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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 5:10 am 
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john8750 wrote:
But we were supplying 38ma. Is that because of the separate filament transformer? I could leave it in if we need it.
Yes, it was because of the separate heater transformer. The heaters take a whopping 450 mA but, when we took that out, it freed that amount of current draw on the main B+ transformer, which is what we used for the 'extra' solid state stuff and there was enough left over for the increase in idle current from 25 mA to 35 mA. Put the 450 mA heaters back on the main B+ transformer and all that goes away again.

If you keep the heater transformer that would, again, free it up to use the increased idle current, with some to spare now that you're doing all the 'preamps' separate.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 5:28 am 
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Pbpix wrote:
4 tubes at idle of 30ma is 120ma B+.
The HV print is showing only 100ma on B+.


Btw
As per my bench measurements the opa604 @24v Vcc produces a max output of 35v peak to peak

The op275 @ 20v Vcc produces 30v peak to peak drive signal
and at 21v Vcc produces 32v peak to peak drive signal.

How much pp drive volts does it require to drive the 6V6 fully?
The print was originally set for the 25 mA. Sims show it could handle 30 mA, though.

You can figure out the needed peak to peak yourself. At 25 mA you say the cathode are at 20V. That's 40 V peak to peak (for each tube), not counting any overdrive. At 38 mA John says the voltage was 18 V, so that's 36 V peak to peak. Neither opamp will fully drive either idle current setting but the OPA604 comes closer than the OP275.

That, btw, is why I suggested the 6BQ5/6GK6 or, even better, the 6HB6. They have a significantly lower grid voltage that either opamp could easily drive. The 6BQ5/6GK6 needs 14V, or 28 V peak to peak, and the 6HB6 is almost half that.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 5:33 am 
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john8750 wrote:
Yes, I had the amp kinda working. Didn't feel the satisfaction though. And it was a real mess after troubleshooting all the problems. And I have time to do it again if it will be better. So, why not.
If I go with the opa604, 38ma CCS, and 310v 150ma for the B+, will the amp perform better?
My old 6V6 rocks out very nicely the way it is with op275, 25ma CCS, 290v 100ma B+.
Probably a good idea if it was unwieldy.

The amp should put out a bit more power with the OP604, how much I can't say. Of course, it would do a lot more if you didn't use the UL taps. And, just to be complete, even more if you used the 6BQ5/6GK6 or 6HB6 (like on Prince John) instead of the 6V6.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 6:16 am 
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Flipperhome wrote:
john8750 wrote:
Yes, I had the amp kinda working. Didn't feel the satisfaction though. And it was a real mess after troubleshooting all the problems. And I have time to do it again if it will be better. So, why not.
If I go with the opa604, 38ma CCS, and 310v 150ma for the B+, will the amp perform better?
My old 6V6 rocks out very nicely the way it is with op275, 25ma CCS, 290v 100ma B+.
Probably a good idea if it was unwieldy.

The amp should put out a bit more power with the OP604, how much I can't say. Of course, it would do a lot more if you didn't use the UL taps. And, just to be complete, even more if you used the 6BQ5/6GK6 or 6HB6 (like on Prince John) instead of the 6V6.




Yes, I can feel more power from the Prince John. I wanted to stay with the 6V6, its so simple with the IC preamp. The 6HB6 would be a good option. But already started with 6V6 tubes.
Without the UL connected, would that still sound good?
What about with no NFB connection?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 6:55 am 
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john8750 wrote:
Flipperhome wrote:
john8750 wrote:
Yes, I had the amp kinda working. Didn't feel the satisfaction though. And it was a real mess after troubleshooting all the problems. And I have time to do it again if it will be better. So, why not.
If I go with the opa604, 38ma CCS, and 310v 150ma for the B+, will the amp perform better?
My old 6V6 rocks out very nicely the way it is with op275, 25ma CCS, 290v 100ma B+.
Probably a good idea if it was unwieldy.

The amp should put out a bit more power with the OP604, how much I can't say. Of course, it would do a lot more if you didn't use the UL taps. And, just to be complete, even more if you used the 6BQ5/6GK6 or 6HB6 (like on Prince John) instead of the 6V6.
Yes, I can feel more power from the Prince John. I wanted to stay with the 6V6, its so simple with the IC preamp. The 6HB6 would be a good option. But already started with 6V6 tubes.
Without the UL connected, would that still sound good?
What about with no NFB connection?
There's nothing 'simpler' about the 6V6 vs the 6BQ5/6GK6 or 6HB6 or vice versa. They're all simply power pentodes, just in different sockets. The 6BQ5/6GK6 are simply newer than the 6V6, so they have better gm, and the 6HB6 is newer still. I was suggesting using the same opamp circuit with them.

