Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dwinstonwood on October 25, 2024, 04:32:21 pm
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This project has morphed a few times over the last couple of months. It started out intended for two 7C5's. It still uses some other less common tubes. I could even wire it for a single 7C5 since I have some NOS examples, and some unused Amphenol Loctal sockets.
These previous threads "chart the path" this project has taken:
https://el34world.com/Forum/index.php?topic=31870.0
https://el34world.com/Forum/index.php?topic=32131.0
So, a big thanks to DummyLoad, HotBluePlates, bmccowan, shooter, and others who shared their insights and knowledge. I learned some good stuff by stumbling my way through this. There's also a lot of things borrowed from Merlin's books in this design.
At any rate, I either have, or have ordered, all the bits I need to build it. Here's the schematic. Or, should I just post my layout... :icon_biggrin:
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looks like it'll rock!
once it's "good enough to jam", find a 4 X12 cab, The guitarist I used, plugged into one, played a Hendricks solo lead and everyone stopped what they were doing. That was through a similar "Champ" 4w build. The amp went into the wild that day
:icon_biggrin:
Spend extra brain-time on the TS position and layout. I would pilfer through Steve's pages til I found something close, then steal the man blind, yet, never quite able to achieve his A-game quality.
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Here's the schematic. Or, should I just post my layout... :icon_biggrin:
:l2:
It'll be a gainy little beasty, that's for sure. Speaking of stealing from Steve (I've already got his car and a couple of TVs) the raw control is one of my favorites.
Since I think 3 preamp tubes is a bit much for a SE 6V6, I'll be watching to see how you make out.
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Since I think 3 preamp tubes is a bit much
I'm beating he's a closest death-metal guy :guitar1
they might come in handy when he finally realizes anything less than a KT88 or EL34 just isn't worth the time :icon_biggrin:
take out V1 n the 6V6 might stand a chance.
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Aw, come on! There's a gain pot before the pentode, and the third tube is a ~unity-gain CF. I'm betting it can be reined in. :icon_biggrin:
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I'm betting it can be reined in.
ya, volume on guitar 1, gain 1, Drive 3-4. when you wear out that half of the pots just rewire backwards to take advantage of the un-used section :icon_biggrin:
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I'm betting it can be reined in.
ya, volume on guitar 1, gain 1, Drive 3-4. when you wear out that half of the pots just rewire backwards to take advantage of the un-used section :icon_biggrin:
:laugh:
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Ok, I've been warned (which amounts to just being more determined). :icon_biggrin:
I'll have fun building it. But, it still has less gain than my Hoffman 6V6 Hot Plexi. Besides, it'll be easy enough to solder in voltage dividers between stages if I think it's necessary. And, I've already made the board...
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Looks pretty hairy. Maybe preemptively lower value volume pots could be used, like 500k or even 250 k...?
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No doubt you will get there - you always do. One of the nice things about a unique circuit is that you feel more free to experiment with resister, cap, and pot values until you get what you want. FWIW I've built a couple amps with a pentode in V2. One has a gain pot between V1 and V2. I had a blast experimenting with plate/cathode/grid resistor values on V1 and V2. I ended up with values very similar to what Tubenit uses in various HoSo56 circuits. After cleaning out Steve's house, I stole the stone stack from Dr. Z. That was harder as unlike Steve he locks his doors.
BTW - nice clean schematic. Do you draw in _.sch format? I think not, but if you do, please share that file.
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No doubt you will get there - you always do. One of the nice things about a unique circuit is that you feel more free to experiment with resister, cap, and pot values until you get what you want.
Thanks bmccowan. That's just what this project is all about. Learning by doing. And, like half of my amps, I doubt it will ever be played through by anyone other than me.
BTW - nice clean schematic. Do you draw in _.sch format? I think not, but if you do, please share that file.
I use DIYLC. I have JSchem and ExpressPCB installed. I'll make an sch file and share it!
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Ciao Dwinstonwood
I like the idea :thumbsup:
Just a question for you
There is a particular reason for the choice of a 5879 instead of an octal pentode (6j7 - 6sj7 - 6sh7 ...... ) ?
Franco
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There is a particular reason for the choice of a 5879 instead of an octal pentode (6j7 - 6sj7 - 6sh7 ...... ) ?
Franco
Thanks Franco. No particular reason for the 5879. But, maybe I consumed a bunch of internet advice saying the 6SJ7GT is too microphonic? They are affordable, though.
One plus for using the 5879 is that rewiring the socket for an EF86 is not complicated. The heaters and cathode connections are the same.
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5879 is surely a good tube, if you go for noval there is also the 6AK5 (5654), a cheap tube, used in tube mikes
BTW, to defeat microphonic effect on some penthodes go for lower gain settings
Franco
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bmccowan, converting my schematic into an .sch file is slow progress. I've never really used JSchem before. I'm maybe halfway there. Here's a screenshot. I'll share the .sch when I get it finished and proofread a few times.
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Hey thanks - that is really nice of you. I almost feel guilty for asking. But not quite as I think that once you figure its kinks, you will enjoy using it. The snap feature is helpful as are the component libraries And Doug maintains a library of sch schematics. You can open something similar and edit rather than starting from scratch. You also can cut and paste sections of schematics. The instructions for doing that are in the help docs. The only nag with that is when pasting a section that was drawn using snap with a section that was drawn without snap. I just get it close enough for rock & roll and then go back and clean it up.
Maybe someone here will say, "hey, you are doing it the hard way!"
About the 5879 and microphonics. Its smart to be careful with that socket. I just use tiny rubber washers or O rings from the hardware store on either side of the screw and nut and avoid using those self tapping screws. Some folks "prove" that pentodes are microphonic (actually all tubes are) by tapping them with a pencil. The cure for that is easy - stop tapping the tube with a pencil. A while back PRR posted a pic of a rubber headed tube tapper. https://www.hammermuseum.org/hammer-highlight-tube-tapper/ (https://www.hammermuseum.org/hammer-highlight-tube-tapper/)
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Thanks bmccowan, good advice on the socket mounting. With this being a head, it should hopefully have adequate isolation from the speaker.
I pretty much finished the .sch schematic in ExpressSCH. I need to review it a few times before launching it onto the web. But, here's an image of it.
I finally got started on the build this weekend. I ordered a blank 17x6.5x2.5 chassis from Hoffman (not only the best price, but very fast shipping). It's nice, thick aluminum like the Stout chassis.
I've finished building the board. The under-board wires come up through small holes near the turrets and wrap around them. I think this is more reliable than soldering into the bottom of the turrets. The chassis is marked up for drilling; I'll get that done next.
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5693 is my go-to for octal pentode - Industrial low microphonic sub for 6SJ7. They sound really nice.
5789 is much more tame, am assuming your B+ is going to be around 250-300V, so should have AV of about 100 - You could take that down to around 50-60 with 470K g2 and 1.5K cathode R, might be bit more stable. If it were mine, I'd start with 100K anode, 220K g2 and 1K cathode.
A V divider for the gain pot will take some of the touchiness out of that control.
Your plan is going to want to howl. Metal amp? :icon_biggrin:
--Pete
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:laugh:
ya, he's been warned on the other hand I just seen in my feed mullets are making a comeback, big production metal bands might be around the corner :icon_biggrin:
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5693 is my go-to for octal pentode - Industrial low microphonic sub for 6SJ7. They sound really nice.
Thanks Pete. Is the 5693 that red metal tube?
I've been considering adding a voltage divider before the pentode. Something along the lines of the pic below.
As for the 5879, I spent a lot of time studying the datasheets and thought I had it set up good. From what I gathered you could either go lower gain and higher voltage output, or higher gain and lower voltage output. I'll revisit the datasheets on that point.
