Next step..attempting Sluckey's AC-15

[ratgon]

Hi all. So I've decided that my next build is going to be Sluckey's AC-15. And I've decided to try and document the whole thing as it goes on here. This is BY FAR the most complex build I've attempted and part of me thinks I'm a fool to document something which is likely to be fraught with rookie mistakes and dumb questions but...that's how I'll learn.

I've got most of the parts. I bought most of it from Hoffman and a few other things from elsewhere. I got my chassis today and, while it's incredibly scratched up (when I emailed them they explained that those gouges are just part of the braking process at their manufacturer's..as if that was an accepted finish! Hell, my harbor freight brake doesn't even leave scratches.) I'll polish it and make use of it.

This'll be my first build machining the chassis as well. That's where I'll start. So...I have a couple questions that will impact layout. For Sluckey and anyone else interested.

I plan to use all of Sluckeys mods. The channel switching/jump switch with one input seems so elegant. Is there any reason to consider not doing this?

Having never played an AC15 is there value in adding a MV? And if so, any directions to look in for ideas?

I'm still trying to find my dream amp. All I've ever wanted was a great sounding, versatile clean to rich distortion, lowish watt amp with trem and reverb. Any thoughts on the idea of trying to add a reverb to this circuit. I certainly have a lot of room in this chassis for additions like this.

Somewhere Sluckey mentioned wanting to use a 5y3, I believe, but he lacked a big enough step bit. I have one. Is there a particular value in changing rectifiers?

And here's the first potentially really silly question but it's born of superstition and fear of Murphy's law more than anything. Hoffmann AC-15 package is listed and ships with nine tube sockets. It seems I only need 8. Am I missing something?

Thanks in advance. I've been sorta lurking around here for awhile now but I'm always reading. I feel like I'm about to try and get my wings. I appreciate the help. If nothing else, I'll likely provide some laughs.

[sluckey]

I plan to use all of Sluckeys mods. The channel switching/jump switch with one input seems so elegant. Is there any reason to consider not doing this?

I don't think the 'standby plus' switch mod is worthwhile so I removed it. In fact, if I were to ever build another AC-15 I would not have any kind of standby switch. The 'Channel select' switch is very useful. I have the single input with special C&K 7211 switch. I highly recommend this mod.

Having never played an AC15 is there value in adding a MV? And if so, any directions to look in for ideas?

I don't think a MV would be useful to me. But if I did one it would be the LARMAR PPIMV. Plenty of info and drawings on the web.

I'm still trying to find my dream amp. All I've ever wanted was a great sounding, versatile clean to rich distortion, lowish watt amp with trem and reverb. Any thoughts on the idea of trying to add a reverb to this circuit. I certainly have a lot of room in this chassis for additions like this.

You're probably gonna need a room full of amps to satisfy that dream.     I wouldn't bother with reverb on this amp. Which channel would you put it on? I'd save my money for a Celestion Blue. If you really want reverb, build a separate reverb unit or a Revibe unit so you can have reverb for all your amps.

Somewhere Sluckey mentioned wanting to use a 5y3, I believe, but he lacked a big enough step bit. I have one. Is there a particular value in changing rectifiers?

I don't recall saying that. And I certainly have the tools for an octal socket. I recommend staying with the EZ81 tube because that's what the original used.

And here's the first potentially really silly question but it's born of superstition and fear of Murphy's law more than anything. Hoffmann AC-15 package is listed and ships with nine tube sockets. It seems I only need 8. Am I missing something?

That's obviously a mistake. I recommend the Belton sockets. Pricey, but much better quality than those ceramic sockets. You only need 5 shields. You may also note that you need to add an EF86 and EZ81 tube to the parts list.

[John]

And here's the first potentially really silly question but it's born of superstition and fear of Murphy's law more than anything. Hoffmann AC-15 package is listed and ships with nine tube sockets. It seems I only need 8. Am I missing something?

I just looked at Sluckey's build. That 9th hole should be 1 3/8"? if so, that's for the cap can. 
Sorry, you said sockets; I was thinking you meant the chassis had 9 holes.

I agree with the one input w/ a switch.


I always like a MV in anything over 5 watts. Even in you're only turning down a bit, it's a great way to keep the tone while dialing back. The Lamar is the one I've always used, and my ears are not the greatest but I find it pretty transparent. You just need a 250KA dual ganged pot, and 2 2.2M resistors.


