AB763 Deluxe Lite Build

[HommeMarrBuckley]

Hello everybody,
I have a second Hammond A0-43 organ chassis with transformers and was going to build Steve's AB763 Deluxe Lite.
It's already underway but was wondering about adding a Master Volume. I tried googling adding a LARMAR style PPIMV to an AB763 layout and couldn't find much.
Anyone have a recommendation how I can add this to this circuit?  I am somewhat dense.  I could be off but it looks like it can be somewhat difficult/dangerous.
Just looking for general consensus---if it's been done frequently and successful, willing to give it a go,
but if not--and risks sound/safety, I have no problem nixing the notion and going forward without it.
Thanks in advance.

[sluckey]

I suggest you build the amp without it but plan to add it as a mod once the amp is up and running.

[HommeMarrBuckley]

The two .047 caps on the far left of the board.
Recommendations to stay with those or use .1?
Or won't really make a difference?

[kagliostro]

I tried googling adding a LARMAR style PPIMV to an AB763 layout and couldn't find much.

Here you can find a well documented collection of mod  for the AB763 that includes also a PPIMV

https://robrobinette.com/AB763_Modifications.htm

Franco

[mresistor]

Robinettes info is priceless...   great website ..   nice person

[sluckey]

Robinettes info is priceless...

Rob may have the answers you seek as well.

[HommeMarrBuckley]

Been sidetracked a bit. 
I need help.
Afraid to start setting up board and components without being sure.
So, in looking at Steve's schematic.
http://sluckeyamps.com/misc/AB763_Deluxe_Lite.pdf
(I feel dumb asking this because I think every amp has one but anyway) Does this amp have pre-amp and tone stack section?
If so, where on schematic, does that change over?
(I ground in sections and just trying to determine)
Would everything on V1-A to the left be considered pre-amp and all that follows to right (up to PI) be tone stack?
Would I then need to add another 20uf cap for the pre-amp and attach (+) that to R4 100k resistor?
Just saying because with the Plexi I finished, I grounded it differently so I needed to make adjustments to the build.
Like that schematic, I know this one is accurate but again I might have to alter what I do.
Thank you


PS I am going to add the MV mod with the push pull pot from Rob's site (Thanks Franco)
I did email him and, indeed, he's a good guy with a lot of info there.


Oh Steve, the pot that was in the Hammond (that I was thinking of using for bias) measured around 9k
Should that value have changed when I turned the pot while measuring?-because it stayed about 9k the whole time.

[sluckey]

Should that value have changed when I turned the pot while measuring?-because it stayed about 9k the whole time.

Resistance won't change if both meter leads are connected to the outside lugs.

[Willabe]

Does this amp have pre-amp and tone stack section?

Preamp is V1A, tone stack recovery stage is V1B, tone stack is in between, red box. Tone stack has 3 pots 'stacked' on top of each other in the schematic. 

[HommeMarrBuckley]

I will check again on that pot Steve.


Thanks Brad.
Alright, so now.
Do you think I should add a 20uf cap with preamp section?


And then should I use the "D" 20uf cap for both tone stack and recovery sections?
OR
is the one 20uf cap like on schematic sufficient for these three parts? (I guess in a way also, is tone stack and tone stack recovery considered part of pre-amp section?)
Lastly, R14 270K is part of the PI, correct?

[HommeMarrBuckley]

In thinking about this,
I believe I should use the one filter cap as shown "D"


The 2nd shielded cable (by Volume pot) was throwing me off for whatever reason.
Am still alittle unsure but will ground all of those pre-amp, tone stack and recovery at one point at hi jack ground with bus
will take some accommodation, a good many points meeting there
So, prior post can be ignored,


But still leaves R14 270K-- that is part of PI? or "C" cap on schematic.

[Willabe]

But still leaves R14 270K-- that is part of PI? or "C" cap on schematic.

What does it say above C6, R13, R14? They are not part of the PI.

As far as adding another B+ filter cap node, you don't need it.

[Willabe]

Do you think I should add a 20uf cap with preamp section?