But now... I'm thinking of buying one of these:
https://edcorusa.com/products/xse15-5k-15w-5k-ohms-single-ended-tube-output-transformer?_pos=15&_fid=c861be190&_ss=c&variant=41118788223163
They're only $47 and are rated for 100mA (the Hammond 125ESE is rated at 80mA). I've read where people say the Edcor works great with a 6L6GC. I have Edcors in my EL34 SE hifi stereo amp and they are solidly built USA tx's.
If so, I'll get one of these chokes, too. They're 6H/200mA at around $20:
https://catalog.triadmagnetics.com/item/inductors-and-chokes/smoothing-filter-chokes/c-14x
That will put me back to where I started this whole project with a 6L6GC or 5881. :icon_biggrin:
And shooter, try as I may, my hair won't grow long enough in the back.
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:laugh:
mines just past the shoulders now and i keep scissoring around the ears, yesterday I laughed as i'm shaving thinking it's sorta mullet looking, then I see the feed today..... :icon_biggrin:
Pete has put me on the right path with my builds every time so don't overthink just steal whatever he's offering, then when the fingers get sore from playing, you can sit back and think
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These are the tables I was referring to above. To be honest, the practical distinction between "Voltage Output" and "Voltage Gain" is not totally clear to me. :dontknow:
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These are the tables I was referring to above. To be honest, the practical distinction between "Voltage Output" and "Voltage Gain" is not totally clear to me. :dontknow:
That datasheet does have an odd way of putting it.
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If the 5693 is not disposable (or too expensive) I can suggest to give a try to the russian 6Ж8, it was planned for military use and it has a sturdy structure
Here’s a detailed comparison between the **6SJ7** and the **6Ж8**:
### 1. Origin and Purpose
- **6SJ7**: An American-made tube widely used in audio amplifiers, radios, and low-frequency circuits. It was designed to provide stable gain with low noise for commercial and home applications.
- **6Ж8**: A Russian tube with similar specifications, often produced for military and industrial purposes. It's designed with greater resilience to mechanical and environmental stress.
### 2. Structure and Build
- **6SJ7**: Typically comes in a glass tube or metal case (depending on the version), offering decent shielding. The glass versions tend to be more prone to microphonics than the metal-bodied ones.
- **6Ж8**: Generally more robust and built to withstand shocks and vibrations better, making it less susceptible to microphonics. Its construction quality tends to be more durable due to military-grade standards.
### 3. Performance
- **Gain**: Both tubes offer similar gain levels, though the 6Ж8 can sometimes provide slightly more stable performance under high-gain conditions, depending on specific production batches.
- **Noise**: The 6Ж8 typically generates less noise than the 6SJ7, especially in noisy environments or with potential interference. This makes it better suited for applications requiring signal purity.
- **Microphonics**: The 6Ж8 generally has lower microphonics due to its sturdier construction, while the 6SJ7 may exhibit microphonics at high gain levels or in vibrating environments.
### 4. Availability and Compatibility
- **6SJ7**: Still relatively easy to find due to its historical popularity and large-scale production, especially in vintage American versions.
- **6Ж8**: As a Russian-origin tube, it may be less common in some Western markets, though it's readily available in Europe and the US through specialized suppliers. It may also have slight pin configuration differences, so compatibility should be checked before use in circuits.
### 5. Ideal Applications
- **6SJ7**: Recommended for vintage audio amplifiers and projects where microphonics are not a major concern. It’s also appreciated in DIY audio projects.
- **6Ж8**: Better suited for applications with concerns over vibration or electromagnetic interference, such as precision instrumentation and circuits intended for military or industrial use.
### Conclusion
Both tubes are great choices but with slightly different optimal use cases. The **6SJ7** is well-suited for general audio applications and hobbyist projects, while the **6Ж8** provides enhanced durability and lower microphonics, making it preferable for demanding environments or where high reliability is needed
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Of course the 5693 is the better of the three
Franco
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output voltage is simply that what you measure at the output and it's "peak" voltage so 1/2 the sin wave.
voltage gain is Vout / Vin typically expressed peak to peak or rms, so 1vac in, 10vac out = voltage gain of 10
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Yes, 5693 are RCA Special Red tubes.
Choke is a bit overkill, but at that price, go for it. Your amp pulls 60mA or thereabouts worst case, depending on how hot you run the 6V6. 7KΩ OT would be a better choice if you're building with Champ power supply plan, however, 5KΩ will work fine. The multi-tap primary Hammond is also a good part.
I <3 Edcor iron, good stuff, only thing I don't like about their "off the shelf" parts is the single tap secondary, but reducing secondary winding complexity keeps their costs down and reduces build time. Meh! I'd rather have the extra taps.
--Pete
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Thanks Franco! That's great info. I'll search around online for the mysterious 6Ж8.
And thanks Pete! I'm also interested in this red metal 5693. I will do some searching for it, too, and see if I can get one at a good price from a reputable seller.
I agree that having multiple primary impedances, and secondary taps is the way to go, since this will be a head. I can order both a Hammond 125ESE OPT and a 159R choke from Hawk and save on shipping. I've decided I want to be able to use a 6L6GC. You can never have enough spare transformers on hand.
I added a couple of voltage dividers that each chop the voltage in half after the gain and volume pots. Sorry for all of the schematic images (they're small PNG's).
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I designed a PCB for Champ amps and I added a couple of mods other than the up-rated output stage. I got tired of punching G10 and staking turrets or eyelets, for every build, so now I just stuff a PCB. They are high temp. FR4, 2.4mm thick, 3oz copper clad. Good stuff.
Anyway, if you're going to jump down the 6L6GC/5881 rabbit-hole, the attached schema with telemetry should help with your final design goals. The One Electron UBT-2 is 4.8K:4/8/16 and is no longer made.
If you're still in the buying phase of the OT, then consider the Heyboer 15W SE OT sold by Amp Parts Direct part no. APD-8031, a clone of the ClassicTone 40-18031 - Details here (https://shop.amppartsdirect.com/collections/transformers/products/fender-champ-style-15w-upgrade-single-ended-4-8-16-ohm-output-transformers-apd-8031h-by-heyboer-transformers-replaced-40-18031). I have built several EL34/6L6GC Champ amps with the ClassicTone part. Very positive reviews on that part. I have a pair of the ClassicTone part for spare/future builds, so I haven't auditioned the APD part as of yet. If it's a true copy, it should please. If I were to build another one of these for a customer, I'd probably use the Edcor, or Heyboer part.
--Pete
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I scored a tested NOS 5693 from a 99.8% positive feedback tube seller.
Can I assume that Leo's operating conditions for the 6SJ7 in his 5C1 are a solid starting point for the 5693? I assume they're probably borrowed from a datasheet?
https://el34world.com/charts/Schematics/files/Fender/Fender_champ_5c1.pdf
Thanks.
David
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I would assume
I would double check the datasheet pinout to doublecheck they're the same and the key is solid
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Ciao David
I'd love to hear how your project is going
Franco
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Hey Franco. I plan to drill the chassis today; the weather's good. I live in a townhouse, so I have to drill metal outside which means setting up a bench and the drill press. Setup and cleanup take much longer than the actual work. Since I bought a 5693 it's going to be "All-Octal" so, it's good I didn't get around to drilling holes until now. Once that's done I can start building the thing.
In the meantime I've been messing with PSUD2. If these voltages are close, then I'm right where I want to be: about 335 on the plate, and 250 on the screen.
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Ciao David
Many thanks for the update
townhouse, do you mean something like this ?
(https://i.imgur.com/Dls11xA.jpeg)
(https://i.imgur.com/CbCZbfp.jpeg)
dont you arranged a workshop in your garage ?
the 5693 is surely a good choice, now, as you say, is a full octal tube project, I like very much this idea
keep us updated
Franco
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dont you arranged a workshop in your garage
:laugh:
my thought exactly, which is more important, obviously a work bench!
