watt finally builds an amp (results TBD)

[[This is sort of a long-winded wind-up to the real questions in post #2. Feel free to skip ahead if you’re so inclined.]]

By the spring of 2010, I was already in pretty deep. I had moved to Austin from Chicago, and to Chicago from St. Louis before that. That kind of displacement led to a fair amount of gear accumulation. If you aren’t from a place, and you don’t already know many people in a place, looking for stuff gives you a way to experience it. Add to that the sort of unstructured schedule of a dissertation-writing grad student, and you have an ideal environment for the fluorescence of audioholism. I had a closet full of stuff, from the Rek O Kut that I bought from a priest cleaning out the rec room basement at Loyola Chicago to the Vandersteens that JohnVF basically gave to me to my dad’s receiver that I’d carted with me when I left for grad school in St. Louis. And more. Lots.

All of that is the backdrop for this one particular day that I remember in the spring (I think) of 2010. I was at Austin Stereo, a repair shop in the central part of the city, picking up a Counterpoint amp that I’d bought out of the trunk of some guy’s car two or three weeks before. I loved the sound, but it had a slight hum that worried me. At that time, the closest I’d come to troubleshooting was using DeOxit, so I was happy to have a repair place within driving distance that I trusted. While I was in the shop, which was basically just a front room with a counter and piles of gear, there was another guy talking to the owner. They seemed to know one another pretty well. When this guy saw the owner bring out my Counterpoint, he said something to acknowledge that he knew what it was, maybe something about its hybrid design. He also invited me to come over to his house to listen to some of his amps. He said I could follow him over—right then—if I had the time. He was close by. He had ridden his bike.

I’m usually a cautious person (stranger danger, kids), but he seemed very cool. And he was cool. I followed him back to his place, and I could see through the front windows, even from my car, the speakers that he was using: large, home-built cabinets. When I went inside, he showed them to me (Altecs, though I’ve forgotten the specific load), along with the amps, which he’d built himself. He let me pick out some records. We listened and chatted for a little while about what I heard. I wish that I had more to say here about the sound, because that seems like it would be the important thing, the thing that really left an impression. I can remember it sounding really good. But what I remember most from that visit was that this guy made the stuff that he listened to. He wasn’t an engineer, but he was really knowledgeable. And—maybe this is the thing that left the biggest impression—he wanted to use that knowledge, not just talk about it. Before I left, he said you can do this too, if you want to. I assured him that I couldn’t. I was a good-for-nothing literature grad student: words good, numbers bad. He told me about Joe Roberts and Sound Practices. We exchanged email addresses and he told me that he’d be in touch.

Over the next few months, we got together a few times. I remember sitting at his kitchen table, with him explaining load lines to me. We started very much at the beginning. He was really generous with his time. He loaned me his copy of Jones’s Valve Amplifiers, which I read dutifully for about two chapters. (Reading it before bed wasn’t a good idea.) I started looking for a first project, excited by the prospect of building an amp, and then I got overwhelmed. Not with the project itself, though there was a lot that I didn’t understand, but with the rest of my life. I was working two jobs and trying to finish school, and I didn’t have the time I needed to learn this new language of triodes, power supplies, and the like. So, I returned Valve Amplifiers and contented myself with other kinds of stereo fun.

In many ways, that experience opened my eyes to a dimension of this “hobby” (I never know if it’s a hobby, an obsession, a way of life, or what) that I wouldn’t have valued as much otherwise. But I’ve always regretted, a little, not being able to participate in it by doing it myself. There’s that thing that Herb Reichert wrote (I think mhardy linked to the piece somewhere on these boards):

I am telling you about these happenings because, for me, they were all formative. Every club, even the first one, with the Barbie-maiming president, taught me things I would have never learned outside its hidden dirt chamber. Each cult taught me to share my devotions with others, while forcing me to bond with souls I would have never known otherwise. . . Most importantly, all of these societies are builder-cults. Their only requirement for membership was: that I know something about something so I could make something. Each of these outlier fellowships taught me to fashion and venerate precisely-formed fetish objects and pray to our ancestors. They taught me science, philosophy and timeless engineering principles, all while reducing my fears of failure and rejection.

Those ideas are really attractive to me, even if I don’t consider myself part of the tribe. I’m not sure if this post is some step in trying to become part of it.

So, that’s a long preface to saying that I’m finally going to build a tube amplifier. Hopefully, it will be fun and I’ll learn some stuff.
 
