Re: Single Channel AB763 no verb/vib

[samato]

Ah yes, I forgot those - thanks.  That's it?  Everything else looks right?

[samato]

While I'm still trying to make sure I have the design right I'm also starting to think about what would be the best size/shape of chasis to use for this project and could use some input from people with experience.  

Keep in mind my goal is to keep this thing as small as is reasonably possible.  My Fender Pro Jr. and Vox Pathfinder 15R are pretty much ideal in the size department.  This amp may need to be a little bigger because I plan to use a 12" speaker, though I'm not 100% sure about that yet either.  I plan to make the amp first and find some safe way to mount it or support it while I try different speakers/cabs.  I'll build the cabinet after I make a decision on the speaker to use.

I originally thought a chasis like the one on my Pro Jr., with the knobs on top, would make the most sense because the chasis doesn't extend all the way to the front which might leave more room for mounting a speaker.  Now I'm not sure.  The knobs on the front type might be actually leave more speaker room because the transformers can be more toward the back, though the speaker has to be a little lower.  Can anyone shed some light on this for me?

Any recommendations on what would be the smallest and best shape chasis to use for this?  I can't afford a nice, pre-drilled one.  I'll be going with a blank one most likely so size and money are both major factors.

[sluckey]

I highly recommend a 12" speaker with this amp. I used a Deluxe 5E3 cab and a Hammond 4"x3"x17" chassis. Makes a neat package. If you want a combo, spend some time planning the cab, chassis, and speaker before you actually start this project. Here's mine...

[samato]

That is a beauty for sure but it looks like it could be smaller, even with the 12", don't you think?  Mine will also have less parts.  The reason I'm so crazy about keeping it small is I'm really enjoying traveling to gigs on my motorcycle and walking in with a guitar in one hand, amp in the other, and a bag with cables & stuff over my shoulder.  I'd hate to give that up as I usually don't drive my truck unless I have to so I'm saving a lot in gas money this way plus it's more enjoyable.

I agree that I need to plan the whole package before starting the project.  So would you say that type of chasis and overall layout/topology/whatever you call it is the most space saving?

[topbrent]

Like Sluckey's awesome Tweed ab763 and AB763-lite builds, you can stuff it all into a very small tweed style chassis if you keep your layout tidy.  

Some folks seem to think that the leads on components must stick out 2" on each side for it to be "correct".  
- If you move away from that style of layout thinking, you will surprise yourself at how much amp you can stuff in a small space.  
- You can put the whole ab763 preamp on a few small terminal strips and eschew the eyelet board topology, also.  
- Using Xicon MPP caps like Doug sells make stuffing an amp in a small chassis much easier.  (IMO, they sound great, also)

Good lead dress becomes much more critical in smaller chassis', though.  

Here is a fun single channel AB763 amp stuffed in a chassis about the size of tweed deluxe.  
Dumble style mid boost on the switch, and a power supply sag resistor.  

Although this layout started out as another manufacturers layout design, but I cut, modified, folded, spindled, boiled, pickled, mashed, diced and chopped it to ab763 specs.

Note: Although I forgot to include in this layout the 820 ohm NFB resistor, and .001 PI coupling cap  : , this is a fully tested, working layout.

[samato]

Thanks for posting that Topbrent.  Do you have any pictures and/or sound clips of that amp you could post?

What Sluckey posted above is the size of a Tweed Deluxe chassis, isn't it?  It seems like mine could be smaller, especially if I follow your advice on how to save space on the board - or would the tubes be too close together if I go smaller than that?

[sluckey]

5E3 chassis dimensions are 14 5/8" long x 4 1/8" high x 2 5/8" deep. Scratch building anything in this narrow chassis will present some real layout challenges that you wouldn't see if using a 6 to 7 inch wide chassis. And you will have to carefully plan each stage of the build. A wider chassis will make the layout design and build sequence much easier.

