Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: pompeiisneaks on May 10, 2016, 09:58:38 pm
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So I've spent a LOT of hours on this, because the Vox AC30/4 (or AC34 0A/032 schematic) online is SO blurry/hard to read, but I think this schematic looks pretty close. I'm thinking I'd like to build this hairy beast, but wanted the guru's eyes on the schematic, how does it look etc?
First I'm looking at this schematic:
http://www.blueguitar.org/new/schem/vox/ac34colr.jpg (http://www.blueguitar.org/new/schem/vox/ac34colr.jpg) (MAN IT SUCKS)
I also found the AC15 schematics a bit more readable, but can see that some values are different, so I've been comparing the two back and forth. These are the two AC15 versions I've looked at:
http://el34world.com/charts/Schematics/files/Vox/Vox_ac151960.pdf, (http://el34world.com/charts/Schematics/files/Vox/Vox_ac151960.pdf,) (or another like it) http://www.drtube.com/schematics/vox/ac151960.gif (http://www.drtube.com/schematics/vox/ac151960.gif)
also http://www.drtube.com/schematics/vox/ac15fact.gif (http://www.drtube.com/schematics/vox/ac15fact.gif)
These all seem to be quite similar schematics with some slight changes. I've read that the AC30/4 is pretty sought after with the EF86 preamp tube etc, and the vib/trem is supposed to be pretty damn nifty. Therefore I'm wondering if I could build clones of these beautifully complex beasts.
Any insight, comments, build suggestions, etc I'd greatly appreciate. I'd also love any second set of eyes that can look for things I've miswired or mislabeled etc. The main normal circuit seems pretty cool, straightforward and I like the top boost switch. Just the EF86, into a PI into the 4 EL84's.
Let me know your thoughts.
Edit: I'll be keeping the schematic updated as I go.
Schematic Change 1: Added the missing 220k resistors to ground for the power tubes. Also added the missing top-cut post PI.
Schematic Change 2: put the cap on the output of the EF86 before the 1M resistor.
Schematic Change 3: fixed cap locations on C, D, fixed missing section for Tremolo Depth.
Schematic Change 4: no longer updating, instead adding Sluckey's version and his board layout. Keeping my old one just for giggles.
~Phil
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Several of the members have built this 1960 AC-15...
http://sluckeyamps.com/VAC15/ac15.htm (http://sluckeyamps.com/VAC15/ac15.htm)
There's a very legible schematic at the bottom of the page.
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Steve,
yeah I've looked over that page quite a few times, your detail on it is incredible. I just was wanting to do the AC30/4 since its a pretty rare amp and is often talked about wistfully in some of the amp forums/facebook groups etc that I frequent. For example, subtle differences exist like the cathode resistor on the first vib/trem has a 2.2k and 1.5k on each half in the AC15 but has a 2.2k on both in the AC30 etc. Just a few locations here and there where things were different. (I'm not sure why, but that's part of why I'm trying to rescue the old illegible schematic). I'll have to go over the schematic on your page though with this one because that one is SO much easier to read than the others I linked!
I also definitely like the layout you've got there. Id didn't realize there was a rectifier so small as that EZ81, pretty cool. It made me realize I'm missing the name of the tube on the AC30/4, that ones a GZ34, I'll fix that right now :P
~Phil
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I've been looking over your layout and the AC15 schematic you posted and it does look almost identical minus a few minor value changes for components, so I think I def can use your layout. What do you think would be wiser:
1. Modify the layout in the power section to support all 4 tubes
2. add a couple terminal strips for the two additional power tubes so the boards are pretty much 'interchangable'? (I see only the need for the two 1.5k grid resistors and the 100 ohm screen resistor, so that's the only two changes needed... .
I've done a sloppy image mod to show how I'd pull lines to the different terminal strips that connect to the two additional tubes for the 4 I mentioned above. of course the OT connections just feed from the one tube to the next for each half of the OT side. (I've done this on my AC30 I built from Doug's schematic, and my AC100 I did).
For my image, basically Pin 2 for the new tubes would come off each red line but the resistor would be between the terminal strips and the socket and thne I'd connect the wire to the TS. Similarly for the 100 ohms in blue, I'd wire in the new TS connnections from tube to TS to wired connection on blue.
What sounds 'right' or 'best'?
Edit: Of course I can also just jumper the grounds from each of the extra tubes to the associated tube before bringing those in as well.
~Phil
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What you suggest will work. That's not how I would do it though. I'd just add 1" to the board and mount those 4 resistors neatly and logically on the board. Very easy to do.
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The only problem is that I don't know if there is a way to do this on Doug's default layouts, I may have to manually redo your layout from scratch. Maybe I'll ping Doug via email and ask if he can accomodate this and just make it Sluckey's AC30 :) I still need to finish auditing what caps/resistors are different between the AC15 and the AC30, its probably only like 3, but I'm going for 'as close as possible' to the original.
Thanks,
~Phil
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I can give you the vsd file and you can edit as you wish. Then you can either make the board yourself or give Doug the edited file so he can make it for you. Let me know.
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Welp I've gone over the whole thing and the AC15 is identical EXCEPT for that one cathode resistor that's for V1, second half of the triode. The AC15 has 1.5k and the AC30 uses 2.2k.
Other than that it's identical. I think that the 1.5k vs 2.2k in the cathode resistor tends to bias the AC30 more clean right? So if you like more drive doing it as 1.5k would likely be better no?
I think I'd like the vsd if you can pm it to me, thanks Steve, you rock! :)
:worthy1:
~Phil
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This is what I had in mind for lengthening the board...
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See how you are, just go and do it for me ;) Yeah that's what I'd expected as well. Doug, want to make that change? :)
Don't think calling his name in posts does it though lol.
~Phil
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I did not have time to read all the text above
A quick look at Steve's PDf looks like you just added two more resistors to the end of the board next to the big cathode resistor?
http://el34world.com/Forum/index.php?topic=17184.0 (http://el34world.com/Forum/index.php?topic=17184.0)
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A quick look at Steve's PDf looks like you just added two more resistors to the end of the board next to the big cathode resistor?
I also added two 1500Ω grid stoppers for a total of four. Follow the 4 green wires from the sockets back to the board. This required adding 1" to the length of the board and sliding some stuff around.
