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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Thu 09, 2015 7:59 pm 
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Pbpix wrote:
Here's the latest state of the amp:

When I used 200 ohm cathode res. the current per tube went up to 30ma and the bias was 12.5v
With that set up and SG connected to B+ , I was able to get approx 6.5 watts out into a speaker and about 5.5watts into an 8 ohm resistor.

I found that when I cut the current back to only 25ma/per tube everything still "sounded" terrific and it will make my power supply a little easier to build... but I will need to do some thinking about that yet.
I intend to make a voltage doubler and I hope it won't be too high in the first stages before I cut it back to +235 for B+. I don't want to have to use big wattage dropping resistors between filter cap stages to bring it into the 235v range.

Anyway.. I have now added individual 25ma CCS for each tube with 1000uf by-pass caps.
That requires the cathodes to be separated... and so ..then I re-coupled the cathodes together capacitively.

The greatest advantage of using separate CCS for cathode-bias, is that each tube will always auto-magically be biased to operate exactly at 25ma. Regardless of the tube age or brand!
... I will not need to have matched pairs and anytime the tubes are ever changed, the bias never has to be readjusted.

It's the perfect "auto-bias" .
Each cathode voltage is now at approx +13.5v which the CCS will automatically vary as needed in order to achieve the exact 25ma bias current.

With CCS as cathode-bias, the current in the OT will also always be perfectly balanced as well optimizing its performance.
What more could one ask for?
Attachment:
6v6 - 6aq5 pp ccs amp.jpg


Here's a regulated version of the supply:
Attachment:
6aq5 supply reg.jpg



Thanks Peter.
Your work is much appreciated.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Thu 09, 2015 8:06 pm 
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I just ordered these

https://www.edcorusa.com/gxpp10-8-8k

For my next 5902 amp. This one will be for my cousin. He has 8 ohm speakers.
I hope they are still in good shape. 20 years old. The speakers, not him.
he says they sound good.... I will check them out.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Thu 09, 2015 10:24 pm 
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john8750 wrote:
I just ordered these

https://www.edcorusa.com/gxpp10-8-8k

For my next 5902 amp. This one will be for my cousin. He has 8 ohm speakers.
I hope they are still in good shape. 20 years old. The speakers, not him.
he says they sound good.... I will check them out.


Hi John:
You just ordered GXPP10-8-8K for which amp? <===(this is the right one for 6V6)

You said "for my next 5902 amp."

But that amp requires 4k

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Fri 10, 2015 8:54 am 
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Oh No
I got them confused. How will the 5902 work with those?
Or I could build him an amp with the 6V6 tubes.
I ordered them for the 5902 version.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Fri 10, 2015 6:46 pm 
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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
6v6 chassis1.jpg [ 139.43 KiB | Viewed 2958 times ]


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

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Fri 10, 2015 6:52 pm 
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Peter
I am getting some 1%s for the 50 ohm resistors in the CCS.
Do you suggest any others be 1 %?
Also, I have a 13K ohm for the preamp power circuit.
Will 1 watt zeners be OK? We should need .6 watts, I think.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Fri 10, 2015 8:38 pm 
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john8750 wrote:
Oh No
I got them confused. How will the 5902 work with those?
Or I could build him an amp with the 6V6 tubes.
I ordered them for the 5902 version.

The 5902 requires 4k... so 8k is not right.

Just call Edcor and Change your order by phone.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Fri 10, 2015 8:43 pm 
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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.

Looks good. From that angle it sure looks longer than 12" .... maybe 12 feet? :lol:

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Fri 10, 2015 8:50 pm 
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john8750 wrote:
Peter
I am getting some 1%s for the 50 ohm resistors in the CCS.
Do you suggest any others be 1 %?
Also, I have a 13K ohm for the preamp power circuit.
Will 1 watt zeners be OK? We should need .6 watts, I think.

You don't need 1% but they are very nice to have. Helps eliminate tolerance build-up oversights in my design.

