I got so tired of looking for a decent and reasonably priced AC30 chassis....

[G._Hoffman]

....I decided to make one for myself. 

I still have a LOT to learn about using a bending break - even one as cheap and shoddy as mine.  Not sure if I'm going to use the aluminum preamp section shown here, or if I might decide to go with the steel one I also made.  I know they used aluminum in the old AC30's, but they had their transformers mounted in such a way as to support the preamp chassis.  On the other hand, if I stick with the aluminum, I'll only have to get the power amp chassis plated (the steel I'm using is mild steel, which is to say it will turn into rust in about a week - not what I want at ALL).  The steel one turned out a bit better, though, so there is that, too.  Of course, the aluminum came from a scrap dealer, and the (16 gauge) steel came new from the home center, so the aluminum is a bit rougher looking for that reason, too!

I forgot to make the holes for captive nuts before I started bending, which means they will suck to make. 

Actually, the thing I most need is to figure out a good way to cut steel in a straight line.  I have a non-ferrous metals blade for my table saw (which isn't much fun, as it sends chips flying EVERYWHERE), so I'm pretty good on aluminum, but the similar blade I tried for steel shot off a crap load of glowing red chips right into the pile of sawdust under the table saw!  NOT a good idea, I don't think.  What I WANT is a sheer, but since I want to be able to use 16 gauge steel, and I can't spend $1,000+, that is not in the cards right now.






(by the way, if you want to see ridiculously large pictures, just click on them)


Gabriel

[G._Hoffman]

Oh, and if you are thinking there are too many preamp tube sockets, you are wrong.  There is one more than you would expect, but it certainly isn't too many!

I got something clever in mind.  Well, not that clever, but cool!


Gabriel

[kagliostro]

You are thinking to add an EF86 channel (like in AC15) or a one tube reverb, those two things are missing on the AC30 

---

About cutting at home a steel sheet you must use a tool like this



and an 1mm thin cutting disk for inox like this



you require also to be patient and to have a steady hand, draw a line with a marker and follow it

K

[terminalgs]

Cutting with a cut-off wheel and a 10KRPM die-grinder cuts steel of nearly any thickness, but!!:  it isn't cutting as much as it is heating to the point of burning to get through the metal.  Similar to a plasma cutter, but a bit more crude and less precise.  You will be left with a piece of metal with a sharp edge that will need filing to make it more like a sheared edge and less like a jagged knife.  With some skill, smooth cuts can be done with a cut-off wheel, but the edges are still super heated..   die-grinders come with two handles... use both!  and know which way the wheel turns.,,   respect the die-grinder!





Your chassis looks great!


To drill holes in the lip for clip nuts,etc.:  cut a piece of wood into a block that'll fit snuggly  into the chassis so that it touches all four planes (top, sides, and bottom where the two lips are)., it should be perpendicular  to the long edge of the chassis... you can slide back and forth in the chassis you position the lip under the drill bit,  with the block directly under, or next to the hole.


as for metal gauge size:  16 gauge steel is pretty thick.  I use tin-snips on smaller gauge mild steel, and use reinforcement brackets to ensure transformer weight doesn't collapse, deform chassis.   I do this so (1) I can use snips, and (2) I can use a cheap bench mounted bending brake.


regarding rust:  imho,  rattle can metal-etch primer is all  the rust-prevention most amps will ever need, especially if its stored in climate controlled place.  lots of 40-50 year old rusty chassis amps probably spend 20 years or more in damp basements, humid garages, or incredibly hot attics.   plating or power-coating is overkill, but if you like the aesthetics,  thats a different story.