So, I’ve decided this maiden voyage to be an RH84 build. It looks do-able, and I already have some parts:
  • OPTs from an Akai M8 (courtesy John Frum)
  • PT from a Hammond AO-43 (courtesy John Frum)
  • Various caps
  • A choke
I don’t need this amp to be a world-beater. I want it to sound good, yes, but mainly I want the experience of doing it, with an eye to building stuff in the future.

In the interest of learning, I want to know how you’d approach parts selection for the schematic below. What kind of caps, where? What kind of resistors? I realize that parts selection may be as personal and idiosyncratic as how you like your coffee, but I’m hopeful that your answers will help me (who has practically no experience) to get a clearer sense of the terrain. I don’t feel any pressure to get this one right, necessarily. I’m more interested in learning about the variety of approaches. So, bring it on! (And thanks.)


RH84 - rev2.png

RH84 - rev2 CLC.png
 
I posted this in Intros and Member Systems? Oof.

Could it be moved to a more appropriate subforum?
 

Redboy

Knobophobe
Mmm, coffee...

Also, this should be fun! I have ideas, but I also need access to a real keyboard!

Back soon. :)
 
The number of ways to make coffee around here is almost as crazy as the number of ways to play music.

Lookin' forward to yer ideas, Redboy!
 

Redboy

Knobophobe
In the interest of learning, I want to know how you’d approach parts selection for the schematic below. What kind of caps, where? What kind of resistors? I realize that parts selection may be as personal and idiosyncratic as how you like your coffee, but I’m hopeful that your answers will help me (who has practically no experience) to get a clearer sense of the terrain.
When I'm shopping for parts I consider quality, cost, and... suitability (? there's a better word for this, but it eludes me at the moment). Let me share some of the inner dialogue...

Tube amps -- and especially single-ended tube amps -- are simple. They have relatively few parts so the overall cost could be kept low... But (I reason), they're also really labor intensive so I might as well put good parts into them, if I am going to invest this much of myself into the build. Also, in a simple build like this everything can affect the sound, so let's not cheap the music out of this thing! Yes, good parts cost more but remember that I'm not buying very many parts, so let's stretch the budget a little more to buy really good parts (uh-oh!).

Experience tells me that I should prioritize transformers, tube sockets, capacitors, resistors, connectors, wire... I suppose that's everything but everything counts so prioritize in that order, more or less:

Transformers (especially OPTs) directly impact bandwidth and tone. You've got some already, so this choice is easy.
Tube sockets account for almost all of the mechanical connections in your amp, so they need to do their job very well. Please skip the cheap Chinese ceramic crap! Nearly anything is vastly superior; I like NOS USA sockets from Amphenol and similar, but there are really good new production options, too -- look for Belton and QQQ in the noval types you need for this project.
Capacitors might account for a good chunk of your cost in this build, if you decide to use film caps over electrolytics in the power supply. I'd be inclined to, since there aren't very many to buy. But film caps will be much larger than electrolytics - make sure you understand this when you do the layout. Buy the best, boutique-est caps you can justify for C1, your coupling caps.
Resistors shouldn't break the bank, here. I use a lot of Kiwames because they're super easy to read and they sound good in nearly every position.
Connectors (RCA input jacks and binding posts) account for the rest of the mechanical connections in your amp. They need to be sturdy enough that you don't bend or break them; I look for gold-plated or tinned copper.
Wire can be contentious but I try to use as little as possible. Plan your point-to-point layout so component leads make most of the connections, and buy high quality wire that's appropriately sized and easy to strip.

I have even more opinions, but I'm sure I have exceeded my single post limit! :)
 
When I'm shopping for parts I consider quality, cost, and... suitability (? there's a better word for this, but it eludes me at the moment). Let me share some of the inner dialogue...

Tube amps -- and especially single-ended tube amps -- are simple. They have relatively few parts so the overall cost could be kept low... But (I reason), they're also really labor intensive so I might as well put good parts into them, if I am going to invest this much of myself into the build. Also, in a simple build like this everything can affect the sound, so let's not cheap the music out of this thing! Yes, good parts cost more but remember that I'm not buying very many parts, so let's stretch the budget a little more to buy really good parts (uh-oh!).