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I don't have a garage. :icon_biggrin: And, yes, it's like a rowhouse. I'm in the city.
But, I live 9 minutes from work. I bought my car new in 2018 and the odometer just hit 13K miles. :laugh:
All of the larger holes are drilled, along with the rectangular IEC inlet hole.
After I'm sure how I want the sockets rotated for the shortest wiring, and the least crisscrossing, I'll drill the socket mounting holes. I also need to arrange the choke and the OPT to decide where I want to drill those mounting holes.
The board fits good (I measured for the mounting holes three times and drilled once).
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Weekend progress.
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I scored a tested NOS 5693 from a 99.8% positive feedback tube seller.
Can I assume that Leo's operating conditions for the 6SJ7 in his 5C1 are a solid starting point for the 5693? I assume they're probably borrowed from a datasheet?
https://el34world.com/charts/Schematics/files/Fender/Fender_champ_5c1.pdf (https://el34world.com/charts/Schematics/files/Fender/Fender_champ_5c1.pdf)
Thanks.
David
:icon_biggrin:
5C1 plan uses grid leak scheme and is biased for highest gain, so I presume that the theory was that with just two tubes the 5C1 plan was not going to distort as easily, however, running the pentode with so much gain, input sensitivity can be so low with so much gain that input saturation with modern pickups is a reality. With your plan, and so many cascaded stages, it may potentially be unplayable.
Suggest starting with the pentode biased for lower gain, experiment swapping different values of R Anode, G2 R and cathode R increasing gain to find the distortion & tone to your liking. In other projects I've used the Matchless DC30 EF86 values that result in a pleasing tone, mostly tweaking for less gain to tame things a bit, usually by just fiddling with G2 voltage.
--Pete
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Thanks Pete. Here is that table that floats around the various forums (I don't know who put it together).
I can start with the DC30 values...
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Or, looking at other pentode values, I might start with this:
Rp - 100K
Rg2 - 330K
Rk - 680Ω
Ck - 4.7uF
Cg2 - .047uF
I'm sure it will take some time experimenting to find what I like.
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Ciao David
Here is how Matchless arranged the circuit on the Clubman (6SH7 tube)
(https://i.imgur.com/jBQle0N.jpeg)
Franco
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... I'll search around online for the mysterious 6Ж8. ...
We might think of "ECC83" as the "European name for a 12AX7." In general, the ECC83 has all the same characteristics as a 12AX7.
"6Ж8" is just a "Russian-made metal 6SJ7" (https://tubes-store.com/product_info.php?products_id=820). A challenge may be that the Russian data sheet (https://www.istok2.com/data/500/) specifies a maximum screen voltage of only 140v, where the American 6SJ7 (https://frank.pocnet.net/sheets/093/6/6SJ7.pdf) can go up to 300v.
The 5963 is de-rated to only 125v on the screen (https://frank.pocnet.net/sheets/049/5/5693.pdf) (though a 300v supply is allowable on the other side of the screen resistor), so perhaps you don't need to worry too much for either the 5963 or 6Ж8. Besides, a lower screen voltage will probably yield higher gain, especially if you also up the plate load resistor (there's a balancing act between screen volts, bias volts, Gm, and plate load to get the desired stage-gain and maximum output voltage swing).
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Thanks Franco and HotBluePlates.
Tonight I'm going to re-read Merlin's chapter on small signal pentodes. It's been a long time since I read it, and I don't remember much of it. I think he does say that you can still retain the pentode's tonal qualities at lower gain settings.
Just glancing at one of his EF86 examples, he has a 47K Rp, 330K Rg2, and a 680 Rk for a gain of 85. That's with 300V before the Rp. My B+ should be somewhere in the neighborhood of ~225-ish.
David
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I remember that he say something like in the past pentodes were used in V1 because of theyr high gain but there may be microphonic problems due to the high gain settings, to maintain the positive effect on tone of the pentodes his council was to use it as V2 at a lower gain setting, this way they are less prone to be microphonic and give the best they can
Or this is what I remember
Ciao
Franco
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...to maintain the positive effect on tone of the pentodes his council was to use it as V2 at a lower gain setting...
Yes, this is exactly what I'm aiming to due. :icon_biggrin:
I have the pentode in the V2 position, and I'm reading up on how to set it up for lower gain.
David
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You told it previously but seemed unsure about what was saying Mr Merlin so I told what I remembered as to confirm also you remembered correctly :wink:
Franco
p.s.: Do you have the glass or the metal version of the 6SF5GT tubes ? (may be I have some glass version but not sure about)
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Thanks Franco! I have the 6SF5GT glass tube. The 5693 is the only metal tube.
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If I've those 6sf5gt also mine have to be glass, not metal, but my tube stock is placed in a place in my garage that is difficult to reach because there is letterally a mountain of stuff in front of it
Franco
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there is letterally a mountain of stuff in front of it
Franco
Do you own climbing gear? :laugh:
I'm going to attempt Merlin's "Designing a Pentode Gain Stage the Easy Way" process.
So, if I want a gain of say, 80: The 5693 datasheet gives a gm range from minimum to maximum with 1650 uMHO as the average. That's 1.65mA/V, so 80 divided by 1.65mA/V = 48,484 ohms, or a 47K plate resistor.
With a 300V plate supply, the load line hits 6.4mA. I'll just pretend the -1V grid curve is my 0V curve (Merlin says to draw one in where we want it), and levels off around 7mA (the load line passes a bit low through the knee).
Looking at the 5693 Average Characteristics graph, 0V and 7mA lands a bit less than halfway between the 100V and 75V screen curves, so I'll fudge it at 85V screen voltage. According to the graph the tube reaches cutoff at Vgk = -4.8V. Biasing warm would be about -2V with a plate current of about 3.2mA.
5693 Anode current is 3mA and the screen is .85mA, so the ratio is 3.5. So, 3.2 / 3.5 = .91mA screen current.
300V - 85V = 215V. 215 / .91 = 236,200; a 220K resistor is closest.
Cathode current is 3.2mA + .91mA = 4.11mA. 2V / 4.11mA = 486.6 Ohms, so a 470 Ohm cathode resistor is close.
Finally, I have:
Plate resistor - 47K
Screen resistor - 220K
Cathode resistor - 470
Hopefully, my math is correct and these values would give a gain of about ~80. :dontknow:
I did make an error in my calculations, and did my best to fix it.
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Great job David :thumbsup: :thumbsup: :thumbsup:
I always get punched in the face by those calculations
I would like to be able as you are
Franco
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Thanks Franco! I'm sure I'm about 20%+ off.
I tried again with my supply voltage of 225V B+ and got these values:
Plate - 47K (rounded from 48K)
Screen - 270K (rounded from 285K)
cathode - 680 Ohm (rounded from 700 Ohm)
Obviously, I would round to the nearest resistors, maybe 680K and 2.7K or 3.3K?
Edited to fix math mistakes. :BangHead:
David
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Do you own climbing gear?
:icon_biggrin:
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I'll begin to try with the values that are more close ...... then, if necessary adjust
Franco
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Ciao David
BTW: Saturday I was at an Ham Fest and I meet my hungarian radio amateur friend Gyula
His father was engaged for long years on repair military russian apparatus so he knows very well russian tubes
I asked him about the 6Ж8 tube (to know if there are special designation military versions like many other tubes as 6p14 or 6n2p that has an EV suffix or other to specify if the tube is in a version with special performance ) and he told me all 6Ж8 are military version, this seems to be a good thing and standard construction will be way more better than for civil use)
I stop here, I don't want to highjack the thread
Franco
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Thanks Franco. I searched the auction site and there are several NOS 6Ж8's for sale from Ukraine at very good prices. Thanks for the info on that tube.
