AB763 grounding questions

[evancorylevine]

Hey loves.

Doing my final weber kit (I ordered three at once). I'm looking forward to doing a Hoffman Princeton Reverb once I get the funds and this all done.

First, some questions.

On the controls, it looks like some grounds are going to the pot cases, while the input grounds are going to the brass plate the controls are on. My guess is that the grounds coming from the top of the board should also go to the brass plate. That sound alright?

There is a brass screw next to the power transformer that's meant for a star ground. I imagine that's all for the power side. So I should individually send each power tube's ground, plus the green/yellow and red/yellow wires from the power transformer there? Where should the grounds of my outputs go? what about the reverb/vibrato I/O?

Also, three resistors on the BOM seem to be not present on the layout: 1/2W 6.8K, 1/2W 820K, & a 1/2W 22K. Whyyyy.

That's all I can think of right now.

Thanks so much!

[labb]

You should take a look at this. It will not quiet match the Weber kit but it is sound grounding. http://el34world.com/charts/grounds.htm

[sluckey]

Weber has three AB763 amps, 6A20, 6A40, and 6A80. There are slight differences between models. Which one are you talking about?

[evancorylevine]

whoops, I meant to post the layout. I'm talking about the 6a80.

[evancorylevine]

You should take a look at this. It will not quiet match the Weber kit but it is sound grounding. http://el34world.com/charts/grounds.htm

Gah! I love it!

so basically I'm replacing the buss wire with the brass plate?

[sluckey]

Also, three resistors on the BOM seem to be not present on the layout: 1/2W 6.8K, 1/2W 820K, & a 1/2W 22K. Whyyyy.

6.8K... Probably an error. The 6A20 and 6A40 use a 6.8K rather than a mid control. The 6A80 uses two mid controls.

820K... Probably an error. None of the AB763s use this value.

22K... This resistor is on the layout and schematic. Maybe you are mistaken.

Maybe you should report these discrepancies to Weber?

[labb]

so basically I'm replacing the buss wire with the brass plate?



Yes.   Just a question....Where do you intend to play this amp?       Unless you are in a huge venue you are never going to be able to play with the volume above about 2.

[bnwitt]

IMHO the brass grounding plate is a no go.  I have had too many old Fender amplifiers in for service which needed to be cleaned at the potentiometer and input jack contact points to the brass plate due to corrosion caused by galvanic action.  I would go with a grounding buss wire rather than using the plate system.  But, that's just me.  In all reality it would take many years for the corrosion to happen, but it will happen if the environmental conditions are right.  That being said, your best source of information for how the plate is connected is gut shots of old Twin Reverb amplifiers.  I've attached a few.  You will notice the brass plate is soldered at several chassis contact points.  You need a big iron to do that.
Barry

[bnwitt]

Take your gut shots and compare them to the Fender Layout Drawing which shows the board and control grounds.  You can also use the gut shots to identify wires that can be twisted without noise consequences.  Fender amps for the most part were pretty quiet layouts except the CC resistor noise.

[bnwitt]

Unless you are in a huge venue you are never going to be able to play with the volume above about 2.

Yep.  That is an outdoor venue amplifier for sure.  I rarely build even 40 watt AB763 amps any more.  Most players have become hip to micing lower wattage amps to the P.A. for larger venues and using that same lower wattage amp for smaller venues and recording.  The times they have finally changed. 

Below is a video link which at 38' 45" has a local player who owns one of my old SRV Vibroverb builds from a few years back (which he describes as a Vibrolux) talking about the amount of power in that 40 watt amp.  Now he is a player, so forgive his non technical descriptions which are not entirely accurate, but the bottom line is even 40 watts is too loud for him and most folks:

https://www.youtube.com/watch?v=0c3LMhzILG8&t=2521s

Barry

[Ed_Chambley]

I agree, the brass plates go unless it is an original amp.  It is not a big deal to remove then and clean them, but not having it at all gives you more threads showing on you pots and jacks.  I like to put a locknut on my input jack(s).  My pots get blue locktite, a drop or 2.  So does everything else for that matter.  Nothing irritates me more than loose jacks.  I also use stereo jacks as they have a better feel and hold tighter.  I just wire them as mono.


