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I think this date code suggests 1989. If so I presume it is type 3 prewar?
Edits: 10/20/16 10/20/16Follow Ups:
They were purchased as Type iii. They have the square thingy the on the plate and was hoping the acid code would determine if they are the non red plating kind.
Despite what has been said there is NO WAY to tell if the tube suffers from the screen misalignment/red plating issues except to run the tube and see. I was able to do that on my test gear, but it's always a bit risky when you have to use the amp as your test bed.
See the link below for my response to a similar question in 2005.
My advice is simply stay away from type III unless you can check for the problem.
Thanks Jim. A tube vendor in my area has an Amplitrex tester. Would they be able to determine if my tubes are the red plate kind? I'd prefer not to test drive them in my amp.
It's not 100% sure if he can. The tube needs to be pushed to 40+ watts of dissipation to be sure it is okay. I suspect he can do it but I can't say for sure.
Thanks Jim I will inquire.
I have a quad of Type III's with that exact same printing. Bought them to use in my Citation II before I learned about the concerns with the Type III. I never tried them.
Would it be less risk to run them in an amp that has adjustable bias in a range of 20 - 25 watts (450 v at 50 mA)? Or, do they just not sound good biased cold?
Warming them up once to check ought to be OK...though the fixed bias would be needed to run them up to full ratings and confirm no red spots, yes? You'll either have good ones or you won't.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
iŽd like to add that i never ever had any problems with type 3. sounds as good as type 2 in my gear.
N.
"Science only illustrates the current state of errors"
Nobody said they didn't sound good. The issue was red plating due to misaligned screens.
jus to put a fine point on that 'red plate' issue, this was at dissipations well under their ratings. IIRC, per Jim's writings on the subject can happen as low as 25-30W.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
iŽd like to add that i never ever had any problems with type 3. sounds as good as type 2 in my gear.
N.
"Science only illustrates the current state of errors"
A lot of people had a lot of problems with them - you were lucky to get good ones!!
Just toasted one of the Quad of iii's I got from you Jim...took a 2W/10R current sense with it. Hope I could find a single somehow...:)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Wow, sorry to hear Doug. You've had those for a LONG time - I went through my records to see when you got them and I can't find it. When did you get them, do you recall?
That would have been 2001-2002 perhaps? I got them for amps build around Dyna A441 outputs...which were basically not as good as I hoped they were...LOL They went on to service in my Mk.iii on and off as those amps went into service( and out ). Up to yesterday, they'd been happily doing service in my W6m. That accounts for probably the last 4-5 years.
I do need some EL84, will send you a note on that momentarily.
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
http://www.ebay.de/itm/201677575326?clk_rvr_id=1112909439432&rmvSB=true
"Science only illustrates the current state of errors"
Those are type III - and as I've posted for over 10 years - you can't tell if the tube is going to red plate or not just by looking at it. It has to be tested.
Yah, no question there Jim. For that price, I would want a guarantee that I could believe in that they'd tolerate 100 mA of plate current at 400V plate and screen...with absolutely no plate red spots( in a dark room ).
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
As Mendel said the "wings" on the plates indicate type III. But type IIIs weren't made in the 1980s AFAIK. And honestly I've had very little luck with Ei coding. I'd bet this tube is from later production.
It is definitely not type 1 or 2.
Looks like type 3 due to "wing" structure where the two anode halves join.
Look for a silver metal square or circle on one side (without the square holes) of the anode plates. If it is square, it is type 3 prewar. If it is circular, it is type 4 post war.
Hopefully Jim McShane weighs in here. I can't tell from the construction.
My thought is from the date it would be at least type II or possibly type I.
There used to be web site, which I can't find, that had pictures of the different evolutions of the EI KT90. It was on the Manley Labs web page.
Edits: 10/20/16 10/20/16
Is this what you're looking for? I believe it is a type 2
no sir, seems to be type 3 (or 4).as i know, type II has anode plates ending flat like a blade. your picture shows angled blades.
N.
"Science only illustrates the current state of errors"
Edits: 10/21/16
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