Experience tells me that I should prioritize transformers, tube sockets, capacitors, resistors, connectors, wire... I suppose that's everything but everything counts so prioritize in that order, more or less:

Transformers (especially OPTs) directly impact bandwidth and tone. You've got some already, so this choice is easy.
Tube sockets account for almost all of the mechanical connections in your amp, so they need to do their job very well. Please skip the cheap Chinese ceramic crap! Nearly anything is vastly superior; I like NOS USA sockets from Amphenol and similar, but there are really good new production options, too -- look for Belton and QQQ in the noval types you need for this project.
Capacitors might account for a good chunk of your cost in this build, if you decide to use film caps over electrolytics in the power supply. I'd be inclined to, since there aren't very many to buy. But film caps will be much larger than electrolytics - make sure you understand this when you do the layout. Buy the best, boutique-est caps you can justify for C1, your coupling caps.
Resistors shouldn't break the bank, here. I use a lot of Kiwames because they're super easy to read and they sound good in nearly every position.
Connectors (RCA input jacks and binding posts) account for the rest of the mechanical connections in your amp. They need to be sturdy enough that you don't bend or break them; I look for gold-plated or tinned copper.
Wire can be contentious but I try to use as little as possible. Plan your point-to-point layout so component leads make most of the connections, and buy high quality wire that's appropriately sized and easy to strip.

I have even more opinions, but I'm sure I have exceeded my single post limit! :)

Whoa! What a great post. I appreciate your taking the time to break it down and explain some of the rationale. Thank you.

I didn't mention it in my long first post, but I remember seeing some of your early build threads (the Olson EL84 clones, iirc) and thinking of them as a kind of model. You were figuring stuff out and sharing it in a way that made this potentially intimidating stuff seem approachable. I didn't understand a lot of the concepts, but I admired your spirit and approach. So, double thanks, I guess!
 
I'll echo Nates insights, I use a lot of Kiwames, KOA SPR series, and where appropriate; Takman REY (metal film) and REX (carbon film).

C1 - Use something good here, depending on budget of course. My recommendations, depending on budget, would be Russian FT3 teflon caps on the less expensive end, as well as CDE 940 series polypropylene. If you want to spend more, ~$20 USD per cap, I really, really like the Miflex KPCU series.

C3 - I would probably use a DC link style polypropylene cap, the Panasonic EZP-E series are nice, but you could absolutely use a decent electrolytic, Nichicon KX (or is it KZ?..I never remember, KG? it has a 'K' in it, clearly)

For resistors I tend to use carbon film on grids (r6), metal film to ground (r1, r5). These are neither hard and fast rules, or deeply experimented, so grains of salt and all that.

Wire - I tend to use mostly teflon insulated, silver plated copper, solid core inside the chassis. It's easy enough to work with, easy to get in various sizes and colors, and isn't expensive.

Also, like Nate said, don't go cheap on tube sockets. Belton are awesome, as are legit CMC. There are plenty of other good ones, but those are ones I use commonly.

Overall, I would probably build with less expensive components for the first one. If you really love the circuit, you can upgrade individual bits along the way and learn a lot about what _you_ like, which is, ultimately, all that matters :D

Now, get to it and soak up every little step of the process, and have a blast!!
 
Thanks, gable. I'll check out some of those caps that you mention. Already have some of the Belton sockets in my cart.

You know, this talk of the importance of C1 reminds me that I did, several years ago, switch out the standard Illinois coupling caps in an Almarro 318B for some Mundorfs. They weren't even the fancy-fancy kind--just the sorta-fancy kind--but they affected the voicing significantly. Maybe I'll get a small variety here, for the sake of experimentation.

On the topic of C1, a minor question: any reason that the value there is given in nanofarads instead of microfarads? Seems to me that the schematic has been around long enough that someone would have noted it as a mistake if it were one, but it stood out to me as I made up a parts list.

Now, get to it and soak up every little step of the process, and have a blast!!

You betcha!
 
. . . On the topic of C1, a minor question: any reason that the value there is given in nanofarads instead of microfarads?
The value looks right to me. A capacitance of 1000nF = 1uf, so a 220nf = 0.22uf. That's a very standard coupling capacitor. With the 475K grid resistors (R5), it gives a low frequency cutoff of 1.5hz which is more than enough. In fact, if you're looking to spend money on this cap then you could even drop it down to a 0.1uf value without too much impact. A rough rule of thumb is that you'd like this low frequency cutoff to be at least 10x below the lowest frequency the amp will be passing. since the filter starts having phase impact at a frequency 10x higher than the cutoff. Given typical output transformers, you're not getting much bass below 30hz anyway, so a 3hz low frequency cutoff is normally acceptable.
 