So, I have a question about the primary connections with a single-ended OPT. Does it matter which lead goes to the power tube plate and which one connects to B+? I'm using NFB with this amp.
Here's the schematic for my OPT. It shows a phase dot for the red wire - which corresponds to the phase dot on the secondary black ground lead.
But, the primary labeling doesn't make sense to me. :dontknow: It seems to say the red wire goes to the plate (PLT) and the 7K blue wire goes to the screen (SCRN). I'm not connecting my OPT to the power tube screen.
I was going to connect the red wire to B+ and the blue wire to the plate. Should I reverse that, or does it matter with single-ended OPT's?
Thanks!
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The screen is to be connected if you want an UL Power Section, elsewere, dont connect it
The answer to your question is ... I don't know, but I know for sure that if you have an NFB connection you can income on squeal but it is very easy to be solved, reverse the B+ and Plate connections and all is done
Franco
p.s.: At DIYItalia we are developing an SE with secret :wink: NFB :icon_biggrin:
you can see something here attached
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Here's the schematic for my OPT. It shows a phase dot for the red wire - which corresponds to the phase dot on the secondary black ground lead.
Who's OT is that? And what model number?
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Who's OT is that? And what model number?
Willabe, it's the Musical Power Supplies OT10SE:
https://www.musicalpowersupplies.com/products/
But, I found another diagram on their site for the OT10SE that answers my question. :icon_biggrin:
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They have that drawing upside down.
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OK, I did Merlin's pentode math a third time, and I think I finally got it right. At any rate, I have a better understanding of how pentodes operate. And, instead of just copying other values (nothing wrong with that), I have a basic idea of what different values will do.
With a B+ of about 225V, I should have close to 140V on the Plate, around 62V on the Screen, a Cathode voltage of about 1.8V, and a Gain of something like 77.
Here're the resistor values I'm using:
Plate - 47K Ohms
Screen - 330K Ohms
Cathode - 820 Ohms
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I think I have all the parts installed. I'll wire up the tube sockets in the morning. I'm going to wire the heaters Fender-style from above.
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Too clean, mate - it'll never sound funky :icon_biggrin:
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he's been binge-studying Slukey's layouts
the funk comes from the heart n fingers, the amp simply provides spice
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Well, if there's funky mojo in this, I can buy some more wire and try to clone it! :laugh:
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Which Gibson is that? :laugh:
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Which Gibson is that? :laugh:
:laugh:
he's been binge-studying Slukey's layouts
Yeah, he set the standard that I've been trying to aim for since joining this forum. Here's mine:
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(http://)
Wunderbar, meine Herren! :icon_biggrin:
David, you know I'll stolen your job :wink: (and use it with russian tubes or a mix)
Nice Layout, very neat :thumbsup: :thumbsup: :thumbsup:
Franco
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Thanks Franco! "Stealing" would be the best compliment. :icon_biggrin:
I caught my first mistake. I had the power tube bypass cap backwards. Fixed.
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Finely somebody got the B+ A node grounding correct!!!!! :icon_biggrin: PT B+ CT directly to the A node cap ground lug by themselves. Then a wire run over to the rest of the B+ ground daisy chain.
Edit, see reply 70;
A few problems;
1. I'd change the power tube section chassis ground from where it is now, see below.
2. 60uF for the B+ A node might eat 5Y3 rectifier tubes. That's a lot uF's for a 5Y3, will draw too much current through 5Y3 at start up to charge the caps. Maybe you get away with it, will depend on how much resistance is in the PT's B+ wind.
3. And that's a SE amp, it will hummm with the B+ filter supply like you have it. PP amps have much better power supply noise rejection that SE amps don't have because PP cancels noise. To fix this, you need to add 1 more filter stage node before what you have now.
So, you can kill 2 birds with 1 stone here.
Use that 1st 30uF cap by itself and leave the PT's CT tied to that 1st caps ground lug. Now put a 470 ohm R as a dropping R from the 1st 30uF cap, A node, to the 2nd 30uF cap, B node. Use the 2nd 30uF cap, B node for the OT B+ feed. And leave the ground lug wire from A node cap to B node cap. BUT, now take the power tube chassis ground from B nodes ground lug. This will greatly reduce the power supply hummm.
Last thing, you might not want to use all 30uF B+ filter caps, for a SE 6V6. Some guys find an amp more touch sensitive with the last or last 2 B+ filter caps of only 8uF or 10uF.
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"Stealing" would be the best compliment.
Not sure that Steve agreed when I stole from him :icon_biggrin:
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OK, Willabe is right, there are some improvements to be made, but overall the layout is very very clean, any build will benefit from this footprint.
On DIYItalia we prefer to use a gyrator on the PS but also old school tricks can solve the SE Humm problems, we also discard the use of Vacuum Rectifiers especially on SE
Franco
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Thanks Willabe!
I'm not sure I follow/understand your recommendations. I thought that having the Choke between the reservoir and A node would isolate the first cap as a single 30uF reservoir cap. I'm not sure where to place a 470 Ohm resistor... before or after the choke, or does it matter? I used this same basic power supply in my AC4 and there is practically zero hum.
Here is the schematic of this amp's power supply. The first 30uF is not a B+ node. A node goes to the OPT, and B node goes through a 470R to the 6V6 screen.
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I'm not sure I follow/understand your recommendations. I thought that having the Choke between the A and B nodes would isolate the A node as a single 30uF reservoir cap. I'm not sure where to place a 470 Ohm resistor... before or after the choke, or does it matter? I used this same basic power supply in my AC4 and there is practically zero hum.
Here is the schematic of this amp's power supply. The first 30uF is not a B+ node. A node goes to the OPT, and B node goes through a 470R to the 6V6 screen.
I missed that, your fine then.
I've never seen the chassis grounding the way you've done it, but I think that will work.
But;
....... you might not want to use all 30uF B+ filter caps, for a SE 6V6. Some guys find an amp more touch sensitive with the last or last 2 B+ filter caps of only 8uF or 10uF.
You have 6 @ 30uf = 180uF total B+ filter supply, that's a lot in a SE with a 5Y3 rectifier tube.
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I've never seen the chassis grounding the way you've done it, but I think that will work.
Thanks Willabe. I've used this grounding method on my last four amps. Other than the PT center tap and reservoir ground lug, which is close to both and makes a small chassis ground circuit away from the rest of the amp, everything else is grounded at the input jack. It has worked really well for me, so I've been sticking with it. :icon_biggrin:
But;
....... you might not want to use all 30uF B+ filter caps, for a SE 6V6. Some guys find an amp more touch sensitive with the last or last 2 B+ filter caps of only 8uF or 10uF.
Thanks, I have plenty of smaller caps I can try. The reason I did use all 30uF's is because I'm going with a "Star" B+ network. Each stage has its own dropping resistor and capacitor, i.e., the filter caps are not in series. This is supposed to provide better decoupling between stages. But, it's easy enough to swap in smaller caps.
David
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I've never seen the chassis grounding the way you've done it, but I think that will work.
I've used this grounding method on my last four amps. Other than the PT center tap and reservoir ground lug, which is close to both and makes a small chassis ground circuit away from the rest of the amp, everything else is grounded at the input jack.
What I meant was that a lot of guys use 2 circuit chassis grounds, 1 power amp ground, 2 preamp. (If amp has -FB, PI goes to power amp ground, if no -FB PI gets grounded with preamp.)
But this is a SE amp, so you put in 1 extra filter stage before the normal B+ filter daisy chain.
I saw that you ran that 1st B+ cap's ground to the chassis along with the PT's B+ CT.