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Ok, I see them now
I can make the board without too much trouble
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Excellent, I hope to get that project rolling pretty soon here, maybe first part of June.
~Phil
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Here's an updated drawing that includes the drill guide and jumper guide...
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So I'm finishing up an AC-30 with an EF86 channel. I'd be happy to share my schematic/layout, though I'm not sure how easy it is to read if you don't have a biggish printer (13"X19"). I've tried making it without the vibe/trem, and it isn't right. This thing sounds right, even through my less than appropriate test bench speaker.
This is not a simple amp, though. Not even close. With care, it is doable, but it sure ain't quick!
Gabriel
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Gabriel, thanks that would be great. Any data gathering would really help. I have built Doug's version with the 12ax7 and really dig the thing, but hope this one will sound interesting.
Phil
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Gabriel, thanks that would be great. Any data gathering would really help. I have built Doug's version with the 12ax7 and really dig the thing, but hope this one will sound interesting.
Phil
Here you go. I'm not sure if the layout will be all that much help, because the PDF printed out with very thin lines so it is kinda hard to see the colors, but with the schematic it should get you there. The big thing you'll notice is I added a bunch of extra sections to the power supply, and I distributed the power supply through out the amp. If you have any questions, feel free to ask. And for what it's worth, the little bit I've heard the amp it sounds great, and is the quietest amp I've made.
Gabriel
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Gabriel, that's great thanks!,
Did vox ever make an ef86 version of the vox a ac30/6? Or did you take the two (ac30/4) and meld them?
Phil
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As far as I can know only AC15 had a pentode in the preamp (1960 version)
the 1959 version of the AC15 had two, 1 with the ef86 and one with 1/2 of an ECF82
Franco
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No I know the AC30/4 had an EF86 Pentode in the normal channel input, that's what I'm planning on building here. (I may even try a hybrid AC30/4/6 so that it has the top boost, or maybe a switch to enable top boost etc. not sure yet. ) Due to vacation I'm going to hold off on the build for a bit, this month I'm going to recap my Blues Deluxe instead, but this is my next major project.
~Phil
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You've put a flea in my ear
but I'm not able to find any trace of an AC30 with EF86 pentode in the preamp
Franco
EDIT: You are right, there was an AC30 with an EF86 pentode on the preamp, the AC30H2 / AC30H2L
http://forum.cxem.net/index.php?app=core&module=attach§ion=attach&attach_id=236890 (http://forum.cxem.net/index.php?app=core&module=attach§ion=attach&attach_id=236890)
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K, look at this rare bird...
http://www.voxshowroom.com/uk/amp/ac30-4.html (http://www.voxshowroom.com/uk/amp/ac30-4.html)
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Thanks Steve
I've never seen the schematic of that particoular AC30/4, those I've seen are without the ef86 tube (1960 -->)
Franco
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Franco,
It is here;
http://www.blueguitar.org/new/schem/vox/ac34colr.jpg (http://www.blueguitar.org/new/schem/vox/ac34colr.jpg)
often listed as vox AC34 for 30/4. it is REALLY hard to read and what I based my schematic on. its called 4 due to having 4 input jacks the 30/6 has 6 and moved to the 12AX7. The 30/4 was based upon the AC15, so Sluckey's amp is almost identical except for a few more power tubes. (I found one other cathode resistor that's different as well, but that's it).
~Phil
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Thanks Pompeiisneaks
and ... yes, That schematic is really difficult to be read, I've found a copy of it on my archive, but my copy is also worse
so I bury it and didn't remember
Franco
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Gabriel, that's great thanks!,
Did vox ever make an ef86 version of the vox a ac30/6? Or did you take the two (ac30/4) and meld them?
Phil
My starting point was the Weber schematic and layout, with a lot of references to old Vox schematics. So, 12AX7's. I added the EF86 when just about everything was done, because I had one laying around, and I thought it would be cool (and because it is the first tube in the amp, it was pretty easy to shoe horn into the board). I just pulled up an AC15 schematic, and pulled pretty much everything for the EF86 from there (I might have used a larger screen resistor, I don't remember - I drew the thing about two years ago!!)
Gabriel
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Ahh gotcha, very nice. Basically a hybrid of the two. I'm wondering if doing the same may not be a good idea.
~Phil
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Ahh gotcha, very nice. Basically a hybrid of the two. I'm wondering if doing the same may not be a good idea.
~Phil
I'm not sure any of this stuff is exactly a good idea.
Gabriel
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Lol no probably not, its an expensive hobby with no payout ... unless I somehow miraculously become the next Dumble (Unlikely hah)
~Phil
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The build begins, I'll show off the videos here, unless i should keep those in the video section.
https://www.youtube.com/watch?v=EEcJ1nanz20&feature=youtu.be (https://www.youtube.com/watch?v=EEcJ1nanz20&feature=youtu.be)
~Phil
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:thumbsup:
Franco
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:thumbsup: ... looking forward to see more of these.
I did notice one mistake on the schematic on the video, the 0.1uf cap on the ef86 should be connected to the other side of the 1M resistor.
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Oh you're right, thanks!
~Phil
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The 8µF filter cap (node D) for the EF86 is connected wrong. It should be connected to BOTTOM of the 22K.
Same goes for the 8µF (node C) for the PI. It should be connected to BOTTOM of the 22K also.
Node E cap is fine.
And one more thing... On the board layout... Change all power supply node labeling. Node A becomes B, Node B becomes C, Node C becomes D, and node D becomes E. This is due to the slight difference between the AC-15 and AC-30 power supply. Sorry, I didn't catch that back when I modified my layout for you. You may want to make those changes on your vsd file.
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Will do, thanks.
~Phil
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Hmm, I don't see any difference on the power, remember this isn't the 30/6 but the 30/4. Or could you explain to me what I'm missing? Heres the 30/4: http://www.davidsonamp.com/sv/VX_34.gif (http://www.davidsonamp.com/sv/VX_34.gif)
I see output from GZ34, into A which is a 16uF cap, then a choke, then a 16uF cap, then on to the rest of the amp. That seems identical on the AC15 except the rectifier is a different type.