[kagliostro]

To cut steel at home also an electric nibbler may be an option, but usually they are expensive



so you can think to an optional tool for your hand driller, like this

http://www.fervi.com/ita/utensileria/utensili-taglio/macchine-per-lamiera/roditrice-per-trapano-pr-7294.htm

but with nibbler the problem is that is difficult to follow a straight line being very prone to follow and execute curved lines

if you don't invent a way to do straight long

K

[eleventeen]

The way I cut long straight lines on metal is to set up a fence on my drill press by clamping a nice piece of hardwood to the table and drill lots of little holes in a straight line, bend/break (or hacksaw) the cutoff section away, then use the 4" grinder, then file, then belt sander. Yeah, it's a pain in the rear end and kind of Fred Flintstone but really, any time you don't have the right tools it's a PITA.

[heresrobert]

Disclaimer. Do this at your own risk. Follow your tool's instructions and use safety precautions for sure!!!!!

Cutting sheet steel is difficult with hand tools.  I use a strong jig saw (Bosch for me) and some fine tooth metal cutting blades. Going slow helps save life on the blade. After carefully measuring and marking, I clamp the sheet metal down to a sheet of ply wood and saw horses. I use a straight piece of plywood under the clamps as my fence for long cuts. Support the sheet metal as much as you can on the plywood. It takes patience and practice. Cutting stainless sheet is a PITA, mild steel is easier, aluminum is easiest for me.

Robert

[eleventeen]

Stainless steel is incredibly difficult without top-notch tools. I wouldn't even try it.

[tubeswell]

For big bits of chassis sheet metal, I get the pieces cut on a guillotine in a metal shop.


I have a decent brake so I can bend it at home. For small bits up to about 1.2mm thick I use a pair of tinsnips

[PRR]

> bending break ... sheer

brake, shear

On your car/bike, brakes are good, breaks are bad.

Specifically... a brake lets you move to the right spot, then holds against movement. Work the handle/pedal, and the sheet stays there while you abuse it.

Shear: "From Middle English sheren, from Old English scieran, from Proto-Germanic *skerana;, from Proto-Indo-European *(s)ker- (“to cut”)." Sheer is how you want women's clothing.


---------------------------------
> glowing red chips right into the pile of sawdust

If you keep the table saw outside, the sawdust stays wet, won't burn. (True, this suits my $20 yard-sale saw better than your $2K Hoffritz saw.)

For ALL metal-work, find your local heating duct shop. I just had a huge duct bent-up perfect for about what I thought the steel alone would cost. While duct-work is mostly thinner gauge, there's some heavy bits and also duct-guys have GAS just as bad as we do, they have machines "too good" which they want to justify. And if not, he's sure to know who in town has the big shears and brakes, and won't over-charge for a small job.

Hand shears can cut 18 gauge (good ones) but it is work. My neighbor has 4-foot shears which attached to an anvil; he says if you heated the steel and had a heavy apprentice they would cut 1/4" plate. However I think they were intended for Wrought Iron, and they are in such bad shape that he welded them up as a bumper for his rat-rod.

Sawing (or abrasive disk) sheet metal is usually a bad idea. The edge comes out ROUGH.

If you must saw, clamp the metal between two hardwood boards. It cuts the vibration, may slow the sparks, and is less likely to get away from you than thin metal.

Stainless Steel is now banned here, after ruining many bits on some SS furnace and gas-line brackets. Who needs to live forever?? Even at your young age, a clean and a Krylon will stay rust-free until arthritis blunts your fingering. If you need "shine", go Aluminum and a clear-coat.

I do think that the $40 4-inch hand grinder is very-very useful for many things, and my neighbor did 99% of his rat-rod metal cutting (and metal roofing) with one before he got his cut-off saw (which is good for rod/tube, not really for wide sheets).

There is a 3-blade metal shear which is handy up to 18 gauge:
http://www.eastwood.com/eastwood-air-shears.html
(also comes in electric, and as an add-on to an electric drill.)

The Throatless Shear is even better, a very nifty device, but costs more; $170 for up to 14 gauge
http://www.eastwood.com/throatless-shear.html

There used to be whole books about brake bending. I would say Lindey's Books but I see he has retired. Archive.org has random scans of old books. IMHO the old books are far better than the new ones which just prepare you to pass a test, not really to bend-up harvester brackets and furnace pots.

