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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Sun 12, 2015 7:15 pm 
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Based upon the value of C2, I don't believe that 47uf is the optimum value for C1 and it needs to be higher. I agree it has to be a very good quality cap and the larger it is physically the cooler it will appear to be.

From what I recall in commercially built stuff (this kind of doubler was very popular in 1950's series string TV's) C1 is typically about 1/3 to 1/2 the value of C2, but part of that is related to the current drawn from the supply. Changing it may make the B+ increase as well. In this circuit I'd try 100uf @ 250 volts. You might want to reduce the value of C2 at the same time using maybe a 220uf @ 350 or 450 volts.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Sun 12, 2015 10:24 pm 
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Flipperhome wrote:
Pbpix wrote:
Tonight I was double checking values and measuring voltages etc in the power supply.
I felt that C1 was a little warm ( 47uf @250v)...
It's the cap ESR. You may need either one with a lower ESR or a larger cap.

ESR... but I don't know what the ESR is for the caps that got warm...
No big brand name.

A larger value? Greater than 47uf?
How will a larger value affect the problem? Drains slower and will have a shorter larger recharge pulse?
The schematic I used to begin with showed a 100uf but it was for a much lower voltage doubler.

I used a reasonably low value to try to give a longer re-charge time vs a shorter big pulse. But I'm only guessing ... nothing scientific.

Here's a similar one at 1/5 the current:
Image

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Sun 12, 2015 11:30 pm 
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I have the 47uf 250 volt. So I should get the 450 volter? Or use a higher value?
What ever we need....
I am a little wound up in motor control work right now. But no big deal.
I am also wiring a model caboose for lighting. Also no big deal.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Sun 12, 2015 11:43 pm 
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john8750 wrote:
I have the 47uf 250 volt. So I should get the 450 volter? Or use a higher value?
What ever we need....
I am a little wound up in motor control work right now. But no big deal.
I am also wiring a model caboose for lighting. Also no big deal.

You can use 47uf @250v... just feel it for warmth. I belive you should not really need more than 250v.
But just check it while testing.
So... I tried upping the voltage to 450v... but even that particular cap seemed a bit warm to.
So I tried a few others at 450v.
I NOW have a 47@450 in there at the moment that is operating cool.

Maybe the other warm ones were poorer quality?

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Sun 12, 2015 11:47 pm 
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Hey Flip:
You are a triode guy.
I saw a commercial iPod amp called Zvex ImpAmp
http://www.innerearmag.com/archives/amp ... PAMP.shtml

I think it uses an OP275 as well driving two 6021W pencil tube triodes. But I'm not sure if they are PP ... probably.
All DC coupling at about 1 watt per channel.

Impressive.

I'd like to see a schematic of the DC coupling and power supply.
Have you seen it yet?

How do you think they did the DC coupling to the grid?

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Mon 13, 2015 1:19 am 
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Pbpix wrote:
john8750 wrote:
I have the 47uf 250 volt. So I should get the 450 volter? Or use a higher value?
What ever we need....
I am a little wound up in motor control work right now. But no big deal.
I am also wiring a model caboose for lighting. Also no big deal.

You can use 47uf @250v... just feel it for warmth. I belive you should not really need more than 250v.
But just check it while testing.
So... I tried upping the voltage to 450v... but even that particular cap seemed a bit warm to.
So I tried a few others at 450v.
I NOW have a 47@450 in there at the moment that is operating cool.

Maybe the other warm ones were poorer quality?



What about two of these in series for 75uf? Cheap enough.

http://www.allelectronics.com/make-a-st ... tor/1.html

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Mon 13, 2015 1:30 am 
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Pbpix wrote:
Hey Flip:
You are a triode guy.
I saw a commercial iPod amp called Zvex ImpAmp
http://www.innerearmag.com/archives/amp ... PAMP.shtml

I think it uses an OP275 as well driving two 6021W pencil tube triodes. But I'm not sure if they are PP ... probably.
All DC coupling at about 1 watt per channel.

Impressive.

I'd like to see a schematic of the DC coupling and power supply.
Have you seen it yet?

How do you think they did the DC coupling to the grid?



Flip should like that cute little muffin pan.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Mon 13, 2015 1:33 am 
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john8750 wrote:
Pbpix wrote:
john8750 wrote:
I have the 47uf 250 volt. So I should get the 450 volter? Or use a higher value?
What ever we need....
I am a little wound up in motor control work right now. But no big deal.
I am also wiring a model caboose for lighting. Also no big deal.

You can use 47uf @250v... just feel it for warmth. I belive you should not really need more than 250v.
But just check it while testing.
So... I tried upping the voltage to 450v... but even that particular cap seemed a bit warm to.
So I tried a few others at 450v.
I NOW have a 47@450 in there at the moment that is operating cool.

Maybe the other warm ones were poorer quality?



What about two of these in series for 75uf? Cheap enough.

http://www.allelectronics.com/make-a-st ... tor/1.html

It would work ... but I'm not saying that 500vdc is the problem.
It really ought to work with 250vdc as well.
So depends on what you have around.
Right now i am using a 47uf@450v and it runs cool.

