5F6-A Bassman

[griehund]

 :help:Just finished 5F6-A Bassman using Ceriatone layout.  Got hum on standby and a loud hum when powered up.  Lifted up the circuit board and found a wiring mistake.  I had bypassed the choke and 4.7k resistor on the line from the #6 tab on the right side power tube (closest to the 12Ax7 s).  I fixed that situation but still get the hum. 
My dumb question is: did I destroy the choke and will replacing it solve the problem?  Feel free to ridicule my dumbassery.  I have thick skin. 

[Willabe]

Welcome! No ridicule, wont help you fix the build, we ALL make mistakes.       

I don't think you killed the choke, you just by-passed it. Take a reading for DCV at 1 end of the choke to ground and then the other end of the choke to ground. Please post those 2 DCV.

Be very careful it's high DCV there. (Sorry don't know how much experience you have working with tube amps.)

Does your PT have a CT for the heater 6.3 winding? Is it connected to ground? If it doesn't have a CT did you forget to install 2 > 100 ohm resistors, 1 from each heater wind lead to ground, to make an artificial CT?


                Brad      

[TubeGeek]

Post pics and we will see if anything appears incorrect.

[eleventeen]

It's really, really, really hard to kill a choke for a tube amp! It's just a dumb coil.

Either a real or the dual 100 ohm resistor synthetic center tap is an absolute must if your heater winding has no center tap (that you have dutifully connected to ground) on its own. It's easy to envision a manufacturer of a kit (such as what you have) to have specified a power transformer with a filament center tap....and then they get a shipment of power transformers from their supplier that does NOT have such a center tap, but the kit instructions (I have never seen a Ceriatone kit) do NOT specify that you need either a real or a synthetic CT on the heater winding....because the instructions were written with the idea that the tranny would have one. lacking one or the other...you'll get serious hum. Fortunately, a cheap and very easy fix!

 

[griehund]

Welcome! No ridicule, wont help you fix the build, we ALL make mistakes.       

I don't think you killed the choke, you just by-passed it. Take a reading for DCV at 1 end of the choke to ground and then the other end of the choke to ground. Please post those 2 DCV.

Be very careful it's high DCV there. (Sorry don't know how much experience you have working with tube amps.)

Does your PT have a CT for the heater 6.3 winding? Is it connected to ground? If it doesn't have a CT did you forget to install 2 > 100 ohm resistors, 1 from each heater wind lead to ground, to make an artificial CT?


                Brad      

First of all, thanks for responding.

Here's the PT model 40-18073 from Classic Tone:



And here's the Ceriatone layout:



The only PT lead that is not accounted for is the orange.  That one is simply cut and shrink wrapped.

When I pull the rectifier tube and power up, The power tubes and the pre-amp tubes all light up and there's no hum.  The rectifier tube is brand new JJ GZ34 and the power tubes are a supposedly matched set of 6L6 Groove Tubes.

BTW as far as knowledge and proficiency go, on a scale of 1 to 10 with 1 being totally ignorant and 10 being a tube amp pro, I would say I'm a 2. 

[griehund]

Post pics and we will see if anything appears incorrect.

Will do.  I've been under the hood so many times it's beginning to look like a tornado went through.

[labb]

have you had a chance to check the power tube's bias?

[Willabe]

BTW as far as knowledge and proficiency go, on a scale of 1 to 10 with 1 being totally ignorant and 10 being a tube amp pro, I would say I'm a 2. 

Don't worry, your among friends here. Everybody starts out not knowing much.


                 Brad   

[griehund]

Got distracted yesterday.  Had to play plumber and fix a leaky shower.  I'll take the chassis outside and take some pics where I don't have to deal with the flash.  Then I'll organize my thoughts and post the entire saga.  I have enough for a short novel. 

Put in a lot of time shortening the tube socket leads and found a funky ground that I re-soldered.  Also re-soldered the feedback loop resistor.  But I'm getting ahead of myself.  Much more later.

TX

[griehund]

When I finished the build I took it to my local tech to check it out, fire it up, and set the bias.  He found several mistakes and fixed them. My initial intent was to set the Imp. selector in the vacant ground switch hole in the front panel.  He said it should be alright.  After abandoning that idea, I simply used the 4 olm tap and set up two 8 olm speakers in parallel.  When the tech attached the feedback loop to the out jacks the hum resulted.  He said there was no hum when the loop was not connected and I might prefer it that way. He said he could not find the cause and his last, best guess was a bad resistor. 