But, really you should run the PT B+ CT directly to the 1st B+ filter cap then run a wire to the rest of the daisy chained star B+ filter cap nodes. This way the PT's B+ CT and filter cap can charge/drain in a small loop with nothing else in that loop. And this keeps that filter caps charging pulses current off of the chassis. So they don't interact with any other grounds.
That's the dirtiest, nosiest ground in the amp.
Those 2 ways of wiring it are very close but have a slight difference, the cap/CT grounds and the chassis connection. And those 2 differences matter.
That's what I meant by I guess it will work. Because the other chassis ground is so far away from the 1st filter cap/PT CT chassis ground.
But;
....... you might not want to use all 30uF B+ filter caps, for a SE 6V6. Some guys find an amp more touch sensitive with the last or last 2 B+ filter caps of only 8uF or 10uF.
Thanks, I have plenty of smaller caps I can try. The reason I did use all 30uF's is because I'm going with a "Star" B+ network. Each stage has its own dropping resistor and capacitor, i.e., the filter caps are not in series. This is supposed to provide better decoupling between stages. But, it's easy enough to swap in smaller caps.
I missed that you wired the last 4 filter caps in || (parallel). I saw in the layout drawing that you were going for ground stars.
......because I'm going with a "Star" B+ network. Each stage has its own dropping resistor and capacitor, i.e., the filter caps are not in series. This is supposed to provide better decoupling between stages.
I've never heard or have read that. I see no reason why it would be better. If it was better, most amp makers would have done that all through the years.
You can just run those caps in series to use a daisy chained wired ground star system. And you'll get better filtering, and can use smaller caps, if you run the filter caps in a series daisy chain.
Filter cap/dropping R/filter cap/dropping R/filter cap/dropping R, etc.
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Ciao David
About the kind of PS with filters in Parallel or In Series I can say that some VOX used the Parallel Arrangement and that this way the voltage are more stiff at any node
To achieve a similar performance in some PP amp I've seen PS that some plan used a diode between the PS Power Section and the PS Preamp section to avoid the draining of the PS Preamp capacitors at the moment of transient that increase the consumption on the Power Section Nodes, but I don't think this is the case to have such a problem, on SE amp the current consumption don't vary so much
On this matter (Parallel or In Series Nodes on PS) I've read on the past explanations about the opportunity to use the one or the other but .... my mind is not efficient like in past and now I don't remember those precious info's
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About the 30uf + Choke + 30uf on the PS a doubt come to me, as Willabe told, to avoid problems on the 5y3 (first capacitor ability excess) you can use a pre first Node A CR filter, it is true that a choke has a resistance, so your approach is similar but ..... a choke is also an energy storage element, the doubt is .... in this arrangement don't the choke will act as a Cap and his charge don't will stress the Vacuum Rectifier :w2: :dontknow:
I really don't know, I hope someone can clarify this situation
Franco
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@dwinstonwood, your power supply is fine just as drawn. No danger to the 5Y3. And the parallel power supply nodes offer one big advantage over the series string nodes. You can dial in the voltage of one node without affecting the voltage on another node. Makes it easy when building a one-of-a-kind amp. Matchless is very fond of parallel nodes in most all of their amps.
@kagliostro, a filter cap opposes a change in voltage (smooths the voltage ripple and spikes). A choke opposes a change in current (smooths current ripple and spikes). Using a CLC filter between the rectifier and plate node greatly decreases hum (especially important in a SE amp). In addition, the choke reduces the current charging strain on the rectifier, similar to the effect of using a series resistor but without the voltage drop of the resistor.
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Thank you SEL49. It's a grounding scheme that has worked well for me on other amps. And, yes, the ability to select individual node voltages was, in fact, another reason I went with series filtering - in addition to better decoupling. I'm using some less-common tubes (that I've never used before), and wanted the freedom to set each one up independently, if needed. :thumbsup:
I did make one grounding change. Originally, I wasn't going to use NFB, and had grounded the speaker with the power supply. But, since I did go with NFB I've now grounded the speaker at the ground star-point with the tube where the NFB is injected.
David
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And the parallel power supply nodes offer one big advantage over the series string nodes. You can dial in the voltage of one node without affecting the voltage on another node. Makes it easy when building a one-of-a-kind amp. Matchless is very fond of parallel nodes in most all of their amps.
1st off, Matchless amps builder was a Vox guy, so yeah, he's used to running || B+ filter string.
And that's true, you can dial in a dcv a little easier with a || filter string, but it's not all that much easier. Use ohms law to try and figure dcv drop to get close and just gator cable clip in the dropping R to test, not so bad.
But a series string has pluses over a || string, it gives better filtering as you go down the string line and you can use smaller value, less chassis space, and cheaper caps as you go down the line, and still get great decoupling/filtering.
Other than starting with a low B+ dcv, like with EL84 amps, It's not really needed in most cases.
You can easily get great decoupling with a series filter string. With a series string the larger the cap and/or the larger value the dropping R, the better the decoupling. As you go down the string to the preamp tubes, they draw much less current, so you can use much larger dropping R's for better decoupling without much, if any voltage drop penalty.
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- in addition to better decoupling.
What are you basing this on?
You've said this twice now with no reasoning/explanation, or link to where you've heard/read this.
You can use either || or series that's fine, but I'd like to see where you are getting that || string offers better decoupling. I don't want to mislead members here with something like this if it's not true and then start newer builders all going to || filter cap strings.
You can easily get great decoupling with a series filter string. So I don't know why anyone would say that a || filter string has better decoupling than a series filter string.
And that's true, you can dial in a dcv a little easier with a || filter string, but it's not all that much easier. Use ohms law to try and figure dcv drop to get close and just gator cable clip in the dropping R to test, not so bad.
With a series string the larger the cap and/or the larger value the dropping R, the better the decoupling. As you go down the string to the preamp tubes, they draw much less current, 1mA/2mA, so you can use much larger dropping R's for better decoupling without much, if any voltage drop penalty.
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About the kind of PS with filters in Parallel or In Series I can say that some VOX used the Parallel Arrangement ....
Vox had to use the || string to keep the preamp tubes plate dcv up. Because they were using EL84 power tubes, they started with a pretty low B+ dcv. So to keep the preamp tubes dcv up as best they could, they had to use a || B+ filter string.
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About the kind of PS with filters in Parallel or In Series I can say that some VOX used the Parallel Arrangement ....
So does/did Matchless, even with the Clubman which employs EL34s running with 430V B+.
--Pete
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About the kind of PS with filters in Parallel or In Series I can say that some VOX used the Parallel Arrangement ....
So does/did Matchless, even with the Clubman which employs EL34s running with 430V B+.
Sure, the guy who started the company cut his teeth on Vox AC30's, he's a Vox guy. He's used to doing || filter strings.
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In the end, this is a hobby for me. So, I'm keeping it fun. :icon_biggrin:
I don't think this needs saying, but for the record, I'm really not advocating; I'm not trying to encourage anyone to use parallel B+ strings, or to use preamp tubes other than 12A_7's. It's a project, and I just always learn more by experimenting. :think1:
The whole point of this project from the beginning was to dive into stuff I hadn't done before on my clone builds. Even if the end product is dismal, I'll have had a great time and learned a ton!
David
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Vox had to use the || string to keep the preamp tubes plate dcv up.
This is not really true, it's not hard to keep the DC voltage plenty high, whatever arrangement is used. I think it was more for convenience of layout.
I've never heard or have read that. I see no reason why it would be better. If it was better, most amp makers would have done that all through the years.
Series string provides better smoothing of rectifier ripple, parallel provides better decoupling between valves. Different concepts. Which one is more important? There's no right answer, but it a guitar amp we usually care more about hum (ripple), whereas a hi-fi amp might prioritise decoupling to improve LF harmonic distortion and crosstalk. The distinction is less important in modern times because we can buy large capacitances very cheaply.
