Advice needed...

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TriodeLuvr
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Re: Advice needed...

Post by TriodeLuvr »

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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The4thWatcher13
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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...

Post by TriodeLuvr »

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...

Post by TriodeLuvr »

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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Re: Advice needed...

Post by TriodeLuvr »

The schematic is correct as-is. DC current is blocked at the pot by C5. Every terminal of the pot has exactly the same DC voltage. The tone circuit works by shunting high frequencies plate-to-plate. That reduces the differential across the plates and therefore also at the 6CU5 grids.

Jack
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Re: Advice needed...

Post by The4thWatcher13 »

TriodeLuvr wrote:
Thu 05/13/21 7:20 pm
The schematic is correct as-is. DC current is blocked at the pot by C5. Every terminal of the pot has exactly the same DC voltage. The tone circuit works by shunting high frequencies plate-to-plate. That reduces the differential across the plates and therefore also at the 6CU5 grids.
Jack
Wow! I have no idea how that works but I'll take your word for it! Looks like I've got even more homework.
I do my best to understand this stuff but sometimes I just have to go "Wow, ...cool". I'll leave it as it is. I'm hoping to be done wiring it up in the next couple of days, and all is well. But no need hurrying.
Thanks Jack, I hope all is going well with you and yours as well.
M
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Re: Advice needed...

Post by The4thWatcher13 »

Well, comrades, I knew something was wrong. And I believe it indeed is. That being I believe that when I did my layout drawing I flipped my socket numbers! I think it's that the wiring diagram was drawn from "above" and the socket images are representations of the view from below! Luckily I haven't soldered anything except the output socket and the output transformer.
I won't even go into the different ways I've thought about this.
I'm not even sure if re-doing the wiring diagram will solve this if it can even be done properly. The problem has to do with the socket numbering. In "reality" my pin 1 is where 7 should be and the same with the 9 pin. They're backward! Honestly I'm not sure exactly sure how bad or really bad I've messed up. Just getting my head around what went wrong continues make me dizzy. I'm hoping re-orienting the sockets 180 deg and re-drawing the layout will save me. Wish me luck!
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Re: Advice needed...

Post by TriodeLuvr »

Unless you see burned resistors or other parts, it's probably OK. Tubes are tough. Fix the wiring and try again. :D

Jack
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Re: Advice needed...

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Pay no attention to this post.
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