plugging in the Light bulb limiter.

I checked the components in the bias circuit, they tested fine, I replaced the Bias resistor and diode even though they tested fine.

The plan is to start up tomorrow afternoon while connected to the Light Limiter and then start testing some voltages.

I would welcome any advice on what might be going on or specific things I should test. 

Thank you

Brian V

[mresistor]

I would take the power tubes out,,  take it off the limiter and check the bias circuit operation.  There could be a bad or intermittant bad power tube. Do you have a spare duet?





 

[purpletele]

I would take the power tubes out,,  take it off the limiter and check the bias circuit operation.  There could be a bad or intermittent bad power tube. Do you have a spare duet?

I will do as recommended.  I cracked the base of one of the tubes somewhere in the testing.  I have since put in a spare pair.  I will replace that pair after I check the bias without the tubes.

Edit; Fixed quote, Willabe

[purpletele]

Princeton Update

I pulled the power tubes and tested the bias as recommended.  I seem to have control of the bias system and I was able to get a negative reading.

I discovered that I had a 5Ar4 Rectifier so I replaced that with the 5U4G.

New 1V Slo Blo fuse, test grade power tubes, new rectifier.

I flipped the switch and smoke came up from where the choke is located.  The choke is tied in between Node A and Node B.

Not sure what to do next.

Appreciate any input.  I'm about ready to seek professional help so I can get this amp back to the owner.

Thanks,

Brian V