Advice needed...

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TriodeLuvr
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Re: Advice needed...

Post by TriodeLuvr »

LOL, I know what you mean. I just finished cutting a chassis for a new hi-fi amp. I had to rotate and re-register it four times on my small mill, plus add a spindle extension for one of the cuts. I'm beat!

Jack

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The4thWatcher13
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Re: Advice needed...

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Jack: that is an awesome chassis job! I can't wait to see it when it's done. Queston: do you bolt or rivet your sockets to the chassis? I assume that your transformers are bolted down. As I mentioned in my reply to Josh, I made some grounding changes and re-twisted my heater wiring. The hum decreased a good deal and I'm actually rather happy with the sound this monstrosity is producing. Especially through the 12" fender cab. I'll almost surely be leaving the original 8" speaker behind and going for a larger driver. This amp can definitely push it. And although I've taken note of all of the recommendations for reducing the hum I'm going end my trouble shooting of that issue here and concentrate on the transfer to the new chassis. Aiming to become a better troubleshooter is never time wasted but at this point it's about to be gutted and swapped so considering the new layout seems more important to me at this point. If there are important things that I really should deal with at this point please let me know.
I know that this is in many ways different from a "traditional" conglomeration of guitar amp parts but I'm sure there are many "rules of thumb" that will apply when it comes to considering a layout scheme. I started creating a template for part placement all the while considering commonalities I've seen in similar amps but I've yet to really run across a "primer" for amp layout. I'm on the search again today. The last of the parts will be here Friday (shielded tube sockets, stand offs, etc.(fingers crossed) ..and some double sided "BusBoard" arrived today. Little by little we're getting there.
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Re: Advice needed...

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Note: I'm finding some good info online about chassis layout, wiring etc! Who'd a thunk it?! 8O
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TriodeLuvr
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Re: Advice needed...

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I agree, it's time to build your amp on the new chassis, then perform final troubleshooting. I've always used screws for tube sockets, but rivets should work. In fact, I almost used rivets in the current project. They have a lower profile than pan head screws, and some octal sockets are designed for this. If normal screws are used, the bottom of the tubes can end up resting on the screw heads, not the socket. Not a problem with 9-pin and 7-pin minis like you're using.

You'll be OK if you design the layout left to right, just like the schematic. That helps to prevent the possibility that wires carrying high level signals will cross over and couple to low-level stages. Locate all the transformers away from the input stage (6AV6). Regarding the transformers themselves, mount the power (isolation) transformer farthest from the amplifier circuitry, then the filament transformer and audio output. It's generally OK if the power and filament transformers are in the same plane, but the audio transformer should be at right angles to both of them. Follow Josh's advice on grounding and you'll be OK.

FWIW, I twist filament wiring, but I don't follow the usual practice of tucking it down onto the chassis or into corners. Balanced cable (e.g. twisted wire) becomes unbalanced and subject to radiating its currents if it's in close proximity to other conductors. So, I prefer to elevate it physically and keep all the single-ended wiring, including signal carrying wires and components, down against the chassis. This isn't a critical aspect of building an amp, just my preference. If it was critical, most guitar amps would hum like mad. :lol:

Jack
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Re: Advice needed...

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TriodeLuvr wrote:
Wed 04/21/21 8:43 pm
FWIW, I twist filament wiring, but I don't follow the usual practice of tucking it down onto the chassis or into corners. Balanced cable (e.g. twisted wire) becomes unbalanced and subject to radiating its currents if it's in close proximity to other conductors. So, I prefer to elevate it physically and keep all the single-ended wiring, including signal carrying wires and components, down against the chassis. This isn't a critical aspect of building an amp, just my preference. If it was critical, most guitar amps would hum like mad. :lol: Jack
Got it. Great advice, thank you Jack! By this logic the heater wiring would be the last wiring to install, yes?
There's a lot of stuff out there regarding amp layouts, lots of build pics and lot's of good advice. I've included a pic, to scale, of the first basic layout. Anything could go either way at this point. As a guy that tries to get things "right" the first time this is terrifying! :lol:
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Last edited by The4thWatcher13 on Thu 04/22/21 2:16 pm, edited 4 times in total.
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Re: Advice needed...

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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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