| hacknet |
i`m looking at a simple 6L6. as you might already know, i am considering this over the leak stereo 20 and the williamson.
let me know if this implimentation would work. its just something i thought of before getting into bed last night.
Thanks! |
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| hacknet |
| i hope to use a 317 regulator as a CCS to draw something in the region of 125ma. would it work? |
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| EC8010 |
If you mean "will it sink 125mA of DC?" Yes, it will. If you mean "will it be a true constant current sink with high output impedance above 100Hz?" Then, no. The 317 is quite a reasonable regulator, but it doesn't belong that close to audio.
You will get far better results using a real audio transistor such as a BD131. Connect its collector to the wiper of your pot. Take the emitter to ground via a 16 Ohm resistor. Apply 2.65V to the base, and you will have a 125mA current sink. Make that 2.65V slightly variable, and the anode current will be adjustable.
Edit: I thought you wanted to keep this thing simple? What's wrong with resistor/capacitor bias at the output stage? |
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| analog_sa |
| I am also in support of the resistor cathode bias or fixed bias. Once you have an amp up and running you can always experiment with adventurous biasing schemes. It will be very surprising if you actually prefer the sound with a 317. |
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| SY |
I would heartily agree with analog and EC. Why complicate a simple task?
And I would add that if what you're after is punchy bass (as you said in your other post), class-A zero feedback is probably not the way to go. That will tend toward looser, softer bass, with less power available. |
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| hacknet |
oh yes... my wrong..
i was told that a current sink using the 317 sounded quite good. it supposedly tightened up the bass.
the way it looks, i may have to look into a NFB or revert back to a proven design. |
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| analog_sa |
That completely slipped my mind. The zero nfb approach is probably best for simpler acousic music and unless you really make an effort may disappoint with rock. Have you looked at some of the Audio Research amps? They have a mod for a 6L6 Dynaco which very possibly has great bass.
Deep and punchy bass is possible even with zero nfb and even in SE designs but is certainly not guaranteed. It will greatly depend on your speakers ability to play without too much control from the amp and on serious attention towards the PS. |
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| SY |
| quote: | | dire straits and eddie van halen |
Analog, that should be a clue that hacknet is not using speakers with a Bessel alignment. ;) |
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| hacknet |
i`m running a pair of open baffles with a sub crossing at 90hz. i would not consider my system to be bass friendly. i saw the schematics for a Dynaco which is based on the williamson.
would that be a better bet? |
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| analog_sa |
I don't think the Dynaco is better than Williamson. I've had both (still have an ST70 somewhere) but a comparison would be unfair - my Willaimson used all Partridge iron and PIO caps while the Dynaco is completely stock. Williamson is triode wired class A and the Dynaco is AB ultralinear with a very marginal PS.
What i had in mind was an AR modded Dynaco. It looks pretty much like a D76 and while AR is not hip with the diyers it produces exemplary bass and solidity and is really able to rock.
Why don't you try listening to a vintage AR amp and see what you think? |
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| hacknet |
i`ve not heard but i`ll look forward to listening to one.
i was looking at this schematics and was quite acrosound 6l6
what do you think. i think its simple enough for a beginner to start with.... |
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| analog_sa |
Not bad. It will certainly get you started and if you build it as a prototype will certainly let you experiment with a lot of different configurations |
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| hacknet |
i`ve got a question thou.
i see a X marked at the cathode and there is another "to X" at to what sees like a heater hum pot. is this to bring the heater`s potential closer to the cathode? do i just have to connect "to x" to x? |
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| hacknet |
another question, i see that the screen is tied to a 270v line. i`m a noob, please answer my silly question.
is this tube operating in tetrode or triode? i guess tetrode rite? |
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| andyjevans |
The zero nfb approach is probably best for simpler acousic music and unless you really make an effort may disappoint with rock. Deep and punchy bass is possible even with zero nfb and even in SE designs but is certainly not guaranteed. >
Yes indeed - I can get deep bass but I wouldn't call it tight. This is the real area of sacrifice. There again, I listen to small scale classsical and jazz music so zero NFB is really in its element - the double bass sounds a bit boomy but not overly so - I can live with it. There again, I'm a double bass player. The cobbler's children have no shoes! Andy |
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| SY |
| quote: | Originally posted by hacknet
is this tube operating in tetrode or triode? i guess tetrode rite? |
Rite. |
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| SY |
| quote: | Originally posted by hacknet
i`ve got a question thou.
i see a X marked at the cathode and there is another "to X" at to what sees like a heater hum pot. is this to bring the heater`s potential closer to the cathode? do i just have to connect "to x" to x? |
Also rite. ;)
This connection puts the heaters above the cathodes in potential, which can (with some tubes) reduce hum compared to grounding it.
