New build Pics with issues

[Bub]

Hi Gent's

First I have to say thanks for answering my rookie questions with respect. For a newbie it means alot. Heres my new build that doesn't work. It's the KOC 5F6-A. I used Doug's board as a template and added the mods where required but I've screwed something up.
I fired it up on the lamp limiter, everthing went well. I plugged it in and when I took it off standby I almost had a brown out, extremely loud high pitched squeal. I traced that down to having the Presence wired incorrectly and having the wrong pot. It requires a 25k and I used a 5k. I have the Presence disconnected right now but I don't know if this is my issue but I think I have bigger ones. Both channels seem to partly work. Full volume hardly any sound and what comes out is very fuzzy. I'll post pics and voltages.

Thanks in advance for any help

Rob

[Bub]

Pics

[Bub]

More Pics

[Bub]

And more

[stingray_65]

Hey Bub!

Now comes the fun part of a scratch build !

It sounds like you have the primaries of your OT backward. It's a 50-50 shot when you wire them up. flip the "brown and blue" wires

The wrong pot would not make it squeal. if you have a 25k it can be dialed through the full range that the 5k goes through and then some. You'll want the spec'd pot in there any how to give you full range of your presence.

A lot of guys as I understand it, don't hook up the NFB/presence circuit until after everything else is dialed in, so leaving it (the pot) out of the circuit for the moment will let you concentrate on the rest of your issues.

Pics, Voltages, schematic and layout are a BIG help to the ace troubleshooters here.

These guys will walk you through step by step to debugging your issues.

They've done it for me in darn near every amp I built!

If you don't understand whats being asked of you to do, let us know! no shame in getting your troubleshooting education.

You may want to get a pair of chopsticks ready and learn real well how to discharge your filter caps and then measure them to make sure they are drained. You'll likely do that many times during the trouble shooting. This is where I've always gotten bit by the lightning.

Trouble shooting is a step by step process that is often a simple matter of elimination, careful measuring and logic. Luck is handy here, but not a requirement if you're thorough.

Ray

[stingray_65]

well dang!

newbie lead dress issues galore!

JUST KIDDING!

That is one sanitary build!

Ray

[Bub]

Voltages
KOC has the pins wired opposite, pin 2 is pin 7 etc.

V1                      V2                      V3                     V4, V5 6L6gc            
pin 1  175V           pin 1  266V          pin 1  324V          pin 3  382V        
pin 3  1.4V            pin 2  148V          pin 2  272V          pin 4  379V        
pin 6  181V           pin 3  149V          pin 3  305V          pin 5  -38V        
pin 8  1.3V            pin 6  148V          pin 6  324V          
                          pin 7  0V              pin 7  271V
                          pin 8  .9V             pin 8  305V
Thanks

Rob

[Bub]

 Thanks for those kind words stingray_65.
Let the fun begin, chop sticks are ready but I honestly don't think it's a cold solder joint ( where have you heard that before )
I could take pics of the schematic and post them but I don't know if I'm allowed to do that. I have no way of scanning them.

Rob

[Bub]

Some clearer pics

[Bub]

One thing I should add is KOC has the Bass and Mid pots wired differently than a stock 5F6-A, also he is using the Presence pot as a rheostat instead of a potentiometer, I think. This is where I screwed up when I first wired the Presence control, I was working off of Doug's schematic and KOC's.

Thanks

Rob

Wow, I just noticed I hit level 2, thats gotta to be a mistake!

[Danskman]

Hi Bub,
don't get me wrong, but sometime it happens that a very neat and clear wiring dress can cause oscillations and crossover problems, that can lead to squeal.
I found your build one of the nicer I ever saw. Did you try to reverse PI output? If you disconnect Presence control circuit and the squeal disappears, try that.
otherwise, it could be a wiring dress issue. parallel wiring dress can cause problems, as you can get low level signal with high level and get some feedback issue. I ever try to avoid this in all my builds. Don't know about KOC, but I built some circuit using Doug's techniques and never had a problem with it.
HTH, good luck and best regards,
Danskman

[sluckey]

Your V3 voltages are all messed up. Could be because the presence pot is disconnected. I'm looking at a Fender 5F6A schematic and it needs the presence pot to work properly. Reconnect your presence pot and swap OT plate leads. Repost your V3 voltages. Does that help?

We really need to see your exact schematic if we're gonna discuss specifics. I don't think anyone will care if you take pics of the schematic and post. Pics will need to be hi-rez and clear enough to read component values.

[stingray_65]

Could be because the presence pot is disconnected. I'm looking at a Fender 5F6A schematic and it needs the presence pot to work properly. Reconnect your presence pot and swap OT plate leads.

I stand corrected! Thanks Steve

[jojokeo]

I agree, very nice looking. But nice looking doesn't mean it works well or was done right. Just like in golf, you don't draw pictures on the score card, it's what happens in the end is all that matters.