I also never solder to the back of POTS.  For instance, some pots are stainless steel where traditional soldering will not work.  PEC and older Clerostat.  I prefer NOS pots like Allen Bradley when I can get them.


I use Electric Fence wire to make a buss that only connects to the input jack and everything is grounded in the preamp.  The grounds coming off the board combined with the ground coming from the pots will hold the buss in place very well.  I like the Electric Fence wire because it easy to solder, stays where you put it.  Is thin and strong.  Sluckey turned me not to this when both of use were building an amp and neither had any copper bus around.


This is the preamp buss if you will.  Everything in the power section gets grounded on a Transformer Bolt.  Finally an earth ground is made near where the plug (IEC).  Personally, I drill a hole for this and use star washers to bite and knockout to insure it stays put.  It will get a little red locktite too.  I never use crimp or spade connectors.  If you happen to get an amp that I built, you will have to have a soldering iron to service it.  Solder and Marine Shrink Tubing.

[Ed_Chambley]

Unless you are in a huge venue you are never going to be able to play with the volume above about 2.

Yep.  That is an outdoor venue amplifier for sure.  I rarely build even 40 watt AB763 amps any more.  Most players have become hip to micing lower wattage amps to the P.A. for larger venues and using that same lower wattage amp for smaller venues and recording.  The times they have finally changed.

Not completely, but for the most part.  I still love my Blond Bassman with the 2, 12 Altec 417's.  I can also get it to sound really gnarly early on the dial.  The only time I use big tubes is when I want a big tube tone.  Is it different?  You bet ya!  Something about some of those real old Tung Sol 5881 and I favor the RCA 6l6GB too.


But I agree that you are seeing more Deluxe Reverbs and Princetons than ever, but oddly enough the amp that I have built the most of is cloning the 63 Vibrobverb, but next is the AC15.  I went to a fairly large show a few weekends ago.  Main guitar was playing through a miked up Vibro Champ and a small pedal board with a Hall of Fame Reverb.  Guy way playing an old Gold Top and I must admit it sounded great.

[bnwitt]

.....but oddly enough the amp that I have built the most of is cloning the 63 Vibroverb

It's that 6G16 brown face bias vary tremolo in that amp which makes it so desirable.  That's why Doug's version of the AB763 with the 6G16 bias vary tremolo is my go to blackface amp circuit.  Sorry for hijacking this thread.

[labb]

I recently built Steve's AB763 Delux Lite for a player and ended up having to add a master volume control to it. it runs two 6V6's.   His go to amp is a 5 Watt SE that I built for him. Every thing is miced and through a pa system. Dang, we really highjacked this thread. Shame on us.

[evancorylevine]

I recently built Steve's AB763 Delux Lite for a player and ended up having to add a master volume control to it. it runs two 6V6's.   His go to amp is a 5 Watt SE that I built for him. Every thing is miced and through a pa system. Dang, we really highjacked this thread. Shame on us.

Hahahhaha. Yes you guys did. But it's alright this time.

Okay. So I'm switching to the grounding buss. Thanks, @Sluckey, for pointing out that the 22k was on the layout and schem. I mixed up a 22k and 220k that's all fixed now.

About the power of this amp... I've been a professional guitarist for ten years, playing 1920's jazz exclusively. I got a call last year to play a more modern jazz solo gig that was really well paying, so I studied up on chord/melody, and then my Blues Jr. crapped out, so I rented an AC30 and fell in love with it. I, um, had no idea that an electric guitar could sound/feel so good. I'd only owned my Blues Jr. I immediately decided to build a bunch of amps because Weber happened to be having a sale. I built a 5F1 which is loud af, and I felt really silly for getting this 80W jawn. I also built an AC30 kit, which I finished and played out a bunch last month. I found that it got much dirtier than I would have expected at volume for a few large gigs I played. At this point, I'm really excited to have a loud, clean sound. Having said that, I'm also really excited to build a Princeton Reverb, because I miss the tone/verb/trem on my champ, which I play the most.

