Hi,
That depends on how you want to drive them...
The reason I wrote that is that IME every time I heard a KT90 it was used with either a 12AT7A (metallic sound) or a 12AU7A (anemic sound) and you could hear those driver tubes as a hallmark of the amps.
IMHO they're better served by something along the lines of a 6463, 6350, ECC99 and family.
Again this pretty much depends on the topology you decide to use, my experience with the KT90 is mostly VTL and some Jadis amps.
Cheers,
That depends on how you want to drive them...
The reason I wrote that is that IME every time I heard a KT90 it was used with either a 12AT7A (metallic sound) or a 12AU7A (anemic sound) and you could hear those driver tubes as a hallmark of the amps.
IMHO they're better served by something along the lines of a 6463, 6350, ECC99 and family.
Again this pretty much depends on the topology you decide to use, my experience with the KT90 is mostly VTL and some Jadis amps.
Cheers,
Took The Plunge...
Well, I bit the bullet and went ahead and bought a matched octet of EH KT90's for a pair of Vanderveen PPP cathode feedback monoblocks I'm building. 
What sort of experiences/recommendations do folks have with grid-leak resistor values for fixed-bias operation?
I haven't seen any recommended values, and am wondering if 220K would work. :mushroom cloud:
If I should go lower, I guess that'll be my excuse to add Gary Pimm CCS anode loads on the driver stage.
Best,
George "Just An Enthusiastic Amateur" Ferguson
Well, I bit the bullet and went ahead and bought a matched octet of EH KT90's for a pair of Vanderveen PPP cathode feedback monoblocks I'm building.
What sort of experiences/recommendations do folks have with grid-leak resistor values for fixed-bias operation?
I haven't seen any recommended values, and am wondering if 220K would work. :mushroom cloud:If I should go lower, I guess that'll be my excuse to add Gary Pimm CCS anode loads on the driver stage.
Best,
George "Just An Enthusiastic Amateur" Ferguson
Hi there.......I'd (had) been using EI KT90's until they basically fell apart internally. (the interelectrode spot welds were so poorly done as to cause internal shorts).
They were orig in yellow cum boxes, but before they died I managed to do some meaqsurements.
I cannot recommend the EI KT90....for UL p-p Hi Fi....simply on specs....I'll show in another mail......I always maintain it has always historically has a switching/sweep tube background rather than a Hi Fi one. I know that other manufacturers have tampered with the internal geometry to try to get a similiar 88 sound out of it.
Although my samples initially worked and were well matched... they couldn't take the rigours of cont use although they gave approx 15% more power out compared to 6550/KT88 types.
EI claim their KT90 is a substitute for the 6550 and KT88 series.......For HiFi DEFINITELY NEIN.
I found some undesirable aspects of the KT90 that are more suited to MI apps rather than Hi Fi ; however if anyone can say there is a difference between the EH types as improved ones......Or they are all clones from one another. I remain interested.
rich
They were orig in yellow cum boxes, but before they died I managed to do some meaqsurements.
I cannot recommend the EI KT90....for UL p-p Hi Fi....simply on specs....I'll show in another mail......I always maintain it has always historically has a switching/sweep tube background rather than a Hi Fi one. I know that other manufacturers have tampered with the internal geometry to try to get a similiar 88 sound out of it.
Although my samples initially worked and were well matched... they couldn't take the rigours of cont use although they gave approx 15% more power out compared to 6550/KT88 types.
EI claim their KT90 is a substitute for the 6550 and KT88 series.......For HiFi DEFINITELY NEIN.
I found some undesirable aspects of the KT90 that are more suited to MI apps rather than Hi Fi ; however if anyone can say there is a difference between the EH types as improved ones......Or they are all clones from one another. I remain interested.
rich
hey all,
my two cents...
background first: david manley of VTL is the one responsible for the KT-90. not long before GE decided to stop making commercial tubes, and 6550's in particular, david went to Niz serbia on the advice of a manager at GE. he was able to introduce and have EI make 6550's. he got an exclusive and distributed them for a time (guess that makes him a "re-brander" right?) and made some money with CJ and AR. a few years after this, he had some prototype octal "super" tubes made based on the EL-519. the problem was that all of manley's big amps were switchable UL or triode... and there was no way any EL-509/519 made would survive with the B+ on the screen (520 and then 590V). it wasn't too healthy for 6550's either if any of you remember (can you spell BOOM?)! so the manley "super" tube was built with the EL-519 tooling and with one crucial change: the screen grid is spaced closer to the plate. this changes the slope (not as much as you would think but yes it does), and it allowed the tubes to survive the manley B+ while running in ultra-linear. so, yes the tube is based on the EL-519 and no it is not exactly the same. and yes it was meant to be interchangeable with 6550/KT-88. whether or not it was a success is still debate-able. but there are a fair number of amps out there that need tubes and therefore there is a market.