And then should I use the "D" 20uf cap for both tone stack and recovery sections?
OR
is the one 20uf cap like on schematic sufficient for these three parts?

It's not 3 parts, it's 2 gain stages and a tone shaping circuit. The tone stack doesn't need a filter cap, it's just a passive filter. It has no B+dcv going to it. Tubes that have B+dcv going to them need a filter cap. 

(I guess in a way also, is tone stack and tone stack recovery considered part of pre-amp section?)

Kind of, the PI needs to see a certain acv (ac signal) so it can supply the output tube stage what they need to reach full output.

[Willabe]

Am still alittle unsure but will ground all of those pre-amp, tone stack and recovery at one point at hi jack ground with bus, will take some accommodation, a good many points meeting there

I like to do my grounding like this, D node B+ filter cap ground goes to this ground also because it's feeding the D node filter cap that feeds V1A and V1B.

[sluckey]

R14 is part of the preamp. If you look at the board layout you'll see that R14 is grounded with all the other preamp grounds.

If you build my board then these grounding questions will mostly be taken care of.

[HommeMarrBuckley]

Good info Brad.  I will commit to memory but leads me to more questions but won't dog down this post with them.
I was planning on grounding it like you have diagrammed.  You wouldn't include the Lo jack in that pre-amp ground?


Steve, I copied your board, I really should have pushed myself to just use the schematic and try it on my own but you already did the work so why not use it.
The Supro build I always mention will come and that will be my test.
How to test the range/wipe of that bias pot? One lead to pot lug and other lead to ground?

[Willabe]

You wouldn't include the Lo jack in that pre-amp ground?

Yes, Lo jack is grounded with Hi jack. (Where else would you ground it? Lo jack is right next to the Hi jack. Just forgot to draw it in.)

Steve, I copied your board, I really should have pushed myself to just use the schematic and try it on my own but you already did the work so why not use it.

Yes, use Sluckey's layout and grounding. 

[sluckey]

How to test the range/wipe of that bias pot?

Just like you would check any pot with 3 lugs. One meter lead on the center lug (wiper). The other meter lead on either outer lugs. Turn the pot shaft.

[HommeMarrBuckley]

Alright, cool.  Will do.


Here's my progress so far, have some more layout work to do and eyelets, looking forward to weekend.
I must say Steve when I was mounting the PT, I was smiling as I was putting the brackets on.  Memory lane.

[sluckey]

There have been several of these amps built. The layout works well. But through the years some questions keep popping up. Mostly about grounding. When I did this layout, it was for a forum member that had good building skills and knowledge of layouts. The main purpose was to provide a BOARD layout. So my docs were pretty vague on grounding. I've just revised the documents and I think the grounding scheme should now be obvious to anyone building this amp. There are plenty of other ways to do the grounding for this amp and I'm not saying this is the one and only way to do it. But if I were building this amp (and I never will) this is how I'd do it.

As always with my drawings, the layout is a full size board design intended to be used as a template to actually build the board and make all connections between the board and chassis mounted components. This is the major portion of an amp. But my layout does not show how to wire the PT, or OT, or some other power supply components. You will have to refer to the schematic to build a complete amp, unless you have this knowledge in your head.

Anyhow, I hope you will find the changes helpful and easy to understand. You may have to refresh/reload the page to see the changes.

[HommeMarrBuckley]

I tested the pot and it is consistent so I am going to use it.


In regards to the filter cap layout, since I am building this as the lite, I assume I should use the values listed on the second filter board?
So the F&T blue 32/32 uf cap im using would be overkill, as the plate/screen cap?


And just to be sure that's (2) 220k resistors on the 10ufs
and a 1k and 4.7k between the 22ufs?

[sluckey]

The first cap board is for 6V6 amps such as the Deluxe and Deluxe Reverb. The second board is for the bigger 6L6 amps. Since you are using AO-43 iron, I suggest using the first board values.

I would use that cap can if I had it. In fact, I'd use two of them if I had them. Even better, use Doug's JJ 40/20/20/20 can.

