Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: purpletele on February 16, 2018, 05:40:19 pm
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I was inspired to build a very nice amp in a Champ cabinet. I have a colleague that is running three Champs, and I recently spent a weekend tweaking a Super Champ X2.
I was not impressed at all with the amp, so I decided to surprised my colleague with a Princeton Reverb in a Champ.
I put together a basic layout or block diagram, it seemed to work fine so I ordered two chassis' from Synaptic Amplification on Reverb. So far I am really liking the chassis style and material.
Barry was kind enough to assist me on a faceplate drawing. Everything seems to fit just fine.
Funny dimension on the chassis taken from Mojotone specs. 1/6th ? I think my chassis is 6 1/8th, that is strange to post and make something in that dimension.
I think this will be another cool Fender project.
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It will be interesting to see how this turns out.. that is alot of stuff to cram into a Champ chassis.. but it looks doable.
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It will be interesting to see how this turns out.. that is alot of stuff to cram into a Champ chassis.. but it looks doable.
I can easily utilize a stand up transformer if needed but I think it works, we'll see next week, I have some iron arriving.
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A Champ sized Princeton or even Princeton Reverb is intriguing to me. Lots of players these days have mentioned having something around 15 watts, small, light an portable for small gigs. This would fit that description nicely. With a stand up PT there would be plently of room inside but I wonder about clearing a 10" speaker in a small champ cabinet. I think it might.
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Princeton Champ Update
I received a TP25 Transformer today so I made a template and moved a little closer to a layout.
My current layout works but it doestn't leave much room for Connection strips and such.
Any warnings or encouragement?
I think I can make it work.
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I don't think I have enough room with the TP25. I'll use that for a standard Princeton Chassis
TP25: Upgrade Power Transformer for BF/SF Champ™, VibroChamp™, Bronco™, and Princeton™. 310V-0-310V @ 150ma, 6.3V at 4.5A, 5V at 2A. 50V bias tap, center-tapped heater winding and internal hum shield brought out to a lead for grounding.
MOJO 760: 330-0-330 V @ 75 mA
Thinking about using this Edcor Stand Up
Edcor XPWR061 Stand Up.
Power transformer for a 120V, 60Hz. line to 600V (300-0-300) at 120mA center tapped, 6.3V (3.15-0-3.15) at 3A center tapped and 5V at 2A.
This looks like a good alternative transformer.
Please let me know if I am not seeing something.
BV
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http://www.classictone.net/40-18085.pdf (http://www.classictone.net/40-18085.pdf)
http://www.classictone.net/40-18066.pdf
--pete
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suggestions: lose the valve rectifier & use a choke. consider a JJ 40-20-20-20 can cap.
--pete
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suggestions: lose the valve rectifier & use a choke. consider a JJ 40-20-20-20 can cap.
--pete
Pete,
That is beautiful, I like the 18085, thank you!
I was wondering about the SS rectifier as well as a choke. I bet that stiffens it up and really drives a 10" speaker.
I am building the HPR so I have the JJ Cap Can on hand.
I am going to build a standard HPR in a Mojo Chassis and use the TP25. That will be a good way to get to know the circuit before I stuff it into a little container.
Thank you
BV
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Great project and there is plenty of room in a Champ chassis.
I built a JCM800 2204 50w circuit into a Champ.
I used a custom Champ size aluminum chassis, Trainwreck Pacific transformers and recycled Ceriatone broken Express faceplate.
Mark
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Great project and there is plenty of room in a Champ chassis.
I built a JCM800 2204 50w circuit into a Champ.
I used a custom Champ size aluminum chassis, Trainwreck Pacific transformers and recycled Ceriatone broken Express faceplate.
Mark
I bet that amp want to launch into orbit.
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Yeah it rocks!
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Hey, that's really nice looking! I wish Doug would get some of that red circuit board material...or blue.
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inductive parts are for a 40W vibroverb - 5881 or 6L6GB or 6L6GC. see notes on drawing. i show 4" chassis straps. champ uses 3" if you use the princeton LTPI you shave 1/2-3/4 of board length. bias pot is type RV6. board mounted on 3/4 standoffs. relocate bias put on chassis and use type RV4 or similar.
--pete
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... My current layout works but it doestn't leave much room for Connection strips and such.
Any warnings ...? ...
I only glanced at Pete's layout file. Whichever one you use, triple-check the orientation... The one you had in your photo of your actual chassis needs to be mirror-imaged: the preamp end was over by the PT and vice versa.
Also attempt to eyeball the depth that the pots will need, as you don't want to find out after installing the pots that the board won't fit.