i have met and spoken personally with the engineer who did this work at EI (Niz) and confirmed the difference. you do not have to believe me. its easy to see for yourself... providing you have the offending tubes. you will need a micrometer or an engineers ruler and a pair of diagonal cutters OK for cutting steel (don't use your fancy wire dikes). take your blown up EI KT-90 and if the glass is still whole, put it into a paper bag. take a hammer or other suitable blunt metal object and carefully break the glass near the base of the tube. shake the loose stuff off the remains of the tube back into the bag with the rest of the glass and dispose of properly. cut the barkhausen plates and the getter structure off the top mica. carefully snip the side rods just under the top mica. peel off the mica. measure the distance between the screen and plate (if the inner structure get s a little deformed at this point, just roughly center the mess and get a measurement). snip the plate support rods at the bottom mica. pull the plate carefully off, leaving the screen and control grid and cathode naked as day... measure the distance between the cathode and grid, cathode and screen. this is done easiest at the bottom near the press stem.
repeat this whole process with a blown up 6KG6 or EL-509/519. compare your numbers. you will find the truth yourself.
there is another way. with a little bit of conversion work you can put your sylvania or philips 6KG6/EL-509 in any of those old manley amps or an audio research anything amp and see how long you get to keep them. not long. the maximum screen voltage allowable on a EL-519 is 350 volts and only if you have a current limiting resistor in series with the screen. normal operation is between 200 and 250 volts. forget 450+ volts. this is because the screen is much closer to the control grid than it is the plate. in a horizontal sweep circuit, this allows the screen to exert a bigger effect on the current moving through the tube. because the tube is dumping current into the yoke (at 512uS intervals) of a 27"color TV tube, and the quality of this manuever is quite dependent upon the amount of current it can dump in the allotted time, everything in the tube's design is tailored for fast low impedance switching. moving the screen closer to the plate has one beneficial effect for audio: it smoothes the knee of the saturation point somewhat. this lowers the production of odd order harmonics slightly in class AB operation.
the KT-90EH has absolutely nothing to do with SED and the actual production 6P45C (6KG6/EL519), which is a splendid tube, by the way. out of production, but you can still get surplus. reflektor never made those tubes. the KT-90EH does NOT come from it. it doesn't look anything at all like the SED because it shares no tooling with it. it is a completely new design from the ground up. the plate is not borrowed from anything else so it doesn't look like any other plate. those familiar with older german tetrodes and pentodes will recognise the extra radiators folded into the plate. this was taken from the F2A Siemens. unlike the original, it has 100uM screen wire (instead of 65uM) and heavy phosphor bronze side rods to help wick away all the heat from those over dissipated screens. the SED has NONE of this.
the build quality is much different from the EI and obviously it looks different. and like the EI tube, it will NOT dump as much current as a 6KG6/EL519. this is because of the shifted screen and not because it sucks. it will, however, work in an ultralinear amp with a stupid amount of volts on the tranny, something no EL519 can claim. i am not recommending this, i always thought it was stupid... but for those who need the tubes for their amps...
jc
my two cents...
background first: david manley of VTL is the one responsible for the KT-90. not long before GE decided to stop making commercial tubes, and 6550's in particular, david went to Niz serbia on the advice of a manager at GE. he was able to introduce and have EI make 6550's. he got an exclusive and distributed them for a time (guess that makes him a "re-brander" right?) and made some money with CJ and AR. a few years after this, he had some prototype octal "super" tubes made based on the EL-519. the problem was that all of manley's big amps were switchable UL or triode... and there was no way any EL-509/519 made would survive with the B+ on the screen (520 and then 590V). it wasn't too healthy for 6550's either if any of you remember (can you spell BOOM?)! so the manley "super" tube was built with the EL-519 tooling and with one crucial change: the screen grid is spaced closer to the plate. this changes the slope (not as much as you would think but yes it does), and it allowed the tubes to survive the manley B+ while running in ultra-linear. so, yes the tube is based on the EL-519 and no it is not exactly the same. and yes it was meant to be interchangeable with 6550/KT-88. whether or not it was a success is still debate-able. but there are a fair number of amps out there that need tubes and therefore there is a market.
