yup i would be inclined to be cautious but dont worry about it...woudl be easier just to get non metal base tubes
From the pinout drawing, pin 1 is connected to the metal base and not used for anything else. So it makes sense that it should be connected to ground for safety if there is an exposed metal base on the valve. I don't know why you have a voltage on it though.
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The SSE design ties pin 1 to pin 8 in order to be compatible with the EL34. This does put the cathode voltage (which should be less than 50 volts) on the metal ring of some tubes.
The metal case of the old metal 6L6's also connect to pin 1. I had an old Stromberg Carlson amp in high school that had B+ on pin 1....That's when I learned that the foil cover of the second Steppenwolf album conducts electricity, then flies across the classroom!
If this is worrisome in your amp you can carefully cut the trace on the bottom of the PC board that runs between pin 8 and pin 1 of each output tube. Then run a short piece of wire from pin 1 to ground (the OPT SECONDARY (NOT primary) terminal that has no trace running to it on the bottom). This may make the amp unusable with some EL34 tubes, while most will still work.
There are lots of tubes called EL34, most are true pentodes, but some are actually beam tetrodes.
The metal case of the old metal 6L6's also connect to pin 1. I had an old Stromberg Carlson amp in high school that had B+ on pin 1....That's when I learned that the foil cover of the second Steppenwolf album conducts electricity, then flies across the classroom!
If this is worrisome in your amp you can carefully cut the trace on the bottom of the PC board that runs between pin 8 and pin 1 of each output tube. Then run a short piece of wire from pin 1 to ground (the OPT SECONDARY (NOT primary) terminal that has no trace running to it on the bottom). This may make the amp unusable with some EL34 tubes, while most will still work.
There are lots of tubes called EL34, most are true pentodes, but some are actually beam tetrodes.
Thanks George, I found that the support of the EL tubes explained the design while reading the prototyping pages over at your site last night, which is making for even more interesting reading now I am slightly more familiar with tube terminology, concepts and circuitry.
So, since one of the big strengths of the SSE is to support tube rolling with affordable and available tubes, can we envision a SPDT switch here connected on the new lines so that we have a Metal-base KT-88/6L6 | EL34/non-metal KT-88/6L6 switch on the SSE control panel?
This way we retain all the design goodness and flexibility of the SSE and make any jolts or sparks improbable in the specific metal-base case?
I also like your story about the origins of the O2. The Japanese seem to have decades of forward thinking and veneration for the art of audio reproduction and the finesse of great sound quality, compared to the pursuit of purely loud and brash in North America.
The original design I made for the chassis top and center-facing sides of the Transformers in my build were shiny chrome (surround by black for the chassis top). The reason for that was I wanted to have a mirror effect underneath and on the vertical sides around the tubes so that the lighting effects are reflected multiple times.
So, yesterday, while I was dabbling in my laboratory, dismantling an HDD to get at the motor and bearings, I had the great idea of taking the mirror-finish platters and putting them on the chassis surface to check the original design effect.
Sparks flew with the accompanying sonic ticks, and the surface of the metal is burned.
Not being familiar with all tube construction details beforehand, this is how I found out.
Hi Spendorite,
Oh yes, the KT-88s get really hot: I can touch almost anything, but I wouldn't even touch my finger to the glass for a second.
I am looking to build high-efficiency speakers for the amp rather than pair them with the Totem Mites (in my room they do sound great though).
Optimal settings for EH KT-88
Now that I've managed to build the SSE without too much damage, I would like to try and optimise the cathode resistor value or other values as I used a default one of 560 Ohms for the cathode res.
My overall goal is to optimise for SQ: fast transients and low distortion.
My B+ voltage is (at KT-88 - is that all correct?):
5. Left P3: 417 VDC
6. Right P3: 418 VDC
The OPT used has an impedance of 5K.
This made me think that the section below is the proper one to look at (and not the 450V one).
Now, it appears this is a multi-dimensional question, since ideally we would also like to optimise for Damping Factor.
So here are a couple of questions still extant for me:
1. How would I optimise further? Is it by choosing let's say a 383Ohm cathode resistor value here? Is that the best I can do
2. Is it OK and possible to consider running at a higher B+ - the power transformer is an Edcor which does 370-0-370 I believe. If so, how?
I guess the over-arching question is what is the best set of values for Electro-Harmonix KT-88s with 12AT7EH, 5AR4 and these specific EDCORs?
Now that I've managed to build the SSE without too much damage, I would like to try and optimise the cathode resistor value or other values as I used a default one of 560 Ohms for the cathode res.