[samato]

5E3 chassis dimensions are 14 5/8" long x 4 1/8" high x 2 5/8" deep. Scratch building anything in this narrow chassis will present some real layout challenges that you wouldn't see if using a 6 to 7 inch wide chassis. And you will have to carefully plan each stage of the build. A wider chassis will make the layout design and build sequence much easier.

I believe that.  Still, I'm stuck on the small size approach.  I always seem to make things difficult for myself so why should this be any different?

Are these the Xicon MPP caps Tobbrent was referring to?

[topbrent]

Thanks for posting that Topbrent.  Do you have any pictures and/or sound clips of that amp you could post?

What Sluckey posted above is the size of a Tweed Deluxe chassis, isn't it?  It seems like mine could be smaller, especially if I follow your advice on how to save space on the board - or would the tubes be too close together if I go smaller than that?

Here is what one looks like built up using huge Jupiter caps.  This was built by tlainhart.
I have changed the circuit around a bit since this pic was taken and have removed all of the Jupiter caps and installed the Xicon MPP caps. 
- can't tell a tonal difference....Sure is nicer to work around in that cramped chassis, too.

[topbrent]

Bare chassis and board.

[sluckey]

I've built 3 amps in the Hammond 3x4x17 chassis. I used Doug's board material for all, but I ripped Doug's standard width of 3 1/8" down to 2 1/4" or 2 5/8". Using the narrower board was very helpful when it came time to put it all together.

[topbrent]

With a circuit this simple, you could easily stuff all of this into a blackface/silverface champ sized chassis, also.  
Reproduction champ chassis are available from Marsh, MOJO and Allen.

Get a nice larger 12" baffle combo cabinet from Allen, MOJO, mathercab.com, JDNewell, and you could have a powerful amp in a small package.  Load it with a very efficient speaker for the maximum effect, 100db+ sensitivity speaker.

http://allenamps.com/minichassis.php

[worth]

Use a vertical mount PT instead of a horizontal - thru chassis PT , and you'll have a lot more room inside the chassis.

[samato]

Use a vertical mount PT instead of a horizontal - thru chassis PT , and you'll have a lot more room inside the chassis.

I'm not sure I know what that means.  Here is the PT I was thinking of using:

http://store.triodestore.com/deretrvipotr.html

[samato]

I'm trying to figure out which resistors, if any, I should upgrade to a higher power rating on this amp.  From my drawing above, would it be making R23 & R25 2W instead of 1W and R24 & R26 1W instead of 1/2W - keeping the values the same?

Should I do this and are there other proven, known issues that I should be aware of?  I really don't want to change anything from the original design unless it seems necessary for the sake of reliability & safety.

[samato]

Okay, I found the answer here:

http://www.el34world.com/charts/fenderservice1.htm

Guess I should have researched a bit more before posting.  Hoffman suggests that R23 & R25 should be 3W and away from the tube sockets.

[Fresh_Start]

Sluckey's Deluxe Lite schematic clearly shows the resistors which need to be over 1/2 watt ratings.  The original AB763 schematics also show resistor ratings in specific spots but Fender was cutting things a bit close at times.  Don't forget that the bias "range resistor" needs to be 1 watt or greater.  Also, make sure your 1 ohm bias measurement resistors are 1-watt, flameproof, and 1% tolerance (it does matter there).  

Lastly, I've got it in my head that capacitors generally only need to be rated for 400 volts except for the coupling caps between the PI and the power tubes.  Don't know where I got that idea...

Chip

[samato]

The problem I have when looking at other people's designs is when I see changes from the original I don't know why they were made - for a different sound, to fix a known flaw, etc.

I have some 16mfd, 1000V caps I was thinking of using where the schematic calls for 16mfd, 450V.  Would this be a problem, other than the fact that they are physically larger and take up more space.  Would the amp respond differently - less "sag" or "squash" maybe?  I don't want that, I like the sag of the original but those caps are $10 each so if I can use what I have...

[oldgitar335]

hello all.    Here is my version of AB763 showman "lite". Waiting on head cab. Stone quiet and
               sold as soon as done. 18x8x2" chassis, All Hoffman Iron.... Wish I kept that one.        oldgitar335

[topbrent]

The problem I have when looking at other people's designs is when I see changes from the original I don't know why they were made - for a different sound, to fix a known flaw, etc.