i have met and spoken personally with the engineer who did this work at EI (Niz) and confirmed the difference. you do not have to believe me. its easy to see for yourself... providing you have the offending tubes. you will need a micrometer or an engineers ruler and a pair of diagonal cutters OK for cutting steel (don't use your fancy wire dikes). take your blown up EI KT-90 and if the glass is still whole, put it into a paper bag. take a hammer or other suitable blunt metal object and carefully break the glass near the base of the tube. shake the loose stuff off the remains of the tube back into the bag with the rest of the glass and dispose of properly. cut the barkhausen plates and the getter structure off the top mica. carefully snip the side rods just under the top mica. peel off the mica. measure the distance between the screen and plate (if the inner structure get s a little deformed at this point, just roughly center the mess and get a measurement). snip the plate support rods at the bottom mica. pull the plate carefully off, leaving the screen and control grid and cathode naked as day... measure the distance between the cathode and grid, cathode and screen. this is done easiest at the bottom near the press stem.
repeat this whole process with a blown up 6KG6 or EL-509/519. compare your numbers. you will find the truth yourself.
there is another way. with a little bit of conversion work you can put your sylvania or philips 6KG6/EL-509 in any of those old manley amps or an audio research anything amp and see how long you get to keep them. not long. the maximum screen voltage allowable on a EL-519 is 350 volts and only if you have a current limiting resistor in series with the screen. normal operation is between 200 and 250 volts. forget 450+ volts. this is because the screen is much closer to the control grid than it is the plate. in a horizontal sweep circuit, this allows the screen to exert a bigger effect on the current moving through the tube. because the tube is dumping current into the yoke (at 512uS intervals) of a 27"color TV tube, and the quality of this manuever is quite dependent upon the amount of current it can dump in the allotted time, everything in the tube's design is tailored for fast low impedance switching. moving the screen closer to the plate has one beneficial effect for audio: it smoothes the knee of the saturation point somewhat. this lowers the production of odd order harmonics slightly in class AB operation.
the KT-90EH has absolutely nothing to do with SED and the actual production 6P45C (6KG6/EL519), which is a splendid tube, by the way. out of production, but you can still get surplus. reflektor never made those tubes. the KT-90EH does NOT come from it. it doesn't look anything at all like the SED because it shares no tooling with it. it is a completely new design from the ground up. the plate is not borrowed from anything else so it doesn't look like any other plate. those familiar with older german tetrodes and pentodes will recognise the extra radiators folded into the plate. this was taken from the F2A Siemens. unlike the original, it has 100uM screen wire (instead of 65uM) and heavy phosphor bronze side rods to help wick away all the heat from those over dissipated screens. the SED has NONE of this.
the build quality is much different from the EI and obviously it looks different. and like the EI tube, it will NOT dump as much current as a 6KG6/EL519. this is because of the shifted screen and not because it sucks. it will, however, work in an ultralinear amp with a stupid amount of volts on the tranny, something no EL519 can claim. i am not recommending this, i always thought it was stupid... but for those who need the tubes for their amps...
jc
Hi,
That part I know nothing about....
Never saw a single 6550 coming out of former Yugoslavia.
According to what I heard, when GE in the US stopped manufacturing electron tubes, the 6550A in particular became a problem to major users such as Manley (still VTL in those days), ARC, CJ, Jadis, etc.
Rumour had it GE had a small plant in the South of France that was willing to pick up the slack.
Good news so far especially since the Chinese made 6550/KT88s were such useless junk in those early days of production.
That French adventure went sour after only a short while though due to reliability problems and where most other manufacturers used what was available (Chinese stuff), Manley did not want to drown his amps with Chinese junk and decided to take the plunge probably figuring that he could easily sell his higher powered version of the KT88 (now nee KT90) to the remainder of the market once the news spread.
Sure enough, after about six months of use in the VTL amps the KT90 started to come as a surplus alternatives either from VTL directly or through the common vendor channels.
There's another story about exclusivity of the KT90 to Manley that did really turn out that way but that's for another day........
The KT90 received good press as being reliable and better sounding (well it did sound different indeed) than the other alternatives...
Note that there wasn't all that much left to compare them with in the first place which no doubt helped market penetration no end.