[G._Hoffman]

Disclaimer. Do this at your own risk. Follow your tool's instructions and use safety precautions for sure!!!!!

Cutting sheet steel is difficult with hand tools.  I use a strong jig saw (Bosch for me) and some fine tooth metal cutting blades. Going slow helps save life on the blade. After carefully measuring and marking, I clamp the sheet metal down to a sheet of ply wood and saw horses. I use a straight piece of plywood under the clamps as my fence for long cuts. Support the sheet metal as much as you can on the plywood. It takes patience and practice. Cutting stainless sheet is a PITA, mild steel is easier, aluminum is easiest for me.

Robert

I used a jig saw (on this one, which was my second attempt of the weekend, because on the first one I put the choke in the wrong place and it was interfering with the preamp tubes), but when I used a fence with the jig saw the blade wandered too much, so it worked out much better to just draw a line and follow it freehand.  I'm pretty good at that, so its probably +- 1/32", but I wanted to be able to do better.

---------------------------------
> glowing red chips right into the pile of sawdust

If you keep the table saw outside, the sawdust stays wet, won't burn. (True, this suits my $20 yard-sale saw better than your $2K Hoffritz saw.)

Just a 1970's Delta Contractor's Saw - nothing special at all, but very well set up!  And in the basement, so sparks in the sawdust are DEFINITELY a problem!!!!  I do have a roofing place near by, though, and I might give them a try next time I need something done - I've seen a rather big brake through their roll up as I walked past a few times!  I don't much like my brake (well, it only cost me $60, so go figure), and I would surely like to find a better way around this stuff.  The nice blank chassis on the internet that I have used in the past are all very nice, but very expensive for what you get, and drilling and cutting on bent chassis is just a pain, and it is too hard to do a good job.


Gabriel

[G._Hoffman]

You are thinking to add an EF86 channel (like in AC15) or a one tube reverb, those two things are missing on the AC30 

An EF86 channel in place of the "Normal" channel - though I might have it be switchable with the 12AX7 normal channel, since the other half of that tube is the preamp for the Top-Boost channel.


Gabriel

[kagliostro]

Some time ago I was thinking something similar

http://el34world.com/Forum/index.php?topic=16273.msg159252#msg159252




K

[terminalgs]

Franco,  On an AC30 designed like that, you might use the other grid input to the PI (like the first AC30s did), rather than ground it.  You don't have to mix channels one and two with those 220K resistors.   There would be a lot more gain available  from the sole 12AX7 triode channel.  or something like this:

[kagliostro]

I agree, but I was using that schematic because I've find it near what I was thinking

so it was simple to modify it as to give an idea about what I was wondering if feasible

My AC30 idea is a "bit" more complicated, I've near all what is necessary to build it
 
but I never finished an adequate layout, also I'm lost on building some equipment for my laboratory

also, last week arrived my CNC Milling machine and I'm studying CAD programs, Artcam & Mach3

I like your AC30 idea and I'll follow you with interest


Franco

[Ritchie200]

PRR, I sure do like your show and tell posts!


Something else to consider guys.  Maybe its because I had been in manufacturing for many years that I notice them, but I'm sure its common everywhere.  I have several shops around me that do general fabrication.  Not necessarily the machine shops, but the welding shops.  The bigger ones around here buy sheets in large qty, have brakes and shears, and many times a complete job is cheaper than I can buy a tiny (relative to them) amount of raw material.  In some cases they have scraps large enough for a chassis so they are happy to use it up and material cost is minimal.  One place I use also has hole punch capability.  Another has an old Whitney that can to squares, rectangles and ovals, as well as holes.  General hands are cheaper than machinists so that's why I use the weld shops, I dont need them to hold +-.001".  I've got a Bridgeport, but if they can set it up and punch it for a couple of bucks, I'm good.


The place I use the most makes roll cages for pulling tractors, milling machine enclosures, coolant sump pit inserts, tanks, and any multitude of farming repairs and fabrication.  They even do powder coating.  Just make some phone calls, you might be surprised at the savings.


