Vox AC15 Tweed Deluxe hybrid w/ reverb schematic

[66Strat]

Those vector sockets are cool, but expensive when they pop-out somewhere on the web... They were making great sockets back then. I believe there was a use for them in high freq radios where mounting parts vertically could prevent oscillations... In guitar amp the usual input low pass filter (usually a 68k in series with the input grid can prevent this, I believe.

I can remember seeing them in surplus military radios. They are very handy in organizing components and connections at the tube socket. When I saw the eBay ads, I thought the prices were for the lot price for 4 sockets depicted in the pictures. I need to put my extra heavy duty reading glasses on.

[Greg]

 Yes I agree 66Strat, only the versatility of these could justify their use. Yes, the price is for the lot of four, so 30 dollars, not bad really...Less than 9$ for one. I've seen higher prices than this. And apart from being a multi-options socket, you can be sure the solder tab on these won't go off the socket still crimped to the tube pin. This kind of things happened to me in low quality current 9 pin sockets. The only thing restraining the tag to go out of the socket while pulling a tube is its wire attached to it!

 And Opry, I understand you in pursuing a different way to do things, I mean your way. A technicien might have a particular way of thinking, a guitariste might have another one. A hobbyst might want to mount a kit or create from scratch or to study technical manuals or all three. I admit I have an annoying tendency to comment and watching for logic in any construction type rather then asking the a priori «which is better» question.

 Other than that, trusting my ear and my wallet would be other considerations for my stuff. As a guitarist and an admirator of old chassis pictures, I am de facto an hobbyist and might be irrational on many aspects, one being to cram many things on a small chassis and using two of those 35$ FP cap cans rated at 450 v. for simplicity and their common ground tags and «stealing» one or two section of each can as low voltage cathode bypass capacitor. I regressed into those 40's ways of building things...

[Opry Audio]

I didn't see a normal channel but maybe you decided to include one. I built both type of circuit layouts (PTP and circuit boards) and I can't tell which is better in a guitar amp. But it can be fun to experiment with both types and I encourage you to do so. A circuit board is easier to work on, and you see them in miltary equipement as far back as in the '30's and even the first gibson amplifiers (although I never had an opportunity to work on such vintage equipement, but saw pictures). A point to point could be neat but a bit of a PITA to work on later as you might have guessed.

Those vector sockets are cool, but expensive when they pop-out somewhere on the web... They were making great sockets back then. I believe there was a use for them in high freq radios where mounting parts vertically could prevent oscillations... In guitar amp the usual input low pass filter (usually a 68k in series with the input grid can prevent this, I believe.

I am really impressed with those PTP photo's you shared. That is a super cool layout and I like these vector sockets too. I think they may be a bit too spicy for me in terms of something that I'd use for more than one build in a sustainable way. I really can't tell what's better in a guitar amp either. I've done one other PTP build that came out OK but was lacking in a lot of what I wanted out of it because of a poor layout (and because of that poor grounding). Random thought for PTP people: do you get effective grounding from using the strips ground tab? I noticed in the one you shared that each stage has it's own star ground to the chassis. I know a lot of people would agree that that's good grounding but is the multiple paths to ground ever a problem? It would make sense that if you took care to ground each stage separately it could really work well. I've seen schemes like this in old Kalamazoo amps

[Greg]

I general, people will NOT agree that a few star ground forming a path through the chassis is the way to go. Although it will work if done logically. Only one point should be at the chassis for reference is the general consensus, using a bus wire. Early tweed, blackface, silverface Fender got away with multiple chassis star grounds but they had to be separated current-wise from one point to the next, as long as it forms an «invisible bus» from input (low current star) to output (high current star). They even used a brass plate for the preamp grounds.

