Kegger KT88 UL PSE?
- Thread starter whoaru99
- Start date
whoaru99
Epic Member
In my context, McShane opines the EH KT88 offers 90% of the performance of the best KT88s at 50% cost of the best. That is fine for me regarding a startup project.
I don't want to risk a nice, new set of Genelex Gold Lion KT88 or whatever in a new to me project amp. Wanna make sure the amp is OK and largely dialed in before going there.
I don't want to risk a nice, new set of Genelex Gold Lion KT88 or whatever in a new to me project amp. Wanna make sure the amp is OK and largely dialed in before going there.
whoaru99
Epic Member
EH tubes are on order from Jim M.
Perhaps this weekend the rest of the bits will be too, but tomorrow the GF and I are going to a Garlic Festival down the road a piece so maybe on Sunday.
I have plenty of good hookup wire but it's stranded. Want to give it a go with some solid core once instead so probably will make an order with ApexJr for that.
Perhaps this weekend the rest of the bits will be too, but tomorrow the GF and I are going to a Garlic Festival down the road a piece so maybe on Sunday.
I have plenty of good hookup wire but it's stranded. Want to give it a go with some solid core once instead so probably will make an order with ApexJr for that.
That's good because there probably wont be be good hook up after the garlic festival
Tom Bombadil
AK Member
Garlic Festival? Near Gilroy, CA? Garlic Capitol of the World.
whoaru99
Epic Member
whoaru99
Epic Member
Update...
Missed out on the garlic ice cream as they ran out just before we got to the stand - got a bit delayed in putting up some sweetcorn before we headed to the fest. But, otherwise, it was garlic overload in a good way.
Probably have enough garlic in my bloodstream to avert a vampire attack for at least the rest of the weekend. And, enough garlic bulbs and other garlic goodies brought home to keep them at bay for a good while beyond that.
Missed out on the garlic ice cream as they ran out just before we got to the stand - got a bit delayed in putting up some sweetcorn before we headed to the fest. But, otherwise, it was garlic overload in a good way.
Probably have enough garlic in my bloodstream to avert a vampire attack for at least the rest of the weekend. And, enough garlic bulbs and other garlic goodies brought home to keep them at bay for a good while beyond that.
whoaru99
Epic Member
OK...back to the amplifier. Next question -
Considering the power transformer filament winding is geared for 4) 6V6 AND 1) 6SN7, I'm going to go out on a limb and say it's probably not enough for 2) KT88s and 1) 6EJ7. So, I'm thinking to use the PT filament winding to power just the 6EJ7, then I have a couple 30VA 12.6V CT transformers. I would use one of these per pair of KT88s
Given the KT88 filaments are 6.3V, is there anything noteworthy to consider in wiring them up like this to the 12.6V CT transformer?
Is there/would there be any benefit to wiring with a specific polarity to the filaments, e.g. as shown by the filament pinout numbers on the upper or lower illustration?
Considering the power transformer filament winding is geared for 4) 6V6 AND 1) 6SN7, I'm going to go out on a limb and say it's probably not enough for 2) KT88s and 1) 6EJ7. So, I'm thinking to use the PT filament winding to power just the 6EJ7, then I have a couple 30VA 12.6V CT transformers. I would use one of these per pair of KT88s
Given the KT88 filaments are 6.3V, is there anything noteworthy to consider in wiring them up like this to the 12.6V CT transformer?
Is there/would there be any benefit to wiring with a specific polarity to the filaments, e.g. as shown by the filament pinout numbers on the upper or lower illustration?
primosounds
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I am with 99. It is more fun to do it by thinking "out of the box" and having it turn out good is the final pay off.
My own personal experience was with a Cary Audio AE3 preamp which is a simple 2 x 6sn7 preamp which had a blown power transformer because the original owner changed out the power supply rectifiers but botched it and thus blew his PT. Anyway i found a potted mil spec pt that had the right high voltage and 6.3 and 5.0v filament voltages. I hooked it all up in a pretty stock way with a 5y3 on the 5.0v circuit and AC on the 6sn7 heaters. That way gave lots of hum. The original used rectified 24v for DC heaters hooked up in series. I looked into adding a 24 fil trans but that is a pretty big one and would not fit in the small 7 x 9 chassis of the ae3. So, i played with shielded cable for the heaters, re routing, rectifying the 6.3 v and reducing the voltage and several other things and never could get the preamp quiet. Then, i stumbled across the 6x5 as a rectifier. It is a 6.3v rectifier and would be adequate for 2 6sn7 tubes. So i flipped it using the 6.3v on the rectifier filament and then, if i ran the 5.0v thru a full wave bridge made with Schottky diodes,i would get 6.0 volts of pure DC which was used for the 6sn7 filaments. And voile, the preamp works great with absolutely no hum and it sounds even better than the original AE3.
