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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Wed 14, 2016 10:44 pm 
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Location: pensacola fl
Hi folks. How about trying a different topology. I have done this with 6V6 and gotten similar results experiment with part values for tube you choose. The nice thing no d.c. in the load at all. Distortion in the 1 percent range without feedback and it drops from there to .2 percent or less. Here is a link to the sample diagram and some graphs on its performance.

http://audioman.dynip.com/6888tx/7695.pdf

The 7754 is the same but different heater voltage. The circuit works with many output tubes and the output transformer can be a push/pull type or single ended works either way.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Thu 15, 2016 2:09 am 
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john8750 wrote:
I like it Flip. Especially the very simple PS. Yes I realize the silicone aspect.
What about the hi-fi and THD value? Any ideas about what power transformer to use.
I would like the best OT's possible, Edcor?
I don't consider power supply diodes as 'polluting' the 'all tube' philosophy.

All the iron is Edcor (as the schematic says, Edcor OPT and PS). The OPT is a standard 8k plate to plate and can be either the XPP, GXPP, or CXPP series. If it were me I would probably use the GXPP, 40 Hz to 18 kHz. It's only a few dollars more than the XPP series, has end bells (looks good), and is the traditional 'tube' Hi-Fi frequency response, which is better than 'normal' speakers can do anyway. The power transformer is the Edcor XPWR195, as shown on the schematic.

Spice distortion comes out under .02% @ 1 Watt but that's with 'ideal' tubes and OPT so actual would, no doubt, be some (unknown) amount more. NFB would bring the GXPP up to the 'modern' (extended) 20 Hz to 20 kHz. As stated, you could use the CXPP, which is natively 20 Hz to 20 kHz, but it costs 60% more for what I consider to be no audibly discernable benefit.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Thu 15, 2016 2:13 am 
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Audioman wrote:
Hi folks. How about trying a different topology. I have done this with 6V6 and gotten similar results experiment with part values for tube you choose. The nice thing no d.c. in the load at all. Distortion in the 1 percent range without feedback and it drops from there to .2 percent or less. Here is a link to the sample diagram and some graphs on its performance.

http://audioman.dynip.com/6888tx/7695.pdf

The 7754 is the same but different heater voltage. The circuit works with many output tubes and the output transformer can be a push/pull type or single ended works either way.

Where did you find the 250 Ohm to 800 Ohm speakers?


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Thu 15, 2016 2:33 am 
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I used output transformer but i used other tubes and standard output transformers work well. Leave the output cap in the circuit.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Thu 15, 2016 2:46 am 
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Audioman wrote:
I used output transformer but i used other tubes and standard output transformers work well. Leave the output cap in the circuit.

"other tubes" ?... which?
"standard OT"? which?

So how does what you posted resemble the final?
And what is that final schematic you actually ended up with?