Sorry if I'm missing something obvious (actually as crappy as that schematic is, it ISN'T obvious :P)
~Phil
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Your 30/4 feeds the OT CT from the first cap BEFORE the choke. You called that first cap node A.
The AC15 feeds the OT and screens from the second cap AFTER the choke. I called the second cap node A because the first cap was not used.
Did you notice that I only have 4 filter cap nodes but you have 5?
If you don't at least make pencil changes on my layout, you 'may' wire it wrong later on. Also remove the OT connection to my node A when you change it to your node B.
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DOH! I see it now, yup that's definitely different, the CT gets only that first phase of filtering. Weird, is that going to have a major impact on the tone? I've heard the power tubes don't need quite as clean power anyway, but I'm used to seeing two nodes with the choke in the middle before it gets to the power tubes.
I'll update the visio.
~Phil
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Now for the biggie... Your trem oscillator and phase splitter are all tangled up. You don't even have a depth control. I don't see an easy way to fix all that. I suggest you just delete that section and draw it exactly like the orig AC-15 schematic, or even better, copy my visio schematic. This area will become troublesome when you start wiring IAW my layout and still try to keep the circuit as original as possible. BTW, the original circuit had a 3 position speed switch and it also had an internal depth preset trim pot.
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I've fixed the missing section for the depth, but I've spent so many hours that starting from 0 would be tough on my brain :(,
I don't see what you mean about the trem to the PI, I look that over and I don't see anything wrong on mine compared to the AC15 in yours?
~Phil
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I've fixed the missing section for the depth
Still not right.
I don't see what you mean about the trem to the PI
Not talking about the PI in the power amp. Talking about the PI that's in the same 12AX7 tube the trem oscillator is in. It's hard to see on the original AC-15 schematic and even harder to see on your sch schematic, mostly because that part of your schematic still has errors.
Look at my Visio schematic. It's drawn out in a logical manner where you can easily see the oscillator circuit and how it connects thru the depth control to the grid of the phase inverter/splitter.
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okay I'll do so. I think I may just bite the bullet and try this in visio, I have so many issues with ExpressSch or whatever it is, due to it not locking well to grid on most of the tubes etc, taht it just starts looking hokey anyway. I just didn't find any valve images in Visio that had the surrounding circles, maybe I'm missing something, I'll give it a try, though.
~Phil
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> valve images in Visio that had the surrounding circles
Circles are for mass publication (Sams FotoFacts, etc).
Much small in-house tube documentation omitted circles.
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It's not really important which program you use to draw the schematic. But it is very important that the schematic and layout agree. Otherwise, there will be confusion when you go to actually build the amp, especially when using my layout. My layouts are mainly used to build a board and show how to connect the board to chassis components. IT IS NOT A COMPLETE LAYOUT! You must refer to the schematic to build a complete amp with any of my drawings.
I just didn't find any valve images in Visio that had the surrounding circles, maybe I'm missing something, I'll give it a try, though.
I have circles on all my tubes. They are included in the Visio Professional version. Look under More shapes -> Engineering -> Electrical Engineering -> Semiconductors and Electron tubes (US units). If you don't have Visio Professional, you may not have any of the Engineering shapes. In that case, just open one of my schematics and copy/paste a tube shape to your drawing. Then right click on the tube shape and you can show/hide the envelop and can also set to direct/indirect heaters.
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I have circles on all my tubes. They are included in the Visio Professional version. Look under More shapes -> Engineering -> Electrical Engineering -> Semiconductors and Electron tubes (US units). If you don't have Visio Professional, you may not have any of the Engineering shapes. In that case, just open one of my schematics and copy/paste a tube shape to your drawing. Then right click on the tube shape and you can show/hide the envelop and can also set to direct/indirect heaters.
I have professional, and I have that section, I get, as mentioned, only the anode, grids and cathode, no envelope. Per PRR, maybe I should just live with it that way, or copy/paste yours and see what happens there.
It's definitely odd. I could use the other app and start from scratch, because I know mines a bit ugly too, but the damn thing's a beast. I'm not sure I understand why you say your's isn't a complete layout? I see all the connections from inputs to tubes, back to pots, etc. What specifically is omitted (otehr than power supply part which is pretty simple for me to gather from mine and isn't 'wrong'.
I still don't see what's wrong with my PI that you're referring to, I compared mine to the AC15 schematic you have in yours, and I only saw the missing section for the depth that I added and was fairly sure was right, but you've indicated isn't. (sorry, this is probably my biggest schematic ever, so I'm learning... be patient lol).l
Thanks,
~Phil
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I have professional, and I have that section, I get, as mentioned, only the anode, grids and cathode, no envelope. Per PRR, maybe I should just live with it that way, or copy/paste yours and see what happens there.
You don't have to live with it. The circles are available just by right clicking on the tube shape.
When I drag a triode onto a drawing it initially has no envelop and doesn't even have a cathode. All that shows is a plate, grid, and heater. Then I right click on the tube shape and select "Show Envelop" and the circle appears. Right click again and select "Set to Indirectly Heated". Now my tube has a separate cathode and heater and also has an envelop (circle). See the attached pic.
Please tell me your Visio does the same. I'm using Visio 2010. Which version are you using?
I still don't see what's wrong with my PI that you're referring to
I hate using ExpressSCH. If I didn't have Visio and some experience with it, I might feel differently. After all, it is free! Attached is a pic of the corrected trem section. There may still be other issues. I quit looking when I spotted this one. That section of your schematic is so twisted around that it makes my head hurt trying to sort it. You really need to swap positions with the triodes or swap positions with all the components that connect to the triodes.
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I've got 2013 I think. I didn't realize that option was there, I'll see if I can get it.
I may redo it basically cloning the AC15 schematic, its so much more legible. (I like yours breaking them out into segments, but I also like one unified schematic if possible)
~Phil
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(I like yours breaking them out into segments, but I also like one unified schematic if possible)
Be patient.
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OK. Here's a one page schematic that agrees with your (hard to read) schematic and my layout. LMK if you find any errors. I can provide the Visio file if you want it.
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Oh that's incredible, thanks!!! Yes I'd love the file, you sir, are a gentleman and a scholar, (unless that's offensive to you lol).
~Phil
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PM sent...