My own personal experience was with a Cary Audio AE3 preamp which is a simple 2 x 6sn7 preamp which had a blown power transformer because the original owner changed out the power supply rectifiers but botched it and thus blew his PT. Anyway i found a potted mil spec pt that had the right high voltage and 6.3 and 5.0v filament voltages. I hooked it all up in a pretty stock way with a 5y3 on the 5.0v circuit and AC on the 6sn7 heaters. That way gave lots of hum. The original used rectified 24v for DC heaters hooked up in series. I looked into adding a 24 fil trans but that is a pretty big one and would not fit in the small 7 x 9 chassis of the ae3. So, i played with shielded cable for the heaters, re routing, rectifying the 6.3 v and reducing the voltage and several other things and never could get the preamp quiet. Then, i stumbled across the 6x5 as a rectifier. It is a 6.3v rectifier and would be adequate for 2 6sn7 tubes. So i flipped it using the 6.3v on the rectifier filament and then, if i ran the 5.0v thru a full wave bridge made with Schottky diodes,i would get 6.0 volts of pure DC which was used for the 6sn7 filaments. And voile, the preamp works great with absolutely no hum and it sounds even better than the original AE3.
thorpej
Super Member
The way I learned it is: P-P valves (on opposite ends of the OT) should be wired IN-PHASE. Parallel SE valves should be wired OUT-OF-PHASE. How much difference it really makes? I can't say for sure, but it's the way I've always done it. Certainly for the P-P case, it seems intuitive (goes right along with the PSRR inherent in a P-P output stage). One of these says I should do an experiment to see what the effect of the phasing of the heaters on a parallel SE output stage is. I would think that for 2 valves in a series string, you'd want to use the SE approach -- out of phase.
I know @kward has done the 6.3V-valves-in-series-with-a-12.6V-transformer thing before, so it would be valuable to have him comment as well...
My build was different--a stereo chassis KT120 PP amp. All I had was a 12V 6A secondary and no center tap. So I essentially wired up the filaments for each PP pair in series (and by default in phase since I had no center tap). The amp was quiet, but I have no idea if the phase relationship of the filaments had anything to do with it.
whoaru99
Epic Member
This project has really languished. Sad, really, because I have all the expensive parts and have for a while. What I could really use now are some suggestions for chassis layout. Attached is what I have sketched up now, but I'm not pleased at all with any arrangement I've done with the capacitor bank and rectifier tube - the illustrated location of the caps and rectifier isn't necessarily where I think they should go, I just got tired of moving them around.
Note the chassis top size is 17 x 11 and all the parts are ~draw to size/1:1. For example, the power transformer (PT) is 5.25" x 4.375".
I'm open to any and all parts being rearranged and size of chassis adjusted if/as necessary. Suggestions most welcome.
Note the chassis top size is 17 x 11 and all the parts are ~draw to size/1:1. For example, the power transformer (PT) is 5.25" x 4.375".
I'm open to any and all parts being rearranged and size of chassis adjusted if/as necessary. Suggestions most welcome.
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primosounds
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Hey 99 , as far as your layout is concerned, it looks very straight forward and you should just go for it. Did you try a layout with all your parts? It is easier to get a better sense of the aesthetics if you put the parts out on say a piece of plywood or the actual chassis if you got it. I am currently working on a KT120/150 SE amp and i am in the wiring stage. I lingered for a long time with the layout and finally decided on a situation with the PT and chokes on one end then the 2 OPT about in the middle and the tubes in the final quarter, since my amp is a stereo amp. I am still a few weeks away from power up but, once you get the ball rolling it will be far easier to move forward. So if you haven't got your chassis sorted try to finalize that and the rest will logically fall into place. cheers,
primosounds
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I like doing it that way. Keeping the power transformer further away from the driver tube and output tubes would help to keep the noise floor lower. I have mono blocks and amps with the power unit separate from the output and it seems that both ways are good.
whoaru99
Epic Member
At least I think I've settled on 17" x 10" chassis. Looks like I can squeeze it all in between those two. The PS would have just the main filter caps to provide a single B+ to the amp. The pre/driver power node I'd do in the amplifier section.
Now I'm debating whether or not to use tube rectifiers or just go with SS.
***I do have another question though. For filament/heater voltage, is there likelyhood the AC would be coupled into the B+ if I ran them in the same umbilical cord between PS and amp?
White background is the chassis size, red box is 1/2" margin all around.
Now I'm debating whether or not to use tube rectifiers or just go with SS.
***I do have another question though. For filament/heater voltage, is there likelyhood the AC would be coupled into the B+ if I ran them in the same umbilical cord between PS and amp?
White background is the chassis size, red box is 1/2" margin all around.
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