AudioCircle
Audio/Video Gear and Systems => Tube-o-phile Circle => Topic started by: Presb4 on 4 Mar 2024, 05:36 am
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So I have been looking at building my first SEP amp using an EL34 or 6L6GC. After significant digging, I think I have settled on Keggers 2015 schematic, the last one I know of before his passing. I do plan on adding a few tricks to his design, namely designing a PS using SS bridge rectifier, adding Decware's CCE mod and having switchable low and high FB. I have been slowly stocking up on the parts and components I will need. The PT and choke arrived from Japan this weekend but I am still waiting on my OPT to come in. They are being custom wound by Thermionic Labs to 5k 8ohm and 42% CT.
Here is my initial lay out.
I would appreciate any feed back more experienced builders might have.
(https://www.audiocircle.com/image.php?id=262025)
(https://www.audiocircle.com/image.php?id=262026)
(https://www.audiocircle.com/image.php?id=262027)
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The table seems to be magnetic steel.
Any soft start?
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The chassis will be all .125" Aluminum, no steel other than transformer laminations and bolting :D
Yes, I will use a thermistor for a soft start and all of my caps will be rated for around 100V over no load B+.
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My PS idea. It should be overkill. I am aiming for about 410VDC to the OPT coil.
(https://www.audiocircle.com/image.php?id=262028)
This part changed a good bit, the image still shows different taps for the OPT vs the Input tube B+. In reality it is all just one B+ tap. I estimated a 140 to 150mA total load running EL34's and input tubes
(https://www.audiocircle.com/image.php?id=262029)
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The chassis will be all .125" Aluminum, no steel other than transformer laminations and bolting :D
Yes, I will use a thermistor for a soft start and all of my caps will be rated for around 100V over no load B+.
Nice, your started on the right way.
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Good point. Small chassis builds more elétric noise.
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Small chassis???, I thought it was a little on the large side.
It will measure 17"W x 10"D x 3"H.... :scratch:
The plate shown above is an old aluminum plate that I use to dream up layouts and to pull measurements from, its not the one I will using.
I placed an order today for this chassis. Its the one I will be using.
(https://www.audiocircle.com/image.php?id=262054)
(https://www.audiocircle.com/image.php?id=262055)
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I'm fortunate to have a group of local diy builder friends who are designing and building amazing sounding transformer coupled tube amplifiers. Two techniques some of them now implement is to attach a sub-chassis to the top plate made of Delrin that they attach the delicate input/gain stage and tubes to (and sometimes the output stage). The damping of the Delrin reduces vibrational and microphonic energy that will be carried to that section if mounted directly to the metal top plate. It requires drilling slightly larger holes in the top plate as the tube sockets will be mounted a bit below the top. The second thing they have been doing is to add a dedicated transformer and power supply just for the input section. Apparently, no matter how large the main power supply is there will be voltage fluctuations and sag feeding the input section, which needs very consistent voltage supply. With these two changes added to otherwise existing amplifiers they have taken their builds to much higher performance levels. Don't know if you're familiar with these techniques but thought I'd mention it since you're at this early stage of your build.
(https://www.audiocircle.com/image.php?id=262184)
(https://www.audiocircle.com/image.php?id=262185)
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I'm fortunate to have a group of local diy builder friends who are designing and building amazing sounding transformer coupled tube amplifiers. Two techniques some of them now implement is to attach a sub-chassis to the top plate made of Delrin that they attach the delicate input/gain stage and tubes to (and sometimes the output stage). The damping of the Delrin reduces vibrational and microphonic energy that will be carried to that section if mounted directly to the metal top plate. It requires drilling slightly larger holes in the top plate as the tube sockets will be mounted a bit below the top. The second thing they have been doing is to add a dedicated transformer and power supply just for the input section. Apparently, no matter how large the main power supply is there will be voltage fluctuations and sag feeding the input section, which needs very consistent voltage supply. With these two changes added to otherwise existing amplifiers they have taken their builds to much higher performance levels. Don't know if you're familiar with these techniques but thought I'd mention it since you're at this early stage of your build.
(https://www.audiocircle.com/image.php?id=262184)
(https://www.audiocircle.com/image.php?id=262185)
Thanks for the ideas Rusty.
I am familiar with the pros of having the tube sockets suspended from a dampening material, I just haven't seen delrin used that way. I would think it would get to soft with the heat in the chassis and droop over time. I was going to do something similar but was going to use old guitar amp turret boards (fiberglass) and mount it with soft rubber gromets between the turret board and chassis. The tube sockets would be mounted to the turret boards inside the chassis. I think this provides similar isolation to the idea you are suggesting.
The power transformer I have for this build is double the size in mA than I need and as its also using a SS bridge, I don't think I will have any sag at the input tubes. But in an ideal world I agree that having the power supplies split, one for the power tubes and the other for the input tubes would be a good idea.
I also noticed that in your photo, it looks like the builder also used a aluminum divider between the power supply side and the audio amplifier side to reduce EMF. If so that is another great idea. I was looking to do that too.
Keep the good ideas coming. My OPT are still a month away from delivery, so I will not lock the layout design down until I have them.
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Do your OPT will be Edcor?
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Thanks, these irons looks nice. Edcor use M6 at lower price and Hashimoto use Hi-B.
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Thanks for the ideas Rusty.