Thanks, Gary. I read your post right after placing an order for those caps and some other components, so I stuck with the 0.22uf value. But I appreciate the explanation.

Another parts-related question for anyone out there who can answer. Lots of choices for the LM317 voltage regulator (U1). What you see below are just the first few results when I search with the keys "LM317 TO220" at Mouser. I looked at a few of the datasheets, but I don't know enough to truly differentiate. Can anyone offer some guidance? I want to be sure that I choose one that's suitable.

Screen Shot 2020-03-16 at 10.05.36 AM.png
 

Thermionics

Post Whore In Training
I'll echo Nates insights, I use a lot of Kiwames, KOA SPR series, and where appropriate; Takman REY (metal film) and REX (carbon film).

To be clear - Kiwame are KOA SPR2 / SPR5-series resistor (the number indicates the wattage rating). I'm not sure where the whole Kiwame vs KOA Speer SPR dichotomy came from, but realize that if you are buying "Kiwame" you are paying a significant premium for the same KOA-Speer resistors from Mouser / DigiKey.
 

Thermionics

Post Whore In Training
Belton or old-stock Cinch top-mount are both fantastic for 9-pin/Noval-type tubes (top mount sockets hide a multitude of drilling sins).

For octal-type tubes (rectifier), I like old-stock Cinch micalex bottom-mount (preferably the type with D-shaped pin sockets as opposed to the -o- style (this is what they look like from the bottom):

1584377759140.png
 

Redboy

Knobophobe
To be clear - Kiwame are KOA SPR2 / SPR5-series resistor (the number indicates the wattage rating). I'm not sure where the whole Kiwame vs KOA Speer SPR dichotomy came from, but realize that if you are buying "Kiwame" you are paying a significant premium for the same KOA-Speer resistors from Mouser / DigiKey.
Exactly correct and absolutely uh huh.
 
To be clear - Kiwame are KOA SPR2 / SPR5-series resistor (the number indicates the wattage rating). I'm not sure where the whole Kiwame vs KOA Speer SPR dichotomy came from, but realize that if you are buying "Kiwame" you are paying a significant premium for the same KOA-Speer resistors from Mouser / DigiKey.
Exactly correct and absolutely uh huh.

That's good, actually. Now I don't feel so bad about omitting Kiwames from my Parts Connexion order.
 
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Thermionics

Post Whore In Training
That's good, actually. Now I don't feel so bad about omitting Kiwames from my Parts Connexion order.
Well, the down side is that KOA-Speer has discontinued the SPR2 / SPR5 series, so you are going to see dwindling stocks and you may have to pay premium prices to Parts Connexion (I couldn't find 270k values so I had to pay the Canada tax for my Darling build).
 
OK, then. I did it accidentally, not realizing that they held the Kiwame stock.

Even making lists ahead of time, I'm finding that it's sort of a challenge not to overlook something, since it seems impossible to get everything in one place. At least it's easier than finding hand sanitizer these days. :)
 

airdronian

Radar Member
Belton or old-stock Cinch top-mount are both fantastic for 9-pin/Noval-type tubes (top mount sockets hide a multitude of drilling sins).

For octal-type tubes (rectifier), I like old-stock Cinch micalex bottom-mount (preferably the type with D-shaped pin sockets as opposed to the -o- style (this is what they look like from the bottom):

View attachment 20823
There's cinch type sockets and perhaps there is a super-cinch like I fear is in my JWN amp. One day I wanted to remove the 6SN7 and try a different one. It did not want to let go. Wiggle back and forth, it was IN there. It finally popped out and went flying across the room. Whoops.

That was a 6SN7WGT and it survived no problem. From then on I used a bicycle tire pry tool to gently coax it out.

Back to your regularly scheduled programming. ;)
 

Thermionics

Post Whore In Training
There's cinch type sockets and perhaps there is a super-cinch like I fear is in my JWN amp. One day I wanted to remove the 6SN7 and try a different one. It did not want to let go. Wiggle back and forth, it was IN there. It finally popped out and went flying across the room. Whoops.

That was a 6SN7WGT and it survived no problem. From then on I used a bicycle tire pry tool to gently coax it out.

Back to your regularly scheduled programming. ;)
I use a spudger sometimes.
 
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