Since I believe that the presence pot won't function without the feedback loop.  I connected it up and started troubleshooting.  I pulled up the circuit board and checked the wiring and didn't find anything wrong, but I'm planning on doing that again. 

As of right now, when I power up it takes about 20 seconds to heat up and hum.  Within 10 seconds I get smoke at the #6 pin on the right power tube.  I fried one 470 2w screen resistor and replaced it.  Problem persists. 

The heater wires have been pushed around so much that yesterday I noticed a broken solder on pin #7 of the left power tube.  Easy to fix and I think that's a result not a cause. 

So my next plan is to disconnect the feedback loop and see what happens.  Then I'll pull up the board again and double/triple check the wiring. 







Could a faulty tube socket cause a problem like this?

Anyway, I was able to fix the leaky shower so my self confidence is on the mend.

TX,   

[sluckey]

When the tech attached the feedback loop to the out jacks the hum resulted.  He said there was no hum when the loop was not connected and I might prefer it that way. He said he could not find the cause and his last, best guess was a bad resistor. 

Try reversing the OT plate leads.

Within 10 seconds I get smoke at the #6 pin on the right power tube.  I fried one 470 2w screen resistor and replaced it.  Problem persists.

Swap the tubes around. Does the smoke stay with the same tube?

[Platefire]

Somebody may have already mentioned this, but I scanned previous post and didn't see anything. If your using Negative Feedback(NFB), there is two ways you can wire up the leads from your OT to your 6L6 pates. One way will cause squealing. The amp will work but with lots of noise especially when you turn it up. You said Hum instead of squeal, so it's probably not your problem--but might be worth a try. The other way if the squealing occurs is the swap the leads and it corrects this problem. When you said it started when you connected the NFB, it made me think of this.  Platefire

[sluckey]

Somebody may have already mentioned this, but I scanned previous post and didn't see anything.

I just mentioned it a few minutes ago.

You said Hum instead of squeal, so it's probably not your problem

Squeal is just a higher frequency signal feeding back. Hum can also be a feedback problem just a lower frequency. I've seen amps that have a presence control in the NFB loop have some very quirky symptoms related to wrong phase feedback signal. And those quirks are often frequency dependent.

[Bub]

Off topic but curious. Is there a cover that fits over the caps on the outside?

Thanks

[griehund]

Off topic but curious. Is there a cover that fits over the caps on the outside?

Thanks

There was no cap cover with the chassis when I bought it.  The 20uf 600v caps are huge.  I'll probably swap them out sometime but my tech said there's nothing wrong with them and they're out of reach in the cab.  They don't seem to be involved in my present situation. 

[griehund]

When the tech attached the feedback loop to the out jacks the hum resulted.  He said there was no hum when the loop was not connected and I might prefer it that way. He said he could not find the cause and his last, best guess was a bad resistor.  

Try reversing the OT plate leads.  

Within 10 seconds I get smoke at the #6 pin on the right power tube.  I fried one 470 2w screen resistor and replaced it.  Problem persists.

Swap the tubes around. Does the smoke stay with the same tube?

I asked my tech about swapping the OT leads and he said they tested correct.  But I'm at the point where it's worth a try.

I did swap the two power tubes and got the same result.  That's kind the reason I thought there might be something wrong with that tube socket.

[griehund]

I've seen amps that have a presence control in the NFB loop have some very quirky symptoms related to wrong phase feedback signal. And those quirks are often frequency dependent.

Is fried screen resistors one of those symptoms?  I'm beginning to believe I have to swap the OT leads just to see what happens.  So first I'll fix the broken heater wire solder.  Then I'll swap the OT leads.  I don't want to disconnect the feedback loop and I sure as shootin don't want to lift the board again.   

[sluckey]

I asked my tech about swapping the OT leads and he said they tested correct.

What kind of test?

I'm beginning to believe I have to swap the OT leads just to see what happens.

It's a good idea to positively rule out on any new build that has NFB from the OT secondary. Only takes a couple minutes to swap them. We're talking about the brown and blue wires from the OT that connect to pin 3 of each 6L6 socket.