I thought you showed me three 39k 2w resistors you were combining for 13k.

1 watt is fine for the 40v Zener string. Esp if you use two 20v 1-w Zeners in series = 2 watts total
Remember the entire 40v load is not more than 15ma. The 2 op-275s use 10ma... so that leave 5ma through the Zeners.
40 x .005 = 200 miliwatt
the other 400miliwats is used by the op-275s.

So the only time you'd see 600mw would be if the op-275s were disconnected and the Zener had to handle the entire 15ma.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Sat 11, 2015 2:36 am 
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Pbpix wrote:
john8750 wrote:
Oh No
I got them confused. How will the 5902 work with those?
Or I could build him an amp with the 6V6 tubes.
I ordered them for the 5902 version.

The 5902 requires 4k... so 8k is not right.

Just call Edcor and Change your order by phone.
Problem is they don't have a 4k standard impedance in the XPP or GXPP line and the CXPP is 25 Watt (and 58 bucks). So, if you don't want to pay for a custom wind, you have to do the 1/2 impedance trick, 16 Ohm with an 8 Ohm speaker, which halves the frequency response for 35 Hz using the XPP, or 20 Hz using the GXPP.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Sat 11, 2015 3:56 am 
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Flipperhome wrote:
Pbpix wrote:
john8750 wrote:
Oh No
I got them confused. How will the 5902 work with those?
Or I could build him an amp with the 6V6 tubes.
I ordered them for the 5902 version.

The 5902 requires 4k... so 8k is not right.

Just call Edcor and Change your order by phone.
Problem is they don't have a 4k standard impedance in the XPP or GXPP line and the CXPP is 25 Watt (and 58 bucks). So, if you don't want to pay for a custom wind, you have to do the 1/2 impedance trick, 16 Ohm with an 8 Ohm speaker, which halves the frequency response for 35 Hz using the XPP, or 20 Hz using the GXPP.

I think he's aware of that because he's NOW doing that 1/2 impedance trick.
I believe he had been intendending to buy the $27.00, GXPP10-16-8k to use w/8 ohm speakers to get 4k.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Sat 11, 2015 4:35 am 
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Pbpix wrote:
Flipperhome wrote:
Pbpix wrote:
The 5902 requires 4k... so 8k is not right.

Just call Edcor and Change your order by phone.
Problem is they don't have a 4k standard impedance in the XPP or GXPP line and the CXPP is 25 Watt (and 58 bucks). So, if you don't want to pay for a custom wind, you have to do the 1/2 impedance trick, 16 Ohm with an 8 Ohm speaker, which halves the frequency response for 35 Hz using the XPP, or 20 Hz using the GXPP.

I think he's aware of that because he's NOW doing that 1/2 impedance trick.
I believe he had been intendending to buy the $27.00, GXPP10-16-8k to use w/8 ohm speakers to get 4k.
It doesn't hurt to be clear.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Sat 11, 2015 4:58 am 
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Flipperhome wrote:
Pbpix wrote:
I think he's aware of that because he's NOW doing that 1/2 impedance trick.
I believe he had been intendending to buy the $27.00, GXPP10-16-8k to use w/8 ohm speakers to get 4k.
It doesn't hurt to be clear.

I full concur.
That's how he accidentally ordered the wrong ones. Hope he was able to correct it.
Haven't heard from him today on the phone... so who knows?

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Sat 11, 2015 9:40 am 
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Pbpix wrote:
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.

Looks good. From that angle it sure looks longer than 12" .... maybe 12 feet? :lol:



Yeah, I get that a lot.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Sat 11, 2015 9:49 am 
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Pbpix wrote:
Flipperhome wrote:
Pbpix wrote:
I think he's aware of that because he's NOW doing that 1/2 impedance trick.
I believe he had been intendending to buy the $27.00, GXPP10-16-8k to use w/8 ohm speakers to get 4k.
It doesn't hurt to be clear.