Ain't no 10µF caps on those cap boards. The 1K and 4.7K resistor values are for the 6L6 amps. The 6V6 amps use 10K and 10K.

[HommeMarrBuckley]

The first cap board is for 6V6 amps such as the Deluxe and Deluxe Reverb. The second board is for the bigger 6L6 amps. Since you are using AO-43 iron, I suggest using the first board values.

Thanks for clarifying that for me.

I would use that cap can if I had it.

Great, I had already it mounted so glad to hear that.

Ain't no 10µF caps on those cap boards.

Yeah my mistake, missed the extra 0


I have the hi/lo jacks set.  That shouldn't pose an issue, should it?  I am just going to build how you had prior with hi/lo jacks.

[sluckey]

I am just going to build how you had prior with hi/lo jacks.

That's fine. The reason I changed to a single input was it seems to fit the "Lite" theme better. If you have any trouble with the hi/lo jacks you can always look at Hoffman's Tube Amp Library of information to see how they should be wired.

[sean_thornton]

Is this what you mean?

[sluckey]

Yes, but I was actually thinking of the Switchcraft jacks just above those Cliff jacks.

[HommeMarrBuckley]

In determining my PT wires.


I set my meter to ohms (for all, I applied one clip to one wire and other clip to wire of matching color)


one clip on each black measured 3.6 ohms (being black have to be primary)


one on each brown .3 ohms (have somewhat matching striped center tap) thinking this is heater


one on each (I dunno color--but appear same color) 141.8 ohms assume this is secondary (there is a very dark green which I assume is CT for this)


last 2 of matching shade measure .2ohms assuming this is 5V without CT


Would my assumptions seem correct?


ADDENDUM


Hold that--I believe I had my centertaps ID'd wrong--I was wondering why I couldn't put my black lead on the CT to determine resistance




ADDENDUM2


Laugh
frustrating but anyway I was reading that those that have CT will have continuity with each other(so all 3 wires will). 


So Primary are done and easy-black.
I believe I figured out my HV because all three have continuity and are high in ohms--one is striped so it's the centertap


Now my heaters should have CT and have found three that all have continuity and are dark in color---2 darkish red brown and one forest green
thing is I am getting .2 ohms


but when I got to remaining 2, only have continuity with each other and dont have CT like they shouldn't so they should be my 5V but they read slightly higher .3 ohms


I would think that the 5V would read .2 ohms and the heaters measure slightly above at .3 ohms but this isn't the case but has to be right based on continuity of the wires, does that sound right?

[sluckey]

Don't fret over 0.1Ω.

[PRR]

> Don't fret over 0.1Ω.

+1.1

There's "ideal" values where all CTs are dead-center and all winding Rs scale exactly with load.

And then there are real transformers where a few tenths either way makes no difference. Normally the resistance is "very small" compared to load so "small" differences are really very-very small. OTOH practical matters suggest some "unbalance". Usually half the winding is wound *over* the other half. Since they have the same number of turns, but the outer half is longer wire, it will measure some percent more Ohms. Also you may calculate "Gauge #16.78 and #17.89" for 6V and 5V windings, but you can only buy whole-numbers (and mostly even-number) gauges, and fewer gauge-changes means faster work, so you throw #16 on both windings.

[HommeMarrBuckley]

> Don't fret over 0.1Ω.

+1.1

Yeah, didn't anticipate some of these issues today.  I hadn't looked at these second set of transformers since I got them a long while ago and just assumed that they would look similar but the PT colors were very different.   I marked them when I got them and for whatever reason, thought to recheck those values today only to cause myself more headache, however, I believe they were right first time around.  oh well, better safe than sorry.


In looking at schematic, im trying to plan out the layout and I believe I have the standby wrong.  I remember Steve saying the standby is between the rectifier and the plate cap but maybe it doesn't apply here.  I have been looking at this to help me because I am using diodes.
http://www.lynx.bc.ca/~jc/63PwrSupply.gif


Does this look correct? I feel comfortable with the power cable, power and fuse.  My 5V will goto the 47 lamp.


