Years ago, I built Sheldon Stokes (SDS labs) version. http://www.quadesl.com/pdf/el84sch.pdf I have been using it as my main living room amp ever since. One plus, is switchable FB level. Although I've done it, better not to switch under power. And listening without FB can be a little addictive, but you need to be careful, without FB, ultrasonic ringing can occur. Even though you might not hear it, it's dissipating power. His original stated goal on the amp was to drive Quad ESL speakers. I also made mine customizeable by either using seperate bias resistors for each channel, that could be jumpered together, as well as bypass caps that could be taken out of the circuit. Good luck, getting your feet wet with a 1st amp, is very rewarding.
Designs, like "El Cheapo" and the ST-35, which place the O/P transformer insdide a NFB loop are vulnerable to core saturation induced by the low frequency error correction signal. The parts values for the I/P high pass pole given in the schematic are consistent with the very limited capabilities of the guitar amp "iron" specified. Use better O/P "iron" and you can move the "corner" freq. of the high pass filter below the audio band. However, even the excellent Z565 is not immune to core saturation. With Z565s, make the I/P cap. 68 nF. and the 'T7 grid to ground resistance 150 KOhms. F3 for that combination is 15.6 Hz. That's as close to having your cake and eating it too as you'll get.
EVERY design incorporates compromises. Loop NFB improves linearity at the frequency extremes and improves the damping factor. Those benefits have associated costs. TANSTAAFL always with us.
Having had a second look your arrangement is definately the most cost effective, I had read the wrong line in a catalog and was comparing transformers of a much lower current rating, and finding all in one solutions, looking at the proper rating your way is definately the best way to go off the shelf. I never doubted your systems effectiveness, I just always try to think up alternatives.
As for the rectifier tube, can you recommend a suitable 6.3v substitute? if I end up going the 6v6 el cheapo route it would be the only 12.6v tube. Otherwise I may just go with a delay circuit.
Would the Hammond 186F120/187F120 be suitable for the PT? 115V primary, 120V secondary, 850ma, and $25.
As for the rectifier tube, can you recommend a suitable 6.3v substitute? if I end up going the 6v6 el cheapo route it would be the only 12.6v tube. Otherwise I may just go with a delay circuit.
Would the Hammond 186F120/187F120 be suitable for the PT? 115V primary, 120V secondary, 850ma, and $25.
Excellent Eli, thank you so much for your help. It is very helpful for my understanding that you are explaining the circuit, and the differences between it and what I am familiar with. It seems like a very well thought out amp, and that it may meet my listening needs quite well. I'm sure I'll come up with more questions, but I think that about does it for the moment. I wish I could buy you a beer!
Oh, actually one last thing, any thoughts on current production 6v6 offerings? The Tung Sol seems to be well regarded, however a lot of what I've read seems to be aimed at guitar amps though. JJ's version doesn't seem too popular for guitar (however some reviews complained about it being too clear so maybe it would be good for hifi?), while the TAD offering is poplar among musicians.
As for the 12AT7, Jan Phillips seem like they would be a good option, really reasonably priced, any tube rolling suggestions on that?
Oh, actually one last thing, any thoughts on current production 6v6 offerings? The Tung Sol seems to be well regarded, however a lot of what I've read seems to be aimed at guitar amps though. JJ's version doesn't seem too popular for guitar (however some reviews complained about it being too clear so maybe it would be good for hifi?), while the TAD offering is poplar among musicians.
As for the 12AT7, Jan Phillips seem like they would be a good option, really reasonably priced, any tube rolling suggestions on that?
If you want to investigate the Baby Huey then the schematics to look at are post #602 (amp) and #603 (power supply) here. Ignore post #604 schematic variation, it is something which eventually was abandonned.
http://www.diyaudio.com/forums/tubes-valves/72536-el84-amp-baby-huey-61.html
Since self recommendation is really no recommendation at all, I simply offer it for consideration.
I use a 6V6 + 6SL7 version of this amp everyday and I have no hesitation in saying it is the best amp I have ever heard, which is to say it suits my speakers and musical taste better than anything else I've tried, either commercial or "stuff" I've built myself.
There are some really good 1980's Russian Military 6V6 around, until I run out, I'm using 1950s 6V6G in the old "coke bottle" shape. Pic below.
I STRONGLY advise against trying to build the amp into a chassis this small. Final result was nice but not worth all the agrevation and cuss words along the way.
Cheers,
Ian
http://www.diyaudio.com/forums/tubes-valves/72536-el84-amp-baby-huey-61.html
Since self recommendation is really no recommendation at all, I simply offer it for consideration.
I use a 6V6 + 6SL7 version of this amp everyday and I have no hesitation in saying it is the best amp I have ever heard, which is to say it suits my speakers and musical taste better than anything else I've tried, either commercial or "stuff" I've built myself.