[Platefire]

I wasn't aware of any Multi Meter test you could do to the OT leads to plates other than swapping them if your getting noise?? Plate

[griehund]

I asked my tech about swapping the OT leads and he said they tested correct.

What kind of test?

I don't know what kind of test he used.  Him being the tech and me being the dumbass, I crossed it off the list of things to try.  It is now definitely on my list.

I'm beginning to believe I have to swap the OT leads just to see what happens.

It's a good idea to positively rule out on any new build that has NFB from the OT secondary. Only takes a couple minutes to swap them. We're talking about the brown and blue wires from the OT that connect to pin 3 of each 6L6 socket.

I surely hope that's the answer.  Stay tuned.   

[griehund]

OK we can rule out swapping the OT leads.  Same result only louder.  Tomorrow's another day. 

[griehund]

Been reading about grounding and have some questions.  First, I soldered a bus wire across the backs of the pots from the presence to the volume.  The volume pot is grounded to the bus wire and is connected to the input jacks.  one article I read say's the bus wire should be grounded to the input jacks.  Does the volume pot ground to the bus wire effectively complete the circuit to the input jacks or should I run a separate wire directly from the bus wire to the jacks?

Second, The large caps on top of the chassis have separate grounds that are supposed to go to the star ground at the PT lug.  The article says that the ground wires should be as short as possible and it's a long way back to the PT.  Would it be a good idea to make a chassis ground closer to the caps and ground them there?  This would keep the cap grounds closer and also keep them far away from the tube sockets.  I'm guessing that the grounding scheme could be contributing to the noise.  Yes/No?

One forum member said he connected his bus wire to the PT lug.   

[phsyconoodler]

I ground my bassman build's right at the chassis where the caps are.Rather I use the cap can as the ground.Just like the original ones did.No noises at all.

[Willabe]

Been reading about grounding and have some questions.

Here's a link to a recent thread about grounding;

http://www.el34world.com/Forum/index.php?topic=15955.msg155144#msg155144

Also this link;

http://www.valvewizard.co.uk/Grounding.html

And, phsyconoodler is (IMO) 1 of the best builder/tech's here and has done dozens of scratch builds and re-builds.

If he says no noise with the way he does it, I believe him, even if I might wire it different. (More than 1 way to skin a cat.)


                Brad      

[griehund]

I ground my bassman build's right at the chassis where the caps are.Rather I use the cap can as the ground.Just like the original ones did.No noises at all.

Thanks, that's good news.  I hated the idea of running long ground wires back to the PT lug. 
Also thinking about redoing my heater wires and notice in you pic your heaters are not raised directly over the tube sockets.  Would I be better off to shorten them up and laying them flat?  My last build had the tubes on top of the chassis so raising the heaters kept them away from everything else. 

[griehund]

I looked at your pictures, and it looks like the black and white wires are your heater wires.  If so, the location within the chassis might be a source of the hum.  It is my understanding, the heater leads should be along the edge of the chassis.  So if you planning to move them, it probably a good idea. 

Thanks.  I spent yesterday afternoon shortening all the leads on the pot side of the chassis and moving them closer to the front panel behind the bus wire.  Next I intend to do the same on the tube side and reroute the heater wires closer to the back panel.  Also intend to shorten all leads from PT. 

Still fiddling cause I didn't hear the fat lady sing. 

[griehund]

OK. Today I feel like I made some progress.  Shortened up all leads on both pot side and tube side.  Found a few funky solders and fixed them.  Moved the heater wires so they lay flat on the back panel except the ones that connect the two power tubes.  Shortened the leads from the PT.  Grounded the large caps to the chassis right next to them.

Power on: no hum.

Standby off (or on depending how you look at it):  A moderate hum that dissipates within a few seconds,  smoke on pin #6 of the right power tube.  When I powered off the right power tube felt hot to the touch and the left one did not.  I swapped the two tubes and powered up again.  This time I got smoke on the left power tube (the one I just moved and the same one that smoked in the right socket).  Both screen resistors still read right around 470 so they were not damaged.

Is it a safe assumption that I have a tube problem?   

[sluckey]

smoke on pin #6 of the right power tube.

I've never seen a tube socket smoke. What exactly are you trying to say???

