Newbie questions on AB763

[sluckey]

You shouldn't have to lift the board very much. I suspect the bad turret is touching something under the board, something like a screw or maybe a pinched wire. It should not touch anything. How tall are the board standoffs?

[lpresnall]

Standoffs are 1/4"...I lifted the entire board and shimmed it up...rechecked and still read 1.1 ohms on the bad pin 5...looking with a dental mirror I see a couple of "globs" beneath a 470 ohm turret and another on the "north" side of the board...

[sluckey]

1/4 inch standoffs are too short. You need at least 1/2" to provide clearance for the transformer wires.

Follow the white wire that connects to the bad pin 6 back to the board. Unsolder the wire at the board. Recheck the resistance between the bad socket pin 6 and chassis. What do you have now?

[lpresnall]

ok...i may have to cut the wire during a commercial...get the reading...report back.....then pick up in the morning...wife is wanting attention...

[sluckey]

Rather than wait for another commercial I'll tell you where I'm headed with this check. When you cut the white wire at the board recheck pin 6 resistance to ground. If it still reads 1Ω then you likely have a short between pin 6 and pin 7 on the socket. If you no longer read 1Ω from pin 6 to chassis, then the short is at the board turret, either underneath or on topside. Either way you should be able to fix it on your own at this point.

I'll check back in sometime tormrrow to see how you did.

[lpresnall]

Rather than wait for another commercial I'll tell you where I'm headed with this check. When you cut the white wire at the board recheck pin 6 resistance to ground. If it still reads 1Ω then you likely have a short between pin 6 and pin 7 on the socket. If you no longer read 1Ω from pin 6 to chassis, then the short is at the board turret, either underneath or on topside. Either way you should be able to fix it on your own at this point.

I'll check back in sometime tormrrow to see how you did.

Awesome!  Thanks!  From the wife too!

[lpresnall]

OK, "0" ohms from pin 6 to chassis...so the short is likely on the board?  I'll check it more thoroughly in the morning...don't have to leave until the afternoon...thanks for talking me thru this!

[sluckey]

OK, "0" ohms from pin 6 to chassis...so the short is likely on the board?

No, read what I said.

[lpresnall]

Ok, I left out the word, "turret"... ...I meant to verify that the short would be the turret itself with the "0" ohm reading?  Do you think it'd be possible to reflow and remove the solder from the offending turrets without unsoldering the caps and removing the board?  If I do need to remove the board to replace the standoffs with something taller I'll just bite the bullet and do it all next time I can get in the shop.  Thanks for sticking with me on this...I know it's irritating for someone who's knowledgeable to have to explain to a kid why you don't eat the paste.   

[sluckey]

So you cut the white wire at the board. Then you still measure zero ohms resistance from the bad tube socket pin 6 to chassis. That means the short is on the tube socket (or the white wire that's dangling in the air). Look at the socket. Does pin 6 touch pin 7 in any way?

[lpresnall]

No, the pins aren't touching...I checked that last night...I was thinking from your post that if I read anything other than 1 ohm that the short was on the board...I ended up unsoldering the white wire at the turret and making sure that it was not touching anything else when I took the reading...could I somehow have a bad tube socket?

[sluckey]

Cut the white wire at pin 6 of the tube socket. Now you should simply have a 1.5K resistor between pin 5 and 6 and nothing else on those pins and nothing accidentally touching those pins. Measure the resistance from pin 6 to chassis. If you still have zero ohms the socket is bad.

[lpresnall]

Ok, will do...I'll report back shortly.

[SILVERGUN]

If you still have zero ohms the socket is bad.

Make sure you are not reading an "O"pen circuit .....(as in 'OL' on my Fluke---Over Limit)

One way to be sure is to set the meter for a continuity beep (if it has this feature), and if it beeps, then your zero ohm reading is correct.

If you touch the 2 probes together it should beep,,,,if you touch pin 6 with one probe and the chassis with the other it should NOT beep

[lpresnall]

Yep, still getting the "beep" after replacing the tube socket...

[lpresnall]

Forgot to say that I replaced the 1.5 along with the socket...bummer, I thought we (by we, I mean sluckey) were onto something!   

