Rich, what you're dealing with here isn't an RCA/GE 6550. It is possible that there's more grid leakage in these tubes- your resistor values are not unreasonable for most tubes, but you're dealing with an unknown. The warmup phenomenon you talked about is suggestive.
If you've got access to a very high input impedance voltmeter, it might be interesting to see how much leakage you actually have by measuring the voltage across the 68K resistors during the warmup phase where you've noticed instability. If it turns out to be OK, then there's fundamental problems with these tubes and you'll probably be restricted to cathode resistor bias. If the grid leakage is high, then you know what to do to compensate for it.
If you've got access to a very high input impedance voltmeter, it might be interesting to see how much leakage you actually have by measuring the voltage across the 68K resistors during the warmup phase where you've noticed instability. If it turns out to be OK, then there's fundamental problems with these tubes and you'll probably be restricted to cathode resistor bias. If the grid leakage is high, then you know what to do to compensate for it.
Hi I was considering getting EH KT90's for the Plitron amp that I've picked out of the flock..
Anyway I was wondering where a humble Aussie could get these apparently fine valves as that website which
was posted a while back has run out of stock...
KT90EH -NOTE: OUT OF STOCK $58.00
Absolutely the best KT90 ever developed.
I was wondering what the final verdict was on these new KT88's ? Are they all they are? Are they better?
http://www.plitron.com/pages/Products/Audio/vtvkt88.htm
I know I'm a pain..
but...
As my 20th birthday is coming up soon I have moved towards the
money-is-no-objective-thought-process and hope to get the best I can in everything but of course cutting
back at the $1000 for 1 channel mark...
Ciao
Anyway I was wondering where a humble Aussie could get these apparently fine valves as that website which
was posted a while back has run out of stock...
KT90EH -NOTE: OUT OF STOCK $58.00
Absolutely the best KT90 ever developed.
I was wondering what the final verdict was on these new KT88's ? Are they all they are? Are they better?
http://www.plitron.com/pages/Products/Audio/vtvkt88.htm
I know I'm a pain..
but...As my 20th birthday is coming up soon I have moved towards the
money-is-no-objective-thought-process and hope to get the best I can in everything but of course cutting
back at the $1000 for 1 channel mark...
Ciao
SY........www.chelmervalve.com is where I get some my beauties from. Pays with todays choatic tube market to order premium run-in tubes. This weeds out the charf from the grain.
I've also sent back tubes to triode elect (US) also without quibbles.
rich
I've also sent back tubes to triode elect (US) also without quibbles.
rich
richwalters
Your'e doing fine.... how come your'e still alive?
Turn everything on from a distance, never leave something plugged in even if it's only a two conductor
cable, never pull by the cord and always have a rubber mat underneath your workstation, not that it helps, but it may when the big accident happens...
I have 8 years in the institute of the mad with computers and their associated PSU's, I once doubled up on a switching power supply to provide my motherboard 400 watts out of two 200watt psu's just to make the Athlon stable all the folk said, and I quote, "the transient voltages from ither PSU's will destroy them both and the distortion from both PSU's will destroy the motherboard"
It worked for 8 months until I upgraded, and the mobo (motherboard) works till this day.
I also have 'experience' when I was 6 at plugging in a braided 240v cord into the power socket and turning it on, a failure of my father to properly place it somewhere.
Today he places all of them in one box, high up
Also I've noted from an old TV repair manual when working on a high voltage live chassis make sure it's unplugged because if you are wearing rubber boots and your wife comes home, creeps up behind you out of the rain and gives you a kiss on the neck, the barber will be laughing his head off for the rest of your days...
Also, microwaves are the most lethal appliance besides televisions and it doesn't matter of the size of either set, still be careful, I have diagnosed in my days one had a blown cabinet-globe from old age, 14 years old to this day it cooks my dinner sometimes a Toshiba huge-model
Capacitors of all sizes and types can hold their voltage for more than a month after disconnection, so ALWAYS discharge them somehow, ither through a well-connected bleed resistor circuit or a handle-insulated screwdriver, and no you should not use a neon test-screwdriver
Always write down where each connection was and what they were, before you trash an appliance for transformers or components falling under that category.