Lastly heaters on the 4,5,9 pins of the 6V6 and on 2,7 on the at7 and ax7

[eleventeen]

Reading ohms on a transformer (with no accompanying datasheet) is a little bit of an art form until you have some experience with it. When you are reading .2 ohms on some winding...your first thought is probably "wow, that's a short ".


With experience, you will come to find out that typical 5 volt and 6.3 volt windings on a tranny have incredibly low resistance. HV winding, oh, maybe 35-150 ohms per side, the 120 winding can be 1-2-5 ohms. Unfortunately, ohms readings this low do not necessarily tell you that much other than "there's continuity", or, assuming the tranny is good, "these 3 wires are the HV because I get 40 ohms from this [striped wire] to one side and 47 ohms to the other side so probably the middle one is the middle one".


Another approach which may give you more confidence: With an extra 6 volts transformer, connect the 6 volts to the primary black-black. Sometimes you can use a junk wall wart for this *provided* you are sure the wall wart puts out AC (most don't) and, some small-small wall warts will not be able to handle the load even in a no-load situation. Use a junk wall wart you get at a yard sale for 50 cents, not something you need to power something you use. You could also tack-solder two wires to an amp chassis and steal his 6.3 volts temporarily. You could use a doorbell transformer. Some of those 12 volts, some are 18 volts. The idea is just a low voltage AC source that will power up your mystery transformer but NOT place 700-800 volts on the HV secondary wires flying around as you are trying to take measurements. 


6 volts is about 1/20th of 120 volts. First thing, measure the actual volts out of the "source" transformer. Get the approximate ratio of those volts to your line voltage. an 18 volts transformer would be 18/120 = 15%. A 6 volt tranny would be 1/20th or 5%.


The idea is just to not have huge volts on loose wires flying around. A 400-0-400 winding (800 VCT) would still have 120 volts on it using an 18 volts powering transformer, but that's a far cry from 800; and better would be just your ordinary 6 volt tranny which would put 40 volts on your HV secondary.

[eleventeen]

Lastly heaters on the 4,5,9 pins of the 6V6 and on 2,7 on the at7 and ax7


That's backwards.


Unless you want the #47 lamp for looks, LEDs are so much easier to use (and drill out for!)

[PRR]

> your first thought is probably "wow, that's a short ".

Your "Ideal" power source IS a "short", with Voltage in it.

Practical numbers. A 6V 6A winding supports a 6V/6A= 1 Ohm load. If the winding could be ZERO Ohms, there would be NO voltage sag from zero to 6 Amps of load.

Said another way: if my house transformer and power line were ZERO Ohms, my lamps would not dim when the well-pump kicked in.

But getting ZERO Ohms takes Infinite money (or more). And a little sag does not hurt. House economics suggests 2% sag in transformer, 2% in the line, 2% in each inside circuit. Space is not a big issue. In a amp-size transformer, wire-space is more precious, we don't have pump dimming lights, and it is reasonable to have 10% or more sag.

That's counting both primary and secondary. Assume half in each winding, 5%; though with many secondaries it does get complicated.

A DeLuxe's 6V winding is 6V at 1.5A or 4 Ohms. 0.2 Ohms in secondary winding would give ~~5% sag just in the secondary. An honest 0.10 Ohms is "too good" but entirely satisfactory. OTOH sub-Ohm measurements are tough to get great precision, so I read the "0.1 Ohm" as a ballpark.

[HommeMarrBuckley]

Alright, I think I understand how to wire up the standby, rectifier and the caps.
I believe this to be correct---the jumpers and resistor around the 32/32 uf cap seems odd but believe it's right and unsure about bias tap but looks accurate in terms of schematic.


My new dilemma is I have a board identical to the layout, but I would like to separate the bias supply and grounds....
(R36 10k and Cap 17, 18 50uf)


From the PI cap "C" and ground.
(R15 100ohms)
so they can be grounded with their dedicated filter cap ground


I am trying to determine which jumper(s) to cut that won't mess up the flow of the circuit.
Any suggestions--many many thanks

[sluckey]

...I would like to separate the bias supply and grounds.... From the PI cap "C" and ground...