My overall goal is to optimise for SQ: fast transients and low distortion.
My B+ voltage is (at KT-88 - is that all correct?):
5. Left P3: 417 VDC
6. Right P3: 418 VDC
The OPT used has an impedance of 5K.
This made me think that the section below is the proper one to look at (and not the 450V one).
Now, it appears this is a multi-dimensional question, since ideally we would also like to optimise for Damping Factor.
So here are a couple of questions still extant for me:
1. How would I optimise further? Is it by choosing let's say a 383Ohm cathode resistor value here? Is that the best I can do
2. Is it OK and possible to consider running at a higher B+ - the power transformer is an Edcor which does 370-0-370 I believe. If so, how?
I guess the over-arching question is what is the best set of values for Electro-Harmonix KT-88s with 12AT7EH, 5AR4 and these specific EDCORs?
You could purchase SE Amp CAD; it's very inexpensive. I wish I had purchased it sooner; I'm sure I could have saved myself considerable angst.
There are a few drawbacks: it ONLY runs in XP ( or maybe lower ), so you have to have a real XP machine around. It's also only a model. You would have to input some data and make a model for your OPT's. Still, it's very useful.
I think you may be looking at that table wrong and may wish to take a second look. What you can see is that, generally, as current increases in the tube, harmonic distortion decreases. Of course your power transformer and choke have to be able to handle the extra current, and the modeled improvement is quite slight.
Win W5JAG
There are a few drawbacks: it ONLY runs in XP ( or maybe lower ), so you have to have a real XP machine around. It's also only a model. You would have to input some data and make a model for your OPT's. Still, it's very useful.
I think you may be looking at that table wrong and may wish to take a second look. What you can see is that, generally, as current increases in the tube, harmonic distortion decreases. Of course your power transformer and choke have to be able to handle the extra current, and the modeled improvement is quite slight.
Win W5JAG
Thanks w5jag, sounds good, I was on the glassware and tubecad sites not so long ago.
Yes, simulation is a good way of exploring the parameters, I am also thinking of trying some simulations with LTSpice for the circuits themselves.
I think you're right as I'm learning a lot of all this along the way.
While looking again at George's instructions today, he actually already has set up various simulations of which these tables are the product (so I don't really need to re-do the simulation myself for now), and he says:
Now, "B+ voltage... that most closely matches the transformers that you have" is where this is a little ambiguous for me (knowing my B+ in-circuit).
Could it be that the B+ voltage most closely matching my Power transformer is the 350V one (since the PT is a 370-0-370)? Load impedance for my OPTs is 5K.
If, on the other hand, the B+ voltage which most closely matches my transformer is the one that is closer to my in-circuit measured B+, then the section of the table should be the previous one I posted.
The question is, what is the correct way of doing this?
Indeed, that's what we see here. On the other hand, it is a multi-dimensional optimisation problem since Power output also decreases with increasing current.
So, with my goals as described, I am tempted to go for the lowest distortion => higher current and lower output.
This, then will necessitate more efficient speakers than I already have, which will be an interesting pursuit as well.
My OPT max current is: 200mA.
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I have been reading those tables trying to understand them for a while. As the SSE is for beginners, It would be great if someone would post an explanation of them or some indication as to what the figures mean.
My reading of them, as a complete newcomer to this, is that to get the best out of your KT88s your B+ is a bit low. With that traffo you should be starting with about 520vdc so considering you don't even have a choke it seems to be dropping a lot. Is your line voltage low?
I'm just wiring up my SSE at the moment so I have loads of questions but not a lot of answers I'm afraid.
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My reading of them, as a complete newcomer to this, is that to get the best out of your KT88s your B+ is a bit low. With that traffo you should be starting with about 520vdc so considering you don't even have a choke it seems to be dropping a lot. Is your line voltage low?
I'm just wiring up my SSE at the moment so I have loads of questions but not a lot of answers I'm afraid.
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Come stai, gcom? 😀
Indeed.
I can, of course, at least comprehend the semantics and how the following vary for SQ:
1. Output Power - ideally we would like to maximise if everything else remained the same
2. Distortion (2nd and 3rd Harmonics) - ideally we would like to minime those
On the other hand, minimising Distortion necessitates a lower output power configuration (which we can live with in the SET world provided we use high-efficiency speakers so as to touch the magic).
It looks like the SSE Design page has a lot of good info, notably considering dissipation for tube life and the rest of the parameters.
Yes, I see that now reasing that page again and looking again at the tables.
