Advice needed...

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TriodeLuvr
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Re: Advice needed...

Post by TriodeLuvr »

I did my heater wiring first. It comes straight up from each socket for about 1-1/2", then bends at a right angle to go to the next location. I have no issues with heater hum, but I also elevated the heater circuit to about +75V.

How high is your chassis? You don't have to mount all the transformers on the same side if one or more will fit underneath. You could mount the power above the filament, and that will leave more room for the audio layout.

You might already know this, but 6-32 and 4-40 nuts are available in standard and narrow size. The smaller size 4-40 is 3/16" across the flats, and that fits better on 9-pin and 7-pin sockets that mount under the chassis.

Jack
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Re: Advice needed...

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TriodeLuvr wrote:
Thu 04/22/21 10:19 pm
I did my heater wiring first. It comes straight up from each socket for about 1-1/2", then bends at a right angle to go to the next location. I have no issues with heater hum, but I also elevated the heater circuit to about +75V.
I see. I'm so used to working with such a cramped original organization and looking at much more complicated amps that I forget that there really isn't that much to this amp and wiring shouldn't be a problem.
TriodeLuvr wrote:
Thu 04/22/21 10:19 pm
How high is your chassis? You don't have to mount all the transformers on the same side if one or more will fit underneath. You could mount the power above the filament, and that will leave more room for the audio layout.
My chassis is 2" in. thick. The height of my trans are: Iso trans: 2-1/4"in. / Filament trans: 2-1/8" in. / Output trans: 1-5/8" x 1-1/2" in. So the output transformer is the only one that could be mounted inside (upside-down) or on the inside edge of the chassis. The others are too tall and wide. I'd been wondering if it was OK to do that with the OPT.
[/quote]
TriodeLuvr wrote:
Thu 04/22/21 10:19 pm
You might already know this, but 6-32 and 4-40 nuts are available in standard and narrow size. The smaller size 4-40 is 3/16" across the flats, and that fits better on 9-pin and 7-pin sockets that mount under the chassis.
I did not know that. I've got a pop rivet tool so I'd planned to use that instead of bolts for the tube sockets.
And speaking of the tube sockets, Mr. Perfect did it again. When I ordered my tube sockets I ordered 4, 9 PIN SOCKETS! I forgot that the 6AV6 is a 7 pin tube! :oops: Froops! So, as is so often the case, I ran out to storage and, as is so often the case, didn't find a usable 7 pin socket. But I did find a couple NOS EBY 9 pin ceramic sockets with built in shield base. I wish I could find more of those!
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Re: Advice needed...

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Thoughts on positioning the OPT on the underside of the chassis. I may have to lengthen the leads of the OPT. They're kinda shorty. I'd think that I'd want to keep the rectifier and filter caps on one side also, maybe under the Iso and Filament trans', kind of like in the first image. Hmmm...maybe time for more reading.
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Re: Advice needed...

Post by TriodeLuvr »

I had to buy 7-pin sockets and shields on eBay for my recent amp project. None of my 7-pin sockets had shield bases.

Mounting the output transformer under the chassis consumes space that might be better used for filter caps or other parts. I don't think it will help you. This concept only really works if you can "double-up" the power and filament trans. Will either of them fit underneath if it's mounted horizontal on the chassis wall (underneath the other trans), rather than being vertical?

Jack
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Re: Advice needed...

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TriodeLuvr wrote:
Fri 04/23/21 11:15 pm
Mounting the output transformer under the chassis consumes space that might be better used for filter caps or other parts. I don't think it will help you. This concept only really works if you can "double-up" the power and filament trans. Will either of them fit underneath if it's mounted horizontal on the chassis wall (underneath the other trans), rather than being vertical? Jack
The filament trans just might. The width of the bobbin is 1.96"in. The iso-trans is slightly over 2"in. so I don't think that'll work.
I was in luck today. There was a big yard-sale type deal in Plymouth MI, about 15 min from me. There lives a great guy named Mark Oppat who is a long time electronics guy specializing in custom controls and pot restoration, cap supply and such. I thought just maybe he'll have some shielded 7 pin sockets. He did! So I got what I needed and then some. So now all the actors are assembled and something that's been bugging me will have to be dealt with. That being wire. Stranded? Un-stranded? Shielded? Un-shielded? Guage? Multi-wire connections (splicing) etc. I've also seen small amps that didn't use a "turret board" of any kind and the parts were just kinda wired in straight, if you know what I mean. (Good, bad, indifferent, circumstantial, preferential?) So many choices..
I guess it's time to disassemble the original amp and start a physical mock-up. That may inform some decisions.
Thanks Jack
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Re: Advice needed...