Why???

[HommeMarrBuckley]

...I would like to separate the bias supply and grounds.... From the PI cap "C" and ground...

Why???

I swear not trying to be difficult or question people.  I just know with my Bassman build that I had my grounds lined up on the buss correctly and all all centertaps, bias, etc by PT like I saw on other builds and I got major hum.  When I broke it down in sections, and followed accordingly, it became quiet.  I am not saying I don't believe in other methods--I just believe in this one because it has worked for me and don't want to test others if this works.  The Plexi I just built, had minor hum with normal vol and bright controls, until I cut one jumper--I wanted to put that on my post.
I cut the jumper between the .68uf cap/820ohm and the 22uf cap and then ran a wire from the 68uf cap/820ohm to meet the tone stack ground and it went away.  It's quiet--but Im thinking of trying that .0047uf cap on the bright switch because it's not that noticeable with the 470pf.  All hum went away but some very bare sounds--dunno like when stylus touches record--very faint---not noticeable enough that I care --sometimes when turn pot can hear--but then goes away when I stop and "set" -thinking maybe it's a solder joint--I dunno. Anyway, I really love that amp---especially with MV feature--but I wouldn't have it if you wouldn't have put it online--so im just trying to figure out how to adjust this--like I did before.
this is what I am thinking to do---I dunno if it will work--been trying to trace path of circuit.


Cut the jumper between the 47uf(50) cap and 100ohm resistor.
Ground 2 will be the bias ground and run a wire from 100ohm to "C" PI cap ground.




Does standby, rec and filter layout look correct?

[PRR]

> separate the bias supply and grounds

The wire from PT through rectifier to first main cap is a total train wreck of HUGE current spikes. This must not be in the midst of other grounds or it will inject crap.

Grounding input jack to chassis and power cap to chassis is dubious. It can be done, without a buss. It is often better to buss and let either power-end or input end float off-chassis.

There are several well documented grounding scheems published. I don't know why this wheel needs re-re-invention. Or even mix/match between different schemes of differing philosophy.

[HommeMarrBuckley]

The wire from PT through rectifier to first main cap is a total train wreck of HUGE current spikes. This must not be in the midst of other grounds or it will inject crap.

I believe my plexi is like that and I don't hear that.  Now, that you say that---I might relook to see if that ground has it's own dedicated point before it goes to the bus or if I have it connected to the bias, power tube grounds, etc before it goes to the end of the bus---that might the reason for my subtle, faint record player sounds.

There are several well documented grounding scheems published. I don't know why this wheel needs re-re-invention. Or even mix/match between different schemes of differing philosophy.

Not trying to re-re-invent anything--just trying to adapt (what I believe came from "Merlin" of whoever in terms of grounding sections on a bus, in order, to the jack) to this schematic/layout.  It has worked for me so that's why I have gone with that scheme.

[sluckey]

...I would like to separate the bias supply and grounds.... From the PI cap "C" and ground...

Why???

I guess my question should have been, "Why...would YOU like to separate the bias supply and grounds.... From the PI cap "C" and ground?" You didn't answer that question yet.

I revised my drawing specifically for you, to clearly show how I would do the grounds in this amp. But you can change it any way you want. Merlin is a member here. Send him a PM and ask how he would do the grounds in this amp?

Does standby, rec and filter layout look correct?

That's not what I had in mind. I was thinking use one 32 cap for node A and the other for node B. OT would connect to cap A, choke between cap A and cap B, and screens to node B. This would be a clean, straightforward way to utilize that dual can.

[HommeMarrBuckley]

That's not what I had in mind. I was thinking use one 32 cap for node A and the other for node B. OT would connect to cap A, choke between cap A and cap B, and screens to node B. This would be a clean, straightforward way to utilize that dual can.

Dang.  Ok--will think about that.

[HommeMarrBuckley]

Ok,
this correct for one can? seems odd that both standby lugs just go to one point.

I guess my question should have been, "Why...would YOU like to separate the bias supply and grounds.... From the PI cap "C" and ground?" You didn't answer that question yet.