Same principle apply to multiple star grounds within a bus except that on a bus, since it is a wire, there is no possible turn around risks of current leaking to an earlier stage star that can cause hum unless you purposely unfollow your B+ schematic ground scheme (i.e connecting a screen supply ground to the PI star ground). For a chassis ground current path, using the ground leg of a strip is ok if it is well bolted with some grip or soldered with some distance between points forming a line. Using hard stainless steel screws/bolts on aluminium make a good mechanical contact. On the other hand, when using a bus wire as a system, you are better soldering it on a floating lug on all of your strips along the signal path except the last one which is associated to the input star ground terminal circuitry being the only one that has to be referenced to chassis, soldered or boltered, so you don't end up with some kind of a parallel path. 

However, when using the chassis as a single current path, the number of those legs bolted (or soldered) to chassis should be ideally equal to the power nodes your power supply has with all associated circuitry to each one of them. The choice of a bus though, would eliminate the «angst» associated with the potential failure of one of the mechanical grounds. Perhaps the problems you stated in one of your previous before was about current leaking onto an earlier stage causing hum.

The photos where from an early build I did in 2007, but later (on another build), I included a ground bus path for peace of mind referenced at one end. That circuit from the pictures (where I chassis-star-grounded each stage) still works dead quiet with all mechanical grounds still in place even with a bare tab on the input jack.

If I had to build an amp for a client, going for a bus would be mandatory for reliability I guess. For personal use, I could play with liberty and go with a few screw grounds using the chassis. But there is a potential «screw up» if  logic is not respected so people dismiss the multiple chassis ground stars as not being a viable idea in general.

[Opry Audio]

I general, people will NOT agree that a few star ground forming a path through the chassis is the way to go although it will work if done logically. Only one point should be at the chassis for reference is the general consensus, using a bus. Early tweed, blackface, silverface Fender got away with multiple chassis grounds but they are to be separated current-wise from one point to the next, as long as it forms an «invisible bus» from input (low current star) to output (high current star). They even used a brass plate for the preamp grounds

Same principle apply to star ground within a bus except that on a bus, since it is a wire, there is no possible turn around risks of current leaking to an earlier stage star that can cause hum unless you purposely unfollow your B+ schematic ground scheme (i.e connecting a screen supply ground to the PI star ground). For a chassis ground current path, using the ground leg of a strip is ok if it is well bolted with some grip or soldered with some distance between points forming a line. Using hard stainless steel screws/bolts on aluminium make a good mechanical contact. When using a bus, you are better connecting it using a floating lug on all of your strips except the last one which is associated to the input star terminal circuitry being the only one that has to be referenced to chassis so you don't end up with some kind of a parallel path. 

However, when using the chassis as a current path, the number of those legs bolted (or soldered) to chassis should be ideally equal to the power nodes your power supply has with all associated circuitry to each one of them. The choice of a bus would simply eliminate the «angst» associated with the potential failure of one of the mechanical grounds. Perhaps the problems you had before is the current leaking onto an earlier stage causing hum.

The photos where from an early build I did in 2007, but later (on another build), I included a ground bus path for peace of mind referenced at one end. That circuit from the pictures (where I chassis-star-grounded each stage) still works dead quiet with all mechanical grounds still in place even with a bare tab on the input jack.

If I had to build an amp for a client, going for a bus would be mandatory for reliability I guess. For personal use, I could play with liberty and go with a few screw grounds using the chassis. But there is a potential «screw up» if  logic is not respected so people dismiss the multiple chassis ground stars as not being a viable idea in general.

This is a great explanation

[Greg]

This was an attempt on how you can get away with chassis grounds (to make a cleaner layout) but it is bad engineering practice (that, you and I knew).

 I went on to read a Valve Wizard article on his great site (15.6 on Grounding and Ground schemes). He doesn't mention at all that the ground current through the chassis «could» make a straight invisible path if well ordered on the plane (chassis) but rather, that current spreads UNIFORMLY on the chassis (regardless of where they connect I believe)!

  I don't know how this idea of the «invisible bus» was planted into my head, maybe from intuition by trying to explain «why» it worked on my early builds but I didn't have all this great information available back then. So I don't want to spread fake news without being moderated around here so I retract my statement above, will still follow your build with great interest but I will STFU for a while  .