Maybe flip can explain what he meant by larger cap.. Value or voltage.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Mon 13, 2015 1:37 am 
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Mr. Detrola wrote:
Based upon the value of C2, I don't believe that 47uf is the optimum value for C1 and it needs to be higher. I agree it has to be a very good quality cap and the larger it is physically the cooler it will appear to be.

From what I recall in commercially built stuff (this kind of doubler was very popular in 1950's series string TV's) C1 is typically about 1/3 to 1/2 the value of C2, but part of that is related to the current drawn from the supply. Changing it may make the B+ increase as well. In this circuit I'd try 100uf @ 250 volts. You might want to reduce the value of C2 at the same time using maybe a 220uf @ 350 or 450 volts.

Thanks..I didn't see this post earlier... sry.

I'll try raising C1 and lowering C2...
Main goal is very low ripple at 100ma + or so.

Now I have only about 150ma ripple.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Mon 13, 2015 2:46 am 
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You can always add a choke instead of the resistor between the two electrolytics C2 and C3 if you need to get ripple down further, but with push-pull output it shouldn't be any issue.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Mon 13, 2015 2:54 am 
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Pbpix wrote:
Flipperhome wrote:
It's the cap ESR. You may need either one with a lower ESR or a larger cap.
ESR... but I don't know what the ESR is for the caps that got warm...
No big brand name.
That's the point, you don't know, but 'cheap' caps are usually higher ESR.
Pbpix wrote:
A larger value? Greater than 47uf?
How will a larger value affect the problem? Drains slower and will have a shorter larger recharge pulse?
Larger value caps will naturally have a lower ESR than a lower value cap. Higher voltage will generally have more than a lower voltage.
Pbpix wrote:
The schematic I used to begin with showed a 100uf but it was for a much lower voltage doubler.

I used a reasonably low value to try to give a longer re-charge time vs a shorter big pulse. But I'm only guessing ... nothing scientific.

Here's a similar one at 1/5 the current:
Image
I don't know what you mean about a much lower voltage double but, at any rate, it's the current that matters and note that the doubler cap is the same value as the first filter.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Mon 13, 2015 5:23 am 
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john8750 wrote:
I was talking to a friend who works in a sheet metal shop about the chassy I needed.
So the next day he gave me this

Attachment:
6v6 chassis1.jpg


It is 12X6 inches and 3" deep.
Should be perfect for the amp.



I mean, that's love, right there....
Think I will glue on some wood ends.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Mon 13, 2015 5:32 am 
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Pbpix wrote:
Hey Flip:
You are a triode guy.
I saw a commercial iPod amp called Zvex ImpAmp
http://www.innerearmag.com/archives/amp ... PAMP.shtml

I think it uses an OP275 as well driving two 6021W pencil tube triodes. But I'm not sure if they are PP ... probably.
All DC coupling at about 1 watt per channel.

Impressive.

I'd like to see a schematic of the DC coupling and power supply.
Have you seen it yet?

How do you think they did the DC coupling to the grid?
Yeah, I've seen it. Been around for a while but they don't publish a schematic.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Mon 13, 2015 6:51 am 
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Flipperhome wrote:
Pbpix wrote:
Flipperhome wrote:
It's the cap ESR. You may need either one with a lower ESR or a larger cap.
ESR... but I don't know what the ESR is for the caps that got warm...
No big brand name.
That's the point, you don't know, but 'cheap' caps are usually higher ESR.
Pbpix wrote:
A larger value? Greater than 47uf?
How will a larger value affect the problem? Drains slower and will have a shorter larger recharge pulse?
Larger value caps will naturally have a lower ESR than a lower value cap. Higher voltage will generally have more than a lower voltage.
Pbpix wrote:
The schematic I used to begin with showed a 100uf but it was for a much lower voltage doubler.

I used a reasonably low value to try to give a longer re-charge time vs a shorter big pulse. But I'm only guessing ... nothing scientific.

Here's a similar one at 1/5 the current:
Image
I don't know what you mean about a much lower voltage double but, at any rate, it's the current that matters and note that the doubler cap is the same value as the first filter.

So are you saying a large cap (say 470uf) at the lowest voltage rating for this ckt (160vdc - 250vdc) would be likely to have lowest ESR? ... or likely to be lower than 47uf- 100uf?


What I meant by a circuit for a lower voltage... is that the one I originally followed used 100uf caps and 100 ohm resistors. It was a doubler for low voltages like 25-30v.

Tonight I tried a 47uf @160v (MIEC brand).... and after 1/2 hour it exhibits just a slight warmness.
(Should stay at room temp I feel.)

Also tried a 100uf @160v (no name brand) and it seems to run cool so far ....but haven't had it on long enough to judge.
This 100uf boosts the B+ by 5v .... ripple stays at 150mvPP

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Mon 13, 2015 7:44 am 
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Pbpix wrote:
So are you saying a large cap (say 470uf) at the lowest voltage rating for this ckt (160vdc - 250vdc) would be likely to have lowest ESR? ... or likely to be lower than 47uf- 100uf?
A higher capacitance is a slam dunk, yes. Lower voltage 'usually' gives higher ripple current but not always. Seems to depend on case size but I'm not familiar with all the nuances of cap design. It's simple to find out, though: look at the data sheet.