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Got it, and I also confirmed my Visio has that same option, I just didn't think to try right clicking :)
~Phil
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Here's a chassis layout for the AC-30.4 that is based on my AC-15 layout, only longer chassis. It will work very well with my board layout. This chassis layout has been added to the Visio file if you want to download the updated version.
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Got it thanks!
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Here's the next vid, I cover the new changes you added sluckey thanks! Then I start trying to lay out the chassis (I've got it actually cut out right now, hopefully I'm not ordering a new one :)
https://www.youtube.com/watch?v=oO0uvCGCbN0&feature=youtu.be (https://www.youtube.com/watch?v=oO0uvCGCbN0&feature=youtu.be)
~Phil
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Chassis setup and layout deliberations:
https://www.youtube.com/watch?v=8hg5F62de1g&feature=youtu.be (https://www.youtube.com/watch?v=8hg5F62de1g&feature=youtu.be)
~Phil
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That's quite a load for those small L-brackets. I believe I would use these 3" corner braces for that job.
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Oh I'll see if I can find some of those that's a great idea... I didn't see anything like that at Home Depot, do they usually carry them? Lowes? Or am I going to have to order online?
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I would expect Lowes and HD to have them. Save some time and look online. I know Ace has them. I know eBay has them.
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Cool thanks, do you think I'll want to double those up as well, one on each side, or is one going to be enough?
~Phil
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Yes, one on each side. It will be much stronger and I think it will look good too.
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I didn't see anything like that at Home Depot, do they usually carry them?
I've bought them at Home D.
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Cool, thanks guys, I'll get those.
~Phil
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Ok I got those brackets, and have installed them, but they'll be in my next vid, I show the sockets in this one:
https://www.youtube.com/watch?v=FPE1encm0OU (https://www.youtube.com/watch?v=FPE1encm0OU)
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I highly recommend you rotate all those 9-pin sockets 180° as shown in the layout. Otherwise the wiring between the board and the sockets is gonna be a mess.
Also, look at some of my pics of the AC-15 and wire your filaments like that.
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So you're saying that even though the gap in the tube is towards the board, it's easier to wire? It seemed to make more sense to me to have that gap back where things were tighter for that reason?
~Phil
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NVM, I looked at the layout and see what you mean. The heaters are all back on that side anyway, so you can keep the heaters away from the routing, AND have the rest setup to be pretty much as you've laid it out.
Makes sense with the picture.
~Phil
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Oh Sluckey, I keep wanting to ask you, where do you get those single point turret like things you're using to connect your inputs? It seems like it also has a grounding point on the bottom? I've not seen those before?
~Phil
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They are called standoff turrets and come in several styles. You find them in high quality industrial or military equipment. Mine are military surplus. You can find them on eBay...
http://www.ebay.com/itm/HARWIN-W2331-00-DOUBLE-TURRET-TAG-STAND-OFF-POST-10-AMP-10kV-Pack-of-10-Tags-/191976499132?hash=item2cb2b0e7bc:g:x64AAOSwPe1T13LC (http://www.ebay.com/itm/HARWIN-W2331-00-DOUBLE-TURRET-TAG-STAND-OFF-POST-10-AMP-10kV-Pack-of-10-Tags-/191976499132?hash=item2cb2b0e7bc:g:x64AAOSwPe1T13LC)
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Cool, I may have to get those for my next project, those you show are in the UK and I don't know that I want to wait for international shipping ;)
I really like the idea of putting the input resistor at the pin, I remember reading that the closer that resistor is to the actual tube, the better it works.
~Phil
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The next video, sluckey, I've got the new braces in the first part :)
https://www.youtube.com/watch?v=63oeElR3AJ8&feature=youtu.be (https://www.youtube.com/watch?v=63oeElR3AJ8&feature=youtu.be)
~Phil
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That's not how I would have used those corner brackets. What I had in mind would only require two brackets and would have been stronger.
I highly recommend you rotate all those 9-pin sockets 180° as shown in the layout. Otherwise the wiring between the board and the sockets is gonna be a mess.
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That's not how I would have used those corner brackets. What I had in mind would only require two brackets and would have been stronger.
So what did I get wrong? Sorry, I guess a picture may help me understand what you meant? Doesn't adding them on both sides provide additional support and strength? If I'm only providing support on 1/2 of the panel, then it could cause stress as the transformers create a bending force due to their weight, and then the other side that isn't supported would tend to flex and move over time?
~Phil
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Oh yeah and your picture makes perfect sense, but I'm pretty sure I figured that out last week when you first explained it. It took me a bit, but I'll rotate them around. Edit: And I'll use your pic there in the video to explain what I lernt :)
~Phil
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This is how to use those corner braces to provide more support. Since you already have 4 of them you could use one between the transformers. That would make it almost bullet proof, unless that sheet metal is so thin as to provide no support. Hopefully this pic makes sense. I'm not good with 3-D drawings.
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As for the tube sockets... The board layout was designed to neatly and logically accommodate a particular orientation of the sockets. I could have oriented the sockets as you want but the board would look much different. My board layout wants the sockets to be oriented the way they are shown on the diagram. Just consider the board layout and the socket layout and the front panel layout to be one optimized layout. Changing any of those three components will throw the others off.
I'm not saying mine is the only way or even the best. But a lot of time was invested to make it all work well together. And the layout has been proven to work very well. There are about a half dozen successful amp builds using this layout.
Bottom line, it doesn't have to be done like this. But we know this works. :wink:
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This is how to use those corner braces to provide more support. Since you already have 4 of them you could use one between the transformers. That would make it almost bullet proof, unless that sheet metal is so thin as to provide no support. Hopefully this pic makes sense. I'm not good with 3-D drawings.
DOH! I see...
/facepalm.
~Phil
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As for the tube sockets... The board layout was designed to neatly and logically accommodate a particular orientation of the sockets. I could have oriented the sockets as you want but the board would look much different. My board layout wants the sockets to be oriented the way they are shown on the diagram. Just consider the board layout and the socket layout and the front panel layout to be one optimized layout. Changing any of those three components will throw the others off.
I'm not saying mine is the only way or even the best. But a lot of time was invested to make it all work well together. And the layout has been proven to work very well. There are about a half dozen successful amp builds using this layout.