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... My current layout works but it doestn't leave much room for Connection strips and such.
Any warnings ...? ...
I only glanced at Pete's layout file. Whichever one you use, triple-check the orientation... The one you had in your photo of your actual chassis needs to be mirror-imaged: the preamp end was over by the PT and vice versa.
Also attempt to eyeball the depth that the pots will need, as you don't want to find out after installing the pots that the board won't fit.
Thank you,
I purchased a Classic Tone Stand up transformer which opens things up quite a bit. I am going to be watching the room that I have for the POTs as well.
I think it should be much more comfortable now for space.
BV
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Princeton in a Champ Update
This amp has come together quite nicely. I am using a classic tone stand up transformer and a 20 watt OT.
Believe it or not it started right up without issue and it is very quiet, maybe slighter more quiet than my other Princeton Tall Boy.
The original offset speaker baffle that I failed to specify correctly certainly didn't work for this amp so I have Mather building a new baffle and grill.
I am very pleased, I think I'll document voltages and wait for the new grill.
Videos forthcoming
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Nice job on that Prince-Champ it will be a great jam machine.
Mark
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Very nice .. ! It'll be great to see it in a cab. :icon_biggrin:
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A Stack of Princeton's
The Princeton in a Champ is whisper quiet at idle
The HPR is very quiet but not as quiet as the PIAC.
I am regretting the use of the standard OT mounting holes to place my OT on the HPR. I would have moved the transformer much further away but that thought just past by me when I was bolting up the engine.
I used the exact same grounding system on both amps. There two different sets of transformers, one is a Classictone, the others are from Allen Amplification.
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Finished Product
this is a very cool amp! It's a 28 lb, 20 Watt Princeton.
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Sharp dressed amp! :thumbsup:
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Sharp dressed amp! :thumbsup:
Thanks Steve, it sounds really full with that Weber Speaker.
I'm very pleased.
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First time seeing this thread - looking & sounding good Brian!
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First time seeing this thread - looking & sounding good Brian!
Thank Joe,
I have a few more projects stacked up as well.
Next is the HoSo 56 6BM8 that I worked on with Tubenit.
Then I am building another Plexi with the Mod5 changes to see how that works and sounds.
I bought a Chravel San Dimas and I think I am going through a mid life thing. I bid on a Jet City 50 this morning and got it for $300, I promptly order a Friedman Mod kit, so that will be fun to peek into the Soldano world a bit.
BV
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That’s all good stuff but hopefully you can get that un-lucky deluxe reverb working first!? Enquiring minds gotta know???
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That’s all good stuff but hopefully you can get that un-lucky deluxe reverb working first!? Enquiring minds gotta know???
I'm hoping to get sometime booked the next couple of days with a colleague that is going to run through some tests. It bothers me greatly, and I know that amp is going to sound fantastic.
Question on the Princeton in a Champ
The amp sounds fantastic all the way until I dime it then it starts to get wobbly, but it seems like possibly the amp just vibrating too much in that tiny box, or maybe the sound waves vibrating the 6 v 6 tubes?
I changed speaker from a Weber Ferromax to a WGS 10GS and that helped for some reason that I am not sure about yet, I need to check out the speaker specs.
The bass seems to be very strong. I need to turn the bass to about 2-3 to get the tone stack working well, but that is too much bass when the amp is dimed and it seems to contribute to the breakdown.
Should I look at changing the Pot to a higher value? It's 250K Audio as specified, or should I consider changing the cap to something smaller, it's a .0047 uf as specified now.
This might also be a condition where a SS rectifier might tighten up the bass on this little gem.
Any thoughts or recommendations?
Thanks,
BV
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suggestions: lose the valve rectifier & use a choke. consider a JJ 40-20-20-20 can cap.
--pete
Pete,
I want to try a SS rectifier for this little amp to tighten it up. Can you recommend a product or size that you use?
Thanks,
BV
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suggestions: lose the valve rectifier & use a choke. consider a JJ 40-20-20-20 can cap.
--pete
Pete,
I want to try a SS rectifier for this little amp to tighten it up. Can you recommend a product or size that you use?
Thanks,
BV
i use uF4007 in 50W and less. uF5408 for 100W amps. if you installed a rectifier socket, build the rectifier strings in a octal base.
--pete
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suggestions: lose the valve rectifier & use a choke. consider a JJ 40-20-20-20 can cap.
--pete
Pete,
I want to try a SS rectifier for this little amp to tighten it up. Can you recommend a product or size that you use?