[Willabe]

Looking at the 2 power tube sockets mounting bolts in the picture that you posted, it looks like are wired differently?

Or are they 2 different sockets with respect to the pin out and the mounting bracket?


http://el34world.com/Forum/index.php?action=dlattach;topic=15979.0;attach=44010


             Brad     

[SILVERGUN]

Yep, still getting the "beep" after replacing the tube socket...

If you put a new socket in, with no tube loaded in it, and didn't connect any wires, and took a measurement from pin 6 to the chassis, you should not get a beep.
If you get a beep, then you might be the first guy in history to have 2 bad sockets in a row.

Is this stuff starting to make any sense?

ALL of the tube pins in a new socket should be electrically isolated from the chassis.

[lpresnall]

Ok, will give all this a go when I hit town again...Silver, at this point I'd totally believe I got 2 bad sockets in a row...this thing just won't get finished!

[lpresnall]

Looking at the 2 power tube sockets mounting bolts in the picture that you posted, it looks like are wired differently?

Or are they 2 different sockets with respect to the pin out and the mounting bracket?


http://el34world.com/Forum/index.php?action=dlattach;topic=15979.0;attach=44010


             Brad     

Brad, I'm not following your question about the "different" sockets...(most likely my fault and nothing to do with your question)...

[Willabe]

Form your picture it looks like the 2 power tube sockets have their mounting brackets in a different position with respect to the sockets pins #'s.

If so I'm wondering if the 1 of the sockets is wired wrong?


              Brad         

[lpresnall]

Form your picture it looks like the 2 power tube sockets have their mounting brackets in a different position with respect to the sockets pins #'s.

If so I'm wondering if the 1 of the sockets is wired wrong?


              Brad     

Oh, ok!  Gotcha!  Well, I ID'd the pins before I stuck 'er in there but I'll re-check given the way this project has gone.  Thanks!

[Willabe]

Use the 'key' way slot in the center hole of the tube socket to figure it out.


              Brad   

[lpresnall]

Use the 'key' way slot in the center hole of the tube socket to figure it out.


              Brad   

Ok, tube socket's in and pins were ID'd and wired properly....next move?

[SILVERGUN]

What ever became of the "globs' of solder under the board...I still think that is where your short is

You're gonna have to get the board all the way off of those wires and find where your problem is hiding....unfortunately, no real shortcut

There's no other logical answer for why your bias voltage is disappearing....it MUST BE an issue where those wires pass under the board

There are no gremlins, secrets, blackholes or mysteries...if the voltage is on the board and then doesn't make it to the tube socket, you've found the problem.
Now you must fix the problem.

You'll get it,,,,hang in there 

[lpresnall]

What ever became of the "globs' of solder under the board...I still think that is where your short is

You're gonna have to get the board all the way off of those wires and find where your problem is hiding....unfortunately, no real shortcut

There's no other logical answer for why your bias voltage is disappearing....it MUST BE an issue where those wires pass under the board

There are no gremlins, secrets, blackholes or mysteries...if the voltage is on the board and then doesn't make it to the tube socket, you've found the problem.
Now you must fix the problem.

You'll get it,,,,hang in there 

Thanks for the encouragement Silver!  I fly out again tomorrow for 4 days, but I'll unsolder enough to lift the board and get the globs and check the OT wires when I get back...man, I was really hoping for a bad tube socket.  I just can't fathom why I get voltage all the way to the south end of that 220K and it stops there of all places...happy 4th to you and all on the forum!

[SILVERGUN]

I just can't fathom why I get voltage all the way to the south end of that 220K and it stops there of all places..

It doesn't stop.....it goes to ground,,,,because of an unexpected short, which is just the touching of 2 conductors that shouldn't be touching
When you find it, and you will,,,,your eyes will be opened forever...it is self explanatory

happy 4th to you and all on the forum!

And the same to you Larry.....you are obviously a nice guy and a good sport, and good things WILL come to you.........amp wise, eventually 

[lpresnall]

I just can't fathom why I get voltage all the way to the south end of that 220K and it stops there of all places..

It doesn't stop.....it goes to ground,,,,because of an unexpected short, which is just the touching of 2 conductors that shouldn't be touching
When you find it, and you will,,,,your eyes will be opened forever...it is self explanatory

happy 4th to you and all on the forum!

