Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: lpresnall on August 29, 2013, 06:31:17 pm
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Ok, at Brad's prompt I'm asking this here as well:
Heater wiring is done...board is in and I got the bias pot in the mail today (thanks Doug!!). I have a new set of questions...I've never wired 12A jacks before and my plan is a single input jack and two outputs with no impedance selector. How should I proceed with this? The common hookup page on the forum has a picture of how the resistors go in, but not any actual wiring (sorry for my being somewhat of a moron...maybe if I built the same circuit twice I'd know something).
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He started out looking for a BOM and it kept growing so......
Here's a link to where it started for back round info, around reply #9;
http://www.el34world.com/Forum/index.php?topic=5513.0 (http://www.el34world.com/Forum/index.php?topic=5513.0)
Brad :icon_biggrin:
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Ok, at Brad's prompt I'm asking this here as well:
Heater wiring is done...board is in and I got the bias pot in the mail today (thanks Doug!!). I have a new set of questions...I've never wired 12A jacks before and my plan is a single input jack and two outputs with no impedance selector. How should I proceed with this? The common hookup page on the forum has a picture of how the resistors go in, but not any actual wiring (sorry for my being somewhat of a moron...maybe if I built the same circuit twice I'd know something).
If I understand, you want to have 2 speaker jacks reflecting 2 impedance. Your OT have separate taps? If so, it is simple as using 2 non-grounding jacks. Select which tap you want for each and solder the common to both jacks.
But, if you only want one output jack with 2 impedance, I cannot tell you how to do this without a switch.
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Got it! Thanks Ed.
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Back at the amp for an afternoon. Spent a while connecting tubes to board, and now have a question or two regarding power, stby, and what the heck the yellow power transformer wires are on the hoffman ab763 lite. I'm using a classictone and it has on yellow 5VAC wires. I'm using a GZ34 tube rec as well. The power and stby switches are different than the DPDT ones I used on the ax84 amps and I think I've got it, but not sure. See pics. Thanks again for putting up with me while I learn my ABC's.
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A few things you must take care of...
1. The red/blue wire from your PT is connected to the wrong turret. Move it one turret to the left right, i.e., to the top of that black resistor in your pic.
2. Since you have no yellow 5VAC wires on your PT you cannot use a GZ34 rectifier. Your choices are to get the correct PT or plan on using a solid state rectifier. Weber has one that will plug into the rectifier socket.
3. You have a mess of wiring between the tubes and the board and that will likely give you a lot of grief. The reason for mess is because you installed the tube lineup backwards. The big tubes go on the end of the chassis near the PT. The little tubes go on the other end of the chassis. Look at the layout.
4. Your choke is shorted by the onboard jumper between the two turrets that the choke is connect to. Snip the jumper.
Don't plug it in just yet!
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I looked at the board pic, input end, before I had coffee. I thought I was still asleep. :icon_biggrin:
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A few things you must take care of...
1. The red/blue wire from your PT is connected to the wrong turret. Move it one turret to the left right, i.e., to the top of that black resistor in your pic.
2. Since you have no yellow 5VAC wires on your PT you cannot use a GZ34 rectifier. Your choices are to get the correct PT or plan on using a solid state rectifier. Weber has one that will plug into the rectifier socket.
3. You have a mess of wiring between the tubes and the board and that will likely give you a lot of grief. The reason for mess is because you installed the tube lineup backwards. The big tubes go on the end of the chassis near the PT. The little tubes go on the other end of the chassis. Look at the layout.
4. Your choke is shorted by the onboard jumper between the two turrets that the choke is connect to. Snip the jumper.
Don't plug it in just yet!
Don't worry Ed! No plans to plug 'er in anytime soon! Not sure how I missed the red/blue connection - fixed straight away. Have a ss rec in the drawer, check! Noticed the tube lineup after everything was drilled...was trying the lazy way out...never ends well and I should know better...we don't do that in the jet where I work! I suppose I could flip the board end for end, but then that'd cause other issues...do you think the long wires will cause noise? Didn't know what to do with the choke...first one I've ever dealt with...jumper snipped! Sorry for the severe cluelessness...the ab763 is brand new (and probably too complex) for me at this stage of the game, but it's for a buddy and I promised to give it a try...I'll report back before applying power to anything, and thanks for the advice!
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I looked at the board pic, input end, before I had coffee. I thought I was still asleep. :icon_biggrin:
Yep, I'd like to blame lack of coffee on this too, but won't stand up in a court o' law! :icon_biggrin:
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Ok, it's clear what I did now...I laid the layout on the TOP of the stinkin' chassis and drilled, not thinking that when I turned it over it'd be backwards...question is, should I just buy a new chassis, start over and get everything in the proper way so as to have short wire runs between board, tubes, transformer and the like?
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If it were my chassis, I would get a piece of aluminium that would cover the existing miss drilled tube socket holes, cut out the area around the miss drilled holes and attach it with pop rivets and redrill the tube socket holes correctly. Might not be pretty but would be cheaper than buying a new chassis. Punky
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pk's idea is a common fix and guys do that all of the time when re-using old chassis where the holes don't line up...
Since this one is for your friend, show it to him, and be honest and see what he wants you to do....
Also, since you've already determined that you're not going to use a tube rectifier, you don't have to worry about that socket,,,and can just wire up a small board for that (so thats 1 hole down)
2 of the other 4 holes you can enlarge to go from 9 pin to 8 pin,,,,and then you could use these adapters (pic) to change the remaining octal hole sizes back to 9 pin
It really just depends on how important the cosmetics are to you and your friend :icon_biggrin:
Weber sells these adapters, plus some hole covers on this page: https://taweber.powweb.com/store/chassis/chord2.html
EDIT: One other thing....If you were leaving the rectifier octal socket in place, you should go back and twist those (2 red) wires tight, just like the heater wires....if you do wind up moving it, just twist em tight from the PT to your new rectifier location..........same concept with ANY AC inside the amp
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Punkykatt's suggestion is a good one. Here's another alternative...
http://www.tubedepot.com/sk-829.html (http://www.tubedepot.com/sk-829.html)
This adapter will allow you to put a 9-pin tube socket in an 8-pin octal hole. You can easily enlarge the little tube holes with a unibit.
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Ok, once again guys thanks for the quick replies. Cover/adaptor thingies ordered and will get all this fixed next week. I'm sure I'll be back whining about something else. Man, jets and guitars are so much more comfortable than this amp-building thing! :w2:
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Those 9-pin socket in 8-pin hole adapters....at $10 each, by the time you need a few of those, you could be better off buying a new chassis. That's pretty pricey. Even the $5 ones...I appreciate sometimes you want/need a bolt-in solution, and it would not be easy to make those little adapters if you didn't have the tooling, because it's not easy to drill (or even punch, without deforming) big holes in small pieces of metal.