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In the end, this is a hobby for me. So, I'm keeping it fun. :icon_biggrin:
I don't think this needs saying, but for the record, I'm really not advocating; I'm not trying to encourage anyone to use parallel B+ strings, or to use preamp tubes other than 12A_7's. It's a project, and I just always learn more by experimenting. :think1:
The whole point of this project from the beginning was to dive into stuff I hadn't done before on my clone builds. Even if the end product is dismal, I'll have had a great time and learned a ton!
David
Well stated David. For those of us that are in this as hobbyists, its the process that is the point. I learned how to not electrocute myself (so far) and then it was off to the races. I, and the collective we, are fortunate to not need to make a profit, and not need to meet a client's expectations. Not everyone is in that situation and I get and respect that.
Enjoy the ride.
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Vox had to use the || string to keep the preamp tubes plate dcv up.
This is not really true, it's not hard to keep the DC voltage plenty high, whatever arrangement is used. I think it was more for convenience of layout.
That could be, they had 2 chassis on those AC30's, I don't know about the AC15's if they also had 2 chassis?
But I still think by using EL84's Vox on those amps started out with a fairly low B+. I don't see many of the AC30/AC15' schematics with dcv's. But this older AC15 starts out with 315dcv for B+. Doesn't leave a lot of room for B+ string dropping R's by the time you get to the 1st triode and it's plate R not much dcv left. Will a triode work with only ~90 to 100dcv, sure, but it will sound different than it had 150/200/250 on it.
This AC15 schematic shows a few dcv's. B+ starts with 315dcv, and at the Vib/Trem channel, the 1st triode, V1, 12AX7, shows 210dcv before the 150K plate R. So that could be down to ~100dcv on that plate? And the normal channel's 1st gain stages plate, EF86, only has 90dcv on it. EF86 spec sheet says it'll handle 250dcv on the plate. So Vox could have left that higher.
https://el34world.com/charts/Schematics/files/Vox/Vox_ac15.pdf (https://el34world.com/charts/Schematics/files/Vox/Vox_ac15.pdf)
I've never heard or have read that. I see no reason why it would be better. If it was better, most amp makers would have done that all through the years.
Series string provides better smoothing of rectifier ripple, parallel provides better decoupling between valves. Different concepts. Which one is more important? There's no right answer, but it a guitar amp we usually care more about hum (ripple), whereas a hi-fi amp might prioritise decoupling to improve LF harmonic distortion and crosstalk. The distinction is less important in modern times because we can buy large capacitances very cheaply.
Ok, but why does parallel provides better decoupling between valves? :dontknow:
We need to know the reason(s), can't learn anything if you don't explain a little bit of why.
On that AC15, both channels last B+ dropping R is 22K. Seems like that's how their getting some increase in the decoupling.
With a series string, the larger the cap and/or the larger value the dropping R, the better the decoupling. As you go down the string to the preamp tubes, they draw much less current, 1mA/2mA, so you can use much larger dropping R's for better decoupling without much, if any voltage drop penalty.
So using larger dropping R's as the string goes down to the 1st triode, why wouldn't that give as good of decoupling as a || B+ string? :dontknow:
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But I still think by using EL84's Vox on those amps started out with a fairly low B+.
Dropping from 300V down to 250V leaves plenty of room for a series string IMO. Marshall used a series string for the 18W which also starts with ~300V.
Ok, but why does parallel provides better decoupling between valves? :dontknow:
In the image below you can see how the two triodes are separated by 20k in parallel case, but only 10k in the series case. So for the same values, parallel offers better decoupling (isolation between stages). But the series case offers better smoothing for the second triode.
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Please, Merlin, can you say your opinion on the practice I've seen in some (DIY) project to add an in series diode in a series PS between the preamp node and the power amp node, obviously the idea is to prevent the preamp node capacitor/s from being dried by the power section during transient, but ... will be it really useful ?
Many Thanks
Franco
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I've taken basic DC voltage readings.
6V6GT:
Plate - 325.5
Plate > cathode - 311
Screen - 246.4
Across Rk - 13
Dissipation - 10.8W; 77%
Plate Current - 34.7mA
I designed for about 330 on the Plate and 250 on the Screen. I'm close.
I need to go down to a 300-ish Ohm Rk to get the dissipation up.
6SF5GT:
Plate - 161
Cathode - 1.222
5693:
Plate - 139
Screen - 66.8
Cathode - 1.894
I did the design math for 140 on the Plate, 62 on the Screen, and 1.8 at the Cathode. Pretty close.
6SL7:
Cathode Follower
Grid pin 1 - 136.7
Plate pin 2 - 231.4
Cathode pin 3 - 136.3
Driver
Plate pin 5 - 137.2
Cathode pin 6 - 1.28
These all look good to me. Next step... switch from dummy load to speaker and plug in a guitar. :icon_biggrin:
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Wow! I need to back way off on the voltage dividers I added. You all had me scared that this thing would be a howling beast, so I really chopped down the voltage. :icon_biggrin:
With the Gain and the Volume knobs on 8 it is quiet but very clean, no distortion.
Speaking of quiet, there's no audible hum or hiss two feet away. I had a friend put his ear close to the speaker, and he didn't hear anything, either.
I'll dial back the dividers to 220K/220K and swap in a 300 Ohm cathode resistor and see where that gets me.
Otherwise, everything is functioning the way it should!
David
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and swap in a 300 Ohm cathode resistor
take the 100uF Ck down to ~~47uF as long as you're reworking it.
i've found 100uf takes out some "mojo"
drop your Rk slowly 270, 250, 220. Gator clips work if you're cautious
you'll find there's a "sweet spot" that gives you enough good distortion before you reach ugly sounds.
you'll wanna tweak the B+ tap to keep plate VDC up as you suck more current.
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Please, Merlin, can you say your opinion on the practice I've seen in some (DIY) project to add an in series diode in a series PS between the preamp node and the power amp node, obviously the idea is to prevent the preamp node capacitor/s from being dried by the power section during transient, but ... will be it really useful ?
I don't think it's useful in a guitar amp. It's more helpful in a hi-fi amp playing classical music, where it's mostly quiet but with the occasional very loud, very short interrupt, like a kettle drum or gong.
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Ok, but why does parallel provides better decoupling between valves? :dontknow:
In the image below you can see how the two triodes are separated by 20k in parallel case, but only 10k in the series case. So for the same values, parallel offers better decoupling (isolation between stages). But the series case offers better smoothing for the second triode.
Thank you, I can see it now.
I should have seen that, I was thinking it was something more complicated. That's why I couldn't see it. :laugh:
Guess it comes down too how much smoothing and how much decoupling is enough. Seems to be some room to adjust, as long as you don't go to extremes, to get enough of both with either a series string or running them in || for them both to be pretty close in both smoothing and decoupling.
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and swap in a 300 Ohm cathode resistor
take the 100uF Ck down to ~~47uF as long as you're reworking it.
i've found 100uf takes out some "mojo"
drop your Rk slowly 270, 250, 220. Gator clips work if you're cautious
you'll find there's a "sweet spot" that gives you enough good distortion before you reach ugly sounds.
you'll wanna tweak the B+ tap to keep plate VDC up as you suck more current.
And the 6V6 screen dcv is holding back some volume. I'd raise it up much closer to the plate dcv.
There's a few Fender SE that have the screens the same as the plate. And few amps that the screen dcv is a little higher than the plate dcv, can't remember if they were guys builds here or Fender or someone.
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SE that have the screens the same as the plate.
one of the reasons I moved to UL OT's, the voltage stays close to plate while opposing fast current changes.
I've always run my xSE with minimal G2 "protection"; typically ~100 ohm R with a wattage rating to smoke before the tube.
