Copper Grounding Bus

[Ron Worley]

I'm attempting to do a pretty close version of Franny, but using PEC or Clarostat stainless back pots; i.e. no soldering to them.

I know that there exists a special grounding washer with an extended strap on it that you wrap around the pot, and it allows you to solder the copper buss wire to it.

I have searched everywhere for them (Ampwares has them, but I'm not excited about using Mark again)- does anyone have an idea on a part number, manufacturer, whatever on these??

I found an Amphenol BNC ground lug that would have been perfect- but it's ~1/4" too short on the lead to make it all the way around the pot's back.

I would be very grateful for some help here!

Thanks,

Ron

[Richie]

Ask Allyn, he should have some, and if not he probably knows the part number,and where to get them.

[Ron Worley]

Allyn had some that he said were Clarostat, but I've had zero luck trying to find them elswhere in case he doesn't have any more....

Thanks Richie!

Ron

[Ron Worley]

Bump-- No other inputs guys??

Ron

[Phil_S]

Unless the "look" is your concern, just run the buss wire along side of the turret board. There is no requirement to solder it to the pots.

Here's my TMB18W showing what I mean.
http://tinyurl.com/2deax9

[drhulsey]

...(Ampwares has them, but I'm not excited about using Mark again)...

That's the only source I could find. I ordered from Ampwares and decided not to be in a hurry They eventually showed up They were 16 cents each.

[nickt]

Don't know about the USA but aussie mains cable tends to be really thick solid copper. I'd assume US stuff would be even thicker give it has to carry double the current.

Buy yourself a meter/yard/whatever and strip the wires - note that I'm talking about the stuff you wire a house with not stuff for powercords.

Maybe skyboltone could chime in (ex-electician and all that if I recall correctly? apologies if not )

[Ron Worley]

Well, yeah... I suppose it's the look I'm after...

I'm trying to be as accurate as I can (even though KF didn't use the lugs 'cause he worked with non stainless pots).

I know that somebody here has found a way to do this.... Is there any kind of way that I can do something else??

Ron

[nickt]

Well, yeah... I suppose it's the look I'm after...

I'm trying to be as accurate as I can (even though KF didn't use the lugs 'cause he worked with non stainless pots).

I know that somebody here has found a way to do this.... Is there any kind of way that I can do something else??

Ron

You *can* solder to stainless but only using silver solder. I've done this with SS gas filltings on various things but that was with an oxy torch!!

Somehow I don't think this would be much good for your $12ea clarostats

No idea if this new lead free stuff would do the job using just an iron (my guess: not!)

Another option might be spot-welding - if you've access to a metal shop (say at a high school) they might have one of these.

[kineteks]

I used PEC pots in my Liverpool build, see "It's Alive...." You can solder to stainless as posted but in my experience it's the flux requirement and not the solder that makes a difference. I used 60/40 Kester to do the ground buss. First you must "tin" the pots, however...
It's easy but some precautions must be taken. The flux I have best luck with is Stay-Brite acid flux.... not good for electronics. I scuffed the area to be tinned with Scotch-Brite, wiped it down with acetone and then masked off everything but the back & a little bit of the sides of the pot. Then I carefully applied the Stay-Brite acid flux with a Q-tip, no puddle just wet the surface, and then with a HOT iron (Weller 900 degree chisel tip) applied the 60/40 solder. I then rinsed the entire pot back with soap & water, dried it, removed the tape and cleaned the back again with soap & water on a paper towel. I actually did the last part several times because I'm anal. You can now solder to the tinned portion of the pot with regular 60/40 rosin core solder.

[Ron Worley]

Wow, it sounds like soldering to the stainless pot back is quite a production... I might do that as a last resort.

I am still sure that somewhere out there somebody has a suitable lug- the Amphenol unit I found is SO close.... just 1/4" too short on the lead...

Thanks much to everyone for their help so far!!

Ron

['67_Plexi]

If you dont mind taking a slight detour from what Ken did then use a multi-star ground system, using the chassis as the main conductor, not connecting more than 2 gain stages to each ground and totally seperating the power amp and preamp smoothing grounds from each other, along with not allowing the speaker current to flow through large areas of the chassis (only reason you ground the speakers is for the feedback loop, which has a very samll current flow). Follow this and you will end up with an amp with a lower noise floor than any original Wreck if thats what you want. It might not be and thats OK to.