There's no question you need feedback. It's just a matter of where you put it: half global and half UL, with less power, or all global with full power.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 7:16 am 
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Thanks Flip. I already have the octal sockets installed. If I was to build a new chassis I would use a different tube. Could the same CCS be used?
If we don't use the UL taps, where would the second screen attach? I guess to B+?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 7:50 am 
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john8750 wrote:
Thanks Flip. I already have the octal sockets installed. If I was to build a new chassis I would use a different tube. Could the same CCS be used?
If we don't use the UL taps, where would the second screen attach? I guess to B+?
Yes, the screens go to B+, usually. It depends on the B+ supply, meaning some amps take B+ from the first filter and screens after the second filter. That way they get 'max voltage' for the plate and the screens are filtered more to reduce hum. In your amp we're taking everything from 'well filtered' B+ (the third filter). In any case, the screens would go to what we currently have labeled B+. The PLATE (transformer CT) would then go to either B+ OR it could be connected to the second filter (one back from B+) or (maybe) even the first filter. The idea of the different connection points is to make up for transformer DC resistance (voltage) loss (due to idle current through it). I.e. the plate goes through the transformer but the screens do not. But with the cap (huge) and resistor (small) values we're using have so little drop from one filter to the next that it doesn't really much matter.

The same CCS can be used and, in fact, it's easier on it because the voltage is less (less chance of overvolting it in case 'something goes wrong'). Idle current is slightly higher at 40 mA (note, that's screen and plate) because the 6BQ5 does 17 Watt vs 14 Watt for the 6V6 (textbook non-UL values).

Btw, the chance of 'overvolting' in case of 'something goes wrong' is one reason why I used the 300 V MJE340 and put them on a heatsink in my Stealth amp.

Attachment:
Assembled Stealth - Bottom Angle 800.jpg
Assembled Stealth - Bottom Angle 800.jpg [ 68.73 KiB | Viewed 503 times ]


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Wed 07, 2018 12:21 am 
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I have decided to build the original amp. I could go crazy with improvements. :(
I thank you guys for all the work you do on this.
Here is the original schematic. I re-routed the UL circuit. Is this correct?
Will get this amp working, then add the other stuff, thanks Flip for that suggestion.
I hope that 100va PT can handle this, plus. :wink:
Attachment:
build.png
build.png [ 247.03 KiB | Viewed 493 times ]

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Wed 07, 2018 12:56 am 
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john8750 wrote:
I have decided to build the original amp. I could go crazy with improvements. :(
I thank you guys for all the work you do on this.
Here is the original schematic. I re-routed the UL circuit. Is this correct?
Will get this amp working, then add the other stuff, thanks Flip for that suggestion.
I hope that 100va PT can handle this, plus. :wink:
Attachment:
build.png

Yes... you can tie off the UL taps and hook the SGs to B+

However, I'm not so sure that you'll actually 'hear' the extra power vs whatever distortion-free added quality UL provides.
Ref:
Advantages of UL:
https://en.wikipedia.org/wiki/Ultra-linear

"Advantages
By judicious choice of the screen-grid percentage-tap, the benefits of both triode and pentode vacuum-tubes can be realised. Over a very narrow range of percentage-tapping, distortion is found to fall to an unusually low value—sometimes less than for either triode or pentode operation[2]—while power efficiency is only slightly reduced compared with full pentode operation. The optimum percentage-tap to achieve ultra-linear operation depends mainly on the type of valve used; a commonly seen percentage is 43% (of the number of transformer primary turns on the plate-circuit) which applies to the KT88, although many other valve types have optimum values close to this. A value of 20% was recommended for 6V6GTs. Mullard circuits such as the 5-20 also used 20% distributed loading (but did not achieve ultra-linear operation), while LEAK amplifiers used 50%."

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Wed 07, 2018 1:03 am 
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john8750 wrote:
I have decided to build the original amp. I could go crazy with improvements. :(
I thank you guys for all the work you do on this.
Here is the original schematic. I re-routed the UL circuit. Is this correct?
Will get this amp working, then add the other stuff, thanks Flip for that suggestion.
I hope that 100va PT can handle this, plus. :wink:
Attachment:
build.png
Yep, that's how you do it without UL. Note that, even though the feedback resistor hasn't changed, there'll be more global feedback due to the increased gain from not using UL, so the 'combined' feedback is the same with or without UL.