Sooooo. There you have it. TL;DR: Weber told me it was a good idea, then I thought it was dumb, now I think it's very exciting.


edit: clarity.

[evancorylevine]

Few quick questions:

-If I ground the Normal channel input to the bus bar, should I ground the other inputs to that input? or let the chassis do the work??

-This kit came with six springs. I imagine that those are to mount the reverb? There are only four rubber grommets with brass bushings on the reverb tank. Also, one of the brass bushings that goes in the grommet is missing. Anybody wanna ship one to Philly? <3

-The transformer has three wires on the mains side, black, brown, and blue. The layout refers to two black wires. I assume they meant black and brown? Here's the datasheet:

[shooter]

they meant black and brown?

assume that's correct

[PRR]

> some grounds are going to the pot cases, while the input grounds are going to the brass plate   .... ground bus...

To a first approximation: it's all metal, it all goes to the same place, it all works.

In practice... it takes a LOT of heat to solder to brass strip, and some pots. The heat does not do a pot any good. No other field routinely solders to pots, so some pots just won't take solder. Unless you file through varnish and plating to the base metal. Which still may not be solderable.

As said, down the road, dissimilar metals will get nonconducting fluff in the joint.

And such tricks make later repairs more work.

Bus wire on the side WORKS and is easily repaired later. Get some #14 copper from an old house or the short-ends rack in the home store wire aisle. White, grey, 3-core or 4- you don'tcare, you'll scrap the insulation and just use the copper.

[evancorylevine]

Few quick questions:

-If I ground the Normal channel input to the bus bar, should I ground the other inputs to that input? or let the chassis do the work??

-This kit came with six springs. I imagine that those are to mount the reverb? There are only four rubber grommets with brass bushings on the reverb tank. Also, one of the brass bushings that goes in the grommet is missing. Anybody wanna ship one to Philly? <3

-The transformer has three wires on the mains side, black, brown, and blue. The layout refers to two black wires. I assume they meant black and brown? Here's the datasheet:

Bump to ask these questions again, plus another:

This first graphic says the preamp caps and the B+ filter caps should be grounded separately, but the layout (second graphic) has them connected, but both grounded. Should I separate the two grounds? One to preamp ground and the other to transformer bolt? Should I disconnect them in the dog house?

[sluckey]

Should I separate the two grounds? One to preamp ground and the other to transformer bolt? Should I disconnect them in the dog house?

Yes, yes, yes

[evancorylevine]

Should I separate the two grounds? One to preamp ground and the other to transformer bolt? Should I disconnect them in the dog house?

Yes, yes, yes

Thank you Sluckey!

Does anybody have any ideas about my other issues in my last post?

[sluckey]

If I ground the Normal channel input to the bus bar, should I ground the other inputs to that input? or let the chassis do the work??

Ground all four inputs to the buss bar.

This kit came with six springs. I imagine that those are to mount the reverb? There are only four rubber grommets with brass bushings on the reverb tank. Also, one of the brass bushings that goes in the grommet is missing. Anybody wanna ship one to Philly? <3

Springs??? I've never used springs to mount a reverb tank. Post a pic so we can see what you're talking about.

Missing parts??? Contact Weber.

The transformer has three wires on the mains side, black, brown, and blue. The layout refers to two black wires. I assume they meant black and brown? Here's the datasheet:

If the line voltage is 120 or less use the black and brown wires. If the line voltage is greater than 120v use the black and blue wires. DO NOT USE BOTH BLUE AND BROWN WIRES AT THE SAME TIME!

[bnwitt]

Most Jazz guitarists I've known were big Roland JC120 lovers.  How did you end up with tube amps?

According to the Weber "All Kits" BOM excel file:

https://www.tedweber.com/media/kits/Weber-Kit-BOM.xls

.. you were supposed to receive (8) springs for the reverb installation.  Since the original amps had reverb bags screwed to the bottom of the cabinet, I have no idea how Weber envisions the pan being installed but Weber has a forum for kit builders:

http://tedwebers-famous-loudspeakers.vanillacommunities.com/categories/weber-kits-and-parts

a search of that forum revealed a thread on mounting the tank "Weber" style:

http://tedwebers-famous-loudspeakers.vanillacommunities.com/discussion/comment/14231#Comment_14231

Barry

[evancorylevine]

If I ground the Normal channel input to the bus bar, should I ground the other inputs to that input? or let the chassis do the work??