[griehund]

smoke on pin #6 of the right power tube.

I've never seen a tube socket smoke. What exactly are you trying to say???

The first time I got Smoke coming from the #6 pin the 470 screen resistor was badly burned.  My local tech said it was  from the tube over heating.  I replaced both screen resistors.  When I swapped the tube to the next socket the over heating repeated and I got smoke from that socket.  I took both tubes to my local tech and he tested them both.  One tested perfect and the other shorted out at three different points.  I never let the tubes get too hot cause I powered off  as soon as the I saw and smelled the smoke but there was an obvious difference between the two.  The bad tube felt hot to the touch while the good one was just luke warm.

My tech said the bad tube was contributing to the hum and thought that was the cause of my problems.  He suggested I buy another matched set of power tubes.  He suggested Sovtecs or Electro-Harmonics.  So tomorrow I'm going tube hunting.  There's a couple of local shops that have tubes in stock.  

I feel like I'm beginning to see the light at the of the tunnel and hopefully it's not a train.  

[plexi50]

Beautiful chassis. You have something wired wrong. Go slowly back over the wiring in comparison to the layout you have from Ceriatone. Confirm every wire point and component connection. A process of elimination. Start at the power supply B+ feeding the standby,choke and PI, and on to the preamp power supply nodes. The layout makes it much easier to understand if you can not read schematics easily. I started out knowing zero. Some times i still think i know zero. It keeps you on your toes and always questioning your work. Even after all the years of electronics learning there is a dead spot some times and we all need a refresher course. Just look at my last post on the 65 deluxe reverb that i posted. I feel stupid for not saying that it was a twin reverb board and chassis before asking any questions. I caused major confusion between the problem and the questions asked. Call it alltimers or just plain not thinking before speaking. You will conquer and find the problem. When you do you will feel proud and worthy of your efforts. We all over look the simple errors. We dont forgive ourselves but we learn a valuable lesson. No one is perfect. Maybe Einstien.e\\\

[griehund]

Beautiful chassis. You have something wired wrong. Go slowly back over the wiring in comparison to the layout you have from Ceriatone. Confirm every wire point and component connection. A process of elimination. Start at the power supply B+ feeding the standby,choke and PI, and on to the preamp power supply nodes. The layout makes it much easier to understand if you can not read schematics easily. I started out knowing zero. Some times i still think i know zero. It keeps you on your toes and always questioning your work. Even after all the years of electronics learning there is a dead spot some times and we all need a refresher course. Just look at my last post on the 65 deluxe reverb that i posted. I feel stupid for not saying that it was a twin reverb board and chassis before asking any questions. I caused major confusion between the problem and the questions asked. Call it alltimers or just plain not thinking before speaking. You will conquer and find the problem. When you do you will feel proud and worthy of your efforts. We all over look the simple errors. We dont forgive ourselves but we learn a valuable lesson. No one is perfect. Maybe Einstien.e\\\

Ok this is my third attempt at posting. 

Thanks for the vote of confidence.

I asked my tech if bypassing the choke could damage the power tube and he said yes.  So, I'm adding that to the list of mistakes I found when I shortened all the leads.  I found a cold solder on the ground bus wire from the 10uf 450V cap, a disconnected ground wire at the board eyelet for the 220uf 25V cap, and a broken lead at the pin #1 V3 preamp tube connection to the 0.1uf 600V orange drop cap.  I hope this makes sense. I'm guessing one or all of those mistakes could damage the power tube. 

Since my good 6L6 didn't over heat in the right power tube socket (V4 ?) after I fixed the above errors and moved the heater wires I'm hoping a new matched set will work.  At least I now have reason to hope.  There's no more real loud hum and my tech said the bad tube could be causing whatever hum is left at this point. 

So now I'm trying to track down some tubes and hopefully get up and running soon. 

Took some new pics after shortening and moving leads.

Pot side:


Tube side:


Board:


Rectifier & PT:


Hopefully no more smoke signals. 

[Jack1962]

Replace your power tubes you have a bad one that's why it's smoking your screen resistor , heater wires should be ran against the back of the chassis and twisted(unless your using dc voltage) also at 90 degree angles . If your tech said it has no hum without the NFB connected then it's not wired correctly , check your diagram it's pretty simple.

[griehund]

Ok, half a success is better than none. 

