Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Archives of favorite topics => Topic started by: richierick on November 15, 2007, 01:27:23 pm
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What is the recommended minimum space between turrets for a build like the AB763?
Richierick
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I think the Hoffman layout uses 9/32" between turrets.
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I use 3/8" but under certain circumstances have used much less.
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thanks a lot. i was thinking of using 5/16" as i need the board as small as possible.
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I did one for a Champ that has 5/16" spacing on G10 board. I would normally use 3/8".
Be sure to leave enough room for the bigger caps.
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Believe it or not it's 19/64ths.
There a long story that goes with why it's 19/64ths.
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There a long story that goes with why it's 19/64ths.
I've always wondered why. Love to hear the story.
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Ok, since you asked. ;D
When I was creating my first hand made turret boards in my garage, it was very difficult to layout and drill holes in a piece of G10.
You could do it, but it was not perfect or very fast.
Then I thought about the template idea, a piece of metal to guide the drill bits at a standard spacing.
I couldn't drill a template myself, the drill bits would walk all over the place.
Starting a hole with a counter punch and then drilling wasn't cutting it either.
Then one day I took apart a computer back up tape cartridge.
It had nice stainless steel hardended pins inside that were 3/32 diameter and about 1/2" long.
It also had an aluminum backing plate that kept the whole tape cartridge rigid, perfectly flat and all the rollers and pins had a nice solid plate to attach to.
This plate also had a matrix of very small dimples in the aluminum.
I drilled out some of the dimples and made a master template that I could drill longer templates with since the tape cartridge piece was only about 6 inches long by about 4 inches wide.
Anywho, I used that tape cartridge backing plate template to create a bunch of templates when I built my amps and the early board kits.
Later on when I wanted to have a CNC machine make the metal templates that I now sell, I took the original tape cartridge template into the CNC guy.
He measured the hole spacing and set up the CNC machine to drill all the horizintal holes at the same spacing.
The templates I sell now are 19/64ths spacing horizontally and 5 or 10mm spacing vertical, cause most modern caps like the Xicons have metric leg spacings.
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Now that's a good story! Thanks
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Any reason you didn't just make it 7.5 mm instead of 19/64 in., as long as the vertical spacings are metric anyway?
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I use 1/10th inch grid graph paper to do a pencil layout and then a scribe to mark the holes on the board by pressing it thru the graph paper.
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> space between turrets
US custom for generic tag-strips was usually 3/8". This is a good fit for 1/4" resistors and 1/2"-3/4" caps, and easy to find on a ruler.
Nobody would use 64ths-inch dimensions. (Unless he already had a 19/64" dimpled plate in hand!)
> didn't just make it 7.5 mm
He already had the CNC-dude set it up to match his tape-plate template. It works. Why pay him to do it again in Metric? All his old boards would end up a silly millimeter off at the end. If we had to have exact interchangability with rigid parts made elsewhere, metric would be wise.... but resistor leads bend and the side-ways spacing doesn't affect fit. This is Pisgah Forest NC, NOT Houston rocket-science. (And why did that Mars rocket miss Mars? Wasn't it a mistake converting english to metric?)
Heck, I've spaced stuff with a beer-can pull-tab. (You younger guys, ask your dads.) Tape-cart gut is so hi-tech.
> i need the board as small as possible.
Probably a mistake. Unless you know exactly what you are doing. If so, then why put different width parts on same-width spacings? You can put 1/4W resistors real close, 0.1u 600V caps need room.
Get your layout order settled, and get your parts. Put a foot of double-stick tape on cardboard. Start from one end. Put down a part, leave a little space, put down the next part. Pencil a line under each lead; this will be the side-side turret placement. Find your longest part, add a little lead-length, this is your front-back row spacing. If you are really cramped you can do 3 or 4 rows for short parts in the length of one long part. You can stagger vertically: set caps high and resistors low underneath. You can even start putting parts down crossword-puzzle fashion like PCBs do (which makes work a real puzzle).
Then as loudthud says, poke the drawing or cardboard layout to guide the drill. (I usta use carbon paper.... ask your mom.)
Of course if you tight-fit a 1/2W resistor, and then discover it shudda been a 2W resistor, you could wind up in a jam. Plan to be wrong about something.
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And why did that Mars rocket miss Mars? Wasn't it a mistake converting english to metric?
Not exactly. The Mars Climate Orbiter didn't miss Mars. It got destroyed because Lockheed Martin - one of the main contractors - had reused old computer code in imperial units (pound/second) instead of the specified metric units (newton/second), resulting in a 4.45 thrust underestimation factor during orbit insertion. The probe enetred atmosphere at 57 km instead of the planned 150 km and got destroyed by atmospheric stress (yes, Mars has got an atmosphere) during it's first orbit. Now NASA and it's contractors have gone fully metric...
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>Plan to be wrong about something.
At the very least.
I built a proto using a very, very cool idea. This idea was to make it as modular on the inside as possible - separate boards for each preamp channel, power amp, effects loop, etc. The really, really cool part was that the two preamp boards would be stacked and - you getting this? - the top one would be hinged and flip up to expose the bottom one! Did I mention how incredibly cool this idea was? Trouble is, once I got everything nailed inside, I couldn't wire it in any configuration that would allow the top board to flip up. I couldn't get to the bottom board at all - and I realized as the proto process developed after it was running that I needed to change component values. Crap!
To make matters worse, I had also decided to flip my pots upside down. This would allow me to run the hookups along the bottom (top) of the chassis and give me room to flip the board up. This obviously turned out to be moot since I couldn't flip the board up anyway AND Murphy the anti-amp tech was around to make darn sure I had a few problems with those pots as well that needed fixing. Of course,I couldn't get to them now because the preamp boards were too close and their freakin' upside down! Grrr!!!! Double crap!!
Solution? Rip the stinkin' boards and pots out and redo the whole thing. I've still got stacked boards in there, but I'm slaving feverishly to use as much of Doug's style of layout style as possible to cram everything that was a problem this time onto one board next time.
If yours will be an untried, untested, unproven layout, absolutely expect failure once or a few times. Note that my problems were nearly all mechanical ones and not signal, but I only got lucky on that. The best laid plans of mice and amp designers often go astray.
If you can use one of Doug's layouts, even if you have to mod it a little to fit your design, you'll be miles ahead. And you can score his board building stuff to make it easy to build others like it. I sometimes feel guilty about taking so much advantage of someone else's hard work, but I'm finding ways to get over it.
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Any reason you didn't just make it 7.5 mm instead of 19/64 in., as long as the vertical spacings are metric anyway?
Cause the tape cartridge metal backing plate is what my CNC guy measured and copied and that was 19/64ths.
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UPDATED 12/31/2021
I started a new topic with more info on Hoffman Turret board spacing
Go Here
https://el34world.com/Forum/index.php?topic=28346.0