Never measure a live 240volt connection without it first being insulated with a transformer and even then only for a few seconds.
Always tie speakers in on themselves and hang them up or place them in a box somewhere for safe use, off the floor so cockeroaches, mice and ants can't eat them.
Always earth Transmitters and Transcievers well.
No need to leave them hooked up to the antenna and earthed after use.
OH and be careful around high-wattage amplifiers or base stations as RF burn of your skin or brain could occour, hehe...
Never leave a TV extension in the wall next to your bed-head or phone extensions for that matter
Anyway, that's my blurg for now and...
I guess the answer is, I'm moderatley sensible and don't like to rush anything.
Thanks guy's I'll be going for a couple EH 90's
Woo: http://www.audioasylum.com/audio/tubes/messages/135132.html
Your'e doing fine.... how come your'e still alive?
Turn everything on from a distance, never leave something plugged in even if it's only a two conductor
cable, never pull by the cord and always have a rubber mat underneath your workstation, not that it helps, but it may when the big accident happens...
I have 8 years in the institute of the mad with computers and their associated PSU's, I once doubled up on a switching power supply to provide my motherboard 400 watts out of two 200watt psu's just to make the Athlon stable all the folk said, and I quote, "the transient voltages from ither PSU's will destroy them both and the distortion from both PSU's will destroy the motherboard"
It worked for 8 months until I upgraded, and the mobo (motherboard) works till this day.
I also have 'experience' when I was 6 at plugging in a braided 240v cord into the power socket and turning it on, a failure of my father to properly place it somewhere.
Today he places all of them in one box, high up
Also I've noted from an old TV repair manual when working on a high voltage live chassis make sure it's unplugged because if you are wearing rubber boots and your wife comes home, creeps up behind you out of the rain and gives you a kiss on the neck, the barber will be laughing his head off for the rest of your days
...Also, microwaves are the most lethal appliance besides televisions and it doesn't matter of the size of either set, still be careful, I have diagnosed in my days one had a blown cabinet-globe from old age, 14 years old to this day it cooks my dinner sometimes a Toshiba huge-model
Capacitors of all sizes and types can hold their voltage for more than a month after disconnection, so ALWAYS discharge them somehow, ither through a well-connected bleed resistor circuit or a handle-insulated screwdriver, and no you should not use a neon test-screwdriver
Always write down where each connection was and what they were, before you trash an appliance for transformers or components falling under that category.
Never measure a live 240volt connection without it first being insulated with a transformer and even then only for a few seconds.
Always tie speakers in on themselves and hang them up or place them in a box somewhere for safe use, off the floor so cockeroaches, mice and ants can't eat them.
Always earth Transmitters and Transcievers well.
No need to leave them hooked up to the antenna and earthed after use.
OH and be careful around high-wattage amplifiers or base stations as RF burn of your skin or brain could occour, hehe...
Never leave a TV extension in the wall next to your bed-head or phone extensions for that matter
Anyway, that's my blurg for now and...
I guess the answer is, I'm moderatley sensible and don't like to rush anything.
Thanks guy's I'll be going for a couple EH 90's
Woo: http://www.audioasylum.com/audio/tubes/messages/135132.html
I've found another source for KT90EH
http://www.musictechbrasil.com/valvulas/ELECTROHARMONIX/VALVULAS_ELECTRO_HARMONIX_TUBES.HTM
http://www.musictechbrasil.com/valvulas/ELECTROHARMONIX/VALVULAS_ELECTRO_HARMONIX_TUBES.HTM
"I also have 'experience' when I was 6 at plugging in a braided 240v cord into the power socket and turning it on"
Good story Layberinthius, I had to chuckle because when I was 6 I made a cord with 2 male ends and plugged them in the wall outlet! PFFFZAPP! Now I find out I'm Mensa qualified. Go Figure!