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I'm pretty sure he only needs two. Think about all the work that has already gone into that blank chassis.
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Here's how I handled this on a CONN chassis > future home of a Princeton Reverb I am building. It *looks* like "the big holes" (eg; for the 6V6 tubes) are properly located at the power transformer end, but a look at the underside of the chassis will show that the big tubes (there were 4 qty 12V6) originally were actually at the *wrong* end of the chassis. Also...there were enough holes (for can caps, for top-mounted volume controls, for preamp tubes mounted off-axis from the "back-row" deal a la Fender) that I wanted them covered up or otherwise dealt with.
(http://i172.photobucket.com/albums/w32/ttm4/PILOTSA-232_zpse3635022.jpg)
(http://i172.photobucket.com/albums/w32/ttm4/hamlin_piano014_zps21a65ac7.jpg)
Another conundrum I am dealing with on this conversions is: Note (from the cutout) that the power transformer (should I choose to use the original, which is electrically, but not mechanically a good choice) places the footprint of the PT right at the corner of the chassis. This is a problem, for me, because ultimately, I would like to find a dead solid state amp and implant this chassis into same, tubes upside down. I do NOT want to build a 2-piece amp...I've considered a Marshall head approach..but I want a one piece combo style amp. It is a problem because for a combo amp, it is a necessity in almost all cases to mount any and all surface components at least 7/8" back from the front edge of the chassis...otherwise, the transformer would interfere with the baffle board. Thus, the (successful) search has commenced for a different power transformer. I COULD move the original laydown transformer maybe one inch back. But this would place the output tubes about 1/8" away from the transformer. Not desirable. Or, it would force me to move the two power tubes towards the preamp tubes...using up spaces (for 9-pin tubes) I want to keep open for future experimentation.
I bring this up to show how one mechanical aspect of re-using this particular chassis forced a number of resultant decisions one way or another.
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How about this style cabinet?
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I couldn't open that, Punky, can you post an alternate link so's I can get a closer look? Thank you!
No innate objection to that style, other than pure and rampant cheapness.
My view of things is several fold:
The purchase or build of an esthetic and reasonably rugged cabinet for a 1-12" amp (roughly the size I am talking about) is almost a $200 affair to either make or buy. Tolex, handle, corners, labor time. Or, buy somewhere...$200+/- with shipping.
I can afford the $200 just fine. But when I can buy a complete Peavey Valveking for $200 used which is a darn good amp if you chuck the ROTTEN speaker that comes with it and throw in one of your choice....(meaning, add $100 to the $200)
It is pretty darn difficult to buy parts for and build an amp for less than what you can buy it for, and while I appreciate the labor of love type of thing....it would be hard to build a Deluxe Reverb reissue properly cabinetted for the $600-$650 I can buy them for (in cherry used condition) without much effort. Or a Peavey VK. Add up the parts cost.
My idea is to find dead solid state amps for $20 and chuck the chassis completely, or, if I am REALLY lucky, be able to reuse the sheet metal and maybe the knobs. The last time I got onto this jihad, I found a FREE Peavey Bandit that was supposedly dead, but I got it home and it WORKED...so I have a hard time ripping it apart.
Anyway, I appreciate the suggestion and I'll eagerly look at it. Thanks again! Bottom line: I like the idea of buying cheapo DEAD solid state amps for $20 and swapping in a tube amp chassis. I would bet you that if you walked into 100 music stores, you would find 60+ of them with a dead SS amp they could not fix you could buy for....next to nothing.
Add: Another thing, is that the present layout of my ex-CONN chassis favors upside-down because the controls would be in "normal" Fender order, input jack > reverb left to right. (No trem going into this one)
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Yep, I bought 2 of the $5 ones and if they work well I'll go that route. If not, then a new chassis is only $20 to the door. That won't break me, I mainly just want to avoid drilling a whole new chassis from square 1! I'm building this for a worship leader kid and am footing the bill as kind of a seed into what he's doing. I just can't believe I got myself into this by not realizing that the layout on top of the chassis would make for a backwards build. :BangHead: Lesson learned!
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Ok, so the adapters came in from Weber and didn't fit. They have a 3/4" hole and the Unibit didn't touch them when I tried to enlarge them to 7/8". So I improvised and now have the sockets in their proper place (more or less). Better words would be that they are in the proper lineup L-R. Anyway, here's where I am now - I have a question regarding the solid state rectifier...I put a pair of diodes in as indicated in the pic and don't know if it's right. Also, does the wiring change on the socket now? And the wiring on the layout shows the greens out of the transformer to the lamp and nothing else. I took the lamp wires to the lattermost power tube as well? And the pic of Doug's AB763 board has a pair of wires going to the pair of 100 ohms on the right-most side of the board, thereby confusing the crap out of me. I suppose it's just my lack of understanding of what does what in this circuit. Any wisdom is greatly appreciated!
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And now, the other two pix: :think1:
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"Anyway, here's where I am now - I have a question regarding the solid state rectifier...I put a pair of diodes in as indicated in the pic and don't know if it's right. Also, does the wiring change on the socket now? "
The wiring on the socket does not change, per se, BUT, the 5xx tube socket terminal where the two cathodes (bar ends) of the diodes come together within your adapter HAS TO be the terminal which your wiring says is the highest B+. (Much easier done than said, sorry)
When you have a 5Y3 or 5U4 rectifier tube in the rectifier socket, you can pull B+ from either pin 2 or pin 8. Does not matter. If you wired the thing planning to use a 5Y3, you did not care which pin was the raw B+ source. If you used a 5AR4/GZ34 you SHOULD use pin 8 ("cathode and filament") and not pin 2 ("filament") but in practice it does not matter much. (It is still wrong to pull B+ from pin 2)
Now, you make a substitute plug-in deal from an old octal tube base with two diodes in it. Fine. The cathodes (bar ends) of those 2 diodes have to junction on THE SAME PIN that your wiring says is your B+ source. If you used a 5Y3 and pulled B+ from pin 2, but your diodes junction on pin 8, you'll get big fat nada for B+.
Surprised as to those adapters you bot. I have never seen a 9-pin tube socket that did not want a 7/8" hole. Even wafer sockets.
"And the wiring on the layout shows the greens out of the transformer to the lamp and nothing else. I took the lamp wires to the lattermost power tube as well?
Yes.
"And the pic of Doug's AB763 board has a pair of wires going to the pair of 100 ohms on the right-most side of the board, thereby confusing the crap out of me. I suppose it's just my lack of understanding of what does what in this circuit. Any wisdom is greatly appreciated!"
The dual-100-ohm (midpoint to ground) is the fabled "synthetic center tap" that is in 98% of cases required to eliminate hum from a tube amp whose power transformer does not have a center tap (which would be grounded and which would eliminate the need for the 2 100 ohms) on the heater winding. Those 100 ohm resistors can be mounted literally anywhere. Fender usually mounted them on the front-panel pilot light assembly. I have never especially liked that but it is not wrong and there are a million Fender amps wired that way, with that particular placement of the two 100 ohm R's.