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The4thWatcher13 wrote:
Sat 04/24/21 11:32 am
The filament trans just might. The width of the bobbin is 1.96"in. The iso-trans is slightly over 2"in. so I don't think that'll work.
I was in luck today. There was a big yard-sale type deal in Plymouth MI, about 15 min from me. There lives a great guy named Mark Oppat who is a long time electronics guy specializing in custom controls and pot restoration, cap supply and such. I thought just maybe he'll have some shielded 7 pin sockets. He did! So I got what I needed and then some. So now all the actors are assembled and something that's been bugging me will have to be dealt with. That being wire. Stranded? Un-stranded? Shielded? Un-shielded? Guage? Multi-wire connections (splicing) etc. I've also seen small amps that didn't use a "turret board" of any kind and the parts were just kinda wired in straight, if you know what I mean. (Good, bad, indifferent, circumstantial, preferential?) So many choices.
Glad you found the sockets. It's always nice when something like that is available locally!

My personal preference for wiring a project like this would be 22 AWG solid with 600V PVC insulation. Jameco has it, and I think Antique Electronic Supply does too. There are certain advantages to stranded wire for some applications, but I don't like it for miniature tube sockets.

You don't need a turret board for the small amount of parts and wiring involved in this. A few terminal strips will get it done.

Here's a layout you might consider. This will be effective in terms of isolation, and it will leave a good amount of space underneath the transformers for the rectifiers and filter caps.

Image

Jack
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Re: Advice needed...

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TriodeLuvr wrote:
Sat 04/24/21 3:15 pm
My personal preference for wiring a project like this would be 22 AWG solid with 600V PVC insulation. Jameco has it, and I think Antique Electronic Supply does too. There are certain advantages to stranded wire for some applications, but I don't like it for miniature tube sockets. You don't need a turret board for the small amount of parts and wiring involved in this. A few terminal strips will get it done.
Here's a layout you might consider. This will be effective in terms of isolation, and it will leave a good amount of space underneath the transformers for the rectifiers and filter caps. Jack
Nice! It makes sense to me. I've been imagining different configs with space and isolation in mind. All with the opt fit inside. And I think you're right. I'm sort of getting the picture of how valuable real estate can turn out to be inside a chassis. This is after drawing up half a dozen different possible configs with the opt inside on the back, side or up-side down. :? I'll spare you guys the posting of said graphics and differ to your suggestion. I know it comes with a lot of experience. Well, ...maybe just one graphic, then on to more measurements of sockets and considering the layout of the front and back.
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Re: Advice needed...

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Ya know, I've got some terminal strips; 5 lug/center g, 3 lug/center g, 1 lug, & a couple 2 lug vertical, but who knew there were so friggin' many available out there?! How the hell am I supposed to know what I'm going to need!! I get it.... they've know I've got a sickness. They're gonna make me buy one of each of the dozen available at about 4 or 5 bucks a go. Nothing worse than "electron pushers"! :lol:
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Re: Advice needed...

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Decide on the layout first. Once you've done that, rotate the tube sockets so signal flows from the grids (inputs) and anodes (outputs) in a logical order. Print this out and pencil in the pins on the sockets. Draw all the components that can connect directly from one socket to another, such as coupling caps. Then add components with one lead attached to a socket pin, but with the other connected to another component or a socket pin too far away. Leave them hanging until this is all done, then you can determine which type terminal strips you need and draw those in. The power supply will be straight forward. Don't forget to include three empty terminal lugs so you can elevate the filaments. This is just two resistors in series from B+ to ground. The values are such that the middle point has +60V or +70V present and current draw from B+ is minimal. The CT of the filament transformer connects here, rather than ground.

I think that last layout you posted is problematic. Tubes are too close to the 60 Hz transformers and the OPT is not conveniently located for connection to the output tubes. Think about A) separation between tubes and 60 Hz transformers, B) shortest wire lengths between tubes and components within the audio section, C) relative orientation of the OPT to 60 Hz transformers, D) signal input wiring at a gain stage should not cross over its output wiring or the signal wiring of a subsequent stage, and E) maintain maximum distance between the input stage and all higher level stages or components that generate magnetic fields.