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Thu 15, 2016 4:04 am 
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Audioman wrote:
I used output transformer but i used other tubes and standard output transformers work well. Leave the output cap in the circuit.
I see. Well, with an OPT needed anyway and twice the tubes and B+ you can see why it never really caught on.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Fri 16, 2016 12:33 am 
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I will use the more expensive OT's. I have them on my 6V6 amp now. It has speaker taps for 4-8-16 ohm.
My Genesis speakers really get down low, 19-23KHZ. I mean bass not always heard and felt. That's why I
prefer to refurbish vintage equipment. Like the dual 1019, fabulous. And the 5902 amp, thanks to Peter's
help. Those little tubes sound remarkable.
The power transformer should be from Edcor also to match. Flip, would that power transformer be ok for
a stereo version, and some extra for a tone amp?
You must understand, you guys are very technical and I use only my ears for testing. So I must start out
with the best I can get. But, still understand and agree with you Flip, the fun with designing an economical
circuit. Man, you all have done just great for me. I can now kinda understand and follow the signal through
an amplifier schematic.
I found a tone amp, one 12AX7 per channel. Plate voltage is 150. Didn't have the load on the schematic.
I would like a separate preamp. I need the tone amp, RIAA amp, and maybe an additional preamp stage.
No problem to use a separate PT and build the two separate units.
Thanks Audioman. Looks like a fun tube to work with.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Fri 16, 2016 1:48 am 
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Location: pensacola fl
howdy all. I did it with 6V6,6L6, and the lower voltage 6DG6 family. 50L6 works nicely and used same output transformer as that is what I had on hand. The B+ on that one was about 280 volts from a line full wave doubler and the whole thing was powered by a power transformer I salvaged that had a 117v and 2 6v windings. didn't run hot. I will estimate the output was about 6 watts. Wanted to try other higher output tubes but then yes the B+ would run high for example the 6L6 could have used over 600v but the most I gave it was around 450. This was in the mid 1970's when transformers were cheap and plentiful from old junked equipment.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Fri 16, 2016 2:35 am 
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That one I linked to in the data sheet is a good performer for its simplicity. It runs class A and has decent distortion levels without feedback. The circuit is used as an output in professional equipment at more modest line levels. Ampex used it in some of their recorders back in the day. They did it with dual triodes 6DJ8 and 12Au7 versions. Breadboard one up with lower voltage tubes like the data sheet shows but if you do not have those tubes try others you will be able to evaluate the circuit. Use the same output transformer you would use say on a 50L6 but with 2 of them in this circuit you can see how it works. The screen grid resistors for that tube would be in the 10K area and the cathode resistors the usual 150 ohm. hit it with 280 volts B+. Add feedback and the usual triode input stage for a nice amp. Not super power though. The 7695 has a higher gain and works better. A pair of 6CW5 lower voltage 6BQ5 could go in this one but I have not tried it.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Fri 16, 2016 3:53 am 
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john8750 wrote:
I will use the more expensive OT's. I have them on my 6V6 amp now. It has speaker taps for 4-8-16 ohm.
My Genesis speakers really get down low, 19-23KHZ. I mean bass not always heard and felt. That's why I
prefer to refurbish vintage equipment. Like the dual 1019, fabulous. And the 5902 amp, thanks to Peter's
help. Those little tubes sound remarkable.
The power transformer should be from Edcor also to match. Flip, would that power transformer be ok for
a stereo version, and some extra for a tone amp?
You must understand, you guys are very technical and I use only my ears for testing. So I must start out
with the best I can get. But, still understand and agree with you Flip, the fun with designing an economical
circuit. Man, you all have done just great for me. I can now kinda understand and follow the signal through
an amplifier schematic.
I found a tone amp, one 12AX7 per channel. Plate voltage is 150. Didn't have the load on the schematic.
I would like a separate preamp. I need the tone amp, RIAA amp, and maybe an additional preamp stage.
No problem to use a separate PT and build the two separate units.
Thanks Audioman. Looks like a fun tube to work with.

It was sized for a stereo amp, 175mA B+ and 4 A heater power. There's 20 mA 'spare' B+ (assuming all comes out as expected) but heater power for 4 6HB6 @ .76A plus two 6BR8 @ .45A comes to 3.94A so unless you can find (x2) 30 mA heater tubes... :wink: (the answer is no on adding more tubes, at least with that power transformer)

Sounds like what you want is something like a Dynaco PAS3 preamp. Schematic and manual here http://www.audioman.com/Dynaco/pas3/pas3.htm

Image

As you see, the 12AX7 was a typical phone preamp stage. You can also find various mods to improve them so you might want to investigate those before just copying the factory schematic.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Fri 16, 2016 5:33 am 
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Now that's cool Flip. Not enough time to read through right now. I noticed the weird pots on the schematic.

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If I did something right, I made a mistake.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Fri 16, 2016 7:40 am 
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john8750 wrote:
Now that's cool Flip. Not enough time to read through right now. I noticed the weird pots on the schematic.
The "weird pots" were common and are for 'loudness' compensation where the base and/or treble (depending on the design) are boosted to make up for the ears diminishing sensitivity at low volume. That's what the 'taps' are for so it's, in a sense, automatic (when switched in) with volume level.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Fri 16, 2016 5:34 pm 
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Had a chance to read some and sounds great. Is the 12X4, selenium stacks, those weird pots available?
Is that a voltage divider for the heaters, or not? I like the idea of separated tone controls, control freak me.
I will not need all those inputs, so can modify it to suite.
Thanks Flip.
Peter, the power supply wizard, see any PS short cuts?

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Last edited by john8750 on Sep Fri 16, 2016 10:42 pm, edited 1 time in total.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Fri 16, 2016 10:28 pm 
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Hi all. I forgot to add you can also use a dual powersuply off the same hv secondary if it is a centertapped one and eliminate the output cap it should work kind of solidstate style. That way not a very high B+.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Fri 16, 2016 10:49 pm 
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Peter
I like the Dynaco amp and preamp. A little pricey but looks like top of the line. And the best thing, vintage. Thank you.
First I need to complete the 5902 for the Zenith in my shop. It needs a separate preamp including the passive tone
circuit using the RS trannys, an input selector. The phono preamp will be in the phono base. Simple.
I will build a separate matching enclosure for this. Am working on the headphone amp for my com right now.

