Greetings friends. I've found myself at the early stages of planning a DIY audio community and have been tasked with finding a suitable amplifier for a DIY kit to be assembled by newbies, and I am here to ask your advice.
I am looking for a PCB-based circuit for a power amplifier, an AB1 Push-Pull amp using EL34/6L6 output tubes and something other than those hard-to-find 7199 to drive em. I would prefer a cathode-biased circuit for simplicity, but will accept arguments for fixed bias design. Above all, I am looking for a DIY project with a high rate of success, so we can bring more people into the glorious world of Tubes.
Any ideas, projects, advice, or warnings welcome.
Thanks!
Will
I am looking for a PCB-based circuit for a power amplifier, an AB1 Push-Pull amp using EL34/6L6 output tubes and something other than those hard-to-find 7199 to drive em. I would prefer a cathode-biased circuit for simplicity, but will accept arguments for fixed bias design. Above all, I am looking for a DIY project with a high rate of success, so we can bring more people into the glorious world of Tubes.
Any ideas, projects, advice, or warnings welcome.
Thanks!
Will
Check out this amp on Pete Millett's site.
http://pmillett.com/push-pull_kt88_class_a_amp_with_universal_driver_pcb.htm
Pete's stuff is well designed and easy to build.
http://pmillett.com/push-pull_kt88_class_a_amp_with_universal_driver_pcb.htm
Pete's stuff is well designed and easy to build.
dubadub,
Often, a suitable amplifier or suitable amplifier kit can be found by defining the needs of the complete playback system.
Room Size
Far field or near field listening
Loudspeaker efficiency
Loudspeaker impedance and impedance variations versus frequency.
Music preferences; classical, jazz group, hard rock at ear splitting levels, chest vibrating pipe organ music, etc.
Signal sources, line level, or phono cartridge, etc. Integrated amp, power amp.
Up-front criteria often saves 10s of postings in a thread.
Often, a suitable amplifier or suitable amplifier kit can be found by defining the needs of the complete playback system.
Room Size
Far field or near field listening
Loudspeaker efficiency
Loudspeaker impedance and impedance variations versus frequency.
Music preferences; classical, jazz group, hard rock at ear splitting levels, chest vibrating pipe organ music, etc.
Signal sources, line level, or phono cartridge, etc. Integrated amp, power amp.
Up-front criteria often saves 10s of postings in a thread.
Hey Mr Summer, thanks for the reply.
It's been said that "A camel is a horse designed by a committee," and I feel this project may come to embody that sentiment.
This is an early effort for a group seeking to offer lessons to build a complete system. That means everything is middle of the road, attempting to please everyone, and hopefully not mediocre. It also means there may be a lack of knowledge among those calling the specs, which can get things pointlessly expensive in a hurry.
I'd say a small-ish room, typical of a NYC apartment, powering speakers of a middling output and sensitivity. Sources include DACs, ipods, and phono preamps, among others. Hard to imagine loud organ music, but better to expect every conceivable music genre.
The more I think it over, a P-P pair of EL34 would supply wayyy more power than required here. EL84 in triode pushes Overnight Sensations just fine in this scenario. Maybe EL84 PP would be more suitable, but so would a single EL34 SE. But then we're buying expensive OTs.
I dig the simplicity of a point to point SE build, especially if I'm overseeing a group of people making them. I also like the higher probably of success that would come from a PCB-based project. Want these things to work with a minimum of troubleshooting. I've got a good 4-5 weeks of travelling coming up, so I won't be buying anything for a while. Time to think.
Appreciate the input
Will
It's been said that "A camel is a horse designed by a committee," and I feel this project may come to embody that sentiment.
This is an early effort for a group seeking to offer lessons to build a complete system. That means everything is middle of the road, attempting to please everyone, and hopefully not mediocre. It also means there may be a lack of knowledge among those calling the specs, which can get things pointlessly expensive in a hurry.
I'd say a small-ish room, typical of a NYC apartment, powering speakers of a middling output and sensitivity. Sources include DACs, ipods, and phono preamps, among others. Hard to imagine loud organ music, but better to expect every conceivable music genre.
The more I think it over, a P-P pair of EL34 would supply wayyy more power than required here. EL84 in triode pushes Overnight Sensations just fine in this scenario. Maybe EL84 PP would be more suitable, but so would a single EL34 SE. But then we're buying expensive OTs.
I dig the simplicity of a point to point SE build, especially if I'm overseeing a group of people making them. I also like the higher probably of success that would come from a PCB-based project. Want these things to work with a minimum of troubleshooting. I've got a good 4-5 weeks of travelling coming up, so I won't be buying anything for a while. Time to think.
Appreciate the input
Will
If you're interested, I've just finished commissioning a PCB for a modified version of the classic American Williamson design, the "Musician's Amplifier" by Sarser and Sprinkle.
https://oestex.com/tubes/mus_amp .pdf
The board is designed for octal-based tubes like the 5881, 6L6GC or KT66, and will work for the triode version or for the revised "ultralinear" version at 20wpc:
https://dalmura.com.au/static/Gilding the Lily - July 1952 - Audio.pdf
Excellent copies of the superb Peerless S-265-Q are available from Heyboer, along with a quality power transformer designed especially for this circuit. I have tweaked the circuit for stability and best performance. The PCB contains everything except the transformers, choke, rectifier and first capacitor. Only one choke is required. Filament leads must also be hand wired.
