Newbie questions on AB763

[lpresnall]

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).

[Willabe]

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


                Brad    

[Ed_Chambley]

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.

[lpresnall]

Got it!  Thanks Ed.

[lpresnall]

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.

[sluckey]

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!

[ajeffcote]

I looked at the board pic, input end, before I had coffee. I thought I was still asleep.

[lpresnall]

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!

[lpresnall]

I looked at the board pic, input end, before I had coffee. I thought I was still asleep.

Yep, I'd like to blame lack of coffee on this too, but won't stand up in a court o' law!   

[lpresnall]

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?

[punkykatt]

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

[SILVERGUN]

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  
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

[sluckey]

Punkykatt's suggestion is a good one. Here's another alternative...

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.

[lpresnall]

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! 

[eleventeen]

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.

[sluckey]

I'm pretty sure he only needs two. Think about all the work that has already gone into that blank chassis.

[eleventeen]

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.






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. 

[punkykatt]

How about this style cabinet?

[eleventeen]

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)

[lpresnall]

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.     Lesson learned!

[lpresnall]

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!

[lpresnall]

And now, the other two pix:   

[eleventeen]

"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!

[SILVERGUN]

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  

[lpresnall]

No problem!  I'll take all the answers I can get!  I have to be told a lot of things twice    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! 

[sluckey]

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".

[punkykatt]

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

[lpresnall]

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!

[sluckey]

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.

[sluckey]

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...

[lpresnall]

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!).

[lpresnall]

  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.    Just ordered the right ones and will get 'em in next week.  Delta calls this morning.    Thanks for the catch - I'd have left them right where they were.

[eleventeen]

Pop! Pop! Pop! Pop! (REALLY fast!)

[SILVERGUN]

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

[lpresnall]

Ok, got it bookmarked!  Thanks!

[lpresnall]

Ok, here's what I have now...does it look right or am I still off track?

[sluckey]

I'd change the wires on the fuseholder for safety. Put the blue wire on the TIP. Put the black wire one the SIDE.

[lpresnall]

Crap!  I get that backwards EVERY time!  Rest ok?

[Ed_Chambley]

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?

[Willabe]

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......           and that's if you live.      

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    

[lpresnall]

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.

[eleventeen]

Check continuity with your meter!

[lpresnall]

See how dense I am?  I didn't think of that!

[sluckey]

I bet you can tell just by looking at it.

[lpresnall]

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!

[sluckey]

Don't lose this. 

[lpresnall]

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...

[SILVERGUN]

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

[SILVERGUN]

Like this:

[lpresnall]

Ok, I'll do it!  Rest of the pic look like it'll stay together when I power up?