IMHO Kens amps sound awesome, his grounding system was not, especially for the inexperienced.

[Ron Worley]

Alan-

Thanks for the tip. I have heard from many other sources that the TW ground scheme is less than optimal. I'm going to try to make this first one as 100% as possible as a known starting point. I know that it's a bit like paint by numbers in approach, but frankly I've learned a ton by copying Franny as closely as possible. Do you have a gut shot showing your grounding scheme?

I've also discovered many little nuiances like grounding the third leg of the Bias pot to ground- it is not shown in some of the layout diagrams, but I discoverd it by reading one of Dana's old posts- then I looked at the updated schematic and had a "Holy Shit" moment discovering that I had overlooked that very obvious thing.

I have sourced enough parts for 4 wrecks- 2 Express and a 'Pool named after my wife and daughters and a final Express for a friend who gave me a bitchin Matamp C7 just to be a bro. I figure that I will use the latter two to experiment with alternate grounding schemes.... once I really understand Aiken's article on the subject..lol

Ron

['67_Plexi]

You're welcome Ron.

I don't have a gut shot, but I can expain it really easily.
This is the scheme I use on virtually everything. Most of my amps are higher gain models that would have issues with the grounding scheme used on TW's. Ken did it his way probably because he knew he could get away with it, and it's pretty simple, I assume.
I can absolutely guarantee that the scheme I use in most situations will be substantially less troublesome and is something to think about if you venture on to anything with more gain or complexity. Like I said it does work in TW style amps and it also means you don't need to solder to the back of pots.
There are many schemes, but this is the one I nearly always use on everything.

Starting at the power and going forward.

1. The incoming power supply earth (ground) should always have it's own ground point as close to the mains input as possible.

2. The filament (heater) ground should also use it's own ground point as close to the first power tube as practical.

3. The power supply centre tap, all three 40uF cap grounds and two bleed resistors connect to the chassis bolt in front of the smoothing caps.

4. The ground for the bias circuit really doesn't cause issues because it has such a low current flow that it can be grounded wherever is convenient.

5. I always use speaker jacks that don't ground themselves to the chassis.
THe largest currents in any amplifier are those flowing in the output transformer secondary. To avoid the flow of this current through the chassis connect the OT ground wire directly to the speaker jack ground.

6. Run a wire from the speaker jack ground and create (drill) a ground point in front of the presence pot. Connect the wire to this ground point along with the ground from the top right (looking from the front) 20uF smoothing cap and the ground tab from the presence pot (don't ground the pots body).
The only current the flows in the wire from the speaker jack to this ground is associated with the feedback loop and this is small.

7. Join the two grounds from the last two 20uF caps and make a ground point in front of the 'Mid' pot. Connect the cap grounds to here. Run ground cables from the mid point ground lug, third stage cathode ground (10K resistor on the board).

8. Create (drill) a ground point in front of the volume control. Run the ground from the volume pot lug, first two stages cathode grounds, 150K resistor.

9. Connect the imput jack ground to a ground point as close as possible to the jack. Switchcraft jacks actually ground themselves, but I use a seperate cable in case the jack nut comes loose in the middle of a gig or something. This avoid crackles and pops.

Some may look at this and think its creates a ton of ground loops. Ground loops only occur with sufficient ground current flow.
It doesn't because it uses the chassis as the main ground conductor (instead of a thin wire hanging off the pots) and by it's layout, controls and keeps heavy current flow away from sensitive areas.

Hope this is useful.

If your a first time builder, save yourself some noise and run a low pF sheilded cable from the volume pot wiper to the second stage grid, connecting the sheild to the pots lug connecting to ground.

Sometimes a small grid resistor at this point tames an out of control amp and will stop you picking up public radio. (10K - 22K usually works).

I named my Company after my wife Carol-Ann !! Actually it stems back to a time when I built an amp even though we didn't have much money. I named it after her so it would be harder to bitch at. The name stuck, but she still bitched at me anyway.


Alan.

[drhulsey]

... I have sourced enough parts for 4 wrecks...

Since Ampwares has the part you want, I would humbly suggest you order from them and just be prepared to suffer the wait I think it took about 3 weeks for mine to arrive.

... she still bitched at me anyway...

She can't help it Alan. That's genetically predetermined
Thanks for sharing your grounding scheme