I'm timid, so I wouldn't try adding reverb to that circuit if it's your most ambitious build yet. There's a high parts count there (well for me anyway). You'd have to re-do the board layout, add another tube and small transformer, and at least 1 more pot. And then troubleshoot the buzz and hum    I've done 2 with spring reverb, and some more with SS reverb, and I like the SS just fine.


All these are my opinions, not gospel!

[ratgon]

Well there ya go! This thread is already paying dividends! Thanks guys!

I'll have all the switches for the mods by tomorrow hopefully and start planning my chassis drilling to accommodate today if I can. I'm gonna spend a little time deciding if I really need or want the PPIMV. Obviously that'll affect the layout and I really want to stay as true to the "original" (Sluckey's) as I can.

Thanks for the Celestion Blue recommendation. That was for sure a future topic of concern as I start to think about the actual cabinet design.

And I've definitely decided to forego the reverb idea. First things first. But, John, in general, I am interested in any SS Reverb solutions you've implemented or investigated.

I'll keep ya posted. Hopefully I'll get out to the shop today and get the baseball game on and get organized to start.

Thanks again

[John]

I have used this circuit with same values in 5W and 30W amps, it works and sounds (imo) great. One guy thought it was spring reverb. I found the basic circuit a while back, and tweaked it to those values. I keep the 10K and .022 (inside the box) on the veroboard with the power supply. Hopefully by the time I build the next one I'll have a nice professional looking layout. 


I found that the only way to power it though, is with a little 6v tranny. Fed from the filaments it injects hum & buzz. I've tried everything I could think of as far as grounding goes. The "ground" on the reverb PS itself is floating. It's always possible there's something simple I'm missing of course. But I tried ground everything, lifting the ground on everything, grounding 1 and not the other... always a buzzzzzzz. With it's own tranny, dead quiet.


It's also possible I wouldn't have to have the Brick between the triodes and it would still sound good? I'll get around to trying that some day.

[ratgon]

Wow. That's pretty interesting. So that's a Belton rev brick with tube circuit? I've been looking to build a pedal with one of those and had thought about trying to incorporate it into an amp. And here it is! I have a couple of those bricks standing by.

I'm not sure this is the amp to try this with BUT it might be worth laying out the front panel To sneakily accomadate one future pot.

[John]

Yes, the Belton.
I was paying attention last evening, and the thing a spring lets you do is have this loooonnnnng delay that gradually dies out, that's not possible with the brick. Or maybe possible, but using lots of parts? Honestly, both have their pros and cons. In some ways the spring is simpler - especially using Tubenit's One Tube Reverb design - and in other some way the Brick is.

[pompeiisneaks]

I just got done talking about how tube tone can't easily be emulated perfectly in another thread, but personally I'm not rabid about tube spring reverb, as I've found plenty of pedals that do an outstanding job of it, imho, reverb works just as well in a pedal.  I have the T.C. Electronic Hall of Fame and it's spring reverb sounds stellar to me.  BUT absolutely do what you think is best/funnest to build etc. 

~Phil

[John]

I just got done talking about how tube tone can't easily be emulated perfectly in another thread, but personally I'm not rabid about tube spring reverb, as I've found plenty of pedals that do an outstanding job of it, imho, reverb works just as well in a pedal.  I have the T.C. Electronic Hall of Fame and it's spring reverb sounds stellar to me.  BUT absolutely do what you think is best/funnest to build etc. 

~Phil

I've got a Behringer reverb pedal, $35 new, and really it sounds good too. Not Holy Grail for sure, but good enuff. I only started putting reverb in amps because it's one less pedal you gotta lug along. And it's the one effect I really "must have".

[pompeiisneaks]

I agree it's a must have, and your reasons are just as good as mine :) just giving my 2c.  I don't mind another pedal, I only have 6, two drive pedals, reverb, delay, volume and tuner, but I don't lug it around right now anyway :)

~Phil

[John]

You gear slut. 

[ratgon]

I thought I'd replied to this earlier but I suppose not. I was just thinking about how and why I got into all this a year or so ago in the first place. It was because these amps just seem magical and beautiful! So "real" Reverb seems like such a must!

But, the fact is that when I write and go into the studio to record I don't care, AT ALL, what makes the sound as long as it serves the song. It can be a plugin for all I care if it sounds right. But in trying to learn how to make these amps I'm so concerned about the aesthetics of the parts and the authenticity. I suppose that's where component religion is born.