Bottom line, it doesn't have to be done like this. But we know this works. :wink:
I totally get it, and I don't want to reinvent the wheel. I'll spin them back around... :)
Thanks!
~Phil
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The next video, sluckey, at the end I fix the brackets and the sockets :) and yet again you get a mention and thanks in the video!
https://www.youtube.com/watch?v=wFoLTTudX24 (https://www.youtube.com/watch?v=wFoLTTudX24)
~Phil
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Where do you plan to mount the node A and node B filter caps?
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That is one of the things I'm still puzzling in my head, I know B, that's attached to the same point as the B+ on the board, so I'll attach that to there, and ground it to the grounding bus, like I've done (Similar to Doug's method). The A one, though, I'm trying to figure out, I may be able to make it a kind of Point to Point between the pin of the rectifier and a ground, or is that not 'good'? Do you need some distance between the rectifier and the actual cap?
If not, I'm open to suggestions. Maybe i need to create a separate mini board to hold them? ugh.
Edit: there is space for them near where the rectifier is, just nothing solid to connect them to... is it 'unsafe' to just glue them down to the chassis?
~Phil
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Mini board? Where would you put it? That little chassis is pretty stuffed already. It's really important that those two caps be grounded at the same point that the red/yellow wire from the PT is grounded. And that ground point needs to be near the PT and kept far away from the preamp grounds. A dual cap can is ideal for those two caps.
Just an idea... Is there room on the transformer panel to mount a cap can near the choke? Then the two choke wires would connect directly to the cap can and the PT red/yellow wire would also connect directly to the cap can. Then you would run three wires from the cap can to the main chassis. One would connect to the rectifier tube, another would connect to the board at the B node connection, and the third would connect to chassis near the rectifier tube.
Without having the chassis in hand it's kinda hard to see where to shoehorn those caps (or cap can) at this point. There was a time that you had plenty of room to put a cap can next to the rectifier as shown in the proposed layout. I wish you had done that. In fact, you could drill another noval socket hole in the space between the power tubes and the PI tube. Then shift the power tubes over. Drill out the vacated noval hole to accept the rectifier socket. Drill out the vacated rectifier socket to accept the dual cap can. Or, just leave the rectifier where it it and drill out the vacated noval hole to accept the cap can. Either way, I think this is a very logical and viable arrangement. At least give it some thought.
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There is still a good 2 to 3 inches of bare space from the end of the board to the edge of the chassis, but I do like the idea of mounting that one cap up by the choke too, I'll have to take a look, I may take some pics tonight and post here to let you see what's going on there.
All great ideas, I may fall back to the cap can at the end if needed, but I already have the caps here, so if I can fit them, I'll be good.
~Phil
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Oh and per your mention of the CT of the PT, should I pull that wire out and ground it right at the PT lug itself? I was planning on running my grounding wire from there anyway, I guess I can just join that wire, and the CT at that point and run it into the chassis through the hole the other wires are in now...
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I don't see any advantage in that. I would prefer to connect the red/yellow lead directly to the main chassis (near the power end of the board) in a location where the negative lead of those first two caps can also be directly connected.
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Ok gotcha, that makes sense. I'm hoping to actually get it all together this weekend, I finished populating the components on the board but haven't soldered yet, because I want to get the wires in first, and then solder, and then drop in after wiring up the inputs, rectifier, output to OT etc and then drop in the board...
I'll post some pics in the next day or two of the current look of things.
~Phil
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Here are a few pics of the board in the chassis, and I set the caps in a few ways to see where it 'may' work...
https://goo.gl/photos/8pshWArzTRsh25WW8
~Phil
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Maybe this will also be of some help as well !!
:think1:
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Looks like plenty of room for the caps. I'm a bit concerned with your OT wires being so close to the VIB channel Volume pot. That's flirting with disaster. Maybe you'll get lucky.
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Thanks Uki!
Sluckey, yeah, I'm planning on bending them flat under the board and straight across, but I too am hoping it doesnt induce noise... The sillyness of trying to cram too much into a small chassis I guess.
~Phil
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Next video is up, I start prepping the under board wires and the basic connection wires
https://www.youtube.com/watch?v=jW-ODoyXbJI (https://www.youtube.com/watch?v=jW-ODoyXbJI)
~Phil
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Video isn't yet done, but I've finished soldering the board and have all the wires coming off as well. Check this album for the last 4 images, I did overview, left right and middle close ups.
https://goo.gl/photos/8pshWArzTRsh25WW8
~Phil
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The next video, I get to the board a bit more...
https://www.youtube.com/watch?v=1Orybin0Ezk (https://www.youtube.com/watch?v=1Orybin0Ezk)
~Phil
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Steve (Sluckey),
Can you please put this thread in ARCHIVES when it's done. This is one of the best collaborative efforts on a complicated build that I can remember on the forum.
with respect, Tubenit
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Thanks! I definitely agree the collaboration with Steve on this has been stellar for me. I think this would have been 10X harder if it wasn't for him. I also drop notes on other things I've learned on this forum etc in the series, I love this forum for the extremely helpful nature of everyone involved. Everyone goes out of their way to help, so long as people are trying to do what's asked ;)
~Phil
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Can you please put this thread in ARCHIVES when it's done.
I can do that.
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Next video, I cover more of how I populate the board etc. May be boring for some, hope not :P
https://www.youtube.com/watch?v=s41MxoOc3bQ (https://www.youtube.com/watch?v=s41MxoOc3bQ)
~Phil
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In the future if you will use 22AWG jumpers under the board you will still have plenty of room inside the turret to put component leads. I have as many as three resistor leads in the same turret hole with an underboard jumper.
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Yeah, that's one of the big mistakes I made here, and I realized it after I had enough done that I didn't want to start over. I'll make sure to use 22AWG from now on for under-board work.