Btw, as you can see, it's a trivial matter to reverse it and use UL since it's simply a matter of putting the screens on B+ or the OPT UL taps.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Wed 07, 2018 2:04 am 
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Yes, I can change the UL taps very easily.
Here is my progress for today. Lookin good.
The PT output unloaded-144.2vac.
Attachment:
20180206_161719.jpg
20180206_161719.jpg [ 137.99 KiB | Viewed 488 times ]

Attachment:
20180206_165139.jpg
20180206_165139.jpg [ 168.02 KiB | Viewed 488 times ]

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Wed 07, 2018 4:24 am 
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John:
Here's an easy efficient and compact way to build the power supply
Use copper clad fiberglass boards and solder terminal strips to the copper at the end terminal mounting point tabs.

Then connect the system grounds to that copper board and/or to the end lugs of the terminal strips.

HERE's the beauty part:
... those large fat caps can lay sideways and their lugs fit perfectly into the top lugs. So the cap grounds can go right into the now, soldered & grounded lug on the end of the strip.
And... any smaller e-caps can also lay down and their leads will also fit nicely into the bottom holes of these terminal lugs.... leaving the upper lug for more parts at that connection.

Then build the remaining components to the other terminals remaining on the strip. Add more strips as needed.

It makes for a beautiful and solid ground plane; and everything stays on that one solid assembly.

The entire board fits right into the bottom of a wood chassis box like that one you are using and you can solder small "L" brackets to the edge of the board and then screw the upper part of the "L" bracket to the side walls of the box.
Image

No glue needed anywhere.

Remember...You saw it here first... :-)

Attachment:
terminal strip and caps.jpg
terminal strip and caps.jpg [ 74.96 KiB | Viewed 483 times ]

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Wed 07, 2018 6:47 am 
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Very cool idea Peter. I will be planning the PS first. That includes the B+, filaments, and 20volt. I need to build it all together in the space I have. I plan on terminal strips. Kinda like your idea, but no room for the copper clad. Need to stand the caps upright to make enough room for everything.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Wed 07, 2018 7:03 am 
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john8750 wrote:
Very cool idea Peter. I will be planning the PS first. That includes the B+, filaments, and 20volt. I need to build it all together in the space I have. I plan on terminal strips. Kinda like your idea, but no room for the copper clad. Need to stand the caps upright to make enough room for everything.

My entire HV doubler supply fits on one strip like this with the caps laying down.

The supply for the opamps on another strip close by.

The copper board can be cut to fit in the available space. This one shown is 3x5 I think

On mine I also soldered a long vertical stub on the copper board bottom and screwed nuts on it, then placed a 2nd copper board above it screwed on the same post, for shielding both heat or noise.

Image

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Thu 08, 2018 7:34 pm 
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You sure do some inspiring work Peter.
I have all power supply circuits installed and operating. At least, I did use that 8pin terminal strip you showed.
Attachment:
20180207_181405.jpg
20180207_181405.jpg [ 145.92 KiB | Viewed 458 times ]

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Thu 08, 2018 9:50 pm 
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Looks a lot less cluttered now.
How did you secure the terminal strip?

Where will the opamp board go? ... near that square hole?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Thu 08, 2018 10:12 pm 
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Pbpix wrote:
Looks a lot less cluttered now.
How did you secure the terminal strip?

Where will the opamp board go? ... near that square hole?



Correct Peter. I am building the amp and CCS on one small board. I have plenty of room for the tone board, If I decide to put it in this box. New pots are on the way. So will get the amp working first. Give me an Itodaso, go ahead. :lol:

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Thu 08, 2018 11:02 pm 
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Pbpix wrote:
Looks a lot less cluttered now.
How did you secure the terminal strip?

Where will the opamp board go? ... near that square hole?


I glue everything down with super glue. Takes about an hour to get a very strong bond. 24 hours and it aint movin. It will glue almost anything, except a broken heart.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Fri 09, 2018 3:14 am 
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My work for today. Really enjoying the thing, so far.
Attachment:
20180208_175218.jpg
20180208_175218.jpg [ 182.52 KiB | Viewed 441 times ]

Attachment:
20180208_175233.jpg
20180208_175233.jpg [ 134.18 KiB | Viewed 441 times ]

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Fri 09, 2018 6:45 am 
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I just noticed that one of my Edcors is missing the sticker. Strange.
Also have two questions.
On the very first 5902 schematic there are 2.2uf ecaps, and some .1 caps in the opamp circuit. We don't need them anymore?
And, in the 20volt supply, I used a 470uf instead of a 220. I am guessing that will be ok.
I should have the amp section working by Sunday. Its going together quick.

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