The fact is, I LOVE Reverb and much prefer digital and even plate Reverb.

I'm about to layout the chassis for this guy today and there's plenty of room to leave space for an extra pot or two, a small board and a socket if need be. We'll see.

Thanks

[ratgon]

Giants beating the Dodgers took over the night but I came home to the choke waiting on the porch and the fancy little channel input select switch!

I'll get the drills out tomorrow and commit to this unless there's something clearly wrong. Pretty much just following Sluckey's but in reverse.

[sluckey]

Which choke are you using? What are the inductance and current ratings?

Pretty much just following Sluckey's but in reverse.

The pic you posted shows the same layout as mine. What is going to be reversed?

I highly recommend you not deviate too much from my layout. The board, front panel controls and tube sockets all work together to give a clean logical working layout with short interconnecting wires with minimum crossover. Even the spacing on the tube sockets is part of the layout. If you do rearrange things at least think about how it may impact the wiring.

[ratgon]

Thanks for looking. What I mean by "reverse" is just the orientation of the chassis in the cabinet as I want to build a combo. Tranny hanging down. I'm trying to follow your layout to a "t". Literally printing pics and trying to judge spacing with a caliper. This is no time for me to be the new guy with all the bright ideas.

The choke is the 159P. 10H at 125ma. The 193 seemed to be unavailable everywhere I looked. But mouser had this and the channel switching switch.

And so I think I've come pretty close with the sockets and cap can and the overall orientation of the iron.

Thanks Sluckey. I'll keep ya posted.

[sluckey]

Thanks for looking. What I mean by "reverse" is just the orientation of the chassis in the cabinet as I want to build a combo. Tranny hanging down.

OK. I got it.

The choke is the 159P. 10H at 125ma.

That fine, probably even better. My amp idles with 100mA flowing through the choke.

I think I've come pretty close with the sockets and cap can and the overall orientation of the iron.

Your pic looks good. I don't know what happened to my chassis layout drawing. But here's the same thing for an AC30.4 that I drew up for someone. The chassis is longer and the board is 1" longer to accommodate the extra power tubes, but the relationship between the circuit board, front panel controls, and tube sockets is the same as my AC-15. All the critical spacing and layout lines are the same as I used on my amp. Just start your layout measurements from the right side of the drawing and everything will work out. Hope that makes sense.

[ratgon]

Thanks for that drawing. That actually helps a lot. My chassis is slightly different (20x8) but working from right to left (from trem end of board) allows me to follow fairly accurately.

I'll run my front panel layout by you in a bit as it's different from yours only in that I'll be incorporating your mods but the "zones" of control and their relationship to their circuits on the board will remain intact.

Back panel will be the same. Clearly that OT renders a simple three way impedance selector switch kinda, um, a puzzle if possible at all so I'll go the 8 and 4 ohm option route.

Thanks!

[pompeiisneaks]

You drew it up for me :)  Yeah his visio stuff is outstanding  :)

~Phil

[ratgon]

I mean, it really is. I'm gonna frame this!

Phil, your videos are helping A LOT as well man.

[pompeiisneaks]

Good to know.  I have a lot of fun making them, but they're also a ton of work to edit when done.  I'm editing the next champ one now... been at it a few hours already :P

~Phil

[ratgon]

Just checking in and one question for you guys. I don't want anyone to think ol Mike's gone and bailed on another amp project. Not a lot of progress these last few days with a kitchen remodel happening but I have managed to get the chassis drilled and was able to polish out most of the gouges it shipped with. Thank you Sluckey for the layout. It helped tremendously.

You'll notice one socket is empty. This is the EF86 socket. I have to get some longer screws today to accommodate the shock mounting. My question is, will this even help the potential microphonics? Will anything? Is it even really an issue? Phil has mentioned it truly was in his AC30 and I've always read that it is.

So, is there anything I should do at this point to address this?
Thanks

[sluckey]

Probably anything you can do to minimize vibration will help. I've seen tube sockets mounted with rubber grommets (Fender did this back in the '50s), more elaborate shock mounted special sockets, special rubber rings to go around the tube glass. I use a special heat dissipating tube shield. The many spring loaded aluminum fingers inside the socket apply firm contact with the glass to easily dissipate heat (just like a heat sink for solid state devices). But the fact that those fingers grip the tube firmly also minimizes vibration. Here's a pic of the shield...