I was simply looking at the power output figures, which I suppose is somewhere to start.
I suppose I won't know what the distortion figures mean until I hear them.
Usually less is better when looking at the distortion numbers. But then the distortion is 2nd harmonic mostly and some like 2nd harmonic distortion. Study the chart some more and it will become more clear what all the numbers mean. George went to a lot of trouble to make that chart and it has a lot of information.
I think it is important to qualify that statement about people 'liking' 2nd harmonic distortion.
Ideally, the lowest distortion figures are the best for a more neutral sound or for more high-fidelity.
What happens is that with tubes, the 2nd harmonic distortion is at an octave above the fundamental. And this is rather musically pleasing to the ear as it's exactly how a fundamental C note would sound with the higher C note, i.e. harmonious.
Yes, it is said some people specifically look for a 'tube sound', but I'd rather my tube amp be neutral personally.
I know I read a lot before choosing the SET topology, then I spent some more time reading about the Tubelab SSE in this forum, so I ended up choosing the KT-88 as well as the larger Edcor OPTs so that I could have a good bass, but have no slouching in the upper registers. This is working as planned.
Been reading a little about the Damping Factor today, and apparently, to prevent some impedance affecting higher frequencies with specific drivers (it was a Lowther), some people can use a Zobel network at the speaker. Quite interesting.
Yes, that seems like an accurate depiction of what some people do.
And indeed, this is why I think there must be a clarification here, because there is a nuance between:
a. looking for a 'tube' sound which is in fact, looking for coloration, and
b. looking to get all the advantages of tube equipment, but not necessarily the coloration, i.e. the pursuit of fidelity, neutrality, openness/no-clipping distortion, circuit-simplicity and no-feedback, in certain topologies.
It so happens that in the world of tubes, the distortion that does occur mainly, is still harmonious musically and that is great but it isn't an end-goal for fidelity.
In that nuance, there is a world of difference.
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Interesting that you mention that as well, because there is yet another nuance in that piece of information:
It can well be that most SET tube amps will have more 2nd harmonic distortion than a PP tube amplifier.
However, SET tube amps have other advantages over PP tube amps, especially when it comes to the detail of the mid-to-lower high range.
So, you shouldn't conclude that all people who prefer SET tube amps to PP Amps do so because they prefer more 2nd harmonic distortion. It's rather that the finesse of reproduction in that crucial musical range in SET tube amps has a predominant importance over that of the higher 2nd harmonic distortion.
I do believe PP tube amps can be great for some things too (higher power needs), and in fact, you could even envision bi-amping with a SET tube amp and a PP tube amp.
Here again in that nuance... a world of difference in reasoning and approach.
So, sub forums's been quiet - how are you guys coming on this? Here's my $0.02 USD on this, coming from someone who is neither a musician, an audiophile, nor blessed with any electronic book knowledge; but I would look at the chart and start at a point that minimizes the second order distortion, or gives you the lowest combination of the two types.
While second order may be pleasing to the ear ( can't say, personally ), on a single ended amplifier I think it's just asking for IMD. I have no proof of this and offer it merely as an opinion from my obversations from sitting on a stool and playing with SE Amp Cad, putting those sim numbers on the board, and twiddling knobs on last century power supplies and analyzers. And they were probably mediocre, at best, power supplies and analyzers even back then. But it sure looked to me like fairly small changes in second order distortion can really drive IMD up dramatically.
I can also say, maybe because I'm not an audiophile, that some points that looked pretty ghastly, sounded perfectly fine when ran through mainstream speakers into an ordinary room. So maybe it is much ado about nothing.
Win W5JAG
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Hey Win,
Interesting observations. I also read this morning some info contrasting the 2nd order harmonic content from SS versus Tubes and it was very interesting in that light, specifically that because of the THD numbers game, SS amps have this figure very low overall but remove 2nd order harmonics but retain the 3rd order ones, making the end result very un-musical.
Quite enlightening, seeing that I have never felt as relaxed as listening to the SSE as when listening through SS amps. The music is effortless with the SSE whereas with the SS, even though it can do 100W per channel in stereo, it feels 'constrained', it's as if something you are waiting for never gets resolved.
I have been listening to my SSE amp a lot, really enjoying it.
The more I listen the more I like it. The sound did have some metallic edge to it with the Electro-Harmonix 12AT7 though, so I thought of changing it back to the generic Chinese. This has helped a little, though I would give the EH the edge on transient reproduction rapidity and general rapidity. The Chinese one in comparison seems a little rolled-off, but is still very enjoyable though. So I would say the Single-Ended Triode nature of the SSE shines through regardless.