I found a couple Ruby tubes put and them in.  No smoke but wicked loud hum.  Swapped the OT leads and got no hum, no smoke.  Plugged in my guitar and got sound from bright channel but nothing from the normal channel.  Not a lot of volume.  Feel like I made decent progress.  Not ready to celebrate but feel like I got over one high hurdle.   

[PRR]

> got no hum, no smoke.  Plugged in my guitar and got sound from bright channel

It's Miller Time.

> nothing from the normal channel

Still Miller Time.

You had a car where the engine wanted to tear itself apart and burn the car down. Now you got a car that works good except one door is stuck. Minor detail.

My first car had a stuck door, but on the tow home it nearly DID burn-down. After some major repairs, it drove; but you still couldn't get in the passenger door. I actually drove it that way for some months until my wallet and back/butt recovered from the burnt-part work; then I got the right kind of jack and eased the door pillar back into shape.

Your dead channel is probably something very simple. Missed wire, wrong jack-lug.

[Steve_P]

Ok, half a success is better than none. 

I found a couple Ruby tubes put and them in.  No smoke but wicked loud hum.  Swapped the OT leads and got no hum, no smoke.  Plugged in my guitar and got sound from bright channel but nothing from the normal channel.  Not a lot of volume.  Feel like I made decent progress.  Not ready to celebrate but feel like I got over one high hurdle.   

First amp I worked on, I forgot to solder in the ground to the volume pot. It was loud.

[griehund]

I was so happy yesterday I had to walk away from my bench before my OCD (obsessive compulsive disorder) kicked in and I  really balled something up.  When I get a chance today I'll swap out the preamp tubes and see what happens.  Since I already bar-b-qued one tube it's entirely possible that I did it to another one.  JJ 12ax7's are easy to find in my neighborhood. 

Don't know what to make of the volume thing.  Maybe when I get both channels working that will fix itself?  Maybe I'll need to get the bias reset?  One step at a time.  Right now I'm happy like a pig in mud. 

[griehund]

Success! Finally!  Found three broken solders on the tube socket pins,  one from a power tube to the board,  one heater wire,  and the wire connecting pins 3 & 8 on the #1 preamp tube.  Now the normal channel is working fine.  put it all together and it sounds wicked sweet.

Thanks for all your help but now my bench looks sadly empty.  HMMMM.

[eleventeen]

If I may say so....

You are having / discovering FAR too many "bad" solder joints.

Technique? Cruddy soldering iron? Dirty tip? Combination of factors?

Only you can tell. But I would urge you to do what you need to do to solve this issue. You should be able to make a solder connection and know from its appearance (as soon as it freezes = solidifies) with near-metaphysical certainty that you've made (or not) a good solder joint.

I often think of troubleshooting as chasing a bunch of cockroaches out of a cheap hotel room. An image developed from years of being on the road...and don't ask! You really don't want this element of randomness in your world. I am sorry if I am stating this in an awkward way. It shouldn't be a problem, is what I'm saying.

A good soldering station is about a $100 thing, maybe $129, zillions are available used on ebay or on your local Craigslist (obviously much better since you can inspect and test and haggle) and is a life-changing item for both building and troubleshooting. But especially building.

Read your posts. It seems to me like you made 1-2 wiring mistakes but had a solid half-dozen soldering snafus. How much time did that snooker you for? Sure, you learned things, and etc; etc; etc;

Nuff said. My reco is to treat yourself to a nice soldering station if you wish to build more stuff. Solve this problem.

[HotBluePlates]

I get a little bit different take-away from you experience...

Don't know what to make of the volume thing. ... Maybe I'll need to get the bias reset?  ...

...  Found three broken solders ....  Now the normal channel is working fine.  ...

When your car breaks down, if you're like me you assume something broke, wore-out, needs replacing... And if you have an OLD amp, that may be the case when it fails.

But when you have a newly-built amp, there is almost never a parts problem. It is almost 100% a build problem (bum solder joint, wire in the wrong place, wrong part value, accidental short-circuit, etc).

Nobody assembles an amp thinking they botched it; just like most people assert their opinion believing they're right, even if they're dead-wrong. So if the amp doesn't work, triple- and quadruple-check every component, wire, solder joint, part value, etc. The error will be there somewhere, though it may be hard for you to spot how you made a mistake.