Thanks,
BV
i use uF4007 in 50W and less. uF5408 for 100W amps. if you installed a rectifier socket, build the rectifier strings in a octal base.
--pete
Thank you
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farting bass can sometimes be eliminated with the addition of a choke in the power supply. Doug's 5E3 is an example of where that is done. Also, to eliminate the cabinet or speaker as the problem plug the amp into a different higher wattage cabinet. You can also alter the coupling cap(s) or cathode bypass cap in the signal chain to reduce some of the bass frequencies getting through to the power section. Remember the power supply may be being taxed by low frequencies you can't even hear and that will put a drain on the power supply circuit. Also, Leo's amp circuits were designed for his single coil guitars and without changes many humbucker guitars have too much low frequency signal output on certain settings.
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Nice work purpletele...looks and sounds GREAT!
Shave some bass by lowering the value of C24 and C25 down to .02uf
This will tighten things up and help that 10" speaker cope
The bass seems to be very strong. I need to turn the bass to about 2-3 to get the tone stack working well, but that is too much bass when the amp is dimed and it seems to contribute to the breakdown.
Should I look at changing the Pot to a higher value? It's 250K Audio as specified, or should I consider changing the cap to something smaller, it's a .0047 uf as specified now.
I'm assuming you mean .047uf, but .047 in the schematic is the MID cap
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Great Looking Build.
I have built a number of PR's and the bass has always been heavy whe I do not use a PR ouput transformer in stock cap configuration, however if it is pluggen into something like a D130 JBL it simply carries it better. If I build a Princeton and use a deluxe output iron it is even more bassy.
I have heard a lot of suggestions for cap changes on Princetons and different folks like different ways. Some shave in mulitple locations. I simply switch the first bypass cap from 22uf to 4.7uf. It is easy and removes the flub, but I still have a spongy feel of a Princeton, but since I really like everything, I would probably dig a SS rectified version with cathode bias, who knows. :laugh:
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Nice work purpletele...looks and sounds GREAT!
Shave some bass by lowering the value of C24 and C25 down to .02uf
This will tighten things up and help that 10" speaker cope
The bass seems to be very strong. I need to turn the bass to about 2-3 to get the tone stack working well, but that is too much bass when the amp is dimed and it seems to contribute to the breakdown.
Should I look at changing the Pot to a higher value? It's 250K Audio as specified, or should I consider changing the cap to something smaller, it's a .0047 uf as specified now.
I'm assuming you mean .047uf, but .047 in the schematic is the MID cap
Thanks Silvergun,
I tried but it didn't do the trick.
This amp is performing very well, it's that last section of the volume knob that puts it into slight chaos, which I understand is typical of this amp.
Next step is to try a SS rectifier.
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Great Looking Build.
I have built a number of PR's and the bass has always been heavy whe I do not use a PR ouput transformer in stock cap configuration, however if it is pluggen into something like a D130 JBL it simply carries it better. If I build a Princeton and use a deluxe output iron it is even more bassy.
I have heard a lot of suggestions for cap changes on Princetons and different folks like different ways. Some shave in mulitple locations. I simply switch the first bypass cap from 22uf to 4.7uf. It is easy and removes the flub, but I still have a spongy feel of a Princeton, but since I really like everything, I would probably dig a SS rectified version with cathode bias, who knows. :laugh:
Thank Ed,
That will be my next test.
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Sharp dressed amp! :thumbsup:
Thanks Steve, it sounds really full with that Weber Speaker.
I'm very pleased.
Is that a ten inch speaker in that champ DX cab?. And what is the model, can't seem to find it on Weber's site.
I'm wondering if I can fix a 10" in my 66 Vibro Champ (6L6) without changing the baffle keeping the 8" hole with a ten...?
al
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Nice work purpletele...looks and sounds GREAT!
Shave some bass by lowering the value of C24 and C25 down to .02uf
This will tighten things up and help that 10" speaker cope
The bass seems to be very strong. I need to turn the bass to about 2-3 to get the tone stack working well, but that is too much bass when the amp is dimed and it seems to contribute to the breakdown.
Should I look at changing the Pot to a higher value? It's 250K Audio as specified, or should I consider changing the cap to something smaller, it's a .0047 uf as specified now.
I'm assuming you mean .047uf, but .047 in the schematic is the MID cap
Thanks Silvergun,
I tried but it didn't do the trick.
This amp is performing very well, it's that last section of the volume knob that puts it into slight chaos, which I understand is typical of this amp.
Next step is to try a SS rectifier.
Ok, I'll take another stab at it...