My first initial question is - are you aware of making sure your heater wiring is correctly phased? Meaning did you check that your power tubes' pin 2 are on the same wire, and all pin 7's on their own wire? This won't mean it directly has to do w/ your initial problems but can give us an idea of your knowledge and experience level and it relates to your other wiring that's been done.

From experience, the best thing is slowly and thoroughly take your schematic and make sure that the layout you used is correctly accurate. Then take your layout and make sure all of your wiring is exactly like the layout going through all runs systematically.

[Bub]

The heater wiring is correctly phased, pin 7 to 7 and 2 to 2 etc. Too straight a lead dress could be the issue, but thats the last thing I want to mess up. I knew I was taking a chance when I did it. I will rewire the presence using the 5k pot for now and switch OT leads, post a picture of the schematic and new voltages. As far my knowledge,  I've read a ton of info but this is only a hobby for me so I don't deal with it on a day to day basis. This is build #2. I've been threw the schematic a number of times and can't seem to find anything but I think I have been staring at it too long and can't pick up something obviuos. Will report back.

Thanks for the help

Rob  

[jojokeo]

Well w/ a build so nicely done as yours is, I kinda figured you knew that basic info for heaters and the like. The oscillation issue should disappear w/ the OT wiring made correctly. Too straight of lead dress is something I seriously doubt is an issue - going back to the golf metaphor, is a drive hit too straight a problem? 

It may likely end up being just a simple mistake somewhere like when someone gets the pinouts backwards on a tube socket or mistaking the grid & plate pins or whatever. Good luck and remember it's the mistakes like this that's where the real learning curve takes place and makes us all the better for it in the future. You have the right attitude in taking a step back to clear your head and being patient. You'll get it taken care of soon enough.

[Bub]

Well I changed the OT leads, wired the presence as a rheostat instead of a potentiometer, found I had wired a 270 ohm 5 watt resistor from the 8 ohm tap to the 4 ohm tap instead of going from the 8 ohm tap to ground, still don't know why it's there but that's for another day. Amp sounds good but not great, very loud, 1/4 volume is easily enough to have a good jam, no hiss and very little hum which I'm sure I can tweek with bias and tubes. I don't seem to have much Middle or Presence response but I do have to change the Presence pot. I don't understand why the KOC tone pots are wired differently than the stock build. I will post schematic and revised voltages as soon as I get a chance.

Thanks

Rob   

[Bub]

Hi Gent's

New voltages

V1
pin 1  166V,  pin 3  1.350V,  pin 6  171V,  pin 8  1.286V
V2
pin 1  252V,  pin 2&6  139V,  pin 3  140V,  pin 8  .940V
V3
pin 1  193V,  pin 2  22V,  pin 3&8  35V,  pin 6  205V,  pin 7  22V

V4 & V5 didn't change enough to list them. I compared these to the Tube Amp Voltage index and they seem way low, but then again it's not a stock build. My B+ voltage is 385V but I can up that a little if you suggest. My PT has two taps, one for 115V and one for 125V which I'm using now. If you can let me know if these are within acceptable limits that would be great. V1 seems good from what I've read but V2 & V3 I'm not sure. I have a couple of more questions after I get my voltages where they need to be.

Thanks for all the help

Rob

       

[Bub]

Schematic

[Bub]

#2

[Bub]

And I just have to say

I don't take offence to anything you guys say. I've been reading all your posts for way to long and appreciate the knowledge you guys share. It is what it is and if I've screwed up please let me know. I know I got a little anal on the the lead dress, but oh well

Rob

[sluckey]

Your voltages look good to me. I would not be concerned about B+ being a little low. Most homebrews worry about B+ being too high.

[Bub]

Thanks sluckey
I feel a little better now.

[jojokeo]

Amp sounds good but not great, very loud, 1/4 volume is easily enough to have a good jam, no hiss and very little hum which I'm sure I can tweek with bias and tubes. I don't seem to have much Middle or Presence response but I do have to change the Presence pot. I don't understand why the KOC tone pots are wired differently than the stock build.

My humble suggestions:
I'm not sure of the presence layout or values and to each their own, but - NFB is there whether you want it or not (despite the presence control network). This can screw up & strangle your tone, decrease your gain, and cancel even order harmonics right off the bat. At the very least you could make it switchable until you're sure it's wanted? Lift that 33k feedback resistor where it connects to the 10k/100n point and then ground those two. This will get rid of the NFB and then listen to your amp's NATURAL tone before you make further adjustments in this area.

The tone controls are fine & the standard way of wiring them up. You should raise the bass cap to .047 or .1uf (the middle of the three), and either leave the mid (lower one) at .02 or go down to a .01uf there. This will help both bass and mid control's ranges better - and/or make the mid pot a 50K-B to extend it's range too. But, with the cap changes alone you'll see a better difference as they act together.