Thanks,
~Phil
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Video 10 is up:
https://www.youtube.com/watch?v=aBPxKUpY1ds&feature=youtu.be (https://www.youtube.com/watch?v=aBPxKUpY1ds&feature=youtu.be)
~Phil
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Video 11:
https://www.youtube.com/watch?v=kB9Me3xyRis (https://www.youtube.com/watch?v=kB9Me3xyRis)
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and now video 12, I cover adding the wires and such:
https://www.youtube.com/watch?v=Pq0RDzUTGUw (https://www.youtube.com/watch?v=Pq0RDzUTGUw)
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Okay I did the first power up, normal channel sounds perfect. Trem/vib channel sounds fine, but no trem/vib at all. I've tried variations of things, I jumpered the footswitch out closed to see if it needed to be grounded to work (It didn't help). I've tried all variations of the pots to no avail. The switch on the front when switched on seems to lower the volume a tad, but htat's it. Here are my voltages from the tubes related to the trem/vib channel (with sluckey's expected voltages from his ac15 schematic in parenthesis after):
V1: (input stage)
1: 149.2V (147V)
2: 0V
3: 1.2V (1.2V)
6: 212V (212V)
7: 10.5V
8: 20V (17.5V)
V4 (modulator 12AU7)
1: 86V (71V) a bit high?
2: 0V
3: 3.5V (3.2V)
6:85.9V (71V) again high
7: 0V
8: 3.4V
V6 (1-3 oscillator, 6-8 PI)
1: 138V (144V) a bit low
2: 0V
3: 1.3V (1.2V)
6: 208V (208V)
7: 15.3V
8: 24.9V (23V)
I've also got pictures of the finished build in my google photo album here: https://goo.gl/photos/8pshWArzTRsh25WW8
The first two are the related ones. I have gone over the jumpers, (Found a missing one, but that was before the tremolo worked at all) I've gone over every resistor and cap in the amp twice, I just don't see what may be missing. Anyone spot anything odd?
Does the footswtich need to be a switched jack to ground to bypass it? (I'm not sure if grounding that point enables the trem/vib or disables it). Does the voltage off by about 10V mean something's off with that tube?
I had a scope on it and could see some oscillation that looked right in one half of the PI at some point, I don't recall exactly, but then nothing later... It seems like it's being swallowed somewhere. The unaltered signal is coming through fine.
No serious noise that I can tell, a minor hum in the trem/vib circuit that doesn't exist in the normal channel.
~Phil
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The footswitch must be grounded to ENABLE the oscillator. No ground equals no vib/trem. I used a Switchcraft 12A jack with the switch lug connected to the sleeve lug so my trem/vib works without a footswitch.
V6 pin 1 will be bouncing all over the place when the oscillator is working. This just looks like an erratic reading on a digital meter. Your plate voltage looks like the oscillator is not working.
V6 also needs to be a strong 12AX7.
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Okay, I've jumpered that to ground for now until I can get a 12A, I'm using the 11 type. is the oscillator always suposed to bounce around? I'm getting rock solid 138 v, swapped tubes with the main input tube and get 140 instead, but still not moving.
One other thing of note is on the regular channel it is very quiet with only a slight buzz as it gets to loud volumes, but the vib/trem channel has a heavy hum almost like transformer hum in it. even at low volumes. I just went over all the jumpers and resistors in that part of the circuit again and it's fine. How can I trace the signal path here? Not sure where it should go from the first V1 exactly, but I see it doing great after the second half of that tube and then levels drop pretty low by the time they get back to the shift network. (it's like 25V after the first tube, but then drops down to sub 5 volts I'd say at the shift network. (100mV inputs sine with this. )
~Phil
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Okay, I've jumpered that to ground for now until I can get a 12A, I'm using the 11 type. is the oscillator always suposed to bounce around? I'm getting rock solid 138 v, swapped tubes with the main input tube and get 140 instead, but still not moving.
Rock solid means it ain't working. It will be jumping around as much as 50v or more.
Keep looking for a wiring error or wrong component. Lot of jumpers on top and bottom. Verify they are in the correct place. Use your meter to check for zero ohms resistance between turrets that should have a jumper. I hope it's not an under board jumper. I didn't like the way you did those.
Signal flow is V1 to V4 then on to volume control.
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I'll give that a go again, I'd checked all the jumpers again in that area after I missed the one. I didn't find any wrong, I retested the under board ones as well, they're right so far as I can tell. I'll go over it again. I did test the input path all the way to the V4, and at the inputs there it's decent still, about 25V with the sine, but I see nothing at the oscillator side.
I'll report back after I mess with it some more.
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Signal flow is V1 to V4 then on to volume control.
Oh and that part I know works, because I get clean signal out just fine, very loud etc, just no wobbly bobbles. :D.
It seems to me like the modulator is fine, but somehow the oscillator and PI for that separate part isn't doing anything.
maybe I didn't ask it right, but should the oscillator be oscillating if there's no signal getting to it, or will it only oscillate the signal coming in?
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Signal flow is V1 to V4 then on to volume control.
maybe I didn't ask it right, but should the oscillator be oscillating if there's no signal getting to it, or will it only oscillate the signal coming in?
The oscillator should always be oscillating. If it's not, you definitely have a problem in the oscillator.
Gabriel
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maybe I didn't ask it right, but should the oscillator be oscillating if there's no signal getting to it, or will it only oscillate the signal coming in?
The oscillator is a signal generator. It puts out a low frequency sine wave (approx. 3Hz to 10Hz). It does not have a signal coming in. It requires a ground at the footswitch jack to be enabled. This low frequency sine wave is many volts and can be viewed with an o'scope. Or you can measure the AC RMS volts with a good Fluke meter.
As long as V6-1 is a steady voltage THE OSCILLATOR AIN'T WORKING! You must have a ground on the FS jack ***AND*** a strong 12AX7. If it's still not working, there must be a wiring error or wrong value component associated with the oscillator circuit (V6 pins 1,2,3). The problem is in the attached pic...
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Sluckey,
Excellent, thanks, that makes sense. (Just never really understood that part of the circuit, now I think I do, or I hope I do). I have a scope, I fixed the missing jumper issue by tracing the input path from V1 to V4 and found where it 'disappeared' and realized at that point what was wrong. I'll double/triple check all of those components again and figure out what's what.
I do have a strong tube, I've been using it in the other AC30, and they're pretty new, only about a year old.
I did try jumpering the jack to ground, I just clipped an alligator lead from the tip to ground of the jack and ensured I got ground. It is possible something else is wrong. (does the vib/trem on/off switch do the same thing? It seem to get a sound volume drop when engaged, but nothing else, but not sure if that's related at all.)