One simple trick to try would be to just tack/clip a 1M resistor across the volume pot, effectively making it 500k, which will shift the cutoff frequency a bit higher.
Obviously, Ed and other's suggestion of smaller bypass cap values is another solid route.
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Nice work purpletele...looks and sounds GREAT!
Shave some bass by lowering the value of C24 and C25 down to .02uf
This will tighten things up and help that 10" speaker cope
The bass seems to be very strong. I need to turn the bass to about 2-3 to get the tone stack working well, but that is too much bass when the amp is dimed and it seems to contribute to the breakdown.
Should I look at changing the Pot to a higher value? It's 250K Audio as specified, or should I consider changing the cap to something smaller, it's a .0047 uf as specified now.
I'm assuming you mean .047uf, but .047 in the schematic is the MID cap
Thanks Silvergun,
I tried but it didn't do the trick.
This amp is performing very well, it's that last section of the volume knob that puts it into slight chaos, which I understand is typical of this amp.
Next step is to try a SS rectifier.
Ok, I'll take another stab at it...
One simple trick to try would be to just tack/clip a 1M resistor across the volume pot, effectively making it 500k, which will shift the cutoff frequency a bit higher.
Obviously, Ed and other's suggestion of smaller bypass cap values is another solid route.
Thanks! How fun, I’ll try that
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Sharp dressed amp! :thumbsup:
Thanks Steve, it sounds really full with that Weber Speaker.
I'm very pleased.
Is that a ten inch speaker in that champ DX cab?. And what is the model, can't seem to find it on Weber's site.
I'm wondering if I can fix a 10" in my 66 Vibro Champ (6L6) without changing the baffle keeping the 8" hole with a ten...?
al
That's a Weber 10150f I believe, its a 50 watt speaker. I haven't found data on the speaker yet.
The cabinet is one that I had Peter Mather build, it has a 10 inch baffle.
I have a 10" baffle with the off set speaker in White Cane if you need one.
I also have some black speaker grill material.
I don't know if the 10" speaker will work.
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Great Looking Build.
I have built a number of PR's and the bass has always been heavy whe I do not use a PR ouput transformer in stock cap configuration, however if it is pluggen into something like a D130 JBL it simply carries it better. If I build a Princeton and use a deluxe output iron it is even more bassy.
I have heard a lot of suggestions for cap changes on Princetons and different folks like different ways. Some shave in mulitple locations. I simply switch the first bypass cap from 22uf to 4.7uf. It is easy and removes the flub, but I still have a spongy feel of a Princeton, but since I really like everything, I would probably dig a SS rectified version with cathode bias, who knows. :laugh:
The by pass change made the most difference at this point.
I tacked on a 1 meg resistor and that worked for the frequency cut off, I think, but it was still getting muddy when dimed.
I have a SS Weber Rectifier coming to try.
What if I went with 5881's ? I think I would have to reduce my Bias resistor from 82K down to 68K or in that range to make the bias balance out.
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Great Looking Build.
I have built a number of PR's and the bass has always been heavy whe I do not use a PR ouput transformer in stock cap configuration, however if it is pluggen into something like a D130 JBL it simply carries it better. If I build a Princeton and use a deluxe output iron it is even more bassy.
I used a Classic Tone 40-18090 OT on this one. I had used the TO26 on the other Princeton. I'll AB them and see if I have that issue on both or just the Classic tone.
I'm not going to do anything else until I try a SS Rectifier. That will be early next week. If that doesn't solve that 1% issue then I may change OT's.
Thanks for the advice
BV
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The reason I cut at the first bypass is the frequencies will never enter. If they do not enter, you do not attenuate using the tone stack and the bass knob moves from 2 max providing wider range.
I do not know of a common issue for the Princeton to be different when volume is maxed. I question this and would check where it is coming from.
Also, I will add. My best sounding 10 inch speaker ceramic is actually a Celestion vintage 30. The alnico gold is my favorite new.
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Been busy Brian, here’s what I’d do at this point because you’ve tried reducing the bypass cap, coupling cap, bass, cap, speaker, etc.
You are just getting too much signal it appears. The lowering of vol value via the resistor across the vol places more of a load to the signal thereby reducing it. Instead you will create a voltage divider here involving the Volume pot by soldering in 220k resistor in-line between the signal wire feeding the pot lug - directly to the lug even. Super simple & easy to install and remove/replace. When turned up you won’t get all of that last bit causing you issues. You may be able to restore any bass you may feel you have lost from the prior adjustments if wanted?
