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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Fri 12, 2018 9:21 pm 
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glue_ru wrote:
A straight through amp, no knobs to play with?
I found an interesting twist to a single knob tone control, the AMZ Presence circuit, I want to try this in an upcoming project.
http://www.muzique.com/lab/tone3.htm
Thank you. Nice article interesting circuit.

For my way of thinking, I belive that a tone control such as that one, may have great benefit for a guitar amp where the player is an artist and wants the modified and "distorted" output to have certain characteristics for his performance as he is "creating" the modified and peculiar, unique sound as part of his art.

I on the other hand look to my HIFI amp with high hope of getting exact fidelity to the original recorded sound as delivered (such as it is on whatever media).
So I have played a bit with add-on tone controls, yes, .... but I really don't like the idea of ME altering the sound of a song ... mostly because i keep wondering if it might have been more enjoyable w/o the tone control.
And normally I listen to hours of recorded music and I don't want to have to get up and tweak the tones for every different song.
And I also, fundamentally, feel that if my amp "needs" to have a tone control to compensate for its shortcomings...then the amp has a flaw in fidelity.
And so I would always just want a TRUE HiFi amp where it does not "need" tone tweaking.

But that's just me.

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Fri 12, 2018 9:36 pm 
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john8750 wrote:
I love it when you talk amp stuff.


oooh... Just shut up a kiss me!
Image

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Last edited by Pbpix on Jan Fri 12, 2018 10:41 pm, edited 1 time in total.

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Fri 12, 2018 9:53 pm 
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Ok peter, enough of that love stuff. The music you like was recorded with analog equipment. Then it was converted to a digital signal. And then it is 'daked' back to analog. So how do you know how it should sound? The only way you could get a true resemblance is from original vinyl.

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Fri 12, 2018 9:55 pm 
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Pbpix wrote:
glue_ru wrote:
A straight through amp, no knobs to play with?
I found an interesting twist to a single knob tone control, the AMZ Presence circuit, I want to try this in an upcoming project.
http://www.muzique.com/lab/tone3.htm
Thank you. Nice article interesting circuit.

For my way of thinking, I belive that a tone control such as that one, may have great benefit for a guitar amp where the player is an artist and wants the modified and "distorted" output to have certain characteristics for his performance as he is "creating" the modified and peculiar, unique sound as part of his art.

I on the other hand look to my HIFI amp with high hope of getting exact fidelity to the original recorded sound as delivered (such as it is on whatever media).
So I have played a bit with add-on tone controls, yes, .... but I really don't like the idea of ME altering the sound of a song ... mostly because i keep wondering if it might have been more enjoyable w/o the tone control.
And normally I listen to hours of recorded music and I don't want to have to get up and tweak the tones for every different song.
And I also, fundamentally, feel that if my amp "needs" to have a tone control to compensate for its shortcomings...then the amp has a flaw in fidelity.
And so I would always just want a TRUE HiFi amp where it does not "need" tone tweaking.

But that's just me.


My project is for a guitar amp! which is why they may like the distortion effects it could do.
I'm the same way, I believe music artists have very carefully designed their music to be played "as-is"
Bass and treble controls mainly make up for a bad speaker choice or other equipment deficiencies
I play mostly at neutral settings on bass and treble, if anything I may bump bass up 1 or 2 to make
up for low freq hearing loss. (I hung around 40mm Bofors AAA guns as a kid with no hearing protection)

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Fri 12, 2018 10:50 pm 
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john8750 wrote:
Ok peter, enough of that love stuff. The music you like was recorded with analog equipment. Then it was converted to a digital signal. And then it is 'daked' back to analog. So how do you know how it should sound? The only way you could get a true resemblance is from original vinyl.

Well... even vinyl recording equipment wasn't/isn't "perfect" ...
And going from analog to digital and back again doesn't necessarily have to change the fidelity.
remember... the digital file is sampling the analog file at many points, hundreds maybe, and saving that p;oint on the analog line as a digital number of volts or whatever.... and it saves it and then later it replaces that digital number again with an analog voltage of that value.
So unless it is broken... the same signal going in replicated ( depending on how many sampling points) on the way out.

But in either case... I can't know or control that part.
So I have to take the music file presented to me as "original" as well as can be done.
So I don't want to CHANGE that because... why? I don't like the amount of bass? Who says there was more bass originally? Right?
So all I want is for my amp to reproduce EXACTLY as possible the signal I feed it from vinyl or CD or whatever.
HiFidelity is what that is called.
Fidelity means truth.
So hi truth.

As an example:
If your wife told you something that she says your sister said.
You don't know if your wife got it accurately or not.
.. but it is YOUR job to only ever retell the story exactly as your wife told you so as to not distort the truth beyond what you were given... Right?