Good story Layberinthius, I had to chuckle because when I was 6 I made a cord with 2 male ends and plugged them in the wall outlet! PFFFZAPP! Now I find out I'm Mensa qualified. Go Figure!
Hehehe
Oh the fun times I'm glad no fires were started tho
I believe the most inquisitive minds are usually the most easiest to brainwash or and the most likely to be the greatest in their field.
First and last time I was electrocuted tho was when I was 12 where a photocopier motor with an inbuilt gearbox was the source of it, I spun it while holding one of the terminals of my multimeter to each strand of wire that came out of it while the meter held a common neutral
Little did I know that my hand which was producing the power was also producing the felt oscillations of 100volts of electricity passing through my body
It only lasted for about 1 second till I pulled my hand off the wheel after the standard spin-&-let-go routine.
Oh the fun times
I'm glad no fires were started tho I believe the most inquisitive minds are usually the most easiest to brainwash or and the most likely to be the greatest in their field.
First and last time I was electrocuted tho was when I was 12 where a photocopier motor with an inbuilt gearbox was the source of it, I spun it while holding one of the terminals of my multimeter to each strand of wire that came out of it while the meter held a common neutral
Little did I know that my hand which was producing the power was also producing the felt oscillations of 100volts of electricity passing through my body
It only lasted for about 1 second till I pulled my hand off the wheel after the standard spin-&-let-go routine.
Sometimes the phone rings at insanely hours on a saturday/sunday or late at night when it's only my brother who want's to be picked up somewhere ;P
SO I have my phone on the desk and a DIY 'illiegal' toggle switch to turn off the 'ringer'..
Seeing I'm a student and haven't got the expense of having two rooms to myself.
SO I have my phone on the desk and a DIY 'illiegal' toggle switch to turn off the 'ringer'..
Seeing I'm a student and haven't got the expense of having two rooms to myself.
Two questions:
1)
why is the KT90EH hard to find in the states? Is it because it's new?
2)
>Rich, it was a friend of mine that did punishing test, he wound them up to 150ma current with 580 plate volts , if you work that out that`s 87watts per valve...
has your friend done this to the KT88EH? I'm wondering about that tube as well. I use Marshall Major guitar amps and my GEC stash is going. I have been using Type II EI KT90's with good results, though not as musical. SED KT88's turned pink on the plates in 5 minutes. JJ's are ok, but I'm wondering about the EH's ability to handle the 630volts in the Major (I crank the amp at all times).
1)
why is the KT90EH hard to find in the states? Is it because it's new?
2)
>Rich, it was a friend of mine that did punishing test, he wound them up to 150ma current with 580 plate volts , if you work that out that`s 87watts per valve...
has your friend done this to the KT88EH? I'm wondering about that tube as well. I use Marshall Major guitar amps and my GEC stash is going. I have been using Type II EI KT90's with good results, though not as musical. SED KT88's turned pink on the plates in 5 minutes. JJ's are ok, but I'm wondering about the EH's ability to handle the 630volts in the Major (I crank the amp at all times).
Steve.....it doesn't look good for the long term. One is having to fork out dosh for really well made tubes that hold up to MI apps.....I'm currently using JJ Tesla 88's which are fine.........as are orig 6550A's RCA/GEC both at a price penalty.
It looks like fixed-bias o/p stage operation shows up the down- side of modern-made-tubes. I suspect alot of todays mades actually prefer to work in cathode auto-bias. The vacuum spec is more relaxed, as are materials, and they get away with this.
Any comments on this ?
I don't like using my NOS stock...orig GEC/MOV Gold Lion KT88's are fetching high prices, infact in a few years time orig branded tubes will fetch antique prices. Same goes for ori 6550A's /JAN spec.......they really do behave like substitute 88's and I don't like pressing them into service.
I've been disappointed with the H.V performance of recent made Svet 6550 ABC's....these also profit from a lightly higher heater voltage. Doesn't it seem strange that the diddy Mullard EL34 holds up better than the Svet 6550 ABC's ?