The Williamson is a wonderful amplifier for natural tone and utterly fatigue-less listening. If you're interested, let me know. All the parts can be ordered directly by your members, I am not a vendor. ;-) I had this developed for my personal use.
I can offer this: a very simple 100x100mm board for push pull EL84/6BQ5, using ECC82/12AU7 as a phase splitter. It a follow-on revision of previous boards using the same mechanicals. Its very straightforward, can be used in UL/Pentode/Triode. Sockets are mirrored as to facilitate mounting the board under a top plate. Holes in the centers of the PCB allow you to use the PCB to drill out the center holes. Sockets are the excelent Belton VT9-PT
Hard to go wrong with this circuit. I can provide PSU boards as well.
No feedback, nothing to go wrong or oscillate. will produce 8-10W of power, more than enough to annoy the neighbours. I will get some sockets in the mail today, i will build a board and post pictures.
Cheers,
V4LVE
Hard to go wrong with this circuit. I can provide PSU boards as well.
No feedback, nothing to go wrong or oscillate. will produce 8-10W of power, more than enough to annoy the neighbours. I will get some sockets in the mail today, i will build a board and post pictures.
Cheers,
V4LVE
Attachments
Generalizations:
A medium performance push pull output transformer will be less expensive, smaller, and lighter; versus a medium performance single ended output transformer with the same wattage rating. Stereo . . . 2 output transformers.
I personally like tube sockets, especially for output tubes, to be mounted to the amplifier chassis; and not mounted to a PCB.
Point to point is easier to repair, and easier to modify if necessary.
12 clean Watts from a single ended amplifier may be harder to get, versus 12 clean Watts from a push pull amplifier.
There are lots of proven circuits out there.
6L6GC, EL34, 5881 can make a sweet amplifier.
7199 are not needed to drive them, there are other options.
An 8 pin Octal is easier to wire than 9 pin Noval.
EL84 is very good; or an Octal 6V6G is good too.
A medium performance push pull output transformer will be less expensive, smaller, and lighter; versus a medium performance single ended output transformer with the same wattage rating. Stereo . . . 2 output transformers.
I personally like tube sockets, especially for output tubes, to be mounted to the amplifier chassis; and not mounted to a PCB.
Point to point is easier to repair, and easier to modify if necessary.
12 clean Watts from a single ended amplifier may be harder to get, versus 12 clean Watts from a push pull amplifier.
There are lots of proven circuits out there.
6L6GC, EL34, 5881 can make a sweet amplifier.
7199 are not needed to drive them, there are other options.
An 8 pin Octal is easier to wire than 9 pin Noval.
EL84 is very good; or an Octal 6V6G is good too.
EL84/6BQ5 with no [global] negative feedback, just UL negative feedback, or Triode wired negative feedback sounds simple and good.
I have done the same with 7591, 6L6GC, 5881, KT77, and KT66. But I used those tubes at far less voltage and far less current than they are rated for, the amplifiers were low power out.
I also built a Beam Power push pull amplifier, with no negative feedback. But that can be scary, there is very little limit to the high voltage swing if the speaker is not connected. Ouch!
And, the very low damping factor is generally not great for the average speaker.
Just my opinions and experience.
I have done the same with 7591, 6L6GC, 5881, KT77, and KT66. But I used those tubes at far less voltage and far less current than they are rated for, the amplifiers were low power out.
I also built a Beam Power push pull amplifier, with no negative feedback. But that can be scary, there is very little limit to the high voltage swing if the speaker is not connected. Ouch!
And, the very low damping factor is generally not great for the average speaker.
Just my opinions and experience.
Great info, thanks to all. I have a personal interest in the Williamson amplifier, especially a modern stabilized version of it, which I may persur as time allows. But it's rather elaborate for a first project. That simple EL84 PP PCB mentioned by @v4lve lover might be an ideal starter amp. Good to keep the parts count to a minimum.
Travelling today, I'll get to look at all those drawings on a proper screen tonight.
Thanks all
w
Travelling today, I'll get to look at all those drawings on a proper screen tonight.
Thanks all
w
As i promised, a photo of a nearly completed set, only missing the coupling caps. This new board revison has strain relief near the tube sockets so the solder joints on the board aren't stressed that much during tube swapping.
It took me 45 minutes to build two boards, a novice helped by some guidance from example photo's and capable of reading color codes on resistors should be able to do it under an hour. Only thing that is left to do is hook the board up. The solder pads are 1.9mm holes facilitating easy wire-to board.
Anyone interested in boards is free to contact me, i bought a ton of boards for my stand at the local radio club swap-meet.