I am familiar with the pros of having the tube sockets suspended from a dampening material, I just haven't seen delrin used that way. I would think it would get to soft with the heat in the chassis and droop over time....
You bet. The Delrin doesn't get hot enough to flex/bend. Not talking about mounting push/pull 845s here. :D It's primarily used for the input/gain section though the amp shown does have p/p EL-34s mounted on Delrin without issue. Birch ply or bamboo ply a good second choice. Fiberglass and phenolic rings, not a great option. The independent input stage power supply will make a remarkable improvement. GLWYB.
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Single ended class A with a proper power supply and solid state rectification shouldn't have a problem.
I know someone that likes to use Delrin for the top plate.
I didn't have an opinion about it as I don't have the engineering chops, but I can tell you when I heard the amplifiers with the input supply added without knowledge of the difference, it was startling. Much more dynamic energy, especially on their SET amps. The output stage apparently needs far more from the power supply to carry the full sine wave compared with p/p. They do typically use damper diodes or tube rectification, but the amplifiers I'm describing now are 211 SET with ss rectification. Remarkable improvement. I'm just the messenger...
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Have you bounced your design off the members at diyaudio.com? They have no shortage of opinions, but there is some real expertise there, too...
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DIYaudio forum is a nice site to learn only the technical aspects of tube amps, however they dont know what features give good sound in a tube amp, they follow strictly the official electrical engineering manual, cables dont make a difference etc.
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The 211 is a different world from an EL34.
Look, the EL-34 amps I posted pictures of (p/p) are one of the amplifier pairs that recently added the independent input supply. I didn't know it had been done, was very familiar with the sound of the system prior and when I visited was really impressed by how much better it sounded. When I asked what changed, he showed me the addition to the amplifiers. That was the only change. Since then, these builders have incorporated this into any new amplifiers they build and added it to existing amplifier pairs they had on which there was room.
I'm not sure if you've tried these suggestions in your own builds and they were unsuccessful, or if you're in the camp of "I've never tried it but I can't believe it will make a difference, therefore it's a bad idea." The OP asked for suggestions for additions to his new build, I responded. Apologies to you for the annoyance.
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Look, the EL-34 amps I posted pictures of (p/p) are one of the amplifier pairs that recently added the independent input supply. I didn't know it had been done, was very familiar with the sound of the system prior and when I visited was really impressed by how much better it sounded. When I asked what changed, he showed me the addition to the amplifiers. That was the only change. Since then, these builders have incorporated this into any new amplifiers they build and added it to existing amplifier pairs they had on which there was room.
I'm not sure if you've tried these suggestions in your own builds and they were unsuccessful, or if you're in the camp of "I've never tried it but I can't believe it will make a difference, therefore it's a bad idea." The OP asked for suggestions for additions to his new build, I responded. Apologies to you for the annoyance.
LOL, annoyed? who's annoyed :D
I welcome the ideas and challenge to they design I was considering. I have not built and compared 2 amps with the only change being a dedicated input supply vs the power section and the input sharing the power supply. So I cant says what the difference would be. I have no doubt there could be a difference. At this point I have all most all the parts I need on hand to build the design I post above, as I will be using a turret board inside, it will not be hard to update/change it in the future if I want to. I think these are all good ideas to explore.
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Have you bounced your design off the members at diyaudio.com? They have no shortage of opinions, but there is some real expertise there, too...
No I haven't, but most of the tube amp circuit design I posted above, did come from posts over on AK where it was heavily vetted for years. It is a very well known and tested design. The power supply is my own design with input from a number of audio engineering books I have and modeled on PSU Designer. I agree that posting over on DIY Audio has its challenges for the non-engineering types so I would rather not. I don't mind finding bugs in my builds as I go, solving them is part of the fun for me.
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Thanks, these irons looks nice. Edcor use M6 at lower price and Hashimoto use Hi-B.
I orders some custom wound OPT from Thermionic Labs.
They will be 20 watt OPTs with 5k primaries and both 8 and 12 ohm secondaries. A 42% CT and air gapped for 80mA each.
If you want to order the non-custom spec, here is the website with the specs.
https://www.thermioniclab.com/en/single-ended-output-transformers/single-ended-5k-4-8r-20w-ultralinear-output-transformers-pair-1.html
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I orders some custom wound OPT from Thermionic Labs.
They will be 20 watt OPTs with 5k primaries and both 8 and 12 ohm secondaries. A 42% CT and air gapped for 80mA each.
If you want to order the non-custom spec, here is the website with the specs.
https://www.thermioniclab.com/en/single-ended-output-transformers/single-ended-5k-4-8r-20w-ultralinear-output-transformers-pair-1.html
The Wattage are correct, 3kg OPT are 20W.
You ordered plastic bobbin?
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I'm not sure what the bobin material is. The OPT should be around 6 to 8 watts greater than I need so i'm sure it will be fine. Now that summer is in full swing, I will have some time to finish this project over the next couple months.
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I'm not sure what the bobin material is. The OPT should be around 6 to 8 watts greater than I need so i'm sure it will be fine. Now that summer is in full swing, I will have some time to finish this project over the next couple months.
If your speakers are hi sensitivity as 100dB 8Ω or 16Ω, six watts of SET bliss are sufice to shake windows, UL are suited only to guitar amps due the extra distortion, IMO. There is an good example in the Decware Rachel EL34SE.