The more I read about SET Tube amps, the more I know George built a very special little amp here: SETs are said to be lacking in the bass department (bloom in the bass) and also sometimes in the higher ranges.
Now, perhaps I have built a special configuration because I chose the big Edcors even for output as well as KT-88s, and on top of that, I am listening to very musical mini-monitors on DIY Stands, with added DIY vibration isolation, and that marriage is a special one, but for sure, this is uncommon in SETs.
Another cool thing that happened is that I am now thoroughly interested in tube circuits and of course, more and more in electronics, so I am building my electronics workshop table, getting re-acquainted with the very basics as the academic knowledge has rusted a lot from lack of practice.
I have gained a lot on the audiophile exploration side though, so if you have any question about that, I can help you get set up for the best sound possible, even with non-gigantic budgets.
In fact, some of the knowledge I acquired will now be put in practice this year, as I feel I need to step up everything else with the SSE in place as well now.
It is quite amusing that most of the so-called audiophile setups are a mixture of high-powered SS amps paired with very low-efficiency speakers for instance.
The 'audiophile' forums can get very heated and often. It's a welcome change to be able to just take a lot of pleasure in listening to music.
I have a couple of steps this year to further enhance my set up and then I can relax a little, but I am well on my way, yet it feels that with the tube circuits, I have a world to explore.
Fascinating subjects (tubes, tube circuits, SS circuits compared, electronics, etc...).
Interesting observations. I also read this morning some info contrasting the 2nd order harmonic content from SS versus Tubes and it was very interesting in that light, specifically that because of the THD numbers game, SS amps have this figure very low overall but remove 2nd order harmonics but retain the 3rd order ones, making the end result very un-musical.
Quite enlightening, seeing that I have never felt as relaxed as listening to the SSE as when listening through SS amps. The music is effortless with the SSE whereas with the SS, even though it can do 100W per channel in stereo, it feels 'constrained', it's as if something you are waiting for never gets resolved.
I have been listening to my SSE amp a lot, really enjoying it.
The more I listen the more I like it. The sound did have some metallic edge to it with the Electro-Harmonix 12AT7 though, so I thought of changing it back to the generic Chinese. This has helped a little, though I would give the EH the edge on transient reproduction rapidity and general rapidity. The Chinese one in comparison seems a little rolled-off, but is still very enjoyable though. So I would say the Single-Ended Triode nature of the SSE shines through regardless.
The more I read about SET Tube amps, the more I know George built a very special little amp here: SETs are said to be lacking in the bass department (bloom in the bass) and also sometimes in the higher ranges.
Now, perhaps I have built a special configuration because I chose the big Edcors even for output as well as KT-88s, and on top of that, I am listening to very musical mini-monitors on DIY Stands, with added DIY vibration isolation, and that marriage is a special one, but for sure, this is uncommon in SETs.
Another cool thing that happened is that I am now thoroughly interested in tube circuits and of course, more and more in electronics, so I am building my electronics workshop table, getting re-acquainted with the very basics as the academic knowledge has rusted a lot from lack of practice.
I have gained a lot on the audiophile exploration side though, so if you have any question about that, I can help you get set up for the best sound possible, even with non-gigantic budgets.
In fact, some of the knowledge I acquired will now be put in practice this year, as I feel I need to step up everything else with the SSE in place as well now.
It is quite amusing that most of the so-called audiophile setups are a mixture of high-powered SS amps paired with very low-efficiency speakers for instance.
The 'audiophile' forums can get very heated and often. It's a welcome change to be able to just take a lot of pleasure in listening to music.
I have a couple of steps this year to further enhance my set up and then I can relax a little, but I am well on my way, yet it feels that with the tube circuits, I have a world to explore.
Fascinating subjects (tubes, tube circuits, SS circuits compared, electronics, etc...).
I think Nelson Pass had this to say in a post on the forum,
I have been building low number amplifiers all my life and I have been pretty successful at it but now I build what I like.
Not his exact words but I think you get the meaning.
I have both push pull and SE and both have strong points and weakness's Sometimes it depends on the music being played or the mood I am in or both. All in all though I would rather listen to SET's.
I have been building low number amplifiers all my life and I have been pretty successful at it but now I build what I like.
Not his exact words but I think you get the meaning.
I have both push pull and SE and both have strong points and weakness's Sometimes it depends on the music being played or the mood I am in or both. All in all though I would rather listen to SET's.