Regards,
JP 

[Opry Audio]

Ok, so I took a different approach to the layout. Fixed most of what y'all had to say in terms of stuff that wouldn't work. I think this is the best mixture of PTP and board layout that I could come up with. I actually like this approach and might be all set to go to build this if nobody spots any miswirings or any other lead dress issues. What do you think?

[Opry Audio]

just saw i didn't finish wiring the cut control but other than that should be good.

[Opry Audio]

Heres the FOR REAL finished one   

[PRR]

> current spreads UNIFORMLY on the chassis

Dinner and a show. Everybody leaves the one door of the restaurant and walks to the one door of the theater.

In a city they'd mostly walk the sidewalk. But suppose there was a large open smooth field between. If they walk in a line it gets crowded. They spread out. They walk faster when "free". It is perfectly reasonable that the crowd could spread in width to half the size of the length to walk. If it spreads much more, they lose more on the longer path than they save by avoiding the crowd. But people being as random as electrons, sure there's a few folks taking the extremes of the field.

In a chassis it won't be dead uniform all over. But it may not vary much all the way to the edge.

[PRR]

Current between points in a field of metal (chassis) is same-as an old brain-puzzle for EE types.

Assume all identical resistors. What is the resistance between the red dots? More to our point, how much current in each resistor?


A real chassis is an infinity of infinitely small resistors (and inductors). But working with 3x3, 4x4, 5x5 grids lets you see the trend.

I'm not saying you need to solve the puzzle to get the idea. But you can see that nearly ALL the resistors will carry current. Here, more current in the area between dots. But that makes voltage and that forces current to flow in the surrounding resistors, out to infinity.

[Greg]

Thanks PRR, I get it... kind of... Not going to solve this tonight, I'll take the bus 

So Opry, I checked your work but I found a few things...

1-The primary circuit is not complete.

2-The signal connection from the treble output to the RC network is missing.

3-The reverb return grid leak maybe better grounded with its related circuit on the bus... Assuming small coax wire with shielding grounded to the jack output etc...
 
4-The 6V6's 1k5 grid stopper ideally between pin 1 and 5

5-The ground bus should ideally be attached to the negative lug of the reservoir double cap can (insulated from chassis at this point) along with the center tap and power cathode resistor etc, all insulated from chassis. 
The only signal ground connection to chassis occurs at the input jack at the end of the bus with a more secure way than to rely on the input jack screw and without touching the back of the pots to avoid loops as much as possible.

6-There was some errors in the B+ distribution and grounding... Which I tried to correct assigning numbers for less confusion? The reverb transformer was getting the full screen voltage about 400v in your original schematic and had to be dropped down 100V to 300V by means of that 10k dropping resistor and extra cap.

7- Maybe that grid wire from the reverb/mixer recovery gain stage (V4). It is unecessary soldered to two lugs and kind of long. I guess it could go straight from the grid #2 pin to the 470k/3m3 junction using coax cable and the shield grounded to chassis at one end. I would use coax on all grids, especially when they travel from back to front.               

Maybe there are other things but I have to go to sleep!

[PRR]

> I'll take the bus

I'll play that game. If you want to go NYC to LA, there's several routes, you'd lean to the shortest/cheapest, but no real difference. However if LOTS of people wanted to go NYC to LA (such as the airliners were grounded), then ALL the routes would get taken, more or less equally.

If the rush was Chicago to Miami, there would be full buses through Missouri and Kentucky, but also extra traffic in Oklahoma and Virginia. IIRC, after 9/11 people were taking the oddest roundabout routes to get home. Electron surge will too.

[Greg]

This is kind of metaphysical overall but I like that route. Or these routes. That's pretty much a description of pre-thanksgiving weekend isn't it? Looks like the Mid-Northern states are carbonized.They are Greyhound free!