Ground all four inputs to the buss bar.

This kit came with six springs. I imagine that those are to mount the reverb? There are only four rubber grommets with brass bushings on the reverb tank. Also, one of the brass bushings that goes in the grommet is missing. Anybody wanna ship one to Philly? <3

Springs??? I've never used springs to mount a reverb tank. Post a pic so we can see what you're talking about.

Missing parts??? Contact Weber.

The transformer has three wires on the mains side, black, brown, and blue. The layout refers to two black wires. I assume they meant black and brown? Here's the datasheet:

If the line voltage is 120 or less use the black and brown wires. If the line voltage is greater than 120v use the black and blue wires. DO NOT USE BOTH BLUE AND BROWN WIRES AT THE SAME TIME!

got the inputs grounded. bwitt got me covered for the springs and all. Thanks bnwitt!!

I'm in Philly. Should I just use the 120v because that's what the US standard is? Even if it wavers by 5%?

[PRR]

> I'm in Philly. Should I just use the 120v because that's what the US standard is?

I have solid 125V here. That is a general trend.

No doubt you can find 105V in the older parts of Philly, and 125v where old distribution was finally upgraded, and 135V where PECO has screwed-up.

I'd go 125V in almost all situations.

[bnwitt]

I'm not so sure about that T-nut/spring method of mounting the reverb tank.  Seems like it would allow a lot of dust bunnies into the spring area.  I've been doing all of mine like the old fender style with the cardboard/plywood bottom plate attached to the tank and mounted into a bag.  But let us know how that works out. 

I'm with PRR on the 125V tap.  I'm using single 120V primary tap PTs and my voltages run higher than the original Fender BFDR amps.  I wish I had the option to drop the secondary B+ that way.

[evancorylevine]

> I'm in Philly. Should I just use the 120v because that's what the US standard is?

I have solid 125V here. That is a general trend.

No doubt you can find 105V in the older parts of Philly, and 125v where old distribution was finally upgraded, and 135V where PECO has screwed-up.

I'd go 125V in almost all situations.

alright. I'm going 125. where in PHL r u?! I'm in the cedar park neighborhood.

I'm not so sure about that T-nut/spring method of mounting the reverb tank.  Seems like it would allow a lot of dust bunnies into the spring area.  I've been doing all of mine like the old fender style with the cardboard/plywood bottom plate attached to the tank and mounted into a bag.  But let us know how that works out. 

I'm with PRR on the 125V tap.  I'm using single 120V primary tap PTs and my voltages run higher than the original Fender BFDR amps.  I wish I had the option to drop the secondary B+ that way.

If the bag is easier/better, I may just do that...

[Ed_Chambley]

I'm not so sure about that T-nut/spring method of mounting the reverb tank.  Seems like it would allow a lot of dust bunnies into the spring area.  I've been doing all of mine like the old fender style with the cardboard/plywood bottom plate attached to the tank and mounted into a bag.  But let us know how that works out. 

I'm with PRR on the 125V tap.  I'm using single 120V primary tap PTs and my voltages run higher than the original Fender BFDR amps.  I wish I had the option to drop the secondary B+ that way.

I began using Coroplast (corrugated plastic) in-place of the cardboard.  I build the bottom of the tank the same way as I would using cardboard just like old Gibbs tanks in Fenders.  The screws hold and if by chance someone spills a drink in the back of the combo, happens more than I realized, it is simple to remove and clean without having to replace the cardboard.


Just my 2 cents.


I do no necessarily select the voltage tap according to wall voltage, I select it based on the plate voltage of the power tubes I am shooting for.  Also, I have used both on a switch to change from Solid State rectification to tube rectification and use the lower on the SS rectifier which keeps the voltage closer to the same when I change.


I guess there are a lot of ways to skin a cat.