Everyone has their own way to do these things. This is just the general process I follow. Yep, tubes are addictive!

Jack
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Re: Advice needed...

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TriodeLuvr wrote:
Sat 04/24/21 11:47 pm
Don't forget to include three empty terminal lugs so you can elevate the filaments.
I see what you mean. Your layout looks best to me and I think all of those conditions can be met. All good information and I appreciate it. I think I was seeing the "elevation" of the heater circuit on other amp circuits and wondered about that. On those amps I was seeing something like a 100 ohm R from each leg of the 6.3V heater legs to ground. Just a different way of achieving a voltage drop, or "elevation"?
TriodeLuvr wrote:
Sat 04/24/21 11:47 pm
This is just two resistors in series from B+ to ground. The values are such that the middle point has +60V or +70V present and current draw from B+ is minimal. The CT of the filament transformer connects here, rather than ground. Jack
I've modified part of the schematic to show what I think you're talking about. Is this correct? Also I'm wondering about when you've got multiple + supplies from a multi-cap/multiple caps, is there a particular order or way to consider which is B+1, B+2, etc.? And in this situation I was wondering which B+ would be the place to put the resistors? Or doesn't it matter as long as a voltage drop occurs? Sorry for all the questions :P
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Re: Advice needed...

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Yes, that's it. If each resistor is 120K 1/2W, it will draw only 1/2 mA from the B+ supply and filaments will be elevated to about +60 V.

Jack
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Re: Advice needed...

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OK, hopefully I've taken everything you mentioned into account.
I think, as far as the layout and the socket components are concerned, this may be what "the doctor" (Jack) ordered. I also made use of Josh's layout and noticed that the pre-amp section and the power supply/ power tube sections were grounded to the chassis separately, so I tried to apply that as well. So one ground for V1 & V2, jack and pots, there will be one for the power supply and three prong power inlet, but I'm not sure where the center-tap for the output trans cathode winding. (The PS ground?) The center tap for the heater trans will go to the heater elevation resistors as Jack recommended. The signal path is indicated in Blue. There is only one little signal wiring overlap and that's under the tube at pins 6 & 7. It's the best config I've been able to come up with. The four plate resistors (black) and one resistor (R6) which is part of the phase inverter have been left hanging. I believe the image constitutes all of the tube connections and wiring (not including transformer and power)
Let me know what you think. If certain lines don't connect where they "should" it's probably an imaging glitch. (something I've been trying to eliminate but no luck just yet) Also, I did start out as Jack recommended, on paper. Lot's and lot's of possibilities printed out and scribbled out. (..just an example. Not the working version which was completed on the computer)
Thanks much!
M
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Re: Advice needed...

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You're almost done. A few 3- or 4-pin terminal strips will finish it up. I would use strips with no ground lugs, other than maybe in the power supply area. It's easier and more effective to use isolated lugs on strips for grounding in the audio section, then run wires from each of those lugs to the star ground elsewhere. I think this layout will work well for you, looking forward to hearing your report on the sound!

Jack
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Re: Advice needed...

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TriodeLuvr wrote:
Mon 04/26/21 8:10 pm
You're almost done. A few 3- or 4-pin terminal strips will finish it up. I would use strips with no ground lugs, other than maybe in the power supply area. It's easier and more effective to use isolated lugs on strips for grounding in the audio section, then run wires from each of those lugs to the star ground elsewhere. I think this layout will work well for you, looking forward to hearing your report on the sound! Jack
Wow, good news! I'm working out the power supply layout today and figuring out where the terminal strips will be needed. I've got some but will have to order the others. I've posted the updated schematic with the heater elevation resistors the the considered grounding scheme. What I was wondering about is the output transformer cathode ground. Can it be connected to the PS ground? As drawn all three transformers are grounded to the same lug but the heater trans CT is "elevated" at the same point.
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Re: Advice needed...

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Yes, use the PS ground for the cathode winding CT. Connect the CT resistor to the ground lead of C3-B if possible.
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Re: Advice needed...