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If I did something right, I made a mistake.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Fri 16, 2016 11:04 pm 
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john8750 wrote:
Peter
I like the Dynaco amp and preamp. A little pricey but looks like top of the line. And the best thing, vintage. Thank you.
First I need to complete the 5902 for the Zenith in my shop. It needs a separate preamp including the passive tone
circuit using the RS trannys, an input selector. The phono preamp will be in the phono base. Simple.
I will build a separate matching enclosure for this. Am working on the headphone amp for my com right now.

The prices of used Dynaco ST70s varies depending on physical condition of course.
If you are happy doing the updating and clean-up work, then all you really care about is that the transformers are all good.
So you can shop Ebay until you find one that's right for how much work you are willing to do.
Remember those circuit boards have had some very cool improvements suggested by the hifi guys and so...it would be good to incorporate those changes.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sat 17, 2016 12:01 am 
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This looks good Peter. I am just learning, and wondering could we use NFB, and ultra linear to make an improvement.

http://www.instructables.com/id/Buildin ... /?ALLSTEPS

Don't like his power supply transformers.
I also like Flips Pauper. I must choose one of these, so I can accumulate parts, and
get Edcor to build the transformers.
Do you like the Dynaco kit preamps? I do....

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sat 17, 2016 12:32 am 
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Peter, you sent me this one, and I like it. Strange tone controls though. The bass can only boost, treble can only cut.
Looking through these schematics is a great way to learn.
http://www.grommesprecision.com/grommes ... review.PDF

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sat 17, 2016 4:43 am 
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john8750 wrote:
Had a chance to read some and sounds great. Is the 12X4, selenium stacks, those weird pots available?
Is that a voltage divider for the heaters, or not? I like the idea of separated tone controls, control freak me.
I will not need all those inputs, so can modify it to suite.
Thanks Flip.
Peter, the power supply wizard, see any PS short cuts?
The 12X4 is 3 bucks from ABCvacuumtubes. Can't get selenium rectifiers anymore, use modern diodes. Frankly, I'd use diodes for the 12X4 as well since I wouldn't go to the effort, and expense, of finding a "PAS3" transformer. Btw, you can find repro kits (which ain't cheap) for the PAS3 but they all invariably use a solid state power supply. See the various options here http://www.tubenirvana.net/pas3-main-page.html

That's not a divider on the tube heaters. They're DC, to cut hum, and that's just the ground reference.

The "weird pots" are almost unobtanium nowadays but modern amps don't do 'loudness' compensation anymore so just ignore that part of the schematic.

Btw, my 6BR8/6HB6 "Princely Pauper" is essentially a 'dollar days' version of the Dynaco ST-35 power section, although it's not exact. I didn't chose to employ the screen feedback but it could be implemented.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sat 17, 2016 5:29 am 
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Flipperhome wrote:
john8750 wrote:
Had a chance to read some and sounds great. Is the 12X4, selenium stacks, those weird pots available?
Is that a voltage divider for the heaters, or not? I like the idea of separated tone controls, control freak me.
I will not need all those inputs, so can modify it to suite.
Thanks Flip.
Peter, the power supply wizard, see any PS short cuts?
The 12X4 is 3 bucks from ABCvacuumtubes. Can't get selenium rectifiers anymore, use modern diodes. Frankly, I'd use diodes for the 12X4 as well since I wouldn't go to the effort, and expense, of finding a "PAS3" transformer. Btw, you can find repro kits (which ain't cheap) for the PAS3 but they all invariably use a solid state power supply. See the various options here http://www.tubenirvana.net/pas3-main-page.html

That's not a divider on the tube heaters. They're DC, to cut hum, and that's just the ground reference.

The "weird pots" are almost unobtanium nowadays but modern amps don't do 'loudness' compensation anymore so just ignore that part of the schematic.

Btw, my 6BR8/6HB6 "Princely Pauper" is essentially a 'dollar days' version of the Dynaco ST-35 power section, although it's not exact. I didn't chose to employ the screen feedback but it could be implemented.



Thanks for the info Flip. I don't mind diodes either. Just wanted the music to see nothing but tubes. Do you believe having ultra linear screens would make a big difference?

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