I'll tinker with it tonight when I get home.
~Phil
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It is possible something else is wrong. (does the vib/trem on/off switch do the same thing?
Of course there can always be something else wrong. :wink:
But the problem you have described will be fixed by concentrating on the pic I posted.
The vib/trem switch is not an on/off switch. One position gives you a pitch shifting vibrato effect. The other position gives you a simple amplitude modulated tremolo effect. Neither effect will work until you fix the oscillator.
Quit jumping around. Focus on the pic I posted.
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lol I know, I tend to go on brain escapades when stuck at work and I can't do what I need to yet :) I'll definitely do that exactly. I've been looking over the pics I have (the last ones above are kinda crap, but earlier ones I had in the same album) and don't see anything wrong. I know I tested the resistors, they're all right, and I can see that from the pics. I can actually see that two of the three caps are .01, but I can't see the third from the angle, but man am I definitely confused as to what could be wrong. I may try another tube, as well as just try jumpering the 'footswitch' connection turret directly to ground as well. At any rate, I knw what to tinker with when I get home. :)
~Phil
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I think I just found it! I was not looking closely enough, but I missed a jumper. See attached pic. (I'll test when I get home). I was thinking there was one here, but there isn't that's the wire going off board that's overlapping a bit but it doesn't touch.
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I was thinking there was one here, but there isn't that's the wire going off board that's overlapping a bit but it doesn't touch.
No jumper there would definitely kill the oscillator. I hope you're right. I had looked at that and decided it was a jumper. Fingers crossed for you!
PS... Ever see this pic before?
(http://sluckeyamps.com/VAC15/04.jpg)
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Yeah in the higher res photos in that album, if you zoom in really close it's still pretty clear it's not. I'm crossing my fingers too :)
~Phil
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I was thinking there was one here, but there isn't that's the wire going off board that's overlapping a bit but it doesn't touch.
No jumper there would definitely kill the oscillator. I hope you're right. I had looked at that and decided it was a jumper. Fingers crossed for you!
PS... Ever see this pic before?
(http://sluckeyamps.com/VAC15/04.jpg)
Heh yup, I need to be better about that, I do a similar 'exercise' but don't cross them off like that, which is where I failed here. I keep thinking I"m being fastidious enough, but I've proved myself wrong every time. I just need to assume the mantra 'something is wrong' and do that.
~Phil
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BOOM! That didn't 'solve' the problem, but I checked all around, and there was another jumper in place, but that I'd forgotten to solder, that somehow wasn't connecting at all (Not sure how, I couldn't crimp it tighter, it seemed like it had a good physical connection) Once I added that jumper, and soldered the other jumper, I got it. The tremolo/vibrato came in.
On the other hand it does seem a bit noisy, and a bit muddy. I'm not sure if I've got something else amiss, or if there is a specific tube that may need to be better quality etc, but it is working. (I still hear that hum in that channel only, nothing at all in the normal EF86 channel).
I'll have videos of the last couple phases coming, including playing it. SOON :) I have to edit them and put them up etc. (most of my videos come up a week or so after the work was done due to this.
~Phil
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Now that the oscillator is working, check the plate voltage at V6-1. Should be jumping around. If you have a good dmm such as a Fluke, measure the AC RMS voltage sine wave at the ungrounded end of the depth control. Maybe write that value on the schematic for future reference. I like to set the speed pot at 5Hz for these reference measurments.
The cut control is the only tone control that affects the vib channel.
How is the power amp doing?
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The tone issues I had were my dumb mistake, I didn't realize I had hte pickup switch in position 4 between mid and bridge out of phase so its muddy on it's own.
I have a nice fluke with AC and hertz.
At the anode itself:
Slow: 3.5 -7.1Hz
AC: 19 - 40V
Fast: 4.7 - 9.8Hz
AC: 32 - 41V
and the AC RMS voltage at the depth control at 5Hz
9-12V at one end of the pot
12-15V at the other.
Power amp sounds great, I need to double check the bias, but It was a bit low, as I recall, was aroun 28mA, but I need to get an exact measurement on the resistor, (measured 14.2V at the cathode resistor, 14.2/130 /4 tubes... seems a bit low, I think el84 can go up to what, like 40mA if I recall? (I'll double check).
Sounds great though right now.
9-15V
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Just looked, seems 48mA is max so at 70% that's 33.6, so if I'm at 27, I could go up a little, but not sure I need to, I do like the tone now. If I go higher, I'll get a bit more 'crunch' right? I seem to recall reading that the JMI ones would often be very hot but chew up tubes, like 40 to 42mA?
~Phil
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I'd leave the bias as is for now and just play it and get familiar with it. When you get tired of playing it, then record all tube pin voltages, power supply nodes and the tremolo voltage. Put them all on your Visio schematic. Never know when you may need them.
4 EL84 tubes with a 50Ω common cathode resistor will be very hot. Short tube life. The original Vox cab compounded the heat problem because of poor air circulation.
You may notice that the trem effect is much stronger than the vib effect. Just the way it is. You'll probably like playing with both channels jumped.
Oh yeah, I have one undocumented mod to mine... I replaced the cathode resistor/cap for V6-3 with one of Doug's LED lamp assemblies mounted on the front panel. Never have to guess if the oscillator is working. It will also significantly increase the amplitude of the oscillator signal.
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Excellent, I may have to do that too. This thing sure sounds great. I played it again for a while tonight, but it's getting late. I'll definitely let it burn in and give it a whirl. It also seems like the sound is cleaning up a bit now that it's been running for a while, not sure, (I also think my house has horridly dirty power).