I haven't looked at Doug's layout drawing, but it wouldn't be the first time that filament wiring is left out from a drawing...because it is assumed, to some extent, in tube work. The assumption is made that the heaters are wired up and the tubes lit up, or you're going to suffer some form of performance deficiency, to put it mildly!
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1) I have a question regarding the solid state rectifier...I put a pair of diodes in as indicated in the pic and don't know if it's right.
2) Also, does the wiring change on the socket now?
3) And the wiring on the layout shows the greens out of the transformer to the lamp and nothing else. I took the lamp wires to the lattermost power tube as well?
4) And the pic of Doug's AB763 board has a pair of wires going to the pair of 100 ohms on the right-most side of the board, thereby confusing the crap out of me. I suppose it's just my lack of understanding of what does what in this circuit. Any wisdom is greatly appreciated!
1) The pic looks correct if you're sure that one diode is coming from pin4, and the other from pin6, and they meet at pin8........EXCEPT, that we suggested that you put 2 diodes in series on each leg
2) No,,,,,,the socket wiring will stay the same,,,,and that's the point of a "plug in replacement"
3) That's OK,, the green heater wires go to the lamp and then off to the tube sockets......some things in layouts and schematics are taken for granted
4) Those two 100 ohm resistors form an artificial center tap for the 6.3vac winding (to reduce hum)........some 6.3 windings come with a center tap and most don't.....as long as you put one resistor from each leg to a common ground point, it doesn't have to be on the board......you could just put a ground tab up near the lamp and have them there.
11teen was responding while I was typing,,,,so this is a duplicate answer,,,but I'll post it just in case my wording helps his wording make sense....
Hang in there :thumbsup:
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No problem! I'll take all the answers I can get! I have to be told a lot of things twice :think1: Ok, so I can add the wiring from the lamp to the 100's then? And add an extra pair of diodes to the ss rec plug -in? I'm going much slower on this one than the ax84's and the 18watt TMB...those seemed really fairly easy. I'm not in a hurry, just want to get 'er right. I took a break and made the head cab and am working on the speaker cab just to be doing something which comes second nature. Then I suppose the caps, jacks, pwr, and stby will finish the amp. I just hope I don't have a month of troubleshooting when I turn it on! Thanks again for all the replies. This forum is awesome! :icon_biggrin:
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Surprised as to those adapters you bot. I have never seen a 9-pin tube socket that did not want a 7/8" hole.
All of my 9-pin sockets use a 3/4" hole. Doug sells a couple different sockets that fit 3/4".
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I couldn't open that, Punky, can you post an alternate link so's I can get a closer look? Thank you!
Eleventeen, can`t post another link. Look at a Matchless Avalon 30 combo amp. The cab has two sections one for the speaker and one for the head.
Punky
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Ok, found an hour to get in the shop today...below are a couple of shots of the caps installed and the resistors soldered in at the input jack. New questions on account of I'm not bright...do I need the shielded wire from the input to the tube? Do I take the ground running across the pots thru the input jack and to the 1.5/22K lug at the leftmost board? And I'm a little lost on the pwr/stby arrangement...I'm not sure about the black and the white wire out of the transformer and where the pwr/stby switches fit into the flow of things...I don't have a really detailed schematic...mainly building from the Hoffman lite layout/schematic hybrid...as always, thanks for the assistance!
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What's the voltage rating on those four electrolytic caps between the board and that ground buss? Sure don't look like they are 400 or 500V caps.
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do I need the shielded wire from the input to the tube?
yes
Do I take the ground running across the pots thru the input jack and to the 1.5/22K lug at the leftmost board?
Not exactly. Terminate the buss at the ground lug of the input jack. Then connect a short wire from the buss to a chassis mounted ground lug near the input jack. Connect another short wire from that 1.5K/22µF to that same ground lug (or to the buss near the input jack).
And I'm a little lost on the pwr/stby arrangement...I'm not sure about the black and the white wire out of the transformer...
I would wire it like this. See pic...
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Awesome! Gotcha on the ground, input, and stby/pwr. Now, I'll have to go and check the caps. I thought they looked small too, but that just shows my lack of understanding of this circuit (as if all my other posts haven't made that perfectly clear!).
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:BangHead: Caps are 50V! I went back and looked at my order and sure enough, although I'd ordered 500's what actually arrived were 50's and I installed 'em without checking. :BangHead: Just ordered the right ones and will get 'em in next week. Delta calls this morning. :think1: Thanks for the catch - I'd have left them right where they were.
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Pop! Pop! Pop! Pop! (REALLY fast!)
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Not sure if you've seen this but there is a ton of useful info on this thread:
http://www.el34world.com/Forum/index.php?topic=3273.0 (http://www.el34world.com/Forum/index.php?topic=3273.0)
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Ok, got it bookmarked! Thanks!
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Ok, here's what I have now...does it look right or am I still off track?
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I'd change the wires on the fuseholder for safety. Put the blue wire on the TIP. Put the black wire one the SIDE.
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Crap! I get that backwards EVERY time! Rest ok?
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I'd change the wires on the fuseholder for safety. Put the blue wire on the TIP. Put the black wire one the SIDE.
Why is this a safer solution?
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Why is this a safer solution?
You want the acv hot on the tip (far/deep end) of the fuse holder so that when you go to pull the fuse with the amp still plugged in, yes you should always pull the power chord from the wall 1st, that it gets disconnected from the acv 1st. Other wise the fuse could still be hot when you pull it by it touching the outside ring on the fuse cap end of the fuse holder. If your touching the chassis or some other ground doing this...... :blob8: :BangHead: and that's if you live. :m19
We all make mistakes and someone could forget to unplug the amp from the wall and get bit real good, 120acv @15 or 20A or 220v and what ever they run for house/building/bar fuse value in EU.
Brad :icon_biggrin:
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Another quick question to demonstrate my density...which is the ground lug on a 3 lug switchcraft 12A? I think that all I have to finish now is the input jack and grounds, and the 4 and 8 ohm speaker outputs and grounds.
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Check continuity with your meter!
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See how dense I am? I didn't think of that! :w2:
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I bet you can tell just by looking at it.
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Well, I can see where each lug corresponds to a cable jack when plugged in, i.e. tip, sleeve...but not what correlates to hot, ground, etc. I've only used Cliff jacks up to this point. See? Dense!
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Don't lose this. :wink:
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Ok, finally back on the AB763 project. (Long story). Anyway, I hooked up the output jacks and made the buss ground/chassis ground connections as well as the shielded from the input jack to pin 2 on the preamp tube. I have a question now as to how the resistors from the input jack wire in. Right now I have a 1000K going from ground to tip and a 68K going from tip to ??? I think this will finish me up if I can get it right...Below is a pic for your perusal...I'll accept any/all advice from you gurus before I throw the switch and potentially burn down my shop...