And the same to you Larry.....you are obviously a nice guy and a good sport, and good things WILL come to you.........amp wise, eventually 

Thanks man!  There are great lot of patient guys on this forum and I really appreciate everyone putting up with me.  I WILL find this thing indeed!  It's personal now!

[lpresnall]

The sad saga continues...removed the board, cleaned the bottom so that it could've starred in a diaper commercial, and wired 'er all back up...STILL no voltage at the bias....

[Willabe]

If you lifted the board and found NO short and you have -bias at the 2 points in the red circle (marked in attached photo) and you have -bias at the 2 points in the blue circle and you have -bias in the 2 purple circles..............

Then it has to be the wire from the purple circle going to the power tube socket. The wire has to be broken inside of it's insolation.

(Or, it's shorting to the chassis or something underneath the board that you can't see when you install the board.)


                  Brad

Edit; I forgot to post the picture.     

[lpresnall]

Yep, even raised the board up another 1/4" from where it was...I'll check the wire Tuesday...(that's my wire checking day  ).

[Ed_Chambley]

1/4 inch standoffs are too short. You need at least 1/2" to provide clearance for the transformer wires.

Follow the white wire that connects to the bad pin 6 back to the board. Unsolder the wire at the board. Recheck the resistance between the bad socket pin 6 and chassis. What do you have now?

Dang, you mean I have to change all the 1/4 standoffs I have used on builds and mods?


Just thought I would let you know I am getting better.

[lpresnall]

Ed,  I'm at 1/2" now...I'm prepared to go up to a foot if it'll solve my problem...I cannot at this point, remain optimistic...gonna try the wire itself next week when I hit town...

[Ed_Chambley]

Ed,  I'm at 1/2" now...I'm prepared to go up to a foot if it'll solve my problem...I cannot at this point, remain optimistic...gonna try the wire itself next week when I hit town...

I was joking with Sluckey.  You will get it.  I have made a lot of mistakes like you have.  I have learned a lot the hard way, but theses guys always dig me out like baby Jessica.


Hang in there.

[SILVERGUN]

I cannot at this point, remain optimistic...

No, no, no....YOU have to remain optimistic.

Positivity breeds positive results.....there is nothing standing in your way of getting that bias voltage to those pins other than your own doubt.
Stop doubting that it will ever work and just do whatever it takes to MAKE IT WORK. 

There is no magic ingredient that you are missing....

If you have to make a small separate bias board just to see it work,,,do it
If you have to run all new wires,,,do it
If you have to lock yourself in a room, and tell your wife you're not coming out until you get it,,,do it.

Don't give up......sluckey is watching.
Success is only a couple moves away.

Give the bias voltage a path and it will follow that path.

[sluckey]

Success is only a couple moves away.

You think? It was determined a month ago that there is a dead short between pin 6 of the offending tube socket and chassis ground. It's hard to believe that he can't find it. I can't help any more without being able to actually touch the amp.

And this is just the first error he's found.

[Ed_Chambley]

Success is only a couple moves away.

You think? It was determined a month ago that there is a dead short between pin 6 of the offending tube socket and chassis ground. It's hard to believe that he can't find it. I can't help any more without being able to actually touch the amp.

And this is just the first error he's found.

Sometimes you just have to get out the solder sucker and clean up everything and return with a methodical build.


You rarely "get lucky" in amp building.  I made the mistake of saying it was easy to build one the other day and of all people, my wife interrupted who I was speaking to and said about 15 things you have to do to get a clean build, and she has never built one.


However, you must make mistakes and learn from them and the one day, BAM you understand how an amp works.  If I had all the money invested, I think I would punch a new chassis.

[SILVERGUN]

Success is only a couple moves away.

You think? It was determined a month ago that there is a dead short between pin 6 of the offending tube socket and chassis ground. It's hard to believe that he can't find it. I can't help any more without being able to actually touch the amp.

And this is just the first error he's found.

I'm still attempting to perpetuate the misconception that we have unlimited patience....

I imagine that within that 1 month period he's only spent a few hours on it.....the marriage is more important than his electronics career.

I also blame the tube socket pin short to a mis-read on his part.......since he replaced the socket, I'm going to give him a second chance.