I have some 16mfd, 1000V caps I was thinking of using where the schematic calls for 16mfd, 450V.  Would this be a problem, other than the fact that they are physically larger and take up more space.  Would the amp respond differently - less "sag" or "squash" maybe?  I don't want that, I like the sag of the original but those caps are $10 each so if I can use what I have...

Samato,  Just a little advice:  

IMHO, just because you have invested some money in a particular set of components and have them on hand, don't feel like you are required to base your build around them just because you have them.  As a new builder, this pathway of thinking will handicap you more often than help. 

If the build is unsuccessful and you need help, it is much easier for the experienced techs to help you diagnose the problem if you have followed a proven design with traditional parts.  

Due to the simple circuit and low parts count, the list of caps and resistors for the amp you are planning is pretty inexpensive, really.  The real money in home building an amp is in the transformers, chassis, cabinet, and speaker. 

Save or sell the other parts.

[sluckey]

Still, I'm stuck on the small size approach.

If that's still your goal then don't use huge over-rated parts.

The problem I have when looking at other people's designs is when I see changes from the original I don't know why they were made

Do you mean the Deluxe Lite? I kept the circuit as near identical to the original as I could. I used 20µF or 22µF power supply caps simply because they are more common today than the 16µFs which were common when that amp was first in production. I added the 220K bleeder resistor across the first filter cap to discharge the B+ more quickly when the amp is turned off. I added another bias cap simply for a smoother bias voltage (an improvement IMO, but certainly not necessary in a cost controlled production amp). I used a 1500Ω cathode resistor for V1B because the Lite doesn't share a cathode resistor with another tube like the original. I added 1Ω resistors to the output tube cathodes for convenience of biasing the amp (another unnecessary improvement since in Leo's time they simply used the 'set it and forget it' bias method). I added the mid pot just because I wanted one.

All the above changes add nothing (nor take anything away) to/from the actual sound or operation of the amp. They do add to the cost and that is a big concern in a production environment, but mean nothing to me as a hobbyist. If you see any other differences (other than obvious layout differences) let me know and I'll try to explain them.

My different layout was simply to make it easier to stuff into that 3x4x17 tweed style chassis. The board layout would have looked quite different if I had chosen a wider chassis. But it still would not look like the original layout simply because figuring out my own layout is part of the enjoyment I get as a hobbyist. Leo had a decent working board layout and he used a very similar layout in all his old amps. That makes for easier and faster assembly and that means more profits. I'm only gonna do this once, so profit is of no concern to me.

[drew]

The reason I'm so crazy about keeping it small is I'm really enjoying traveling to gigs on my motorcycle and walking in with a guitar in one hand, amp in the other, and a bag with cables & stuff over my shoulder.  

How exactly do you manage to transport a guitar, and amplifier, and a bag on a motorcycle?

[samato]

The reason I'm so crazy about keeping it small is I'm really enjoying traveling to gigs on my motorcycle and walking in with a guitar in one hand, amp in the other, and a bag with cables & stuff over my shoulder.  

How exactly do you manage to transport a guitar, and amplifier, and a bag on a motorcycle?

I'll have to take a picture to show it.  It's much easier than it might sound through - it's all just strapped to the seat behind me.  It wouldn't work on all bikes but my '98 Honda CB750 Nighthawk is perfect for this. 

Sometimes I even take extra stuff like a mic stand, camcorder, and other small recording equipment.

[samato]

I'm finally ready to get started on this build.  It's taken me a while to find the time and money.  I've been away from this for several months and I had just started understanding things so I'll have to go back and re-learn a lot but that's okay.