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TriodeLuvr wrote:
Tue 04/27/21 1:35 pm
Yes, use the PS ground for the cathode winding CT. Connect the CT resistor to the ground lead of C3-B if possible.
Okie dokie, the resistor placement shouldn't be a problem.
A couple quick questions:
1.Should I be concerned about AC and ground wires either crossing over or running parallel to one another? I seem to remember reading about that and I'm searching again now for that info. In either case I'm having a bear of a night trying to figure out how to mount and run wires while considering this. It's actually making me crazy.
2. Should I be concerned about the number of ground connections I've got? I can imagine one wants to keep it to a minimum. I've been referencing Josh's grounding scheme diagram and have been trying to keep it to 3 ground points.
On another note: the tone pot is a stacked AC switch /Variable resistor type, and I was thinking of bypassing the pot mounted AC switch and going with a regular "bat" style switch. That will remove the "mains" AC from the tone pot, pre-amp proximity completely, just in case. Well, I can't figure out what type of terminals I'm gonna need until I figure out this AC, ground, layout situation. What were we talking about earlier? Internal real estate?! There may not be a lot of parts but there ain't a lot of room in there either, Maynard! :D
The diagram below is where I am right now.... 6 or 7 different power supply layouts later...I'm toasted again. Everything is there except the heater wiring,..and all the lugs,....I think. See ya tomorrow!
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Re: Advice needed...

Post by TriodeLuvr »

The work you've done so far looks good to me. Don't wear yourself out, it's easy to over-think these things!
The4thWatcher13 wrote:
Wed 04/28/21 12:41 am
1.Should I be concerned about AC and ground wires either crossing over or running parallel to one another?
All the AC wiring is on one side of the chassis, so I don't see a problem. If you meant signal-carrying wires, lead lengths are short and you're not working with an ultra-high-gain design. Again, I don't see a problem.
2. Should I be concerned about the number of ground connections I've got? I can imagine one wants to keep it to a minimum. I've been referencing Josh's grounding scheme diagram and have been trying to keep it to 3 ground points.
The only concern I have is the chassis ground at the lower left of the CAD drawing. I would remove this and add a ground wire from the terminal strip back to the power supply ground near the top. The only other chassis-connected ground should be the green wire from the AC cord.
On another note: the tone pot is a stacked AC switch /Variable resistor type, and I was thinking of bypassing the pot mounted AC switch and going with a regular "bat" style switch. That will remove the "mains" AC from the tone pot, pre-amp proximity completely, just in case.
I think the separate switch will be more convenient to operate, but OTOH, the tone pot switch is already there. If you want to use the existing switch, route the two AC-carrying wires away from the pot at right angles along the edge of the chassis. They don't need to be twisted because they're not out of phase like filament wires. Just do whatever is necessary to keep them tucked away. It's difficult to know whether the proximity of this switch to the 'AV6 will create hum, but it's easy enough to add the separate switch later and shorten the wires if that's the case.

Remember, part of the process of designing and building a new amp is debugging after it's built. Put it together with that in mind and don't sweat the little stuff. Actually, yours is simpler than many. I think it's going to work great right out of the box! :)

Jack
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Re: Advice needed...

Post by The4thWatcher13 »

Thanks Jack, that takes a load off my mind. All points taken.
So I guess as long as all of the AC components are on one side, away from the audio circuits, the way transformer and filter cap grounds are run isn't a problem with regard to proximity to one another. Otherwise I'd have to "commit" myself right this very minute! :P
OK, time to settle on a config and get lugs.
Thanks again!
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Re: Advice needed...

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Well, things are moving along smoothly aside from some issues ordering lugs. The chassis is all but completely drilled and all parts are here. I've been considering putting a pilot lamp in as well. Not sure what kind yet. I've got a "Linrose B1052C5", 125VAC, neon lamp but not sure if using that in the AC primary is a good thing or not.
Other than that I'm just about ready to consider a paint job and start building. I went the drill press step bit route for the holes and the amp building Gods smiled upon me by directing me to a 10" in Ryobi drill press in excellent condition for $50 bucks! Ya gotta love it.
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Re: Advice needed...

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Greetings, all is going well so far with the build, delays not withstanding. But I have a quick question: I've posted a zoom in of the schematic and I noticed that the way it's drawn that C7 allows the tone control to have +61V across pins 1 & 2. I'm wondering if it should be like that, or if I should use "C7" to isolate the tone control from the "V2" plate pin 1? I've been looking at various tone controls on old amps, especially Vox, but I don't see one similar. And honestly I'm not really sure how it works, but it did, ..and didn't sound bad either.
Any info would be appreciated. I'll keep looking around also..
Thanks,
M
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