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I have a question now as to how the resistors from the input jack wire in. Right now I have a 1000K going from ground to tip and a 68K going from tip to ???
It should be wired in series directly from the signal wire of your shielded cable to the grid pin of your first tube stage.....
It's referred to as a grid-stopper, and most guys just solder it right up close on the tube socket pin
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Like this:
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Ok, I'll do it! Rest of the pic look like it'll stay together when I power up?
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Rest of the pic look like it'll stay together when I power up?
I don't want to leave you hanging, but I also don't want to be the guy that "green-lights" your work...
In the end it comes down to your confidence in your own work.....
- Have you done your homework?
- Do you have a current limiter built, and plan on using it on initial startup?
- Do you know what failures could occur?
We all have our own techniques and systems for testing our builds to be safe and prevent damage to components on initial startup....
....my own builds still make me a little nervous, so I always make sure to check separate sections of the whole circuit as I build them (and that works for me)
I wire my heaters first and then install tubes and check that wiring first...
Then I wire my power xfmr secondary to my rectifier and test that separately...
Then I wire my power section, and when I'm ready to power up I use a variac to ramp up the input voltage to feed the new capacitors slowly.....etc, etc, etc
I am a bit of a control freak that way, but that method does take a lot of the mystery out of the inevitable troubleshooting...
Nobody plans on making mistakes,,,but to be honest, I have had at least one mistake in each amp that I have built so far that I have had to troubleshoot....and when you're excited to hear your new creation, that can be a "buzz-kill"...
But you will learn to love the whole experience and expect that your amp wont work when you first fire it up....one of these days I'm going to be pleasantly surprised to take the amp out of standby for the first time and actually have nothing to fix... :icon_biggrin:
Here's a guide that was created to help you in this situation:
http://www.paulrubyamps.com/info.html (http://www.paulrubyamps.com/info.html)
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For those who may not have a variac and are weird (like me) about want to insure filter caps form properly there is very good discussion on the Metro Forum Here:
http://forum.metroamp.com/viewtopic.php?f=4&t=8396 (http://forum.metroamp.com/viewtopic.php?f=4&t=8396)
I believe most people using new filter caps do not concern themselves with this, but it is not a bad practice.
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I think you're ready for the smoke test. During all the following tests be ready to quickly kill the power at any sign of smoke, fire, arcing, explosions, unusual noises, etc. OK, let's go...
Unplug the rectifier and lay it aside for now. Plug the amp into the wall and turn it on. Verify that all tubes light up. Measure the negative voltage on pin 5 of EACH power tube. Verify that the bias pot changes that voltage on pin 5. Adjust for maximum negative voltage on pin 5 and leave it like that for now. If there is a problem with the filaments or the bias, FIX IT NOW. Otherwise, turn the power OFF and proceed...
Now pull both power tubes and lay aside. Plug in the rectifier and turn the power on. Measure the B+ voltages on each of the filter caps. Then measure the plate (and screen) voltages on all the tubes. Start with the power tubes and work your way to the preamp tubes. Voltages will be a bit high since the power tubes are not in the amp. If there's a problem with any of the B+ voltages, FIX IT NOW. Otherwise, turn the power OFF and proceed...
Plug in the output tubes and connect a speaker. Don't connect a guitar yet. Turn all controls to zero. Turn the power on. Look, listen, and smell for any problems. Turn it off immediately if you have any problems. If all is well, plug in a guitar and see if it makes a joyful noise.
There's a 50/50 chance that the NFB will be reverse phase. Squealing or howling are big indicators of this. If so, turn the power off and swap the OT primary leads that connect to pin 3 of the output tubes.
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Thanks guys! I'll get to try all this out today, hopefully. I did build a current limiter and this is the first amp that I haven't taken to a pro to actually power up - hence the apprehension! I'll let you know how it goes.
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I think you're ready for the smoke test. During all the following tests be ready to quickly kill the power at any sign of smoke, fire, arcing, explosions, unusual noises, etc. OK, let's go...
Unplug the rectifier and lay it aside for now. Plug the amp into the wall and turn it on. Verify that all tubes light up. Measure the negative voltage on pin 5 of EACH power tube. Verify that the bias pot changes that voltage on pin 5. Adjust for maximum negative voltage on pin 5 and leave it like that for now. If there is a problem with the filaments or the bias, FIX IT NOW. Otherwise, turn the power OFF and proceed...
Now pull both power tubes and lay aside. Plug in the rectifier and turn the power on. Measure the B+ voltages on each of the filter caps. Then measure the plate (and screen) voltages on all the tubes. Start with the power tubes and work your way to the preamp tubes. Voltages will be a bit high since the power tubes are not in the amp. If there's a problem with any of the B+ voltages, FIX IT NOW. Otherwise, turn the power OFF and proceed...
Plug in the output tubes and connect a speaker. Don't connect a guitar yet. Turn all controls to zero. Turn the power on. Look, listen, and smell for any problems. Turn it off immediately if you have any problems. If all is well, plug in a guitar and see if it makes a joyful noise.
There's a 50/50 chance that the NFB will be reverse phase. Squealing or howling are big indicators of this. If so, turn the power off and swap the OT primary leads that connect to pin 3 of the output tubes.
Ok, turned the power on just now. No bangs, booms, pops, or smoke! That's the good part. Now, the preamp tubes glow but nothing on the power tubes. This is with no rectifier and no speaker load. I made a quick check of the layout against my pin wiring and so far don't see anything out of place. I did however see that my layout has a heavy dot at pin 2 of the rectifier but no wire? I may be misinterpreting what that means, but I have nothing wired into pin 2 there, so....anyway, I'm assuming (perhaps dangerously) that the problem is in the wiring between the 2nd preamp tube and the first power tube? I did see a couple of solder connections at board components that could be better while I was tracing the wiring from the tubes.
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Ok, turned the power on just now. No bangs, booms, pops, or smoke! That's the good part. Now, the preamp tubes glow but nothing on the power tubes. This is with no rectifier and no speaker load.
I'm assuming that you mean the filaments aren't lighting up....check for 6-7VAC by holding your meter leads from pin 2 to pin 7 on the power tube sockets....
without the rectifier tube in there,,,not much else is going on
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Pin 2 on the rectifier is critical...:
when you get that far :icon_biggrin:
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Ok, turned the power on just now. No bangs, booms, pops, or smoke! That's the good part. Now, the preamp tubes glow but nothing on the power tubes. This is with no rectifier and no speaker load.
I'm assuming that you mean the filaments aren't lighting up....check for 6-7VAC by holding your meter leads from pin 2 to pin 7 on the power tube sockets....
without the rectifier tube in there,,,not much else is going on
Ok, I get 6.92VAC on checking pins 2 and 8 together on the power tubes. Not sure what I'm looking at on the rectifier diagram, but that's my lack of understanding...I am using a SS rectifier.