Almost similtaneously the supplies of ECC81/12AT7As, (Manley used them almost exclusively in those days, started to dry up and that's how my company started negotiating with the Nic (read Neesh) plant to have them manufacture a run of those.
That run never happened, partly due to difficult communication with the folks at the EI plant and the fact they wanted a 10K/year run paid in full up front. Not exactly peanuts, let me tell you.
Manley found alternatives in the 6350s and 6463s to replace 12BH7A and I can't remember what happened to the 12AT7As...
Maybe Richardson Electronics (the group behind GE among others) jumped on it, not sure how it went.
Now don't tell anyone at Manley's a KT90 is a reworked EL509/519 or someone will be jumping all over you....
Check previous threads on the topic if you don't believe me.
I'm sure glad someone else from within the industry is confirming my story about the KT90 though.
There's more interesting stuff to be told....Sure brings back fond memories for me.
Thanks for the very informative post, J.C.
Cheers,
That part I know nothing about....
Never saw a single 6550 coming out of former Yugoslavia.
According to what I heard, when GE in the US stopped manufacturing electron tubes, the 6550A in particular became a problem to major users such as Manley (still VTL in those days), ARC, CJ, Jadis, etc.
Rumour had it GE had a small plant in the South of France that was willing to pick up the slack.
Good news so far especially since the Chinese made 6550/KT88s were such useless junk in those early days of production.
That French adventure went sour after only a short while though due to reliability problems and where most other manufacturers used what was available (Chinese stuff), Manley did not want to drown his amps with Chinese junk and decided to take the plunge probably figuring that he could easily sell his higher powered version of the KT88 (now nee KT90) to the remainder of the market once the news spread.
Sure enough, after about six months of use in the VTL amps the KT90 started to come as a surplus alternatives either from VTL directly or through the common vendor channels.
There's another story about exclusivity of the KT90 to Manley that did really turn out that way but that's for another day........
The KT90 received good press as being reliable and better sounding (well it did sound different indeed) than the other alternatives...
Note that there wasn't all that much left to compare them with in the first place which no doubt helped market penetration no end.
Almost similtaneously the supplies of ECC81/12AT7As, (Manley used them almost exclusively in those days, started to dry up and that's how my company started negotiating with the Nic (read Neesh) plant to have them manufacture a run of those.
That run never happened, partly due to difficult communication with the folks at the EI plant and the fact they wanted a 10K/year run paid in full up front. Not exactly peanuts, let me tell you.
Manley found alternatives in the 6350s and 6463s to replace 12BH7A and I can't remember what happened to the 12AT7As...
Maybe Richardson Electronics (the group behind GE among others) jumped on it, not sure how it went.
Now don't tell anyone at Manley's a KT90 is a reworked EL509/519 or someone will be jumping all over you....
Check previous threads on the topic if you don't believe me.
I'm sure glad someone else from within the industry is confirming my story about the KT90 though.
There's more interesting stuff to be told....Sure brings back fond memories for me.
Thanks for the very informative post, J.C.
Cheers,
Rich,
re: "The history behind the EL509 cum KT90 (or whatever) seems to enamanate from the early colour TV frame line output tube app....a beefy 50W plate dissip....recently turned into an audio tube."
As the legend goes, Dan Armstrong went up to visit Traynor (in Canada) and went home with a YBA-3A and two of the "Big B" speaker cabs (8x10") that went along with it... shortly after that, Ampeg had a new amp design, the SVT. Everybody knows the SVT, nobody knows the YBA-3A that was its inspiration. Most folks have probably never seen an original SVT, plate caps and all, and think they always ran 6550's.
The YBA-3A produced somewhere in the 300W range (higher if you consider that a some distortion can make for a great rock bass tone, and crank it up) using four EL-509's. The first YBA-3A I bought still had the original Philips EL-509's in it, with suspiciously Mullard-looking date codes, some 35 years after it was made. Pretty impressive.
My point is that the EL-509 as a high-power audio tube is not a new thing. Pete Traynor was doing it in the 1960's.
Here's the schematic for the YBA-3A "Super Custom Special" amp, at the end of this pdf.
I found this thread while trying to decide what kind of tubes I want to get for the Marshall Major I'll be receiving next week. From everything I've read about the Major, it's really good at killing weak KT88's. I've been looking at recent-production KT88's and KT90's, trying to figure out which ones I'm going to hopefully not blow up.
Scott
re: "The history behind the EL509 cum KT90 (or whatever) seems to enamanate from the early colour TV frame line output tube app....a beefy 50W plate dissip....recently turned into an audio tube."