I wanted to separate the bias ground because I am going to put it on end of the bus at same point with the power tube ground, plate/screen grounds, CTs, and then put the PI cap ground with the 100 ohm resistor ground on the same point on bus some distance after/before (however, you're looking at it) that point mentioned previously.
So, not separate bias and PI completely, just their grounds so I guess I will just cut that one jumper.


But I wouldn't have got anywhere if you hadn't answered all of my elementary questions, so I am grateful for your help.

[sluckey]

seems odd that both standby lugs just go to one point.

Think about that for a while.

[HommeMarrBuckley]

 


How could I forget my own quote.  Ventured up to post 29.
Ok--so rec to standby
other standby to A+, red OT, Choke and 220k resistor leg.
So much for starting this weekend--oh well, I feel better about this circuit though.
It's IPA time.
 

[HommeMarrBuckley]

Alright, spent a good deal of the weekend on this.
Should put a love/hate list in ampbuilding but don't want to bore anyone.


Alright, so my current situation is this.
I have installed the MV (trainwreck 3) as Franco put a link (post #3 here) to Robinette's page.
I am using the 1M push/pull pot connected to the 220k resistors, however, I realize now that I probably should have twisted the wires-but that can be corrected.
Anyway, while working, I was thinking, how will I be able to bias this with this mod? (with MV on or off?)
Perhaps, this mod is not choice for this circuit, I dunno
I spent past couple hours looking for someone that as done this similar and with my limited knowledge Im at a loss.
I believe someone mentioned that if the pot fails, I risk doing damage to the output tubes.
I realize many have utilized different types of MVs but I just want to know if this will work? then biasing bit and if it's true that if the pot fails, the damage to the output tubes.
Thanks

[EKDENTON]

It is just my humble opinion but the amp that you are building will be a challenge if it is your first amp of this level. It might make the amp build less stressful for you and easier for those helping you to just concentrate on building it exactly like the plan first and then after you have it up and working good, document all your voltages and all, you can easily add a master volume, or experiment with other mods. If you start in the middle of the build changing capacitor sizes and adding things that are not on the stock build and then have trouble it seems like it may be harder to troubleshoot.

 I never had a MV on any of the first 4-5 amps I built but then later I went back and added them on the amps I wanted them on.

[kagliostro]

You must use decoupling caps like here



Franco

[sluckey]

I just want to know if this will work? then biasing bit and if it's true that if the pot fails, the damage to the output tubes.

Yes, it will work. You will still bias the amp just as you would without that simple crossline MV. Nothing will happen to the tubes if the pot fails, unless the pot actually shorts to chassis.

[HommeMarrBuckley]

Alright, great to know.
I will follow previous post's advice and make sure it works first, then check out applying the mv.
Have a bit to go, but will post voltages later assuming startup goes well.

[HommeMarrBuckley]

Finished up wiring and hooked it up to the limiter.
It is pretty late but was pleased to see illumination.  I need to get shorter spacers--ones I had were too long--the board needs to be elevated about 3/4 - 1" off chassis.  The bottom edge of the board sits on top half of preamp tube pins (6-9) 
Even with board elevated, might be tricky when I measure those voltages.  Angling the meter leads in there.

[HommeMarrBuckley]

Alright,
with limiter hooked up and in operate position, I started checking dv voltages and all readings are low and off.
Plate cap had like 4.4 volts.
Im assuming my wiring is wrong or I have messed up the PT wires.
I don't think it's my PT wires, but who knows.


Here's how I have it wired
I used the 32/32 F&T cap as the plate cap
2ndaries go to rec board---from the board they goto a point and meet wire from standby lug and 1st (+) 32 plate cap.
Red OT and red choke meet and goto other standby lug.
2nd(+) of 32 plate cap meets 220k resistor


Should I have a jumper across both (+) lugs of plate cap?
I don't think that's it, but I dunno.


Or I could have my heaters and 2ndaries wrong---when I turn it on--I have pilot light but there is absolutely no light through lamp limiter  bulb at any point during switching on which seemed kind of odd.