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Ok, I get 6.92VAC on checking pins 2 and 8 together on the power tubes. Not sure what I'm looking at on the rectifier diagram, but that's my lack of understanding...I am using a SS rectifier.
I hope you mean pins 2 and 7
If it is 2 and 8, that would explain why they are not lighting up
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Ok, I get 6.92VAC on checking pins 2 and 8 together on the power tubes. Not sure what I'm looking at on the rectifier diagram, but that's my lack of understanding...I am using a SS rectifier.
I hope you mean pins 2 and 7
If it is 2 and 8, that would explain why they are not lighting up
No, I meant 2 and 7...sorry
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Looking at your rectifier diagram again...are we saying that pins 2 and 8 are jumpered together?
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Looking at your rectifier diagram again...are we saying that pins 2 and 8 are jumpered together?
Sorry Larry,
I'm very busy tonight and wont be able to hold up my end of the deal.....
Pin 2 doesn't get used if you are using a SS rect
One leg of the 5v supply would get connected to it if you were using a tube rect
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Gotcha! I understand life happens! I appreciate all of your input. I leave for 2 weeks tomorrow to train on a new aircraft so I'll be back to the amp and on the board after then. Be well!
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Ok, it's been months and I'm back on this amp. I'm rushing (not a good thing) trying to get it running before I leave again. I get all the way to plugging the SS rectifier in and the fuse blows. I did get a noise thru the speaker before the fuse blew tho...I'm wondering if my rec is ''wired" wrong...by "wired" I mean the pairs of I4007N diodes from pins 8-6 and 8-3...any ideas or am I not forthcoming enough? I can get more readings if need be.
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I'm wondering if my rec is ''wired" wrong...by "wired" I mean the pairs of I4007N diodes from pins 8-6 and 8-3...
Yes.
Pin 6 to pin 8 for 1 diode (or pair in series) and pin 4 to pin 8 for the other diode (or pair in series). Both/all with the band going to pin 8.
Brad :icon_biggrin:
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Thanks! I will re-do it in the morning!
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Ok. Wired diodes into SS rec properly and it didn't blow the fuse this time. Went thru the rest of the procedure recording voltages without power tubes, then with everything in place. Light glow to all tubes, no noise, smoke, etc. Connected speaker, turned power on and went looking for guitar. Returned to VERY bright tubes and then fuse blew. B+ values are 483/483/483/483/467. Pin 1 on the preamp tubes 300 and 476. Pin 3 on power tubes 478/478. Pin 4 478/480. Pin 5 Neg. .05. Was kind of scary seeing all the brightness in the power tubes and I think there was a like amount of heat as well. I don't know where to start looking for the trouble now. Any wisdom from the gurus out there?
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I'm not a guru, but a couple of things;
1. From the voltages you posted it sounds like the tubes aren't drawing any current. (No voltage drop.)
Do you have a light bulb limiter? Any time on a new build for 1st power up you should use it to check for shorts in the B+ power supply (PSU).
Pin 5 Neg. .05.
2. With all the tubes out you need to check for negative DC voltage on pin 5 of the output tubes.
With the amp off and the B+ filter caps discharged take your meter and use your meter probe clips. Clip the negative to chassis ground and clip the positive probe to pin 5, set meter for DC voltage. Now turn on the amp and take a reading. If your amp has adjustable -bias turn the -bias pot kind of slowly from full counter clockwise to full clockwise watching for -bias dcv. Write down both extremes. Then do the same thing for the other power tube socket.
Brad :icon_biggrin:
Edit; added underline.
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Number 1 priority is to fix the negative bias voltage on pin 5 of the output tubes. You say you have neg .05. You should have -30 to -50. Don't put the output tubes in the amp until this is resolved.
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Look at reply #52 from Sluckey, he explained how to 1st start up the amp and to check for -bias dcv.
Brad :icon_biggrin:
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Number 1 priority is to fix the negative bias voltage on pin 5 of the output tubes. You say you have neg .05. You should have -30 to -50. Don't put the output tubes in the amp until this is resolved.
Ok, I feel kind of stupid asking, but if I'm not getting the voltages I need, how do I proceed? The bias pot didn't seem to change anything, but this was with the preamp tubes in. I may've misinterpreted your earlier advice...I'll go back and re-check the readings and report back.
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I'm not a guru, but a couple of things;
1. From the voltages you posted it sounds like the tubes aren't drawing any current. (No voltage drop.)
Do you have a light bulb limiter? Any time on a new build for 1st power up you should use it to check for shorts in the B+ power supply (PSU).
Pin 5 Neg. .05.
2. With all the tubes out you need to check for negative DC voltage on pin 5 of the output tubes.
With the amp off and the B+ filter caps discharged take your meter and use your meter probe clips. Clip the negative to chassis ground and clip the positive probe to pin 5, set meter for DC voltage. Now turn on the amp and take a reading. If your amp has adjustable -bias turn the -bias pot kind of slowly from full counter clockwise to full clockwise watching for -bias dcv. Write down both extremes. Then do the same thing for the other power tube socket.
Brad :icon_biggrin:
Edit; added underline.
Yep, I have the limiter...I'll check the setup again...I had preamp tubes in when I checked the first time.
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Yep, I have the limiter...I'll check the setup again...I had preamp tubes in when I checked the first time.
Number 1 priority is to fix the negative bias voltage on pin 5 of the output tubes. You say you have neg .05. You should have -30 to -50. Don't put the output tubes in the amp until this is resolved.
Ok, I feel kind of stupid asking, but if I'm not getting the voltages I need, how do I proceed? The bias pot didn't seem to change anything, but this was with the preamp tubes in. I may've misinterpreted your earlier advice...I'll go back and re-check the readings and report back.
No need now, do what Sluckey said, fix the adjustable -bias 1st.
Brad :icon_biggrin:
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Ok Brad. Thanks! Just have to figure out why the bias pot isn't having an effect...all of the soldering and connections to and from look proper.
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Just have to figure out why the bias pot isn't having an effect...all of the soldering and connections to and from look proper.
Something's not wired correctly in that circuit.
Brad :icon_biggrin:
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Ok, with no tubes or rec pin 5 on the 6L6's is now "nothing". The 2nd one (blue wire from OT to pin 3) will start at - .030 VDC but then count down to "0" in a couple of seconds. I've traced and re-traced my wiring against the Hoffman Lite layout but can find no mistake...Also, the bias pot still does nothing. Thinking I may've omitted the under board wire from the pot to the 220K resistor I jumpered the points above board, still to no effect. What could be going on here? I'm (as usual) at a loss. Looks like this amp won't be making the trip with me on the 10th.
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Measure the voltage directly across the bias cap. How much?
It's probably time to post some hi rez pics.