There are some really good 1980's Russian Military 6V6 around, until I run out, I'm using 1950s 6V6G in the old "coke bottle" shape. Pic below.
I STRONGLY advise against trying to build the amp into a chassis this small. Final result was nice but not worth all the agrevation and cuss words along the way.
Cheers,
Ian
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I haven't heard an El-Cheapo so can't compare but have respect for Eli's demonstrated knowledge and experience so assume it is a good amp.
The things I really like about the Baby Huey (the schematic link above version) is its PRATT (Pace, Rhythm and attack), It makes a lot of amps sound "slow" in comparison. Stereo imaging is also superior, you don't hear 2 speakers, just a 3 D sound source with individual instruments easily discerned in that image. I've tried many tube and solid state amps over the years, both commercial and home designed and built, this amp is the best I've ever heard, or perhaps I should say it best suits my speakers and music preferences.
Does it have weakness? - Well YES, It is only 10 Watts per channel, with my 95dB/W/m speakers that is more than adequate for more volume than I will ever need, but it may struggle with inefficient speakers.
Cheers,
Ian
The things I really like about the Baby Huey (the schematic link above version) is its PRATT (Pace, Rhythm and attack), It makes a lot of amps sound "slow" in comparison. Stereo imaging is also superior, you don't hear 2 speakers, just a 3 D sound source with individual instruments easily discerned in that image. I've tried many tube and solid state amps over the years, both commercial and home designed and built, this amp is the best I've ever heard, or perhaps I should say it best suits my speakers and music preferences.
Does it have weakness? - Well YES, It is only 10 Watts per channel, with my 95dB/W/m speakers that is more than adequate for more volume than I will ever need, but it may struggle with inefficient speakers.
Cheers,
Ian
Ian makes a VERY important point. Amps and speakers must be viewed as a organic whole. Otherwise quite good individual items can, and do, combine badly.
SY's "Red Light District", Ian's "Baby Huey", and "El Cheapo" are all competent. Any of the 3 will make you smile. Don't ask the "parents"; ask folks who've built the projects. Other competent setups are "out there" too. For instance, there's nothing wrong with the style of topology in the ST-35. Implementation details drag the ST-35 down. Little ingenuity is needed to raise the ST-35 from OK to good. More than 1 person has stated that the Z565 is the best of Dyna's O/P "iron" offerings. No "weak link" there!
SY's "Red Light District", Ian's "Baby Huey", and "El Cheapo" are all competent. Any of the 3 will make you smile. Don't ask the "parents"; ask folks who've built the projects. Other competent setups are "out there" too. For instance, there's nothing wrong with the style of topology in the ST-35. Implementation details drag the ST-35 down. Little ingenuity is needed to raise the ST-35 from OK to good. More than 1 person has stated that the Z565 is the best of Dyna's O/P "iron" offerings. No "weak link" there!
Thanks for everyone's input!
I think I'm going to go with a 6v6 El Cheapo, using the Z565 opts. I think it fits better for what I want out of this project. That said, I will probably try the Baby Huey circuit at some point as I like to experiment, as building and learning is at least half the fun for these kind of projects for me.
I'd like to order parts from as few vendors as possible, usually I use Digikey, as for shipping to the great white north Mouser gets a little expensive. Unfortunately Digikey is out of the N-68X until August, I'll have to look at some alternatives.
One Questions, as I don't need the 6.3v side of the allied transformer, is there any reason I can't run the B+ and B- circuits parallel of a slightly higher rated transformer?
Direct alternatives I'm seeing are:
VPS230-570 Triad Magnetics | 237-1272-ND | DigiKey
Although regulation is worse than the triad isolation transformers.
VPS230-760 Triad Magnetics | 237-1273-ND | DigiKey
Same as above but higher rating, might help with regulation.
186F120 Hammond Manufacturing | 186F120-ND | DigiKey
No regulation or other specs.
VPT230-430 Triad Magnetics | 237-1338-ND | DigiKey
Spendy, but I do like toroids, and it fits within the budget I had set aside for this project. Kinda defies the "el cheapo" ethos.
Thanks
-Chris
I think I'm going to go with a 6v6 El Cheapo, using the Z565 opts. I think it fits better for what I want out of this project. That said, I will probably try the Baby Huey circuit at some point as I like to experiment, as building and learning is at least half the fun for these kind of projects for me.
I'd like to order parts from as few vendors as possible, usually I use Digikey, as for shipping to the great white north Mouser gets a little expensive. Unfortunately Digikey is out of the N-68X until August, I'll have to look at some alternatives.
One Questions, as I don't need the 6.3v side of the allied transformer, is there any reason I can't run the B+ and B- circuits parallel of a slightly higher rated transformer?
Direct alternatives I'm seeing are:
VPS230-570 Triad Magnetics | 237-1272-ND | DigiKey
Although regulation is worse than the triad isolation transformers.