I'm going to start by ordering the transformers.  Do any of you think it would not be a good idea to use these?

http://store.triodestore.com/deretrvipotr.html

http://store.triodestore.com/dedereoutr.html

http://triodeelectronics.com/40-18040.html

I know there is much "better" iron on the market and many people choose the best quality they can afford.  I'm on a tight budget.  Besides, I'm not sure I would prefer the sound of the high quality stuff anyway.  I guess I'd just like to know if any of you have used these and what the results were.

Anyway, I plan to post my progress here and bother you guys with lots of questions.  

[topbrent]

Solid choices.

If it were me ordering from that vendor, I would choose the larger 40w output transformer with 4/8/16 taps. 
The larger transformers will sound more solid and will be much more future proof.  (You will probably want to install 6L6 tubes at some point, right?....) 
With that in mind, I would also choose the slightly more powerful Vibrolux style power transformer for the same reason. 
http://store.triodestore.com/babareproreo.html
http://store.triodestore.com/trvirepotr.html

These changes will sightly add more cost to your build (~$45.00'ish), but will ultimately make your amp more versatile.


PS:  Doug Hoffman sells transformers also.

[samato]

I gave some thought to what your saying about using larger transformers.  I see the benefit in flexibility and power but I don't think that's what I'm going for on this build.  One of my main goals is keeping this thing as small as possible.  I don't think I need or want any more power.  If I can make it sound close to what a real Deluxe Reverb sounds like I'll be beyond happy.

[3choplex]

Note: Although I forgot to include in this layout the 820 ohm NFB resistor, and .001 PI coupling cap  : , this is a fully tested, working layout.

I think it's also missing the positive connection between the 47uF and 22uF caps. Cool layout!

[samato]

I'm coming up with a lot of questions as I'm trying to get my parts together.  I'm currently wondering what the reasons are for running some wires under the circuit board and if it would be okay not to do that.

I'm considering using a small piece of wood with nothing protruding from the bottom of it.  It would sit flat on the chassis so I wouldn't be able to run anything underneath.

Are the wires run underneath just to keep things cleaner or are there more important factors to consider with this?

[Fresh_Start]

You don't have to run under-board wires.  I try to keep them to a minimum.  You can have flying leads over the top of the circuit board, but that looks messy and could make populating the board with components more difficult.

You aren't suggesting a wooden circuit board, are you?  I know that a few guys have done just that, but the potential for an electrical fire doesn't appeal to me.  Besides, I'm still not skilled enough with the soldering iron that some turrets wouldn't scorch the wood around them.  There's also the potential for the wood to become slightly conductive in a very humid environment, but that can happen to tag board too.

Cheers,

Chip

[samato]

Yeah, I'm considering a wooden board.  Not because I think it's better or anything, just it might be easier and cheaper in this case.  I know there is potential for fire but I was doing some "testing" and I think it's highly unlikely that this piece of wood could catch on fire inside the amp.  A spark is not going to do it.  Maybe prolonged, direct contact to high temperature could but none of the parts on the board get that hot, as far as I know.

Basically, I was holding a lighter to the board and it was very hard to make it burn.  It got scorched but would not go up in flames.

I'm also considering plexi-glass and other plastics.

[samato]

I need some help with this.

I've been researching the theory involved in how to layout transformers, tubes and how it relates to different parts of amp circuits.  My understanding is that in general it's best to have as much space as possible between the PT and the OT to reduce noise.  The angle is important too.  I read about the headphone trick to test for this and I might try it but it might not matter in this case because the chassis I'm trying to use is so small that there are only so many possibilities.  If it really seems like it won't work I might try a larger chassis but I want to give this a shot.

The problem with moving the OT as far away as possible, as I understand it, is that at some point you face the problem of long wire runs and risk having the OT too close to the preamp circuitry - another kind of noise.  So it seems this is a balancing act of sorts.  Compromises must be made somewhere when you're dealing with limited space.  I'm trying to find the best compromise here.  Maybe this amp will be noisier than it could be because of the tight spacing but maybe the choke will help with that?  Anyway, I'd be willing to deal with some noise if it's not too bad and it means I get the sound and portability I want.  I'm used to dealing with a noisy Pro Jr. anyway.  I've decided this will be a head, not a combo by the way.