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Make sure you didn't put a 470K resistor where you only need 470 ohms
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Ok, I'll look in the morning and get a pic or two posted. Thanks for the replies!
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Well, I had hoped for a simple value mistake on the 470 but alas, it's 470 ohms. I'll post a pic or two so you guys can have a look...don't laugh! :w2:
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Board and wiring
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SS rec
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With no rec, tubes, or speaker connected and the black meter probe to chassis ground I get the following:
(Top view of bias pot, starting with single leg and going clockwise)... - 24.5VDC, - 24.5VDC, - 37VDC
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The board and wiring pic is way too small to see anything clearly....
But, let me ask you this:
Do you have a wire going from the bias pot to the correct spot on the board?...so that the bias voltage is making it to pin 5 on both power tubes?
See [12] on the bias circuit pic I posted above (coming off of the bias pot)...
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I'm not sure what layout you were using but if you were using one that had vibrato,,,,and didn't adjust for removing the vibrato circuit,,,,then that's hao you would have missed this connection...
I have adjusted this layout to show you where that [12] connection needs to be:
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Ok, I'll repost the pic...I got carried away shrinking the size after getting a few "file size" errors when posting. I'll also re-check the bias circuit. There's one under board wire that I thought I could've missed but jumping the connection above board changed nothing. I'm using the layout from Sluckey's thread "no verb/no vibe".
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Bigger pic
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With no rec, tubes, or speaker connected and the black meter probe to chassis ground I get the following:
(Top view of bias pot, starting with single leg and going clockwise)... - 24.5VDC, - 24.5VDC, - 37VDC
What voltage do you get here for the bias tap in the red circle. Will be AC voltage, should be ~60acv.
Brad :icon_biggrin:
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Everything in red must be connected....
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And what AC voltage do you read in the blue square?
Brad :icon_biggrin:
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With no rec, tubes, or speaker connected and the black meter probe to chassis ground I get the following:
(Top view of bias pot, starting with single leg and going clockwise)... - 24.5VDC, - 24.5VDC, - 37VDC
What voltage do you get here for the bias tap in the red circle. Will be AC voltage, should be ~60acv.
Brad :icon_biggrin:
54.5VAC
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53.7VAC 0n the middle (connecting wire) of the blue square.
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When you say, "everything in red must be connected" do you mean to each other as in, underboard?
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54.5VAC
Ok, that's pretty good.
What about the blue square now.
Brad :icon_biggrin:
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When you say, "everything in red must be connected" do you mean to each other as in, underboard?
Inside red circles must be connected to each other....
And bias pot must be connected as marked..
You are missing some jumpers!
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53.7 VAC in the blue and I noticed that on my layout, the pair of 220K's is connected by a jumper on the ground side...I see that in your picture these 220K's aren't connected....
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When you say, "everything in red must be connected" do you mean to each other as in, underboard?
Inside red circles must be connected to each other....
And bias pot must be connected as marked..
You are missing some jumpers!
Yikes!!! :BangHead: The layout I have must be off a bit...I remember getting a post from someone a while back that I cut the jumper somewhere...which I did...I'll go back and look. I still get nothing on pin 5 of the power tube with the brown OT wire and -24.3 on the power tube with the blue OT wire...
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The iron's heating up for the missing jumpers....just to be sure, there needs to be a direct connection from the single leg of the bias pot to the first 220K and the pair of 220K's should be jumped together as well?
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Ok, the jumper that Sluckey advised me to remove was at the choke...nothing to do with our thing...
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there needs to be a direct connection from the single leg of the bias pot to the first 220K and the pair of 220K's should be jumped together as well?
Yes.
There is no single leg on a pot, they have 2 ends, 1 full counter clock wise (CCW), 1 full clock wise (CW) and 1 wiper which is the center leg.
Brad :icon_biggrin:
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53.7 VAC in the blue and I noticed that on my layout, the pair of 220K's is connected by a jumper on the ground side...I see that in your picture these 220K's aren't connected....
In Doug's layout (which is what SG posted) they ARE connected look again.
Brad :icon_biggrin:
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Yikes!!! :BangHead: The layout I have must be off a bit...I remember getting a post from someone a while back that I cut the jumper somewhere...which I did...I'll go back and look. I still get nothing on pin 5 of the power tube with the brown OT wire and -24.3 on the power tube with the blue OT wire...
Slow down Larry....and stay calm....sorry for the exclamation mark on my last post, but I need you to focus. :icon_biggrin:
1) Verify that the turrets in ALL 3 of those red circles are connected
2) Then figure out how to read -24VDC on both socket pin #5...if you don't get that reading, then one of those connections is still missing
3) Do nothing else until we are sure that everything is connected properly there
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Would you post your layout in this thread? Tubenit was the person that made that layout back in'08. Unfortunately the full size layout pic has disappeared.
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Red circle looks connected above the board, green circle does NOT look connected at least above the board, blue square does NOT look connected at least above the board.
You don't have to pull the board to check if their connected below the board, do a resistances check with your meter.
We also need a -dcv check for/at/in the blue square.
Brad :icon_biggrin:
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Point taken, Brad! I guess I meant that there are two legs on the "tube" side of my board and one leg that connects with the 47 on the "ground" side.... :dontknow:
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Red circle looks connected above the board, green circle does NOT look connected at least above the board, blue square does NOT look connected at least above the board.
You don't have to pull the board to check if their connected below the board, do a resistances check with your meter.
We also need a -dcv check for/at/in the blue square.
Brad :icon_biggrin:
Hi Willabe,
They were in the process of being connected while everyone was posting. (Thanks all for the quick replies). I get - 23.5VDC between the pair of 220K's.
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I get - 23.5VDC between the pair of 220K's.
I'm betting either the 22K R is not really 22K or the bias cap is bad.
The R colors are correct, I'd still measure it at this point with your meter.
The bias cap is 47uF. If it's leaking that would drop your -dc bias voltage.
I think the pots good because the -dcv drops right after the bias diode.
Your dropping to much -dcv.
The only other thing that's left that I can think off (if the 22K reads correct) is that the PI coupling caps are leaking the PI +plate dcv which would cancel out the -dc bias voltage.
Brad :think1:
Edit; Some how I goofed up and posted under lpresnall. So I deleted it and added my post into this post.
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Would you post your layout in this thread? Tubenit was the person that made that layout back in'08. Unfortunately the full size layout pic has disappeared.
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Ok Brad...if you ask me about jets I can tell you...but, I need the PI thing "Forrest Gumped" waaay down for me...where are these caps? I'm gonna check the 22K and replace if need be right now...
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I have another 47 cap from an old Peavey but it's HUUGE! I'll try to temporarily wire that in and see what happens if the 22K tests out ok...
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I need the PI thing "Forrest Gumped" waaay down for me...where are these caps? I'm gonna check the 22K and replace if need be right now...