Bub, going by your comment of, "I don't take offence to anything you guys say. I've been reading all your posts for way to long and appreciate the knowledge you guys share. It is what it is and if I've screwed up please let me know." I will offer my constructive criticism and it's not meant to offend please...The first two input stages and related stuff for the only difference of a bright cap on one of the gain controls is limited & un-creative. Despite this and/or their interaction, you can use the other stage to bais & design totally different giving you two flavors or amps in one w/ much more flexibility and mojo as a whole. You could do a lot more here than what you have & KOC has done w/ the design, Fender clone or not. Just a suggestion and saying I would if it was mine anyway.

[Bub]

Hi jojokeo,

Thats awsome info, thanks. I'll give your suggestions a try. Being a newbie, this is the kind of stuff I have no idea about but want to learn and try. This is why I built this amp, not to play through but to play with. I plan on spending more time with a hot iron in my hands than my bass. I have to order a bunch of parts so I'll through some extra caps in but my amp will have to go on hold for a week or two. This getting up before breakfast and having to work between meals is for the birds.

Thanks

Rob

[The_Gaz]

jojokeo's inclination is right - that's a lot of NFB in that circuit. I've tried that value in a 5F6A in hopes of more power amp headroom, but the amp because very constricted and sterile - felt very weird to play. i imagine you'll get a big fat smile on your face when you remove the NFB. my guess is you'll be happier with a value of 47k or 56k off the 8 ohm tap, like a Plexi. you may even prefer a 100k or no feedback at all! good luck.

[tubeswell]

Another tweak you could try to decrease the global NFB is to put something like a 4k7 resistor between eth OT secondary and the junction of the 4k7/25k presence pot - this should knock the GFB down by an order of 2 x and open it up a bit. Or you could put a 10k in there and knock it down 3 x, etc

[Bub]

Hi Gent's

Thanks for the great suggestions, I'm writing them down and plan on trying every one. Maybe someone can help me with this. I'm biasing my 6L6GC tubes. I am using the 1 ohm, 1 watt cathode sence method with a test port. Plate voltage today is 390V. I have both tubes set at 40mV. Just for something to do I check the voltage at pin 5 of each tube, V5 is -36V while V6 is -40V. Does the difference in voltage of V5 tube give me any indication of the quality of that tube or thats just the way it is. I can see now why adjusting the bias using pin 5 is highly inaccurate.

Thanks for all the help

Rob

[jojokeo]

Although your tubes work together, they are not exactly the same and you're seeing the result of this. Matched tubes will still show slightly diff readings while unmatched will show greater differences.

[Bub]

Thankyou.

Rob

[Bub]

Hi Gent's,

As recommended I grounded the NFB, WOW!, what a difference, this thing with a Hofner sounds sweet, the tone is perfect for what I'm looking for but I still have to play.
I have the parts on order to do the cap swap and presence pot. I think I'll make the presence a push/pull to play with the NFB. I think I read a PRR post where he recommended some NFB to stop speaker flapping for Bass but I don't know if that's an issue.
I still have a problem I've been chasing, I have a hum that I can't pin down. I used Doug's grounding method. This is what I've done so far that has made no difference in hum.
Swap out all tubes, Disconnect elevated heaters, Install 2 x 100 ohm resistors for heater circuit, Run heaters on a battery, Disconnect bus wire for pots at input jacks, Ground either side of pot bus wire to PT ground bolt, Move around all wires leading to pots, Run an additional wire from board ground where input jacks ground to PT bolt, Chopstick all connections. Disconnect lights.
What does make a difference is when I remove the ground wire for the input jacks from the board the hum gets louder. I moved the input jacks outside the chassis and ran two ground wires, one to the board and one to the chassis, the hum seemed a little worst. Everything I've done seems to point me to the V1 end of the board. Input jacks are wired correctly. On V1 I used I used 1 watt 10k grid stops cause thats all I had. I do have 1/2 watt on order but I don't know if that would make a difference. I'm stuck at what to do next. I've ordered a complete set of pots and was thinking of trying without shieled cable for something to do. Can I bridge a cap across something to narrow it down?. Any help and direction is greatly appreciated.
Thanks,  Rob  
      

[Bub]

I should add that I have the tone controls at half, no guitar plugged in the hum starts at about 6 on either volume. I cheched the shorting bars on each input jack and they seem to be working. When I lift the shorting bar on the input jacks that have the 1 meg resistor the hum gets really loud and the ones with the 33k resistors the hum increases a little bit. When my guitar is plugged in I get a buzz and a hum and when I touch my guitar toggle switches the buzz gets louder. I tried my bass and cord on my other amp with no issues.