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Thanks Willabe! I had already switched the power Rk to a 25uF/50V.
All I have on hand are 330 and 270 Ohm 5W resistors. With the 330 (329.4 actual) it's getting there:
Plate - 325.5
Plate to Cathode - 311.2
Screen - 246.8
Across Rk - 12.85
Dissipation - 11.5W, 82%
36.9mA
I will follow your advice shooter and step down until I'm just at 100% - maybe a tad less.
Part of the plan for this project was to set the Screen up at 250V. Most of this project was about trying things I haven't done before. :icon_biggrin:
I switched to 220K/220K 50% voltage dividers and it made a world of difference. With the input Gain dimed and the post-tone stack Volume on 4 it has some good distortion. With the input Gain on 4 and the Volume on 8 it's clean but not too bright. I happy with it!
Sorry for the poor lighting. It's already dark on the East Coast.
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Wow! I need to back way off on the voltage dividers I added. You all had me scared that this thing would be a howling beast, so I really chopped down the voltage. :icon_biggrin:
Guilty, yes I'm guilty
And I'll be guilty the rest of my life Randy Newman
Congrats on a great project - and hey, doesn't that red 5693 look great on the chassis?!
Have a great Thanksgiving, all.
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Guilty, yes I'm guilty
And I'll be guilty the rest of my life Randy Newman
Congrats on a great project - and hey, doesn't that red 5693 look great on the chassis?!
Have a great Thanksgiving, all.
Hey, you weren't the only one here saying this was going to be a death metal animal. :laugh: With no dividers at all it probably would be uncontrollable.
And, yeah! I love that red metal 5693 with the cool vintage RCA logo on top. Thanks to HBP for recommending that one.
Also, the James tonestack (first one I've used) is cool. Turning the Treble and Bass up in unison brings in the Mid-scoop and boosts gain a bit at the same time.
Have a great holiday!
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Very cool David
Many thanks for the answer Merlin
Franco
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Thanks Franco. And, I also need to thank Merlin. I copied a lot out of his books for this project.
Tomorrow I might try a GZ34, instead of the 5Y3GT, just to see if I can even tell a difference with higher voltages. But, I like it the way it is with all NOS (and inexpensive) tubes.
David
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You've tried the lower screen dcv with the 8k2 B+ dropping R.
You can change that dropping R to 1K that'll bring up the screen dcv to close to the plate dcv.
See if you like it better.
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I will follow your advice shooter and step down until I'm just at 100% - maybe a tad less.
the tonal "sweet spot" may be at 90% or 87%, so play long enough between changes to know "Oops, to far" :icon_biggrin:
also, play with NFB, then without, you may find you want that a switchable option.
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Thanks Willabe. So, this is only the 7th tube guitar amp I've built (not counting a couple of rebuilds to optimize my earliest projects). All of those amps have the screen voltage at, or close to, the plate voltage. With this project I chose to do things a bit differently than my previous builds. That's what makes it fun; there were a lot of "unknowns" for me. I really like the way this amp sounds. It's full, not too bright, and definitely not muddy (through a Celestion Creamback). It must be a combination of the Octal tubes, the voltages, and the various preamp stages I decided on. I'm honestly a bit surprised that it sounds this good, since I'm not familiar with another amp using these same exact choices - though nothing with tube amps is actually new. I'm not going to change anything anytime soon. I have more than enough amps with conventional voltages, and it's cool to play through something different for a change. And, to be able to try and hear any audible differences.
Thanks shooter. I tacked a 2.2K across the 330 Ohm Cathode resistor which gives me 287 Ohms. Here're the results. Oh, I took out the sacrificial new EH6V6GT and plugged in an old GE 6V6GT. As you suggest, I'll stay here long enough to really get to know the amp.
Plate - 324
Plate to cathode - 312.8
Screen - 248.6
Rk - 287 Ohms
Across Rk - 11.9
Plate current - 38.4mA
Dissipation - 12.3W, 87.9%
And, here's the "final" schematic.
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All of those amps have the screen voltage at, or close to, the plate voltage. With this project I chose to do things a bit differently than my previous builds. ......I have more than enough amps with conventional voltages,
I know that. And it's not about conventional voltages.
Wow! I need to back way off on the voltage dividers I added. You all had me scared that this thing would be a howling beast, so I really chopped down the voltage. (https://el34world.com/Forum/Smileys/default/icon_biggrin.gif)
With the Gain and the Volume knobs on 8 it is quiet but very clean, no distortion.
When I said try raising the screen dcv and see how it sounds, I didn't mean tone, I meant volume output and output tube distortion.
It's not just the voltage dividers between the preamp stages.
This is why I said to try raising the screen dcv. It's low and it's part of why your hearing what you said above. Lowering the screen dcv chokes the tubes output. The lower you go, the more it shuts off the tubes output. It's a grid, it's allows electrons to flow to the plate or it stops/impedes electrons from flowing to the plate. The grid is why the English call vacuum tubes values.
Change the screen R and see it opens up the volume and allows some distortion.
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Sorry Willabe, but if I crank up the Input Gain this amp has way more distortion than I ever really use ( but, it's nice to have it on tap).
With the Input Gain down around 4 or 5 and the post-tonestack Volume dimed it sounds great. Hair, but controllable by string attack, i.e., clean to breakup depending on how hard I hit the guitar.
It's very versatile. It does a lot, and does it at volumes that I can use at home at night. No, not everyone would like it. But, beyond my own expectations, it does what I hoped it would do. Plus, it's crazy with its 5693 Pentode, 6SF5GT input, 6SL7 Cathode Follower, and James Tone Stack. The most fun I've had building an amp. Maybe the best I've done yet.
Unless I feel like there's a need to mess with it, I'm not. :icon_biggrin:
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With the Gain and the Volume knobs on 8 it is quiet but very clean, no distortion.
I was going by this, I must have missed something.
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I've been twisting knobs all night. With the Input Gain on 5, the Post-Tonestack Volume on 10, the Treble and Bass both at 7, and my Tele in the middle position with the Volume up full and Tone about 2/3rd's up, it has more Chime that my AC15. Without the ringing. This amp is cool. :icon_biggrin:
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With the Gain and the Volume knobs on 8 it is quiet but very clean, no distortion.
I was going by this, I must have missed something.
That was before I went from 820K/220K to 220K/220K dividers.
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What brand/model# did you end up with for power trans, output trans, and choke?
--Pete
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This amp is cool.
welcome to the dark side :laugh:
now for Christmas ask nice for a KT88, and Iron :icon_biggrin:
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What brand/model# did you end up with for power trans, output trans, and choke?
--Pete
PT = Hammond 270EX
Choke - Hammond 194B
OPT - Musical Power Supplies OT10SE 12W
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If the 5693 is not disposable (or too expensive) I can suggest to give a try to the russian 6Ж8, it was planned for military use and it has a sturdy structure
Here’s a detailed comparison between the **6SJ7** and the **6Ж8**:
### 1. Origin and Purpose
- **6SJ7**: An American-made tube widely used in audio amplifiers, radios, and low-frequency circuits. It was designed to provide stable gain with low noise for commercial and home applications.
- **6Ж8**: A Russian tube with similar specifications, often produced for military and industrial purposes. It's designed with greater resilience to mechanical and environmental stress.
### 2. Structure and Build
- **6SJ7**: Typically comes in a glass tube or metal case (depending on the version), offering decent shielding. The glass versions tend to be more prone to microphonics than the metal-bodied ones.
- **6Ж8**: Generally more robust and built to withstand shocks and vibrations better, making it less susceptible to microphonics. Its construction quality tends to be more durable due to military-grade standards.
### 3. Performance
- **Gain**: Both tubes offer similar gain levels, though the 6Ж8 can sometimes provide slightly more stable performance under high-gain conditions, depending on specific production batches.