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Next vid, going over more of the wiring hookup, shorter one, but getting there (as you know I'm done, but trying to keep the entire build videos together in a semi sequential series)
https://www.youtube.com/watch?v=JSwsRZGcmpY (https://www.youtube.com/watch?v=JSwsRZGcmpY)
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Video 15:
https://www.youtube.com/watch?v=6_lEHQx7PRM (https://www.youtube.com/watch?v=6_lEHQx7PRM)
~Phil
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Video 16:
https://www.youtube.com/watch?v=d22Zf_zZj-o&feature=youtu.be (https://www.youtube.com/watch?v=d22Zf_zZj-o&feature=youtu.be)
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Video 17, a few messes made, but recovery was somewhat manageable :P
https://www.youtube.com/watch?v=4ve8fmNN_Gc (https://www.youtube.com/watch?v=4ve8fmNN_Gc)
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Video 18, In this one, I finish through to the last tube socket and the next should finish the entire chassis.
https://www.youtube.com/watch?v=bQgIdZEKmjk (https://www.youtube.com/watch?v=bQgIdZEKmjk)
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Video 19, I get all the pots done too.
https://www.youtube.com/watch?v=XVdiD7JJdw8 (https://www.youtube.com/watch?v=XVdiD7JJdw8)
~Phil
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Video 21, I finish up the grounding, and it's pretty much ready to power on, next video!
https://www.youtube.com/watch?v=YTh8vci_coA (https://www.youtube.com/watch?v=YTh8vci_coA)
~Phil
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Here you go. I'm not sure if the layout will be all that much help, because the PDF printed out with very thin lines so it is kinda hard to see the colors, but with the schematic it should get you there. The big thing you'll notice is I added a bunch of extra sections to the power supply, and I distributed the power supply through out the amp. If you have any questions, feel free to ask. And for what it's worth, the little bit I've heard the amp it sounds great, and is the quietest amp I've made.
Gabriel
That looks like a very good version, better than any combination of channels that Vox has ever released...
Maybe it would be even more flexible, if the triode would be used to boost the EF86 instead of waisting it in the TB channel. I found this in another thread:
http://i.imgur.com/7L7s7hX.jpg (http://i.imgur.com/7L7s7hX.jpg)
(Gridstoppers etc are missing, off course...)
Would you mind to share a bit more info about your amp, including some pictures? Esp. some explanation of the mods in the power supply (filtering...) would be helpful. And would you share your original schematic- and layout files? I'm planning a very similar build, but maybe with some changes...
regards from germany, Immo
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Are you asking Gabriel or Me? mine are all at the first post of the thread if you want them.
~Phil
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Gabriel!
But I really like your amp as well, I watched all the videos via the Vox facebook group... Maybe I'll use that layout to rebuild my chinese AC15H1TV.
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Well, here's video 21, with first power up and some of the troubleshooting shown here:
https://www.youtube.com/watch?v=TQUUurAKBOA (https://www.youtube.com/watch?v=TQUUurAKBOA)
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Here you go. I'm not sure if the layout will be all that much help, because the PDF printed out with very thin lines so it is kinda hard to see the colors, but with the schematic it should get you there. The big thing you'll notice is I added a bunch of extra sections to the power supply, and I distributed the power supply through out the amp. If you have any questions, feel free to ask. And for what it's worth, the little bit I've heard the amp it sounds great, and is the quietest amp I've made.
Gabriel
That looks like a very good version, better than any combination of channels that Vox has ever released...
Maybe it would be even more flexible, if the triode would be used to boost the EF86 instead of waisting it in the TB channel. I found this in another thread:
http://i.imgur.com/7L7s7hX.jpg (http://i.imgur.com/7L7s7hX.jpg)
(Gridstoppers etc are missing, off course...)
Would you mind to share a bit more info about your amp, including some pictures? Esp. some explanation of the mods in the power supply (filtering...) would be helpful. And would you share your original schematic- and layout files? I'm planning a very similar build, but maybe with some changes...
regards from germany, Immo
I split up some of the of the preamp power sections. It's pretty easy, in the AC30, since the power sections are in parallel, instead of in series. I think I just added one extra section, so the bright and normal inputs aren't sharing the same power resistor and cap. Double the value of the resistor, and all's good. (You could use a smaller cap, but why?) Then, instead of putting them all in the power amp chassis, I put them right next to the rest of the circuitry they are driving. It's just about trying to decouple things a bit more.
Gabriel
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These are great videos. I was curious what you were using to capture such clear audio?
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I have a azden mic that fits on a camera hot shoe that's on my camera that I've used for a long time because it works so well. I believe it is this one:
https://smile.amazon.com/Azden-SGM-990-Shotgun-Microphone-Black/dp/B00CRMB79C/ref=sr_1_1?ie=UTF8&qid=1487140295&sr=8-1&keywords=azden+dslr+microphone
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Thanks. I'll check that out.
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Phil, we're all waiting for video 22! ;-)
@Gabriel: Thanks for explanation! As I'm planning a normal channel with an ef86 driven by a triode, decoupling of the power supply doesn't work for me anyway. I think I'll use the weber layout and try to put in the ef86. Which might be difficult, because I have a pre-drilled chassis...
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@Gabriel: Thanks for explanation! As I'm planning a normal channel with an ef86 driven by a triode, decoupling of the power supply doesn't work for me anyway. I think I'll use the weber layout and try to put in the ef86.
I can't think of any reason you couldn't add a couple extra PS sections. It's one extra resistor, and one extra cap per section, so pretty easy to shoehorn in.
Which might be difficult, because I have a pre-drilled chassis...
Greenlee punches are wonderful things. Expensive, but wonderful.
Gabriel
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I can't think of any reason you couldn't add a couple extra PS sections. It's one extra resistor, and one extra cap per section, so pretty easy to shoehorn in.
Sure, but it wouldn't make much sense, because I'll use one triode of the first tube for the top boost and the other for the normal channel anyway. We'll see...
Greenlee punches are wonderful things. Expensive, but wonderful.
The hole is not the problem... I'll just have to find a good place for the EF86. There's no space to put it in a row with the other preamp tubes.
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Here's the final video, the demo! Let me know what you guys think. (I always post here for the gang first :D)
https://www.youtube.com/watch?v=G8E-oJm_8vc (https://www.youtube.com/watch?v=G8E-oJm_8vc)
~Phil
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Several of the members have built this 1960 AC-15...
http://sluckeyamps.com/VAC15/ac15.htm (http://sluckeyamps.com/VAC15/ac15.htm)
There's a very legible schematic at the bottom of the page.
Sluckey, which software do you use to draw your layouts?
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I know this one, because I've asked the same question, Visio. I ended up buying a version so I can too. I live in Redmond WA though and have friends that work at the evil empire (Microsoft that is) so it was quite cheap for me, vs normal price :)
~Phil