I full concur.
That's how he accidentally ordered the wrong ones. Hope he was able to correct it.
Haven't heard from him today on the phone... so who knows?


I will call Edcor in the morning, Saturday and try to correct the order.
GXPP10-16-8K, right?
Was really busy at work tonight.
Will call soon.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Sat 11, 2015 9:59 am 
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Pbpix wrote:
john8750 wrote:
Peter
I am getting some 1%s for the 50 ohm resistors in the CCS.
Do you suggest any others be 1 %?
Also, I have a 13K ohm for the preamp power circuit.
Will 1 watt zeners be OK? We should need .6 watts, I think.

You don't need 1% but they are very nice to have. Helps eliminate tolerance build-up oversights in my design.

I thought you showed me three 39k 2w resistors you were combining for 13k.

1 watt is fine for the 40v Zener string. Esp if you use two 20v 1-w Zeners in series = 2 watts total
Remember the entire 40v load is not more than 15ma. The 2 op-275s use 10ma... so that leave 5ma through the Zeners.
40 x .005 = 200 miliwatt
the other 400miliwats is used by the op-275s.

So the only time you'd see 600mw would be if the op-275s were disconnected and the Zener had to handle the entire 15ma.



I am using 3-39Ks to get a 13K.
That's what I figured about the wattage of the zeners.
I don't understand how the two 1 watt zeners in series will handle 2 watts.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Sat 11, 2015 6:47 pm 
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john8750 wrote:
Pbpix wrote:
john8750 wrote:
Peter
I am getting some 1%s for the 50 ohm resistors in the CCS.
Do you suggest any others be 1 %?
Also, I have a 13K ohm for the preamp power circuit.
Will 1 watt zeners be OK? We should need .6 watts, I think.

You don't need 1% but they are very nice to have. Helps eliminate tolerance build-up oversights in my design.

I thought you showed me three 39k 2w resistors you were combining for 13k.

1 watt is fine for the 40v Zener string. Esp if you use two 20v 1-w Zeners in series = 2 watts total
Remember the entire 40v load is not more than 15ma. The 2 op-275s use 10ma... so that leave 5ma through the Zeners.
40 x .005 = 200 miliwatt
the other 400miliwats is used by the op-275s.

So the only time you'd see 600mw would be if the op-275s were disconnected and the Zener had to handle the entire 15ma.



I am using 3-39Ks to get a 13K.
That's what I figured about the wattage of the zeners.
I don't understand how the two 1 watt zeners in series will handle 2 watts.

Zeneres in series are similar to resistors in series.
Each zener has its own separate voltage drop so the wattage is divided across them
If a 40V Zener passes 5ma ...
40 x .005a = .2 watts

But two 20v Zeners in series share that load.
each Zener:
20V x .005 = .1 watts

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Sun 12, 2015 12:59 am 
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I see now how each zener works. Thanks. I knew you could explain it.
I called Edcor this morning, left a detailed message about changing my order. I guess they are closed on the weekends. I will call again on Monday.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Sun 12, 2015 7:08 am 
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Tonight I was double checking values and measuring voltages etc in the power supply.
I felt that C1 was a little warm ( 47uf @250v)
so I tried increasing the voltage rating and put in a 47uf @450v .... but that one too seemed to get a little warm.
This puzzled me.

I tried a few different styles and brands of 47uf @450v .... and I did find a couple that do not get warm at all.
1.) axial type 40uf @450v .... ran cool
2.) radial but physically larger than the "warm" one... and that runs cool too.

So maybe the warm ones I had are just bad or a little leaky or poor quality.
So I suggest you keep a good eye on that C1 cap. ( it actually should be fine @ 250v)
But just to be safe... feel it to see if it stays COOL after a while of use ...and just be sure to use a good-quality 47uf@450v just to be safe.
Image

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Apr Sun 12, 2015 11:14 am 
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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.


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