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. It has an attractive spec but does my circuit really warrant such a monster ? B+ capability Yes; but Pout, no change.....I'm stuck making my mind up, so I'm having a good peep at the KT77 spec as an interim 88. This time I'm very wary whom I get it from...
I've become very dubious in designing amps with tube specs from the Radiotrons handbook....Why ? it's an excellent bible....but very few todays made tubes come anywhere near yesterdays brand name performance expectations. There will always be tube manufacturers that claim ABC' versions of the same tube to be better than originals.....from my bench.......it doesn't look that at all ....No WAY.
The only way I'm going to survive longevity with tube sound is like steam loco's, run them slower and kinder. Same with tube amps.....lower B+ and parallel configurations.
rich
It looks like fixed-bias o/p stage operation shows up the down- side of modern-made-tubes. I suspect alot of todays mades actually prefer to work in cathode auto-bias. The vacuum spec is more relaxed, as are materials, and they get away with this.
Any comments on this ?
I don't like using my NOS stock...orig GEC/MOV Gold Lion KT88's are fetching high prices, infact in a few years time orig branded tubes will fetch antique prices. Same goes for ori 6550A's /JAN spec.......they really do behave like substitute 88's and I don't like pressing them into service.
I've been disappointed with the H.V performance of recent made Svet 6550 ABC's....these also profit from a lightly higher heater voltage. Doesn't it seem strange that the diddy Mullard EL34 holds up better than the Svet 6550 ABC's ?
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. It has an attractive spec but does my circuit really warrant such a monster ? B+ capability Yes; but Pout, no change.....I'm stuck making my mind up, so I'm having a good peep at the KT77 spec as an interim 88. This time I'm very wary whom I get it from...
I've become very dubious in designing amps with tube specs from the Radiotrons handbook....Why ? it's an excellent bible....but very few todays made tubes come anywhere near yesterdays brand name performance expectations. There will always be tube manufacturers that claim ABC' versions of the same tube to be better than originals.....from my bench.......it doesn't look that at all ....No WAY.
The only way I'm going to survive longevity with tube sound is like steam loco's, run them slower and kinder. Same with tube amps.....lower B+ and parallel configurations.
rich
quality
Hi Rich,
I think I know what you mean. I haven't worked with the Svets 6550 in a long time, back then they seemed to work pretty good. But it really seems to be a hodpog, things always changing.
For instance, I have some JJKT88s, from 2 or 3 years old. They turn cherry at 35 watts plate dissapation. Same for 2 or 4 matched, recent EH KT88s. Now the SED (USA version of Svetlana) KT88 seems to be working just fine, no cherry.
I have an old pair of Phillips 6550, and they turn cherry at around 34 watts plate dissapation. Go figure.
Anyway, I haven't been working the modern tubes with all fixed bias. Sounds like from your experience they don't do too well. The SED KT88s seem pretty stable in my operations, at least for the past couple of years.
I also run my output tubes easy, always have and probably always will. Don't have trouble this way.
ps. My grandmother came from Bern. Very far away from where you live?
Hi Rich,
I think I know what you mean. I haven't worked with the Svets 6550 in a long time, back then they seemed to work pretty good. But it really seems to be a hodpog, things always changing.
For instance, I have some JJKT88s, from 2 or 3 years old. They turn cherry at 35 watts plate dissapation. Same for 2 or 4 matched, recent EH KT88s. Now the SED (USA version of Svetlana) KT88 seems to be working just fine, no cherry.
I have an old pair of Phillips 6550, and they turn cherry at around 34 watts plate dissapation. Go figure.
Anyway, I haven't been working the modern tubes with all fixed bias. Sounds like from your experience they don't do too well. The SED KT88s seem pretty stable in my operations, at least for the past couple of years.
I also run my output tubes easy, always have and probably always will. Don't have trouble this way.
ps. My grandmother came from Bern. Very far away from where you live?
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