VPS230-760 Triad Magnetics | 237-1273-ND | DigiKey
Same as above but higher rating, might help with regulation.
186F120 Hammond Manufacturing | 186F120-ND | DigiKey
No regulation or other specs.
VPT230-430 Triad Magnetics | 237-1338-ND | DigiKey
Spendy, but I do like toroids, and it fits within the budget I had set aside for this project. Kinda defies the "el cheapo" ethos.
Thanks
-Chris
Jim Mcshane who sells tubes that he carefully checks , also has a kit of parts if you didn't see that on his site which may help.
http://www.mcshanedesign.net/elcheapo.htm
http://www.mcshanedesign.net/elcheapo.htm
Are these the Russian Military 6v6 equivalent that was mentioned?
? 6P1P 6AQ5 6V6 EL90 Tubes new NOS Qty 1pcs | eBay
? 6P1P 6AQ5 6V6 EL90 Tubes new NOS Qty 1pcs | eBay
As far as I can tell, the Russian 6P1P is equivalent to a 6AQ5 (small sized 6V6 equivalent) in a 9-pin mini bottle.
You could conceivably try your amp with 6P1P and with a minimum of changes try EL84 instead. Only for those who just have to experiment. But that could be fun and instructive. You may decide you like one tube more than the other.
--
You wouldn't happen to have done the number crunching on what changes would have to be made to use EFB with a 6v6 el cheapo would you?
On the subject of tube "rolling". Build with Octal sockets for 6V6s. Make adapters out of Octal plugs and appropriate other socket types; then: 7C5, 6AQ5, 6CM6, and 6П11П (6p1p) tubes can be tried.
IIRC, Allied takes good care of Canadian customers, just like DigiKey does. A complete set of power magnetics can be sourced from Allied. The following Allied stock #s are what's needed: 2X 70218526 (Triad N-68X), 70218219 (Triad VPL24-2000), 70218145 (Triad C-24X), and 70009000 (Allied 6K27VF). Usually, I would suggest 70218140 (Triad VPS24-1800-B), not 70218219 (Triad VPL24-2000), but it's out of stock.
When Greinacher doubled, 1:1 isolation trafos come up a bit "short" in meeting the B+ rail voltage need. A winding of the 2X "12" VAC filament trafo is used to boost the B+ rail voltage. The uploaded graphic shows how it's done. The 2nd winding energizes the O/P tube and 12AL5 heaters. Wire the 6V6 heaters in series connected pairs. Mount ferrite beads on the wires of the winding used for heater power, as close to the VPL24-2000 as is possible.
In current production, SY likes the JJ 12AT7. IMO, Philips JAN 12AT7WCs are best left to FM tuner front ends and guitar amp vibrato service. In spite of the high cost, NOS Mullard CV4024s get my nod. The famous Mullard midrange accent will blend well with "reissue" TungSol 6V6 "finals".
IIRC, Allied takes good care of Canadian customers, just like DigiKey does. A complete set of power magnetics can be sourced from Allied. The following Allied stock #s are what's needed: 2X 70218526 (Triad N-68X), 70218219 (Triad VPL24-2000), 70218145 (Triad C-24X), and 70009000 (Allied 6K27VF). Usually, I would suggest 70218140 (Triad VPS24-1800-B), not 70218219 (Triad VPL24-2000), but it's out of stock.
When Greinacher doubled, 1:1 isolation trafos come up a bit "short" in meeting the B+ rail voltage need. A winding of the 2X "12" VAC filament trafo is used to boost the B+ rail voltage. The uploaded graphic shows how it's done. The 2nd winding energizes the O/P tube and 12AL5 heaters. Wire the 6V6 heaters in series connected pairs. Mount ferrite beads on the wires of the winding used for heater power, as close to the VPL24-2000 as is possible.
In current production, SY likes the JJ 12AT7. IMO, Philips JAN 12AT7WCs are best left to FM tuner front ends and guitar amp vibrato service. In spite of the high cost, NOS Mullard CV4024s get my nod. The famous Mullard midrange accent will blend well with "reissue" TungSol 6V6 "finals".
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You asked if those tubes ( ebay link ) are the Russian 6V6 equivalents I was mentioning?
No these are what I was referring to:
2 x 6V6GT / 6n6C REFLEKTOR MIL. POWER TUBES * NOS * MATCHED PAIR * | eBay
I've run some of these (from the very same bulk box) in Ultralinear at B+ of 350V, they sounded lovely.
Cheers,
Ian
No these are what I was referring to:
2 x 6V6GT / 6n6C REFLEKTOR MIL. POWER TUBES * NOS * MATCHED PAIR * | eBay
I've run some of these (from the very same bulk box) in Ultralinear at B+ of 350V, they sounded lovely.
Cheers,
Ian
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