PI = phase inverter, sorry. They block the dc plate voltage from the PI yet let the ac signal voltage pass to the next tube stages controll grid, in this case the power tubes.
They are the 0.1uF caps that connect to the 220K R's and the power tubes grids pin 5.
Brad :icon_biggrin:
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I think the pots good because the -dcv drops right after the bias diode.
Have we tried adjusting the bias pot from MIN to MAX and seeing what those voltages are?....I feel like I missed something :dontknow:
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Silver, the bias pot wasn't changing the values at all...that's what the initial issue was....the 22K tests good btw...on to the bias cap now....
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Silver, the bias pot wasn't changing the values at all...that's what the initial issue was....the 22K tests good btw...on to the bias cap now....
Yes, but now that you made all of those other connections, the bias voltage has somewhere to go...
Try it again
I thought you were taking your original measurement of -.03VDC at a point that wasn't actually connected
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I've traced and re-traced my wiring against the Hoffman Lite layout but can find no mistake...Also, the bias pot still does nothing.
Brad :think1:
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With no rec, tubes, or speaker connected and the black meter probe to chassis ground I get the following:
(Top view of bias pot, starting with single leg and going clockwise)... - 24.5VDC, - 24.5VDC, - 37VDC
Brad :think1:
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He ALWAYS HAD bias voltage present....
He was taking a reading at a point that wasn't connected
:wink:
I'm talking about when he was reading -.03 VDC :l2:
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No, you might be right.
I assumed he was still trying to turn the -bias pot when he posted -bias dcv at the 3 pot legs.
Brad :dontknow:
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With no rec, tubes, or speaker connected and the black meter probe to chassis ground I get the following:
(Top view of bias pot, starting with single leg and going clockwise)... - 24.5VDC, - 24.5VDC, - 37VDC
OK, so the range of his pot should NOW read -24.5VDC at MIN and -37VDC at MAX
If he's reading -24.5VDC then he's got the pot set to MIN
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When you say, "everything in red must be connected" do you mean to each other as in, underboard?
Inside red circles must be connected to each other....
And bias pot must be connected as marked..
You are missing some jumpers!
No problem on the exclamation point Silver! :icon_biggrin: I checked the red circles again and everything's connected. The 22K tests good. The meter still says, "no" on pin 5 of the first power tube but now I'm getting - 24VDC on pin 5 of the other tube and the bias pot does change it...
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With no rec, tubes, or speaker connected and the black meter probe to chassis ground I get the following:
(Top view of bias pot, starting with single leg and going clockwise)... - 24.5VDC, - 24.5VDC, - 37VDC
OK, so the range of his pot should NOW read -24.5VDC at MIN and -37VDC at MAX
If he's reading -24.5VDC then he's got the pot set to MIN
I go from - 23 to - 64 on pin 5 of the second power tube by adjusting the bias pot.
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The meter still says, "no" on pin 5 of the first power tube but now I'm getting - 24VDC on pin 5 of the other tube and the bias pot does change it...
OK,,,you still have one missing connection that is not allowing the bias voltage to get to pin 5 on the tube with no reading
The bias voltage gets "shared" by those 2 tubes.....if it's on one tube then you're just one connection away from the homestretch :icon_biggrin:
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Work backwards from the pin 5 that has no voltage on it until you find where you're losing it...
It looks like it goes through the grid stopper (resistor from pin 5 to pin 6) to pin 6 - check there
Then go back to the board and check where the 220K and the 1uf come together....
Etc., etc,
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I need the PI thing "Forrest Gumped" waaay down for me...where are these caps? I'm gonna check the 22K and replace if need be right now...
PI = phase inverter, sorry. They block the dc plate voltage from the PI yet let the ac signal voltage pass to the next tube stages controll grid, in this case the power tubes.
They are the 0.1uF caps that connect to the 220K R's and the power tubes grids pin 5.
Brad :icon_biggrin:
Should my next step be to swap the 47 cap at the bias pot? Seems that if it was bad I wouldn't get voltage on pin 5 of the second tube. The fact that pin 5 of the first tube is "0" makes me think I've got a bad solder somewhere since all the jumpers are in place...
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Work backwards from the pin 5 that has no voltage on it until you find where you're losing it...
It looks like it goes through the grid stopper (resistor from pin 5 to pin 6) to pin 6 - check there
Then go back to the board and check where the 220K and the 1uf come together....
Etc., etc,
Sorry, posted that before reading your last post...will do it right now...
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Should my next step be to swap the 47 cap at the bias pot? Seems that if it was bad I wouldn't get voltage on pin 5 of the second tube.
No do like SG said.
I thought your max -dcv was only -37dcv. I thought you were giving max dcv. :BangHead:
Brad :laugh:
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If you've got it on one pin, then it's made it that far onto the board... you can forget about the pot, cap,,,etc., etc. for now
It comes into the board at the point where those two 220K resistors come together...
- Are those 2 turrets connected?
It then passes through those 2 resistors to the 2 points where each 220K meets up with it's companion .1uf cap
- Are the 220K resistors now connected to their corresponding .1uf cap?
Do you read -24VDC(ish) at both of those points?
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Work backwards from the pin 5 that has no voltage on it until you find where you're losing it...
It looks like it goes through the grid stopper (resistor from pin 5 to pin 6) to pin 6 - check there
Then go back to the board and check where the 220K and the 1uf come together....
Etc., etc,
Ok, replaced the .1uF for good measure and re-flowed the connections around the entire bias debacle. The last time I get good - VDC is at the positive side of the board at the .1uF-jumper-220K-pin 6 of the second power tube (farthest from bias pot). The other half of that circuit (the positive side of the 220K, the other .1uF-pin 6 of the power tube closest to the bias pot) still reads "0"...am I getting closer or further away from an amp?
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If you've got it on one pin, then it's made it that far onto the board... you can forget about the pot, cap,,,etc., etc. for now
It comes into the board at the point where those two 220K resistors come together...
- Are those 2 turrets connected?
It then passes through those 2 resistors to the 2 points where each 220K meets up with it's companion .1uf cap
- Are the 220K resistors now connected to their corresponding .1uf cap?
Do you read -24VDC(ish) at both of those points?
I have it on the top and bottom right sides but "0" on the bottom left. (Sorry, I wish I knew how to notate on the pic like you gurus do).
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"...am I getting closer or further away from an amp?
Look at my last post.....you're that close
BUT,,,all we are doing so far is making sure that your power tubes don't light up orange again.
With the problems that we have had getting to this point, there's just no tellin' what else might go wrong. :wink: :l2:
Sorry Larry,,,but I'm not much for sugar-coating :icon_biggrin:
The bad news is, the bias circuit is one of the EASIEST things to get straightened out. :l3:
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Here's what I have now:
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It's okay Silver, sugar-coating would likely only caramelize at the high heat I'm likely to get on power up, resulting only in a bad batch o' brittle.... :cussing:
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This is the point where your own skill must take over and YOU must figure out how to get that voltage over to the other side.