Your wife's story represents the ORIGINAL "music" as best you know.
And you as the re-teller (amplifier) must not change her story as she told it.
You must be a high truth reteller.

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Thu 18, 2018 11:45 pm 
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Today I received a couple 820uf filter caps for the power supply.
I'm still waiting for a little warmer weather to go out in the garage to stain and finish the wood project box I've selected for this amp.
So I will add more as soon as more stuff arrives and then when that box is ready.. things will start moving quickly.

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Fri 19, 2018 2:37 am 
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Hi Peter. I have seen a .01 disc cap right across the filter caps. Is this just an idea from some, or is there a reason for it?
Seems like those big caps would be enough filtering.

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Fri 19, 2018 3:25 am 
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Hi all. That 6SL7 can drive a 6V6 into overdrive. If the B+ for the triode is 300v the 6SL7 can deliver 65v if the 6V6 has a grid leak resistor of 470k. With a plate resistor of 220k and a bypassed cathode resistor of 3200 ohms though a standard 3.3k will work well this from the 1964 rca tube manual. It will have a voltage gain of 46 so if you need more lash up the other half and get all the gain you can stand and more. If you do not bypass the cathode resistor the gain will drop but so will distortion and you can insert negative feedback at the cathode from the output. I would bypass the input stage cathode and put a gain control between the two stages. The frequency response as well as distortion will be better too with the feedback. Should make a good 4 watt amp that sounds good. Hope these suggestions are helpful.

Bob


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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Fri 19, 2018 3:40 am 
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john8750 wrote:
Hi Peter. I have seen a .01 disc cap right across the filter caps. Is this just an idea from some, or is there a reason for it?
Seems like those big caps would be enough filtering.

The smaller cap in parallel is for short duration noise spikes.

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Fri 19, 2018 4:07 am 
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Audioman wrote:
Hi all. That 6SL7 can drive a 6V6 into overdrive. If the B+ for the triode is 300v the 6SL7 can deliver 65v if the 6V6 has a grid leak resistor of 470k. With a plate resistor of 220k and a bypassed cathode resistor of 3200 ohms though a standard 3.3k will work well this from the 1964 rca tube manual. It will have a voltage gain of 46 so if you need more lash up the other half and get all the gain you can stand and more. If you do not bypass the cathode resistor the gain will drop but so will distortion and you can insert negative feedback at the cathode from the output. I would bypass the input stage cathode and put a gain control between the two stages. The frequency response as well as distortion will be better too with the feedback. Should make a good 4 watt amp that sounds good. Hope these suggestions are helpful.

Bob

Hi Bob:
Thank you very much for the ideas.

The original print came from the Lacewood amp Ver 2. which used 6SN7

I'll be using his basic design but with the 6SL7 instead.

So I'll initially build it this way and see how it goes and then refer to your hints for any changes.
How do you feel this semi-final design will work?
Attachment:
lacewood 6sl7 - 6v6.jpg
lacewood 6sl7 - 6v6.jpg [ 58.11 KiB | Viewed 525 times ]

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Sun 28, 2018 7:55 pm 
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Peter, don't forget the tube rectifier :lol:

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Mar Sun 11, 2018 11:26 am 
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Update:

Today some interesting new parts arrived for the HV power supply.
The key item is a tiny, little $5 DC to DC HV booster module.
https://www.ebay.com/itm/8-32V-to-45-39 ... Sw3ZxaEjLf
Image


This thing is fantastic. It's only about 2 inches
Wow.

What a great cheap & easy way to get an entire 300v HV supply at 100ma.

It can take 8-32vDC input and deliver 45 to 390vDC out at up to 200ma

So I decided to try driving it with an 18v DC wall-wart that I also just bought but it does not have enough current to drive the DC converter.

Since I have three 6.3v tubes, I thought I'd put them in series for 18v @450ma.
The 6V6gt tubes use 450ma ...however since the 6SL7 only uses 300ma so I have to add a 43 ohm resistor in parallel with it.

I happened to have several Triad F-41x (2.5 amp) transformers around (115v to 25.2vAC ) so I decided since it fits nicely in the wood box/chassis this will be a good choice for a power transformer.

But my AC mains here is 122vAC ... and so, since the F-41x was meant for only 115vAC there will be a few volts boost on the secondary side to about 27vAC.

With a full wave bridge rectifier and 2200uf filter cap the DC side feeding the HV-boost module comes out to 32vDC. The booster requires about 1.2 amps to boost the output to 300vDC @ 100ma.