[kagliostro]

You can use the tube shield that Sluckey suggests

and, in addition, this anti vibrating socket (£ 1.99 + £ 4.50 )

http://www.ebay.co.uk/itm/9BA-RUBBER-VALVE-TUBE-BASE-SOCKET-MCMURDO-Vintage-1960s-/172653157711



I've some similar socket made by Geloso

Franco

[ratgon]

Thanks for the anti-vibration tips. I'll start with some, not-too-tight rubber grommets while I look for some of the solutions you all mentioned.

In the meantime, I'm about to start some wiring and I'll start with the power section. Sluckey, you mention testing the power as you finished it, on your site. I've never done this. Always tested everything when the whole amp was completed. So how far does one go with the power before testing? To the rectifier? All filter caps? I'm sure it's a silly question but just wondering what the move is.

Anyway, stoked to have time tonight to start into it. I'll do you proud I hope.
Thanks.

[sluckey]

Sluckey, you mention testing the power as you finished it, on your site...So how far does one go with the power before testing? To the rectifier? All filter caps?

Just like in the pic just above that caption. Primary wiring, fuse, switch, filament string, cap can, choke, standby switch. Plug in the rectifier tube. Measure filament voltage at every tube socket and measure dc voltage on the caps. If something doesn't work, stop and fix it now. Then you don't have to worry about the power supply later. Just remember, that cap can will hold a charge for days unless you use a resistor to bleed the voltage!
 
I like K's idea about shock mounting the socket and also using my shield. Look at how Fender shock mounted the sockets in this 1957 Harvard...

     http://sluckeyamps.com/harvard/h02.jpg

[kagliostro]

Look at how Fender shock mounted the sockets in this 1957 Harvard...

I don't know if I see well, is that sistem using a pair of OR between the <sockets + screws> and the chassis ?

something like this ?



Franco

[sluckey]

It's a single grommet per screw. The grommet is mounted in the chassis like the bottom grommet in your pic.

[kagliostro]

Ah, OK, I understand


Franco

[ratgon]

Thanks again for all the help and with the power section testing question. I got it. I've held off on the power section last night in order to concentrate on the board jumpers. Lotsa high-lighting. Posting a couple pics to simply keep up with the documentation. Two checks only revealed one mistake but I'll be checking again.

[ratgon]

Just finished the board. I sure hope it's right.

[sluckey]

Scary stuff when the board has so many components on it! Imagine doing the first one and wondering if you got it right. And also wondering if the unproven layout really agrees with the schematic! And is not gonna have physical layout issues! I was sweating bullets, not just for me, but there were two other guys building this at the same time.

I hope you got a good solid connection on those underboard jumpers. 

[ratgon]

oh man! I can't even imagine. It's scary enough to do it with a roadmap in front of me!

I went as overboard as I could with the underboard jumpers. Up and over and around the turrets. If they're in the right place they're there to stay. Definitely  made a few multi-connection points a bit challenging but worth it.

[ratgon]

Ah. I remembered a question I had. Somewhere I believe, Sluckey, you mentioned that if you were to do it again you'd forego the standby switch. Is that decision specific to this amp or in general? So far I haven't planned for a standby. Thanks.

[sluckey]

That's a general statement for any low power amp. The AC-15 was the last amp I built with a standby switch. I've built 4 amps since without a standby switch.

[pompeiisneaks]

I've started building all of my amps without a standby.  It's not needed at all, one of those myths that won't die. 

~Phil

[ratgon]

I like switches. I just like em. But no standby on this one. Thanks guys.

[ratgon]

Hey Sluckey, I'm a bit confused about this 270fx iron. Not sure how to wire the primaries concerning the 115v or 125v connections. I'll use the 125v (black) so do I simply cap off the grey 115v?

Thanks

[sluckey]

yes

[ratgon]

Hi there. So I've finished the power section and tested all the voltages. For the most part they seem fine but I need to ask about one. I'm referencing the voltages using the conventions of Sluckey's schematic.

Vac In (with variac) = 119.7

EZ81 pins 1 and 7 = 282.4 Vac

EZ81 output (Pin 3) = 394.5V

Point "A" = 394V

This seems high compared to Sluckey's "A" = 336V

Or is it simply a matter of not having the load of the tube compliment?