Cheers,
V4LVE
It took me 45 minutes to build two boards, a novice helped by some guidance from example photo's and capable of reading color codes on resistors should be able to do it under an hour. Only thing that is left to do is hook the board up. The solder pads are 1.9mm holes facilitating easy wire-to board.
Anyone interested in boards is free to contact me, i bought a ton of boards for my stand at the local radio club swap-meet.
Cheers,
V4LVE
Attachments
Idk how ‘DIY’ you want, or if you want stereo, but his old McIntosh looks like a good schematic: https://www.bonavolta.ch/hobby/en/audio/mc240.htm
That's a beauty! Never did understand how Mac uses that many preamp tubes....
But I'm definitely looking for something much simpler for this project. That Dynaco 6v6 circuit is nice because it only requires 3 tubes per channel, but the grounding/fb scheme requires a pretty good output transformer with a decent amount of bandwidth, driving up the price. I do like the ST-70 style driver/splitter setup, and those 6AU8 tubes are still cheap. But I also think for a tube noobie it's better to stick to the well-known, still-in-production tubes. Maybe I should check out the ST-35 again...they still make that 12DW7.
w
But I'm definitely looking for something much simpler for this project. That Dynaco 6v6 circuit is nice because it only requires 3 tubes per channel, but the grounding/fb scheme requires a pretty good output transformer with a decent amount of bandwidth, driving up the price. I do like the ST-70 style driver/splitter setup, and those 6AU8 tubes are still cheap. But I also think for a tube noobie it's better to stick to the well-known, still-in-production tubes. Maybe I should check out the ST-35 again...they still make that 12DW7.
w
Mc used that many preamp tubes because the transformers+output tubes were close to unity gain, and all the voltage needed to be made before the finals. A rare approach in the day and almost never copied today. (For a reason, IMO…)
If you are doing this project as a first-timer, the circuit and board presented by @v4lve lover looks to be a fantastic choice… 1) it’s simple, 2) has a PCB which will greatly reduce wiring errors, 3) has no feedback so will be very tolerant of using essentially any output transformer, 4) uses in-production tubes (this is getting more important as time gos by) and 5) it’s very difficult to make a bad sounding EL84 amp, is it was designed to be an audio tube - in fact, it may be the last of the dedicated audio designs. They are sweet and beautiful.
Get some suitable Edcor transformers and have at it!
If you are doing this project as a first-timer, the circuit and board presented by @v4lve lover looks to be a fantastic choice… 1) it’s simple, 2) has a PCB which will greatly reduce wiring errors, 3) has no feedback so will be very tolerant of using essentially any output transformer, 4) uses in-production tubes (this is getting more important as time gos by) and 5) it’s very difficult to make a bad sounding EL84 amp, is it was designed to be an audio tube - in fact, it may be the last of the dedicated audio designs. They are sweet and beautiful.
Get some suitable Edcor transformers and have at it!
Done and done. This thread is 5 months old! I had a pair of PCBs from a seller out of Hong Kong using the "Dynaco 6V6" circuit and whipped up an amp with a top plate CNC cut at a friend's shop, and I built a maple base.
The OPTs aren't to spec so I had to learn to use a scope to find the best value for that cap in the Fb loop - the phase lead cap?
Anyway, good times. Thanks for taking a look
Will
The OPTs aren't to spec so I had to learn to use a scope to find the best value for that cap in the Fb loop - the phase lead cap?
Anyway, good times. Thanks for taking a look
Will
+1 for an EL84 amp. The biggest PITA with scratch builds is chassis work.
The least expensive kit including a chassis is this eBay item from China:https://www.ebay.ca/itm/22414694483...ZcwOzPW3hFRmHL5G4D2vZolYA=|tkp:Bk9SR6jZgfiSYw
A few people on this forum have built one, look around for the threads. The Xraytonyb channel on YouTube did a series on this:
As a CYA, building something with a decent chassis might make you less liable to any unintended incidents with an unsafe home-brew chassis.
S.
The least expensive kit including a chassis is this eBay item from China:https://www.ebay.ca/itm/22414694483...ZcwOzPW3hFRmHL5G4D2vZolYA=|tkp:Bk9SR6jZgfiSYw
A few people on this forum have built one, look around for the threads. The Xraytonyb channel on YouTube did a series on this:
As a CYA, building something with a decent chassis might make you less liable to any unintended incidents with an unsafe home-brew chassis.
S.
Oh I'm good at sheet metal work. Sure, I can get a nice top plates cut for free when my buddy can slip one in with a real work order, but then I gotta get the saw out to make the base, stain, all that. Urban carpentry is a hassle. Easier to get one of those Hammond boxes and drill holes in it. Then I got the problem of my wife fine by the little steel shavings when I tread em in the living room, but that's another problem 😬
biggest problem with those diy kit amps is the cheap OPTs. And that stainless steel they use is the hardest stuff I've ever tried to work. Has to be a brand new, real Cobalt bit.
biggest problem with those diy kit amps is the cheap OPTs. And that stainless steel they use is the hardest stuff I've ever tried to work. Has to be a brand new, real Cobalt bit.