Pbpix wrote:
Tonight I tried a 47uf @160v (MIEC brand).... and after 1/2 hour it exhibits just a slight warmness.
(Should stay at room temp I feel.)

Also tried a 100uf @160v (no name brand) and it seems to run cool so far ....but haven't had it on long enough to judge.
This 100uf boosts the B+ by 5v .... ripple stays at 150mvPP
Larger cap value = higher ripple current.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Mon 13, 2015 8:04 am 
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A larger cap .... I thought... will boost the DC level and help smooth out ripple.

Anyway... after running with a 100uf @160vdc as C1 for an hour or so... that cap doesn't seem to get warm at all. Only the B+ went up 5v.
So I changed R3 from 150 to 180 ohm and B+ is back at 235v ... and the ripple improved from 150mvpp down to 100mvPP.

Image

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Mon 13, 2015 9:05 am 
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Pbpix wrote:
A larger cap .... I thought... will boost the DC level and help smooth out ripple.

Anyway... after running with a 100uf @160vdc as C1 for an hour or so... that cap doesn't seem to get warm at all. Only the B+ went up 5v.
So I changed R3 from 150 to 180 ohm and B+ is back at 235v ... and the ripple improved from 150mvpp down to 100mvPP.

Image
You pretty much swamped any effect ESR might have on the circuit with those honker 50 Ohm resistors and I have no idea why you're limiting B+ to 235 V.

Btw, your schematic shows 25 mA plate current and 25 mA cathode current, which leaves 0 for screens.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Mon 13, 2015 9:18 am 
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Flipperhome wrote:
Pbpix wrote:
A larger cap .... I thought... will boost the DC level and help smooth out ripple.

Anyway... after running with a 100uf @160vdc as C1 for an hour or so... that cap doesn't seem to get warm at all. Only the B+ went up 5v.
So I changed R3 from 150 to 180 ohm and B+ is back at 235v ... and the ripple improved from 150mvpp down to 100mvPP.

Image
You pretty much swamped any effect ESR might have on the circuit with those honker 50 Ohm resistors and I have no idea why you're limiting B+ to 235 V.

Btw, your schematic shows 25 mA plate current and 25 mA cathode current, which leaves 0 for screens.

Show us how it should be designed please. Why not help here a bit.
You sound like you think I designed it myself... but all I did was try to follow a print I saw on line..
I only trimmed it from the initial print I found to try to achieve voltages needed.

The original print showed c1 & C2 as 100uf caps and r1 & r2 as 100 ohm.
That's it.

So I cut the 100 ohms to 50 to bring the final voltage near my goal.

My only goal originally was to keep the B+ around +235v ... because that was just because I was planing on using a 470uf/250v filter cap as C2 and C3. Because John and I still had some of those around from the 5902 design.
(I added R3/C3 and R4)
But I quickly saw that C2 must to be higher voltage.
So I can use C3 as 250v .... but why would I bother with trying to keep 250v caps now?

So what do you suggest now?

The voltage currently at C2 is 258v

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Mon 13, 2015 11:48 am 
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Pbpix wrote:
Show us how it should be designed please. Why not help here a bit...
First I want to say I do NOT endorse a line powered supply, because I don't consider it safe, so purely as a thought experiment...
Attachment:
Line Power Supply3.jpg
Line Power Supply3.jpg [ 49.32 KiB | Viewed 3786 times ]

There's no reason for two series resistors other than to stay within power ratings and the lower 10 Ohm dissipates 5 Watt, hence the 10 Watt rating. 10 Ohm is more than enough limiting to keep max surge current under 10 A (a 1N4004 is rated 30 A). Average current is 175 mA (rounded up).

C1 has to sustain roughly 713 mA ripple. The Nichicon is rated 800 mA at 85 C and 120 Hz (The factor is .8 at 100 Hz and isn't good enough). At 132 VAC (+10 %) it has to sustain 785 mA of ripple and the Nichicon, again, makes it. Of course, a higher ripple rated cap increases reliability (the Nichicon was just the first I ran across) so the more the merrier (and costly). As a side note, when looking for 'high ripple' caps watch out for "at high frequency" types. The rating goes up with frequency and they often don't list what it is at 120 Hz (and it isn't the 'high frequency' number).

B+ current is for Class AB, 10K, which is 75 mA per PP pair (150 mA total), at a grid bias of 15 V. With plate (- cathode) voltage of 250 V that places B+ at 265 V. Simulations place B+ at 271 V but doesn't take into account AC source impedance and cap ESR losses so I figure it should come out about right, but it's close enough if not.

Edit: Corrected C1 wrong polarity.


Last edited by Flipperhome on Apr Tue 14, 2015 4:58 am, edited 1 time in total.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Mon 13, 2015 7:05 pm 
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I was successfully able to change the transformer order with Edcor. Thanks Peter.
I have a few components for the power supply, but not a lot of designing knowledge.
So will wait for you guys to get a good design. I want to build this amp along with Peter.
So I want to finish the test speakers first.
Thank you guys..

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