- **Noise**: The 6Ж8 typically generates less noise than the 6SJ7, especially in noisy environments or with potential interference. This makes it better suited for applications requiring signal purity.
- **Microphonics**: The 6Ж8 generally has lower microphonics due to its sturdier construction, while the 6SJ7 may exhibit microphonics at high gain levels or in vibrating environments.
### 4. Availability and Compatibility
- **6SJ7**: Still relatively easy to find due to its historical popularity and large-scale production, especially in vintage American versions.
- **6Ж8**: As a Russian-origin tube, it may be less common in some Western markets, though it's readily available in Europe and the US through specialized suppliers. It may also have slight pin configuration differences, so compatibility should be checked before use in circuits.
### 5. Ideal Applications
- **6SJ7**: Recommended for vintage audio amplifiers and projects where microphonics are not a major concern. It’s also appreciated in DIY audio projects.
- **6Ж8**: Better suited for applications with concerns over vibration or electromagnetic interference, such as precision instrumentation and circuits intended for military or industrial use.
### Conclusion
Both tubes are great choices but with slightly different optimal use cases. The **6SJ7** is well-suited for general audio applications and hobbyist projects, while the **6Ж8** provides enhanced durability and lower microphonics, making it preferable for demanding environments or where high reliability is needed
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Of course the 5693 is the better of the three
Franco
Franco, the 6zh7 is a copy of the 6J7 - It is dissimilar electrically to the 6SJ7. The 6J7 has less transconductance, so lower overall gain in like bias states. Typically the 6J7 were used in PA amps that were built in the 40's into the early 50's as a first stage amp. I shy away from them because of the grid cap, however, they do sound really nice when pushed hard, and IMO, they are better sounding than the 5879 in a guitar amp.
Hope all is well in Italia mio amico.
Con rispetto,
--Pete
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Ciao Pete
Health is going up and down but this last days the tendency is to be better than the last year
The tube I refer is the 6Ж8 (in Cyrillic) (6J8 in our alphabet) (it is a no topcap tube) and also there is a bit of confusion because there is one other tube that calls 6J8 (in Cyrillic) but isn't the same tube (this last is a pentagrid + triode)
Anyway I'm not referring to a 6J7 tube but to a 6J8 (in our alphabet)
The spec I've find ate this
6J8 / 6Zh8 / 6SJ7 tube
6J8 is a Russian HF pentode tube. The tube is covered with black metal screen. Equivalents to the 6SJ7.
Name: 6J8;
Type: HF pentode;
Application: HF voltage amplification;
Cathode type: oxide, indirect heating;
Envelope: metal;
Mass, g: 42;
Filament voltage, V: 6,3;
Filament current, A: 0,275-0,325;
Anode voltage, V: 250;
Anode current, A: 0,002-0,004;
Anode power, W: 2,8;
Grid1 voltage, V: minus3;
Grid2 voltage, V: 100;
Grid3 voltage, V: 0;
Steepness, mA/V: 1,3-2,0;
Reverse grid current, uA: 0,5;
Microphnic noise, mV: 100;
Socket type: rsh5-1
And in many comparison sheet they say (may be wrongly) that they are a 6SJ7 correspondent tube
Franco
p.s.: For Cyrillic to our alphabet conversion I use this correspondence table find at duncansmps
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Ciao Pete
I reread your last post in a different way ....
Are you suggesting to recover and also use the 6J7 tube (and Russian versions) as a good one for our Old Wild Amp constructions ?
Thanks
Franco
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Tonight I dimed everything. Gain, Treble, Bass, Volume, and Telecaster Volume and Tone.
Through a Celestion Creamback it sounds insane! Very edgy, but not harsh. At full on overdrive it has great distortion. Maybe it's the James tone stack scooping the mids when, or the tubes I used.
At any rate, it really does its thing when cranked.
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Happy to hear you are happy :icon_biggrin:
Franco
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I just played it dimed through my Warehouse G12C/S. This speaker is brighter and more efficient that the Cream Back, so it's somewhat louder. There's no oscillation, or weird sounds that I can detect. It seems to be stable.
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Very Well :thumbsup:
Can you post the last version of Schematic and Layout ?
Franco
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Ciao Pete
I reread your last post in a different way ....
Are you suggesting to recover and also use the 6J7 tube (and Russian versions) as a good one for our Old Wild Amp constructions ?
Thanks
Franco
Yes, I do recommend using the 6J7, but the grid cap can can cause problems with hum if you don't use a shielded cap. I haven't built anything permanent with them, just on a breadboard. If I repurpose an old PA amp that used 6J7, I rewire the socket to use 6SJ7.
--Pete
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And TopCap Shields aren't easy to be find, I searched for it some time ago
I must ask to my ungarian friend, he is my russian tube supplier and he has acces to things that are difficult to be find here
Thanks Pete
Franco
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dimed through my
:occasion14:
I rolled about 8 different speakers, sticky notes on each, I just couldn't find "That perfect speaker". someone suggested 2 at once, bought a 2 X12 cab, rolled them again, more sticky notes, settled on a Cream-back and Eminence and quit rolling, that cab became "the standard"
never rolled speakers again :icon_biggrin:
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Very Well :thumbsup:
Can you post the last version of Schematic and Layout ?
Franco
I've been sidetracked with other stuff. And, I wanted to add my measured voltages after a few hours of banging on it.
There's a lot of room in this design to change things up (voltages, tubes, tonestack, etc.). But, as I built it, it was relatively inexpensive and uses all "cheap" NOS tubes. Plus, wiring up those nice Belton Octal sockets - especially the heaters - has made me never want to use a 9-pin tube again. :icon_biggrin:
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I installed a NOS RCA JAN CRC 6V6. I rewired the socket with Pin 1 (metal shield) to ground, and the 1.5K Grid Stopper connected directly to Pin 5.
It's a really nice sounding tube. The box is dated July, 1953, so right at the end of the Korean War. But, when that black paint started heating up for the first time it got a bit stinky. :laugh:
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It's a really nice sounding tube. The box is dated July, 1953, so right at the end of the Korean War. But, when that black paint started heating up for the first time it got a bit stinky.
That's how you know it really is NOS. :icon_biggrin:
I've got some metal 6L6s like those - they are about 8" tall and sound great.
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My spin on this - See attached. I biased the 6SJ7 for Va to be at ≈1/2 B+, CF trim adds some dark tone, reduces output swing to driver triode, so better for cleans. I like the 6L6 tone better when B+ is pushed with a class A output. EL34s in parallel sound ever better. I had planned originally to build || EL34s but I don't have an OT with the proper reflected load. In this iteration, I used a One Electron UBT-2, which is no longer made, too bad - Use a Hammond 125GSE w/5K reflected. Built on the breadboard & sounds killer.
On the breadboard I didn't build in the vari-NFB shown in schema, nor the switched selectable bypass for the driver, however, I did wire a switchable .68uF. Bypassing the driver really kicks the output stage in the pants. I plan to wire in the vari-NFB in the next day or two. Lastly, I'll most likely ditch the CF trim pot, i tend to favor it dimed (97K setting) anyway.
--Pete
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EL34s in parallel sound ever better.
:laugh:
he's almost there, i know he's smiling after a good session, but......
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Here's a good candidate for an All-NOS-Octal build using affordable metal power tubes.
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Here's a good candidate for an All-NOS-Octal build using affordable metal power tubes.
6SFGT? - Is 6SF5 what you intended?
That preamp with the 5693 would be very similar to many early Fender tweeds and early Gibson and Valco amps, but with fixed instead of cathode bias.
I built a Rickenbacker M11 with that preamp - sounds great. The preamp is very similar to that used in the earliest Fender Pro/Super which is on my build wish list.