Thanks

[sluckey]

Or is it simply a matter of not having the load of the tube compliment?

yes

edit... May I suggest you swap the wires on your fuse? It's safer to connect the hot wire from the IEC socket to the end terminal of the fuse holder.

[ratgon]

Absolutely! You can suggest everything! I'm following your lead entirely on this deal!

[purpletele]

Are you using Michigan Team colors on the heaters or Cal Berkely?

[pompeiisneaks]

Or is it simply a matter of not having the load of the tube compliment?

yes

edit... May I suggest you swap the wires on your fuse? It's safer to connect the hot wire from the IEC socket to the end terminal of the fuse holder.

I think I get why but wanted to double check.  The hot voltage is on the outer metal edge of the fuse if not right?  So you can accidentally shock yourself.  In your suggested way, the hot end is clear inside the base right?

~Phil

[sluckey]

I think I get why but wanted to double check.  The hot voltage is on the outer metal edge of the fuse if not right?  So you can accidentally shock yourself.  In your suggested way, the hot end is clear inside the base right?

That's correct. Ever go to check a fuse but the fuse remained in the holder rather than politely coming out with the cap? Then you take your car keys or nail clipper to dig the fuse out of the holder? Bad idea! But it happens. You may just get a big surprise if the hot wire is connected to the side lug of that fuse holder.

Back in the '70s I worked in the test equipment repair/cal facility (PMEL) at Robins AFB. There was a standing safety modification that was applied to every piece of line operated test equipment. Verify the fuse wiring and correct if not already correct. Then put a red paint dot next to the fuse holder to signify it complies with that safety regulation.

[shooter]

Are you using Michigan Team colors on the heaters or Cal Berkely?

[pompeiisneaks]

I think I get why but wanted to double check.  The hot voltage is on the outer metal edge of the fuse if not right?  So you can accidentally shock yourself.  In your suggested way, the hot end is clear inside the base right?

That's correct. Ever go to check a fuse but the fuse remained in the holder rather than politely coming out with the cap? Then you take your car keys or nail clipper to dig the fuse out of the holder? Bad idea! But it happens. You may just get a big surprise if the hot wire is connected to the side lug of that fuse holder.

Back in the '70s I worked in the test equipment repair/cal facility (PMEL) at Robins AFB. There was a standing safety modification that was applied to every piece of line operated test equipment. Verify the fuse wiring and correct if not already correct. Then put a red paint dot next to the fuse holder to signify it complies with that safety regulation.

OW :) yeah that sounds like something you'd not want to do more than once :_) so far I've only gotten bitten by AC in amps, I accidentally touched the fuse connection with my hand while doing something.  Power was off, but not unplugged.    I've been hit enough by 120 to not be to scared by it but when I'm in an amp with 400V it does make the pucker factor that much stronger :)

~Phil

[ratgon]

Hey there. So I'm about to move on and start on control wiring. I'm putting in a PPIMV using the Lar Mar circuit you've recommended. Now, while it may be patently obvious to a non-neophyte, I have a basic question about how to implement this.

Does each pot and attached protection 2.2meg resistor replace each 220k resistor (R53 and R54)? Or are they meant to be placed parallel with them? Or somehow else. My understanding at this stage makes me believe they replace R53 and R54.

Thanks.

[pompeiisneaks]

Yes they replace them (thus why you need the protection resistor, or you'd have a big problem if there was no resistance there.  Say the wiper comes unconnected etc.  If you don't have the resistance needed, you lose bias as that's where the bias voltage comes in.  The pot's work like the 220k resistor, but at max value they shunt the volume to ground instead of over to the tubes, and at minimum value they let the circuit work as if it wasn't there. (220k replaced with 250k of course). 

~Phil

[ratgon]

Ok great! Thanks. I guess I'm starting to understand this stuff a little better. I appreciate the help. On to the next step!

[Ed_Chambley]

Sluckey is leading you on.  I was building one at the same time and had no worries at all. 


I did hold off a tad until one fired up, his.



 Gotta say it has turned out to me my most used amp of the last few years.  Most used for playing that is.  As I mentioned before, I use this as my clean and overdrive amp along with a Princeton reverb and the 2 together are really nice.


Here is a couple of pix of mine complete.  I went with my Early Restored 62 Bassman having a baby look.