The next 3 posts show 3 options I've come up with.  My circuit board will be very small compared to most I see here and I should be able to play around with it's position.  I think it should be pretty close to the front but I can slide it all the way left, toward the middle, etc. - if that helps.  I'd like to hear your thoughts on what's preferable or any other options.  Thanks.

[samato]

Option 1

[samato]

Option 2

[samato]

Option 3

[samato]

Option 4 - This is now looking to me like the only way that would work.

[sluckey]

What is the height of that chassis? 1.5" or less? Is it high enough to mount the PT and still put the bottom cover on? And don't forget about the filter caps. They take up a lot of real estate. Building in a small chassis has it's rewards, but it can be a bitch to plan and build or work on later. I like your option 4 and think you can pull it off if you plan well.

I built 3 combo amps (including my TDR) using a Hammond 3x4x17. It's tough. I've since switched to the typical Marshall style chassis 2.5"H x 6.5"D x whatever length I need. It's a pleasure working in a chassis of those dimensions.

If you have any reservations about cramming your amp into that small chassis, just get a bigger one.

[samato]

Chassis height is 1-14/16" (10-13/16" wide, 6-1/16" deep).  I checked and it would be enough to for the PT but I'm thinking about using spacers and keeping the PT above just to have the extra room inside for other things.  

I'm also thinking about using an Altoids can to put my filter caps in.  They all fit but I'm a little concerned about the wire runs that would be necessary to do it this way. 

I'm also wondering if it might be better to mount the choke underneath.  I don't see anybody else doing that but I think I could fit it and it would allow me to get it farther away from the pots.  Should this even be a concern?

I decided this will be a head.  I originally wanted a combo but it's just too much to think about for me at this point.  Doing it as a head simplifies things and is probably better in the end anyway.  Combo amps, especially small ones, are torture chambers for tubes.
 

[samato]

Got my board ready.  I used a piece of what I think is some kind of fiberglass I found at a surplus store.  The sheet cost $3 and I could make about 5 of these boards with it.  The eyelets were done with a grommet tool I got at Harbor Freight for $2.99, with 100 grommets included. 

Now I'm struggling with making the chassis holes and cutouts without the proper tools or know how.

[samato]

Big Rookie Mistake!

I made my board layout by following the original Deluxe Reverb layout.  This would've been fine with the combo amp design I was originally going for but I've since decided to make this a head.  Now my board is upside down!  

I think I'm going to make a new board and get it right because not only would doing it this way look messy but running the wires that go to the tubes across the wires that go to the pots and the extra wire length can't be good for noise.  

Re-doing the board would be the smart move at this point, right?

[JayB]

Just do it in reverse and call it a Marshall Twin. 

[Magic_Man_Amps]

I did the same thing on my first build, ended up with a left handed 5F1 head. 

[samato]

Yeah, maybe it's not a big deal.  It's correct from left to right, I just don't like having the points that connect to the tubes being on top and the points that connect to the pots being on the bottom.  

Anyway, the new board is underway.  I wouldn't have bothered re-doing it if I hadn't already made the holes for the PT and power connector - I could have just moved those to the other side. 

[samato]

2 questions:

1 - The AB763 Deluxe Reverb schematic calls for a 250K-A pot for the Treble control.  All I have on hand at the moment is a 500K-A.  What differences can I expect if I use the 500K-A pot?

2 - Does the layout of the tubes & transformers below look like it will cause problems with heat?  This will be a head with LOTS of ventilation, almost completely open like it is now.

[samato]

I'm confused by the voltages I'm reading on my PT secondaries with nothing connected to them:

Yellow - 214 V (specs say 5 V)
Yellow - 216 V

Green - 303 V (specs say 6.3 V)
Green - 299 V

Blue - 231 V (specs say 50 V - bias)

Red/Yellow - 186 V (CT)

Red - 113 V (specs say 660 V)
Red - 491 V


I know the voltages should read higher than the specs because the PT is unloaded but I didn't expect this big of a difference.  Is this normal?