Jim

[PRR]

> bigger ones ...buy sheets in large qty, have brakes and shears, and many times a complete job is cheaper than I can buy a tiny (relative to them) amount of raw material.  In some cases they have scraps large enough...

+1

[G._Hoffman]

...regarding rust:  imho,  rattle can metal-etch primer is all  the rust-prevention most amps will ever need...

Well, I went this route.  It looks alright, and it's not going to be visible, but I still kinda would have liked to get it nickel platted:






On the other hand, I really like the stiffness and solidity of the fairly heavy steel chassis.


Gabriel

[kagliostro]

Very nice, I like it 

Can you post some other photo with a perpendicular view of the turret boards ?

K

[Willabe]

Looks great!


                           Brad     

[terminalgs]

Really outstanding!

[G._Hoffman]

Very nice, I like it 

Can you post some other photo with a perpendicular view of the turret boards ?

K

I'll try to bring the good camera home and get some decent (i.e., non-camera-phone) photos.  it should be noted, this thing is far from being finished - I'm working on it as I have time, but am currently very busy finishing some guitars.


Gabriel

[G._Hoffman]

Kinda nice though, to not need an amp stand, nor to prop it up on blocks of any sort. 


Gabriel

[Willabe]

Kinda nice though, to not need an amp stand, nor to prop it up on blocks of any sort.

 

[G._Hoffman]

(Definitely NOT done.  And I have to rewire the preamp heaters.)


Gabriel

[Ritchie200]

That is some beautiful work!

By the way, socks are not good insulation to bare concrete floor!

Jim

[eleventeen]

Beautiful work! Heavy parts count in there.

[G._Hoffman]

Beautiful work! Heavy parts count in there.

Well, it IS an AC30!  Lots of parts is the name of the game.

By the by, I started on the layout by copying the Weber layout, and then modifying it as needed to fit in the parts for the EF86 and to distribute the filter caps.


Gabriel

[G._Hoffman]

By the way, socks are not good insulation to bare concrete floor!

Jim

Well, first of all, I wasn't working on it, and second of all, it hasn't had power yet, so I'm not too worried about getting a shock! 


Gabriel

[kagliostro]

Just a curiosity, you have 7 inline preamp tubes, the chassis is longher than the original or is the standard lenght of the AC30 ?


K

[G._Hoffman]

Just a curiosity, you have 7 inline preamp tubes, the chassis is longher than the original or is the standard lenght of the AC30 ?


K

Standard length.  There is a fair bit of extra room in an AC-30 chassis.  Plenty of extra current on a standard AC-30 heater winding, too!  I counted 5.1 amps of heater current for all the tubes, and the PT has 6 amps available.  That made life easier, for sure.


Gabriel

[G._Hoffman]

Just powered this thing up and played through it for the first time just through my test speaker, naked on the bench - no cabinet yet!), and the only problems I've run into were a bad tube (plate/grid short - it's definitely not good to only have 24V on a plate!  Even worse when the rest shows up on the grid!!!), and the speed control isn't working for some reason - not sure why yet.  Oh, and the Bass control is backwards. It's reasonably quiet, and the EF86 channel sounds fucking awesome!!!!!
 
 On the whole, I'm a bit baffled.  I mean, normally when I make an amp, there is some near disaster - a blown transformer, or at least I'll go through a few fuses.  This time ... nothing serious.  A couple minor things that shouldn't take too much to fix.  How the fuck does THAT work?  I was a bit worried by the 75V plate voltages at the mixer, but I looked at an old schematic, and it's correct.







(Click on the pictures if you want to see really big versions)

I'm gonna try to get the cabinet done this week, though work might get in the way.


Gabriel

[G._Hoffman]

It is amazing, though, that when you start to really follow all those basic concepts of layout, things really do work!


My next amp, however, will be a LOT simpler.  One channel, cathode biased EL34s, just as simple as I can make it!