As the legend goes, Dan Armstrong went up to visit Traynor (in Canada) and went home with a YBA-3A and two of the "Big B" speaker cabs (8x10") that went along with it... shortly after that, Ampeg had a new amp design, the SVT. Everybody knows the SVT, nobody knows the YBA-3A that was its inspiration. Most folks have probably never seen an original SVT, plate caps and all, and think they always ran 6550's.
The YBA-3A produced somewhere in the 300W range (higher if you consider that a some distortion can make for a great rock bass tone, and crank it up) using four EL-509's. The first YBA-3A I bought still had the original Philips EL-509's in it, with suspiciously Mullard-looking date codes, some 35 years after it was made. Pretty impressive.
My point is that the EL-509 as a high-power audio tube is not a new thing. Pete Traynor was doing it in the 1960's.
Here's the schematic for the YBA-3A "Super Custom Special" amp, at the end of this pdf.
I found this thread while trying to decide what kind of tubes I want to get for the Marshall Major I'll be receiving next week. From everything I've read about the Major, it's really good at killing weak KT88's. I've been looking at recent-production KT88's and KT90's, trying to figure out which ones I'm going to hopefully not blow up.
Scott
SY said:
Please don't get the electric bass guitar amp I was talking about, the Traynor YBA-3A, confused with the high-end/reference tube amps made by the manufacturer YBA.
The life of the EL-509/EL-519's in the YBA-3A is something I can't speak to with any accuracy. I have two of these amps. The first, when I bought it, it had the old (and I believe possibly original) Philips (Mullard) tubes that the Traynors came with in the 60's/early 70's. I have no idea how many hours were put in on them, but they were still functional when I got the amp about 2 years ago.
After playing them hard, with the volume on the amp up near max, driving 2x15" and 4x10" speakers, playing bass with plenty of great 'grit' type distortion (all from the amp), maybe a few months later three of the four tubes all went down at once.
I have a stock of probably 30 or so EL-509's and EL-519's, mostly old US and UK stock (branded RCA, Philips, Sylvania, Zenith, etc), with a few EI's in there. I went through them all, trying different combinations until I could find a quad that were as closely matched as I could find... the amp, stock, only has a single bias control for all four tubes. This is something I'll change at some point, putting in separate controls for each tube.
The second Traynor YBA-3A I bought was set up by a tech in Ohio, and he put in a new quad of EI's, and biased the amp using a scope. I haven't gone in there yet and checked how the individual tubes are operating, nor have I played the amp at high volume at all yet to make sure they're even gonna be happy being beat on. Basically with the second one, I bought it because I had the chance, and I am such a huge fan of the amp that I wanted to have a backup. As they only come up on eBay about one every year or so (it's a fairly rare amp), it was a "now or maybe never" kinda thing...
So all I can say about the tube longevity is that I bought one of these amps with roughly 30-year-old Philips tubes that were still functional when I got it. I don't know how much they were used over the course of those 30 years, but I'm sure it was at least *some*. And since I put the new (old production) tubes in there, I've only put in maybe 20 hours of playing time on them. They've worked fine in that time.
One of my favorite aspects of the design of the amp is that it has separate taps on the power transformer for bias, plate, and screen voltage. Having separate taps for the screen is something that rarely if ever happens in musical instrument amps. Then again, this is the only MI amp I'm aware of that uses the EL-509/EL-519.
Scott
I'm 10 years late to this party.
I did the re-design on the original screen/anode geometry for Manley's first Ei KT90s. The factory had the spacing wrong, the anode was too far from the screen with the result the 'virtual cathode' couldn't work properly and the plate curves were a mess at lower anode voltages.
I also commissioned the use of SAES continuous acting strip getters on the anodes and was about get titanium wire used in the grid winding but the Daddy Bush had to have his little war over and US importation of anything from the war zone was embargoed.
Things never really did recover, at least not as far as I know
I did the re-design on the original screen/anode geometry for Manley's first Ei KT90s. The factory had the spacing wrong, the anode was too far from the screen with the result the 'virtual cathode' couldn't work properly and the plate curves were a mess at lower anode voltages.
I also commissioned the use of SAES continuous acting strip getters on the anodes and was about get titanium wire used in the grid winding but the Daddy Bush had to have his little war over and US importation of anything from the war zone was embargoed.
Things never really did recover, at least not as far as I know
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.