IT IS just as easy as my last picture posted.
You WILL find which connection is not getting through.
Take a break, get some lunch, digest what we've said, and realize that's all you need is to split the same path that's getting through to the one tube....
YOU got this!
:thumbsup:
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Thanks man! And thanks for putting up with me, all of you... I'll look again in an hour... After all, Rome wasn't burned in a day :icon_biggrin:
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Ok, went back one last time for the evening and traced the bias circuitry. I even replaced the 220K where I lose the signal and re-flowed the connections at the spot where the 220K, jumper, and .1uF meet. Specifically, I lose the plot at the positive (side toward the tubes) end of the 220K closest to the bias pot (which is also the tube where I'm getting no voltage on pin 5. I'm at a loss but I hope to give it a week and then get back at it again. Thanks again to everyone who has posted here offering solutions. This is a great forum and you are a good bunch of folks.
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Back in town and gave the amp an hour today...compared the layout to the actual board and re-secured and re-flowed connections. Tried connecting the "good" 220K feed to the "bad" pin 5...of course, got voltage there. When I put everything back still nothing...replaced 220K and .1uF on the "bad" side of the bias circuit...still nothing...as before, it's narrowed down to the south (tube) side of the 220K nearest the bias pot...I'm glad I don't do this for a living! :w2:
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Measure resistance from pin 5 of each output tube to chassis ground. What do you get?
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"0" and - 23 VDC
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Here's the board...
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Welcome back Larry... :icon_biggrin:
Measure resistance from pin 5 of each output tube to chassis ground. What do you get?
"0" and - 23 VDC
See the problem with your answer?
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Yep, on my way back upstairs! :think1:
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The problem pin reads 1491...the other -17.87
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If you really do have everything connected properly, there is still a chance that there is an error in this area...
If those OT wires are touching the bottom of your board and you heated the turret up to the point that you melted through some insulation,,,that could be where you are losing your bias voltage.
Unbolt the board, lift it up and check for a short.
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Or just check for continuity between those bias circuit turrets and your speaker jack connections if you don't want to lift the board....with power off
Bedtime for me Lar,,,,I think sluckeys still up :dontknow:
Good luck sir
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The problem pin reads 1491...
That's kinda what I was expecting. Now check the resistance of the problem tube pin 6 to chassis. I am expecting about zero ohms. What do you measure?
I'm suspecting a short circuit that is killing the voltage for the problem tube. Over...
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Stick around for a few minutes and we'll have this thing sorted out.
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Or just check for continuity between those bias circuit turrets and your speaker jack connections if you don't want to lift the board....with power off
Bedtime for me Lar,,,,I think sluckeys still up :dontknow:
Good luck sir
Power off, problem turret on south side of 220K to speaker jack is 1 ohm more or less...on the "good" turret south of the 220K 216 ohms.
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The problem pin reads 1491...
That's kinda what I was expecting. Now check the resistance of the problem tube pin 6 to chassis. I am expecting about zero ohms. What do you measure?
I'm suspecting a short circuit that is killing the voltage for the problem tube. Over...
1.1 ohms
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OK, that's what I thought. Now, unbolt the board and look to see what's shorting the bad turret. I'll stay on the board with you.
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Ok, there's not a lot of room for movement with the caps in tight as they are...I'll give it a go...
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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?
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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...
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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?
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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... :icon_biggrin:
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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.
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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!
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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!
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OK, "0" ohms from pin 6 to chassis...so the short is likely on the board?
No, read what I said.
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Ok, I left out the word, "turret"... :w2: ...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. :worthy1:
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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?
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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?
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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.
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Ok, will do...I'll report back shortly.
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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
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Yep, still getting the "beep" after replacing the tube socket...
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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! :BangHead:
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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 (http://el34world.com/Forum/index.php?action=dlattach;topic=15979.0;attach=44010)
Brad :think1:
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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.
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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!
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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 (http://el34world.com/Forum/index.php?action=dlattach;topic=15979.0;attach=44010)
Brad :think1:
Brad, I'm not following your question about the "different" sockets...(most likely my fault and nothing to do with your question)...
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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 :icon_biggrin:
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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 :icon_biggrin:
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!
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Use the 'key' way slot in the center hole of the tube socket to figure it out.
Brad :icon_biggrin:
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Use the 'key' way slot in the center hole of the tube socket to figure it out.
Brad :icon_biggrin:
Ok, tube socket's in and pins were ID'd and wired properly....next move?
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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 :thumbsup:
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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 :thumbsup:
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!
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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 :wink:
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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 :wink:
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!
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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.... :BangHead:
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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.
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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 :icon_biggrin: ).
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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? :wink:
Just thought I would let you know I am getting better. :violent1:
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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...
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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. :icon_biggrin:
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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. :icon_biggrin:
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.
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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.
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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. :icon_biggrin:
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. :icon_biggrin:
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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.... :l2:
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
:BangHead: :BangHead: :BangHead: :BangHead: :BangHead:
Hold on, whilst I create more patience...........
:BangHead: :BangHead: :BangHead: :BangHead: :BangHead:
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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.
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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.....
?
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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! :BangHead:
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 :think1:
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Eastwood- A Man's Got to Know his Limitations (http://www.youtube.com/watch?v=_VrFV5r8cs0#ws)
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I'd still change that wire before I thru in the towel.
Brad :icon_biggrin:
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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.
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That's a LOT of shorts. :w2: (I thought he cleared those up?)
I don't think I'll live long enough to see the solution.
:laugh:
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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? :grin:
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No, it's only one short. All those items I mentioned are connected together.
:w2:
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David Soul - Don't Give Up On Us (http://www.youtube.com/watch?v=YY8APrYU2Gs#)
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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.
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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 :w2:
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Larry,
I would like to apologize for my posts today if they insulted you at all.
I want you to know that this is all said in a light-hearted manner, and I am always more kidding than serious.
I try to approach this all with a sense of humor, and loosen up the group when possible.
With the good hearted intensions that you are working with, I really can't see how you could possibly fail.
(yes, I really did finish a couple!)...
That fact greatly increases your chances for success.
If you can just get the bias conundrum straightened out you could fire the amp up and see where you are.
Don't let my silliness get in the way of your determination.
We are all behind you and just cant wait to hear the story of your success.
You don't owe us a more timely story.
Good luck getting this hammered out, and finding the time it's gonna take.
I appreciate your patience but it sounds as though I've used it up...
Nope...there's more to be had.
Everytime you stop back I read what you write.... I have dedicated myself to seeing this through to the end.
Keep typing,,,,we are obviously listening.
**Brad was posting while I was typing.....he's possibly the nicest guy you'll find here.
I would like to echo his sentiments and would also be willing to fix the amp for you...I'm 5 minutes from PHL.