Since the filament string in series only requires 18vAC @ 450ma I'll have to drop the 27vAC secondary voltage down with a 20 ohm series resistor to drop that extra 9 vAC

Here, so far, is the supply as I have tested it on the bench tonight.

That tiny little 300v DC booster module runs cool as a cucumber.... Very nice.

I'm open to feed back... so give me your ideas.

Here's what I have tested with dummy loads on the bench so far.

Attachment:
se 6v6 power supply.png
se 6v6 power supply.png [ 74.12 KiB | Viewed 261 times ]

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Mar Sun 11, 2018 10:01 pm 
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As I think about the filament layout a bit more, I believe that perhaps I can come up with a better arrangement.
I'll do a little thinking on it and post the results later.

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Mar Sun 11, 2018 10:49 pm 
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Okay.
After giving this a little more thought, I realized that if I replace the 6SL7GT with either the 12SL7 octal version or the 9 pin 12AX7 version I can split the secondary voltage more efficiently.

So instead of using the full winding with all filaments in seriers with a couple extra resistors to waste energy and heat... I can allow one half to supply 450ma to the two 6V6s in series and the other half of the winding will supply150ma for either 12SL7 or 12AX7.

Here's ver 2:

Attachment:
se 6v6 power supply2.png
se 6v6 power supply2.png [ 71.3 KiB | Viewed 240 times ]

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Mar Mon 12, 2018 1:45 am 
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Cool Peter. I would like to rebuild my 6V6, or build another one, with that power supply. Might follow your SE ideas for something different.
Thanks for the 'show and tell'

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Mar Mon 19, 2018 10:57 am 
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Update:

I've been testing this 6V6 SE amp on the bench for a day or two.

I found that the 115v/24v Triad F-41x (50 VA) power transformer gets a bit hotter than I think it should.
So I tried a new type Signal 14A-30-24 (30VA) and it seems to run cooler than the Triad even though it is rated 20VA lower. Strange.

My mains is 122vAC not 115vAC so that's why the 2ndary is higher than 25v.

Since it's all in bread board stage now... I am testing only one channel.
So I have temporarily used a 12V6 and a 12SL7 so I can feed it from the CT 24v winding.
So the current is only 225ma right now (instead of 450ma for two 6V6s in series) on that one 12v winding.
The 12SL7 will stay and it only draws 150ma on the other 12v winding.

The good thing is that it sounds very very nice with the 12SL7 feeding the 12V6.

But the exciting part is that I am running this neat, low-cost $5, tiny-little DC-DC HV booster to produce a solid 300vB+ from the 24v winding & w/a simple 2 stage rectified power-supply.

So as you can see this is extremely simple as far as parts count and labor goes.

I've been testing for several hours and the 1st two hour test had the F-41x transformer rather hot, But the 30V Signal transformer is rather warm but I can comfortably hold it. However the filament currents will go up when I have two 6V6s going for the final 2 channel version.

Wonder why the Triad is hot? I tried two of them and they both got hot the same way.

Maybe the Signal trans is using higher quality laminations?

Attachment:
lacewood 12sl7 - 12v6gt.jpg
lacewood 12sl7 - 12v6gt.jpg [ 57.37 KiB | Viewed 200 times ]


Edit: corrected PS to show 2 ohm resistor in pi filter and that also changed 28v@300ma to 32v@530ma
Attachment:
se 12v6 power supply.png
se 12v6 power supply.png [ 61.48 KiB | Viewed 167 times ]

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Last edited by Pbpix on Mar Wed 21, 2018 5:44 am, edited 2 times in total.

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Mar Mon 19, 2018 5:19 pm 
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Just a thought Peter, maybe bolting the transformer to a metal chassis would be a heat sink.

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Mar Mon 19, 2018 6:19 pm 
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Perhaps a clue comes from comparing the mechanical ratings:
The Triad is 2.2 pounds and is rated to 130 degrees C, class B.
The Signal is 1.2 pounds and is rated to 155 degrees C, class F


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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Mar Mon 19, 2018 6:59 pm 
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Dale Saukerson wrote:
Perhaps a clue comes from comparing the mechanical ratings:
The Triad is 2.2 pounds and is rated to 130 degrees C, class B.
The Signal is 1.2 pounds and is rated to 155 degrees C, class F

Thank you dale,
That sheds light on it that I had no awareness of. Great. That's the kind of help I needed.. a little real thinking... lol

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Mar Tue 20, 2018 6:30 pm 
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I believe I remember reading that Triad trannies tend to run a little hot.

One other thing; I don't know the circuit that your DC-DC converter uses, but I know certain ways of getting more voltage result in higher currency requirements. For example, a voltage doubler circuit will result in half the current capacity. I don't know if your step-up in DC is straining the PT or not; just thought it would be something to mention.


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