Thanks

Rob   

[stingray_65]

HUM
1st thing to do is identify if it is 60hz or 120hz

I plug a cord into the jack and touch the tip. this is a 60hz hum. compare that to the hum you hear in the amp.

60hz hum USUALLY means it is coming from the heaters

120hz hum Usually the power supply.

after you ID the hum you can go into further troubleshooting from there.

Ray

[PRR]

> when I touch my guitar toggle switches the buzz gets louder.

The amp isn't grounded. Un-plug from wall. Check the Ohms from guitar plug sleeve to wall-plug ground (U) pin. Better be dead-Zero. If not, find where a ground is not connected.

Oh. KoC has that ground-lift. Put it on "Not Lift" (switch closed) or try both ways.

[Bub]

Thanks PRR,

I did what you said to all four jacks and got 0 ohm's. When I built the amp I didn't install the ground lift, instead I followed Doug's grounding method and ran all grounds to the PT bolt including centre tap. I hooked the battery up to the heaters again and the hum is still present. I checked all four input jacks again to make sure everthing is correct and they check out. I did the test stingray_65 recommended and by touching the end of the guitar cord and the hum appears to be the same. I checked board grounds to PT bolt and get 0 ohms. Don't know what to do next. Everything sure points to a ground issue but I'll be dammed if I can find it.

Thanks

Rob

[Bub]

The first four caps are on one ground buss, the remaining 7 on the other and my third ground wire is attached to the first cap of the bias circuit, I hope this is correct.

[67polara]

This might be a stupid question but do you have a computer in the room with you that is on?  I notice when my computer is on I get a hum and when I turn it off it goes away.  Just a thought.  I guess what I am saying is maybe the hum is from something out side your amp.  Try moving the amp to a different room and see if you still have the problem.

Tony

[Bub]

Thanks for the tip.

I did have my laptop on the bench and learnt that lesson a couple of days ago, it did contribute a very small amount of hum. Since then I have turned off everything including my beer fridge. I also tried another outlet that I know is on a separate breaker. At one point I had a candle lit.

Thanks

Rob

[67polara]

It was just a thought sometimes something right in front of you can cause you a lot of work for nothing.  Guess you can figure out how I found the computer was causing the noise in mine LOL.


I'm not understanding this.

My humble suggestions:
I'm not sure of the presence layout or values and to each their own, but - NFB is there whether you want it or not (despite the presence control network). This can screw up & strangle your tone, decrease your gain, and cancel even order harmonics right off the bat. At the very least you could make it switchable until you're sure it's wanted? Lift that 33k feedback resistor where it connects to the 10k/100n point and then ground those two. This will get rid of the NFB and then listen to your amp's NATURAL tone before you make further adjustments in this area.

I'm kinda dumb but could someone draw me a schematic of what he just said please.

Tony

[Bub]

Hi Tony,

There's a schematic posted a couple of posts up. If you look at V3, you will see a 100n cap coming from pin 2, it connects to the 10k resistor, ground at that point, disconnect the 33k resistor and 100n cap to the left. Hope this helps.

Thanks

Rob

[Danskman]

BEWARE, Bub!

!! DON'T EVER unplug the beer fridge!! Doing this can seriously alter your health  

Ok, I'll stop there...
You are facing a big problem with that hum... You test your axe and its cable, OK. You checked all the appliances around your bench, OK. You checked heaters with a battery, OK, Jacks are OK. All is right, but you still get hum.
What is intriguing for me, is the fact that you become an antenna when touching metallic parts on your guitar. Whenever I got that problem, either it was a bad ground on my axe, or my input jacks were defective or badly grounded. It seems that as you checked your input jacks out of the chassis with their own ground wire, it shouldn't be that. Did you checked them one by one, disconnecting each other?
What you could do is try to separate the preamp grounds from the high power grounds, connecting them (preamp grounds) on the chassis, near the input jacks. All other grounds (PT CTs, B+ & PI filter caps, bias filter cap, output tubes grounds) should stay on the PT bolt.
I hope it can help... As we say in french, it's a "cas d'école" !!
Good luck,
Sincerely,
Danskman

[Bub]

Thanks Danskman,

I plugged it back in, I started to get the shakes.
The way V1 & V2 are grounded is all four grounds are tied together and attach to the ground wire from the input jacks which is attached to a main buss for seven 22n, 450V caps. If I understand you correctly, I think I'm partly there. I will separate tube and input jack grounds from the buss and try a separate wire to PT bolt or try it through the chassis. I am going to try one jack on each triode. I was thinking of disconnecting the ground for one triode and trying that. Is there a chance I over did it with shielded cable and have a capacitance issue?

Thanks

Rob    
 

[67polara]

OK, that is what I thought but then it said ground both points and I was wondering if he meant the nfb also and that didn't sound right.

Tony