Mistakes help you learn to do better next time. If I know a little more than someone else here, it's only because I read a few more books, built a few more circuits, made a few more (bigger?) dumb mistakes, and had a few more people point out to me where I've got things all mixed up.

Now... ENJOY YOUR NEW AMP!!! 

[griehund]

Two things I learned for certain is I need more light over my bench so I can see what I'm doing and never to score the casing on solid core wire.  The vast majority of my soldering problems where more accurately broken wire problems because I nicked the wire when trimming off the casing (a lesson learned the hard way).  Also, this is only my second build.  Before my first build (a Champ) I knew absolutely nothing and stumbled my way through.  This time I had to step back a few times and figure out why something wasn't working (normal channel).  That provided a place to look for my mistakes.  Followed the heater wires back from #1 preamp and checked all socket pin solders.

It's been a great learning experience.  Had an English prof who said the secret to good writing is reviewing and rewriting.  I'm finding the same process holds true in building.

The more I learn, the more I realize how much I don't know. 

[griehund]

Wondering if this falls into the category of fixing or fine tuning.

When I started this build I was looking for an amp that was both loud and pretty clean.  Getting it up and running was an accomplishment that I'm pretty proud of.

Bias was set at 30 and I increased it to 35 but was not happy with the earlier break up so  I'm taking it back down to 30 ASAP. Incidentally, The so called matched set of 6L6GC power tubes read 31 and 35, 4 full clicks difference.  But I digress.

Completely happy with clean tone cause I prefer to distort with pedals.  But volume controls are acting a little funky.  I have no hum, hiss, snap, crackle, pop, smoke or smells.  But, I have very little volume at the bottom of the spectrum.  Sound does not become evident until 5 or 6 on the dial and does not become noticeably loud until 8 or 9.  10-12 are loud and clear.  It's perfectly loud enough for playing in the basement but is not what I was expecting.  Same with both normal and bright channels. 

I'm making a list of questions to check to see if I can locate the culprit.

1) check all resistor values on board?

2) better matched power tubes?

3) breaking in speakers?

4) different tube in V1? (now using JJ gold pin 12ax7)

5) since bright and normal channels are the same can I assume the pots are functioning properly?

Anyone have any other suggestions?  I can live with it the way it is but I'm just anal enough for it to bother me just a little.  Just bought a "Fat Bastard" clean boost pedal so I can get it up to way too loud.  But still.

[HotBluePlates]

... I have very little volume at the bottom of the spectrum.  Sound does not become evident until 5 or 6 on the dial and does not become noticeably loud until 8 or 9.  10-12 are loud and clear. ...

I'd almost want to see a video, with your volume starting at zero and you strumming as you bump it up 1-2 notches all the way to the top of the pot.

"No sound" until 5-6 doesn't make sense, but the rest of the control operation seems correct.

Measure resistance of your volume pots (with power off) between the 2 outer lugs. Now tun the knob until it's exactly halfway of the sweep. Measure resistance from ground (left lug looking at the back of the pot) to the wiper (middle lug).

I'm guessing you have 10% taper pots, in which case the 2nd measurement will be about 10% of the first. I'm also guessing you're used to hearing 20% or 30% taper "volume pots" which get louder faster and don't follow a true log curve as closely.

[silverfox]

With 2 6L6 output tubes this amp should start to get really loud after 3.

Not sure how relevant this is to the low output problem. I, not too long ago modded a Kustom 10 watt practice amp by adding a 3 control tone stack and a master volume. I've found that in some tone settings the output from the amp is decreased. I'm wondering if I wired up the tone stack incorrectly.

So my suggestion would be to check the tone stack wiring and be sure it is wired correctly.

I also have limited experience with tube amps circuits so this advice could be inaccurate. But, it may be worth a look.

After you have played the amp for a while you may want to go back and physically check all the connections and solder joints. In doing so, check several and then check the amp again to be sure you haven't introduced a new problem.

Courtesy of Kagliostro- A Forum Member: Some helpful soldering videos- http://www.el34world.com/Forum/index.php?topic=14655.0



Silverfox.

[griehund]

Thanks guys.  That gives me some things I can check.  In the end, I'm a happy camper with it the way it is but I dearly love to tinker.  More later.