Gabriel

[sluckey]

That looks really good!

the only problems I've run into were a bad tube (plate/grid short - it's definitely not good to only have 24V on a plate!  Even worse when the rest shows up on the grid!!!),

If there is a plate/grid short then you should have the same voltage on each element.

Those AC30s are known to run really hot. With that style chassis some forced air would be beneficial.

[G._Hoffman]

That looks really good!

the only problems I've run into were a bad tube (plate/grid short - it's definitely not good to only have 24V on a plate!  Even worse when the rest shows up on the grid!!!),

If there is a plate/grid short then you should have the same voltage on each element.

Those AC30s are known to run really hot. With that style chassis some forced air would be beneficial.

Well, I measured 68kΩ between the plate and the grid (out of the amp), so I threw the tube and put in a new one, and all the voltages went up to the right range (all the other plate voltages were 10%-20% low, not surprisingly, until I replaced the tube). 

As for the appearance - it looked so neat and tidy until I started running the shielded wire!!!!!!  But I'm much less concerned about that than the sound.  And it sounds GREAT!

And you're definitely right about it running hot.  Absolutely gonna need a fan when it goes in the box!


Gabriel

[HotBluePlates]

Very nice!!

It looks like you ventured into the "cross-the-socket" routing of the heater wiring, as I did in my Standel-type amp. So tell me... Did it turn out quieter than you thought it would? 

[G._Hoffman]

Very nice!!

It looks like you ventured into the "cross-the-socket" routing of the heater wiring, as I did in my Standel-type amp. So tell me... Did it turn out quieter than you thought it would? 

How else I could do it with that much circuitry?  It wasn't so much a choice as a requirement.  It's also how they made the old AC30's, so you know ... It works well, though.

The Vibe/Trem channel is dead quiet, the EF86 is pretty good, and the top boost channel is kinda hissy.  But no 60 cycle hum, so yeah, it's worked pretty well.


Gabriel

[tubenit]

Just like all your stellar work, that looks great!  Very well done and thought out!

Thanks for sharing your pictures and success!

With respect, Tubenit

[kagliostro]

Really an impressive job 

So, if I understand correctly you have an unused triode, those of the normal channel ?

and your configuration is

2 triodes (1 tube) for the LTPI

6 triodes (3 tube) for the vibrato/tremolo channel

3 triodes (2 tubes - one triode unused) for the Top Boost channel

1 pentode (1 tube) for the ef86 channel

do you used a tone control on the pentode channel ? a standard rotary switch with capacitors ? or what else ? on the faceplate I don't see controls for that pentode .....

Franco

[EKDENTON]

Looks awesome. Very nice work! I haven't ever seen the inside of an AC30, it has a ton of caps on the one board.


And looking at all the empty tube boxes......looks expensive to build.

[p2pAmps]

Very impressive man...  Nice work.

So, I would love to hear about the technique you used on the twisted wire to connect turrets????  I might have to try that one out...

[HotBluePlates]

...  It's also how they made the old AC30's, so you know ... It works well, though. ...

No kidding!?

Huh, I must never have noticed. Or I subliminally-stole it from seeing old AC-30 pictures. I'd used it in the amp I referenced earlier, but didn't recall seeing/stealing it at the time.

[Paul1453]

Your work looks outstanding.   

Note to self, scratch the AC30 off any list of amps I might want to try to build.
The parts count and layout look like more than I could handle.   

I hope yours sounds as good as it looks when you finish! 

[G._Hoffman]

Really an impressive job 

So, if I understand correctly you have an unused triode, those of the normal channel ?

and your configuration is

2 triodes (1 tube) for the LTPI

6 triodes (3 tube) for the vibrato/tremolo channel

3 triodes (2 tubes - one triode unused) for the Top Boost channel

1 pentode (1 tube) for the ef86 channel

do you used a tone control on the pentode channel ? a standard rotary switch with capacitors ? or what else ? on the faceplate I don't see controls for that pentode .....

