tube breadboard - grounding advice sort

[andrew_k]

I'm in the midst of building this: (click for larger version)


(pegboard-based design entirely copied from "Tubelab 3")

I'm reasonably satisfied with the heater supply routing; points marked "AB" and "CD" are joined via separate sets of twisted pairs routed far below the pegboard. I big fat 6.3V transformer from a 'scope and/or a 12V SMPS will provide ample current for my needs.

My question is on grounding. How would you suggest I provide ground reference for circuits on the breadboard? The box marked "B+" is a  meter, switch and a pair of heavy-duty terminals wired up to a remote variac-fed 400-0-400 PT. The ground reference for the entire board will come from this point. The "AC1 AC2 AC3" box is a set of three independently fused mains supplies provided for convenience, the earth connection within will not be used in a circuit.

When looking at the larger version of the plan, you can clearly see a brown/gold bus-bar running from the "input" end, across the front, up the right side and around the back to the "B+" breakout box. My original plan was to use this for grounding, keeping all paths to ground in order throughout a circuit. I see three main problems with this approach:
 - alligator clips everywhere attaching to ground bar
 - ground bar would need to be slightly elevated to allow alligator clips to attach securely, thereby interfering with with  barrier strips that are long 3 sides of the breadboard.
 - the ground bar will oxidize, providing a poorer ground over time.

My current thinking is a fat stranded ground wire wired underneath, running the same routing, but bought up above board in a few places to barrier strips. This would avoid the first two problems above, and is what I'll go ahead with unless anyone can suggest otherwise.

Thanks for taking the time to read all this rambling, I look forward to any insight or advice offered.

[tubesornothing]

For my breadboard, I just made up a series of euro plugs for the ground bus, then ran all ground wires back to it.  That way I was able to avoid alligator clips.

[jjasilli]

I too have been toying with the idea of an amp breadboard. 

Ground:  sheet of aluminum mesh covering the top of the board.  The holes in the mesh would facilitate the screwing down of sockets, trannies, etc., eliminating the need to drill through solid sheet metal. 

Pentode sockets:  relay sockets that screw-mount to the board and have screw terminals
Novals:  ???

Parts substitution:  use some pre-fab, plastic, solderless perfboard breadboards.  That would be for odd values, or high wattage components.  Otherwise substitution/decade boxes could be used.  Maybe house a couple of 2 or 4 gang rotary switches to safely and simultaneously A/B various pairs of  components (e.g., screen resisotrs) on the board. 

What do yo guys think?

[stingray_65]

I have been pondering the thought of a protot board too.

I'll be very interested in the details of yours, the devil is in the details...

I'm not sure I would like a buss running around the perimiter like that, but a wire running around the underside, "popping up" to a barrier strip sounds all right to me

Just my .02.....
I tell this to all people starting a first time project, this is your FIRST (go kart, chopper, tube amp, guitar,kitchen cabinet, proto board) it doesn't have to be perfect!

after you build this, and use it ( a lot I hope) you'll find  there are features you built in that will seldom be used. Invertly you'll find features you should have put in but never considdered.

the SECOND one will be MUCH better I promise! ( and more useful too)

[tubesornothing]

I built mine a while ago and have used it on several projects.  Far from the real cool one buttery developed. 

I just basically built "modules" out of 1/8" FRP and euro terminal strips.
- PT module
- rectifier module (ss or tube)
- B+ filter module
- triode module
- triode with CF module
- PI module
- power stage module
- reverb module
- pentode module
- a few different tone stack modules

I just the use the euro terminal strips to wire in and out different values.

It is amazing how quiet it is without a big chassis and lots of wires.  Works really well just to quickly slap something together and give it a try.

Its true power is in the quickly and easy re-arrangement of modules.  Want to move a gain stage after the tone stack?  2 minutes.  Want to try a different tone stack? 2 minutes.  Want to try a different PT?  2 minutes.


I gotta picture around here somewhere, I'll see if I can dig it up.

[tubesornothing]

I didn't have a pic, so I just lined up the modules and put them on the bench:

The top one is power supply, rectifier and B+ filtering.

The bundle of black/white wires are heater wires.  I use 1/4" blade connectors for those.
The bundle of red wires  are B+ wires
There usually also is a collection of green grounding wires, going back to the power supply area.


Then from L-R:

input
triode gain stage
5879 gain stage
EF86 gain stage
James tone stack
PI
Push pull power stage
OT

I have about a dozen more modules: reverb, TMB tone stack, etc.

[stingray_65]

That is a REAL neat idea to make those stages modular, It's sort of how I think an amp through.

[DummyLoad]

far from the real cool one buttery developed.  \

ah-hem! that was not just buttery...   

if i had it to do all over again, instead of the mylar coating, i'd laminate a piece of .062" G-10 onto the aluminum plate. there is a 3rd version, it's 20" x 36" (larger), has more flexible mount points for the PT/OT/Chokes, etc., it's drawn up but the plans are on my home PC, so if anyone wants a copy just send a PM. one would likely need the services of a machinist to complete unless you have access to a large table drill press or vertical mill.

use whatever grounding scheme will work, but don't lock yourself into one scheme, after all, it is a breadboard; you may want to experiment with star, bus, and closest point grounding techniques... we have found that running grounds to tie points on the fly work best, that way if you have shift components the ground points move easily. we tend to follow the star method, it seems to work best with our breadboards. use 22-24AWG wire with those smaller DIN strips, yer gonna cuss it when you have 3 or more wires/components on on tie point unless you do. if you're going to have more than 4 wires/components land on one tie point, then bridge to the adjacent tie point.

filament wiring is crucial, if you don't twist and tuck the wiring away from signal and DC power, your circuit(s) will pick up hum. try to keep your wiring neat but as short as possible. wiring up a birds nest will give you ckt. performance problems, make things difficult to troubleshoot, and hinder ckt. moves/adds/changes - in short, try to wire things up as they would lay in a chassis.

above all be careful and have fun!

--ISO

[tubesornothing]

far from the real cool one buttery developed.  \

ah-hem! that was not just buttery...   

gotta post a picture to receive any credit...

[andrew_k]

tubesornothing: Thanks for taking that pic and posting up details of your board. After having seen a pic of Buttery's when he was developing his bass preamp I've been pondering a design that would suit me and scouring the intertubes to find what others have made.
Originally I was planning a single large board with rows of fahenstock clips, but the inherit limitations of that format combined with my inexperience in lead dress kept me second guessing my plan until I found Tubelab 3.

ISOTone: Thanks for the advice! I really like the boards you and Buttery' made.This one measures 22" x 30", a limitation set by my main workbench. All good tips regarding hookup wire and heater routing. I've collected a stockpile of 22 and 24awg stranded wire from the PSU looms of discarded computers, and will be routing the two pairs for heater supply "outside" of the board area, as shown in the attached image (AB and CD). These do come a bit close to he DC supply, but will be 2" below the DC supply and if need be I will put a grounded sheet of aluminium between the heater supply and the DC breakout box.

[RicharD]

Here's what's on my breadboard at the moment.

Top left - 12VDC supply for relay controls.
Top center - Power supplt for the BzDz amp
Left bank - Copy of an Altec1576a preamp experiment for kagliostro sans the power supply (tomorrow)   
Right bank - BzDz audio circuit.

Zilla has a built in variac 0 - 130VAC, 6.3VAC, and 12.6VAC transformers.

[andrew_k]

There it is!

That integrated variac is a killer feature, I wish I could copy it. I can't afford a second variac, and my existing one is over a foot tall  :shocked:  Enough typing from me, I need to get back to building this thing.