These readings were taken with just the main power, fuse, power switch and transformer primaries connected.  I have Neutral going to the fuse which goes to the black PT primary lead.  Hot from the wall is going to one terminal of the power switch, PT white primary lead to the other terminal.  Ground connected to a ring terminal bolted to chassis ground.  My meter was set to 700 VAC and I had the black lead connected to the chassis, red lead to each secondary - one at a time.  Here is a link to the transformer I'm using: http://store.triodestore.com/deretrvipotr.html

[sluckey]

All those readings are bogus because you don't have any secondaries connected to chassis. You must connect your voltmeter ACROSS the windings for the correct voltage.

Yellow to yellow will read 5vac.
Green to green will read 6.3vac.
Red/yellow to either red will read 330vac.
Red/yellow to blue will read 50vac.
Red to red will read 660vac.

[samato]

Ah, across the windings, not to ground - duh!

So now I get:

Yellow to Yellow - 5.65vac
Green to Green - 7.06vac
Red/Yellow to Blue - 53vac
Red/Yellow to Red - 364vac
Red to Red - 730vac

[samato]

Everything is assembled and wired.  The amp doesn't work.  

Here are my voltages.  I think these are close to normal based on some others I compared them to on the Valve Data Page.  

V1 - 12ax7
Pin 1: 247
Pin 2: 0
Pin 3: 2.02
Pin 6: 241
Pin 7: 0
Pin 8: 2.09

V2 - ECC81 (12at7)
Pin 1: 225
Pin 2: 65
Pin 3: 100
Pin 6: 230
Pin 7: 67
Pin 8: 100

V3 - 6V6s
Pin 3: 489
Pin 4: 488
Pin 5: -59
Pin 8: 0

V4 - 6V6s
Pin 3: 489
Pin 4: 488
Pin 5: -59
Pin 8: 0

I think I may have wired my input and output jacks wrong or the jacks I'm using are no good.  They are switching jacks but looking closely at them it seems like they are not actually shorting when no plug is inserted.  

With a guitar plugged into either input and a speaker connected to my main "Speaker" output I got no sound.  Not even a little hum or buzz.  Volume control had no effect.

With guitar plugged into "Hi" input and speaker connected to "Ext. Speaker" output I got no guitar sound but I did get hum/buzz.  Volume control increased noise.

With guitar plugged into "Lo" input and speaker connected to "Ext. Speaker" output I got guitar sound but not good.  Sounded like I was using an octave pedal (guitar signal plus an octave or 2 below).  Lots of noise.

Please have a look at my jack wiring and let me know if anything looks wrong.  I feel like I'm very close but I'm also very lost at the moment.

[samato]

.

[sluckey]

Those jacks don't look like Switchcraft so the lugs may be arranged differently from Switchcraft lugs. You'll need to verify which lug is which on those particular jacks.

If your speaker jacks are wired properly, you can't get any sound from the EXT. SPKR jack unles you have a plug in the main SPKR jack because the switch on the main jack will have the OT shorted out.

You can test the input jacks with your ohm meter and a guitar cord. Connect one meter lead to V1 pin 2 and leave it there.

1. With nothing plugged into either input you should read 34KΩ from V1-2 to chassis.

2. Plug your cord into the Hi jack. You should read 34KΩ from V1-2 to the free end tip of your guitar cord plug and you should read 1MΩ from V1-2 to the sleeve of the guitar plug.

3. Plug your cord into the Lo jack. You should read 68KΩ from V1-2 to the free end tip of your guitar cord plug and you should read 68KΩ from V1-2 to the sleeve of the guitar plug.

Here are some pics that may help. Your layout looks good for the jacks and if you had Switchcraft jacks wired IAW your layout they would be right.

[sluckey]

Oh, I forgot to mention... The tips of those speaker jacks 'appear' to be dangerously close to those screen resistors. Hopefully there's plenty of clearance. If the jacks come in contact with the leads on those resistors your speaker will blow almost immediately and the OT secondary will follow close behind.