Franco

Yup, one unused triode.  The pentode was a kind of late addition to the design, or I would have used that triode as the standard Normal channel - one jack for each channel.  By the time I thought of it, though, I'd already finished the board layout, and didn't want to try to jam more crap in there.  There is a volume control for the EF86 channel, but the only tone controls on either the Vib/Trem channel or the Normal control is the Cut control, which feeds a bit of the inverted side of the phase inverter to the non-inverted side.  Fine by me - I tend to leave tone controls all the way up anyway. 

Looks awesome. Very nice work! I haven't ever seen the inside of an AC30, it has a ton of caps on the one board.


And looking at all the empty tube boxes......looks expensive to build.

Well, I tend to keep myself well stocked in most parts, and get them from mostly wholesale sources, so not TOO expensive.  Making my own chassis helped, and this is about the third amp I've used the transformers and choke on, but the others just didn't sound the way I wanted them to, so I decided to just build the real thing!  All the big Electrolytics are just power supply caps, but I like to distribute them through the amp so they are closer to their respective gain stages (helps with noise), with the caps on either side of the choke being paired in series, since radial caps are hard to find in 500V ratings.  Most of the rest of the caps are related to the Vibrator part of the Vib/Trem channel.  I've had it explained to me (I think further up in this thread), but it's all black magic to me!!!!

So, I would love to hear about the technique you used on the twisted wire to connect turrets????  I might have to try that one out...

A couple of smooth jawed pliers, and a lot of patience.  Fortunately, you do it while the board is unpopulated, and there aren't all THAT many joints in most amps.   Not sure it was worth it, but I do like the way it looks.  One could buy a pair of safety wire pliers (used to hold bolts in place in jet engines and rockets, where Loc-tite is just an unwanted source of combustion - but I think it looks awesome, so I wanted to use that twist here), but the cheap ones have really rough jaws that ding up the buss wire, and the ones with smooth jaws are expensive.  It's a bit too precise to try with a cordless drill (which is how I do other twisted pairs of wire).


Gabriel

[G._Hoffman]

Note to self, scratch the AC30 off any list of amps I might want to try to build.
The parts count and layout look like more than I could handle.

It was definitely the most complex amp I've ever built, BUT I've always been a fan of these things, and like most things, if you take each step in the process carefully, none of them are all that hard.  This amp just has a lot more steps than I'm used to!!!!!!

I think I might have all the parts I need for a 5E3 deluxe.  That should be a nice, simple job, right?


Gabriel

[p2pAmps]

A couple of smooth jawed pliers, and a lot of patience.  Fortunately, you do it while the board is unpopulated, and there aren't all THAT many joints in most amps.   Not sure it was worth it, but I do like the way it looks.  One could buy a pair of safety wire pliers (used to hold bolts in place in jet engines and rockets, where Loc-tite is just an unwanted source of combustion - but I think it looks awesome, so I wanted to use that twist here), but the cheap ones have really rough jaws that ding up the buss wire, and the ones with smooth jaws are expensive.  It's a bit too precise to try with a cordless drill (which is how I do other twisted pairs of wire).


Gabriel

That is exactly what I figured you used...  Safety wire pliers.  I have to try it out.  thx

[G._Hoffman]

That is exactly what I figured you used...  Safety wire pliers.  I have to try it out.  thx

Well, I didn't, because the ones I used to have are cheap and damage the wire, but you COULD.  I just used a couple of smooth jawed pliers.  (Buss wire is a lot softer than safety wire.)


Gabriel

[SoundmasterG]

How did you do the front panel for the amp? It looks really good....very nice work!


Greg

[G._Hoffman]

How did you do the front panel for the amp? It looks really good....very nice work!


Greg

I've got a CNC machine I made a while back (well, really, I'm in the middle of making it, but it is running).  The front plate is red laminated on white, so I just engraved it with a V-bit (30 degree bit, with a .015" tip, made by company called Precise Bits - who make really nice small bits, though nothing with a 1/4" or larger shaft).


Gabriel

[tubeswell]

Top notch job. The metalwork looks dandy too.