Oh, yeah, and don't take the schematic literally and use a selenium stack for the screen supply. Use a proper silicon HV rectifier (high speed one, if you prefer). When you start getting the itch to experiment, regulating this supply will be the single most effective change you could make. |
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| hacknet |
selenium stack? i did a seach and i still don`t get it. mind explaining?
you advise regulating? i always thought power amps were always better left hanging as current was always a problem with regulating. |
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| fdegrove |
Hi,
The two diodes in series on the Acrosound 6L6 schematic you linked to.
| quote: | | you advise regulating? |
The screengrid of the 6L6.
Leave it hanging for the time being....;) |
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| SY |
To amplify Frank's comments, the schematic shows a stack of selenium rectifiers running the screen supply. That's an old technology which, happily, has not become retro-cool (though maybe this year someone will "discover" that selenium rectifiers are enormously better-sounding because they perform so badly).
And as he says, build as-is for the first go-round, but do plan in enough chassis space to add regulation to that screen as your first upgrade. |
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| fdegrove |
Hi,
| quote: | | that selenium rectifiers are enormously better-sounding because they perform so badly). |
Not to mention they're poisonous to the environment IIRC...
In short, what we mean is that the sreengrid benefits from having its PS regulated.
As for schematics, anything using 6L6, 807, 5881 and no doubt a raft of others will work for inspirational purposes; from the mere basic to the lunacy fringe.
Cheers,;) |
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| hacknet |
haha... okay.. then its diode stacking time;)
but, can i sub the 6sl7 for a tube of my choice? say a 12au7? |
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| fdegrove |
Hi,
| quote: | | but, can i sub the 6sl7 for a tube of my choice? say a 12au7? |
No.
For comparison: a 12AU7 is related to, but not the same as, the 6SN7/12SN7, amplification factor is about 17.
A 6SL7 is ........,the 12AT7, amplification factor is about 60.
IOW, if you have 12AU7s, who hasn't, and you must use them then try to find a schematic that uses those.
Otherwise I'd recommend sticking with a 6SL7 . The Chinese and Russian ones are not that expensive.
Cheers,;) |
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| EC8010 |
If you're still at the design stage, you don't need to restrict yourself to 6.3V heaters. If you use 12.6V heaters, the valves are much cheaper. 12SL7 is much cheaper than 6SL7. Loctal equivalents are even cheaper, I recently bought some 14F7 for US$3 each.
A 12AT7 is not nearly as good as 6SL7. |
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| hacknet |
sad thing being that the local tube store doesn`t carry a wide selection. i`m limited to common tubes. 12at7, 6sl7, and the rest of the mess....
i was thinking if it was a good idea to use cheap pentodes insted? maby a el34 driving a 6l6? just a silly idea... would it work? or output impedance of that stage be too high? i`m just throwing out ideas.:D |
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| SY |
Might as well use the EL34s as outputs.
There are a large variety of tubes available out there- all it takes is a phone call in most cases. If I had to rely on what I could buy locally, I'd never get an amplifier built. |
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| analog_sa |
| quote: | | sad thing being that the local tube store doesn`t carry a wide selection |
?!
Have you been to Wellaudio? Frankie will not only offer the tubes but also excellent advice what to do with them.
| quote: | | use cheap pentodes insted? maby a el34 driving a 6l6? just a silly idea... would it |
Nothing silly here. I've used triode strapped 6L6 to drive 2A3 with excellent results. |
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| hacknet |
| haha... frankie doesn`t have a fantasic selection. i`ll give him a call and see what he recommends. |
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