If the added resistance seems to knock away any slight treble you feel has changed? Then put a 100pF across the 220k.
If the 220k isn’t enough increase to 470k. If too much the decrease to 100k. Adjust to taste as necessary?
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Been busy Brian, here’s what I’d do at this point because you’ve tried reducing the bypass cap, coupling cap, bass, cap, speaker, etc.
You are just getting too much signal it appears. The lowering of vol value via the resistor across the vol simply places more of a load to the signal thereby reducing it a tad. Instead you will create a voltage divider here involving the Volume pot by soldering in 220k resistor in-line between the signal wire feeding the pot lug. Super simple & easy. When turned up you won’t get all of that last bit causing you issues. You may be able to restore any bass you may feel you have lost from the prior adjustments if wanted?
If the added resistance seems to knock away any slight treble you feel has changed? Then put a 100pF across the 220k.
If the 220k isn’t enough increase to 470k. If too much the decrease to 100k. This should fix your issue no doubt?
Thanks Joe, I'll try that a little later today.
BV
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Been busy Brian, here’s what I’d do at this point because you’ve tried reducing the bypass cap, coupling cap, bass, cap, speaker, etc.
You are just getting too much signal it appears. The lowering of vol value via the resistor across the vol places more of a load to the signal thereby reducing it. Instead you will create a voltage divider here involving the Volume pot by soldering in 220k resistor in-line between the signal wire feeding the pot lug - directly to the lug even. Super simple & easy to install and remove/replace. When turned up you won’t get all of that last bit causing you issues. You may be able to restore any bass you may feel you have lost from the prior adjustments if wanted?
If the added resistance seems to knock away any slight treble you feel has changed? Then put a 100pF across the 220k.
If the 220k isn’t enough increase to 470k. If too much the decrease to 100k. Adjust to taste as necessary?
Joe,
Thanks, that worked perfectly! I am going to adjust the other Princeton as well.
BV
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Brian,
Which of Joe's suggestions did you implement?
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Brian,
Which of Joe's suggestions did you implement?
Barry,
I soldered a 220K resistor in line on the volume lead. It seemed to solve my issue.
I can dime the Princeton and have a solid, slightly distorted note.
I am very pleased.
BV
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Been busy Brian, here’s what I’d do at this point because you’ve tried reducing the bypass cap, coupling cap, bass, cap, speaker, etc.
You are just getting too much signal it appears. The lowering of vol value via the resistor across the vol places more of a load to the signal thereby reducing it. Instead you will create a voltage divider here involving the Volume pot by soldering in 220k resistor in-line between the signal wire feeding the pot lug - directly to the lug even. Super simple & easy to install and remove/replace. When turned up you won’t get all of that last bit causing you issues. You may be able to restore any bass you may feel you have lost from the prior adjustments if wanted?
If the added resistance seems to knock away any slight treble you feel has changed? Then put a 100pF across the 220k.
If the 220k isn’t enough increase to 470k. If too much the decrease to 100k. Adjust to taste as necessary?
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
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Been busy Brian, here’s what I’d do at this point because you’ve tried reducing the bypass cap, coupling cap, bass, cap, speaker, etc.
You are just getting too much signal it appears. The lowering of vol value via the resistor across the vol places more of a load to the signal thereby reducing it. Instead you will create a voltage divider here involving the Volume pot by soldering in 220k resistor in-line between the signal wire feeding the pot lug - directly to the lug even. Super simple & easy to install and remove/replace. When turned up you won’t get all of that last bit causing you issues. You may be able to restore any bass you may feel you have lost from the prior adjustments if wanted?
If the added resistance seems to knock away any slight treble you feel has changed? Then put a 100pF across the 220k.
If the 220k isn’t enough increase to 470k. If too much the decrease to 100k. Adjust to taste as necessary?
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
Ed,
I have that amp working perfectly, well beyond a standard Princeton. It is very impressive now.
I went to tweak my other Princeton that was rock solid and inadvertently broke a wire on V2. So after I finished surgery I played it for a few minutes and the it burned a fuse. So I think I have it worked out but I’m chasing fuses.
This would be the amp for me to try something clever if you have a blessed idea.
Otherwise I’m good with getting it back to solid.
BTW, I have some Weber SS Rectifiers to try once I get the amp corrected.
BV
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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.
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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.
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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.
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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.
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> 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."
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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
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The amp worked, and now it doesn't.
Replace filter caps, test and replace any components that don't fall into spec.
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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.
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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.
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Read through this https://el34world.com/Forum/index.php?topic=15729.0
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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.
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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.
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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
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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?
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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
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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