I completely missed the fact that we you had determined it was a short on PIN 6....I (and I'm sure he) was still thinking about pin 5

        
Hold on, whilst I create more patience...........
        

[sluckey]

Think about what's connected to pin 6. There's a 1.5K resistor that connects to pin 5. There's a white wire that connects back to the board. That's it.

[SILVERGUN]

Think about what's connected to pin 6. There's a 1.5K resistor that connects to pin 5. There's a white wire that connects back to the board. That's it.

LARRY...don't read this.....
((sorry sluckey, I was picturing "my" setup, where I'd run the screen res. from pin 6 to pin 4))

OK, back to your regularly scheduled programming...

Larry, pin 6 is just a tie off point....it is not internally connected inside the tube....it's just a place to solder a resistor to and run a wire from.

And this is just the first error he's found.

Larry,,,this is our big concern....
Lets say you do get the bias voltage to "show up".....
The next wave of (inevitable) troubleshooting will be much more difficult than this was, due to the fact that the rest of the circuit is much more involved than this very simple bias circuit.

I think we are suggesting that it might be IS in your best interest to find someone locally who can help you get this thing up and running.
It could take someone an hour,,,
OR take us four (or forty) more pages of walking you through troubleshooting.....

?

[Willabe]

Forgot to say that I replaced the 1.5 along with the socket...bummer, I thought we (by we, I mean sluckey) were onto something!   

Use the 'key' way slot in the center hole of the tube socket to figure it out.

Ok, tube socket's in and pins were ID'd and wired properly....next move?

If these reply's are correct and he has -bias in ALL the circles in the drawing in reply #179, then it has to be a broken power tube grid wire.


                         Brad   

[SILVERGUN]

Eastwood- A Man's Got to Know his Limitations

[Willabe]

I'd still change that wire before I thru in the towel.


                Brad     

[sluckey]

If these reply's are correct and he has -bias in ALL the circles in the drawing in reply #179, then it has to be a broken power tube grid wire.

He doesn't have neg bias in ALL those circles. He has a dead short in one of those purple circles. So he's missing voltage in that circle. He's also missing voltage at the bottom end of one of those 220K resistors. Pin 6 is shorted to ground. Bottom end of one of the 220K resistors is shorted to ground. The bottom end of one of the coupling caps is shorted to ground. The white wire is shorted to ground.

He continues the saga on Thursday but he wont actually check anything until next Tuesday. I don't think I'll live long enough to see the solution.

[Willabe]

That's a LOT of shorts.       (I thought he cleared those up?)

I don't think I'll live long enough to see the solution.

             


 

[sluckey]

No, it's only one short. All those items I mentioned are connected together.

This morning I got a big cup of coffee and read the entire thread again. Monday is the first anniversary of this project. Maybe have a party? 

[Willabe]

No, it's only one short. All those items I mentioned are connected together.

             

[SILVERGUN]

David Soul - Don't Give Up On Us

[lpresnall]

I get it guys, the project's dragging on...a job change to a new airline and the death of my youngest daughter in november slowed me a bit, I admit.  I've tried to get the amp to a local tech but believe it or not, he's slower than me...there's stuff in his shop that's been there for 5 years...if the amp was for me i'd have put it on a shelf a while ago but it's for a church kid who was living with us temporarily when we started it.  I'm about ready to give him one of the working amps I've already built (yes, I really did finish a couple!)...I appreciate your patience but it sounds as though I've used it up...thanks for all the help tho.

[Willabe]

Larry so sorry to hear about your daughter. We had no idea. I can't imagine losing a child. And under your circumstances I can see where it's been extremely difficult to focus on this amp. 

I've seen Sluckey and SG and others say on line for hours to all day or till it was tracked down and fixed. I believe we still would like to see you through but it's been a little hard going about it this way. I still think you can fix it.

But with saying that and hearing your heart for the young man in your church even when your heart must be broken and your still trying to persevere through it all is quite amazing.

I live just NW of Chicago and would be more than willing to try and finish the amp for you at no charge if you pay for the shipping. I have no idea where your located and if that would work for you?

Where are you located? Maybe 1 of the guys here on the forum lives close to you and may be able to help?


                     Brad