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Old 26th April 2008, 04:56 PM   #11
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Jeb, I have a set of the EH, I'll let you know when it's working.
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Old 26th April 2008, 05:09 PM   #12
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Quote:
Originally posted by itsmejto
oh my, such negativity.
I don't think anyone meant to be... I think the prevailing thought to be considered is that you shouldn't be trying to build that large of an amp on a ST70 chassis. Even if you get it all to fit, the heat will reduce all component life. I am in the process of building a similarly rated amp - and I am using a 17x22 inch chassis to give the components breathing room. Personally, I am not found of tube rectifiers in hi-fi gear at all, let alone run at max specs. If you are going to push 400ma, you should go solid state for rectifiers. From what I read your rectifier tube is max rated at 415ma -- 400 to 415 is not what I would call a safe headroom margin. Again, I think this is what everyone is looking at - this amp will have a much higher chance of failure than it should - especially if you are building it to sell to someone who likely has NO tube repair experience. Ultimately your customer is likely to have an unpleasant experience with your amp - repeated/premature tube failure or a complete failure of a major component requiring repair. From a DIY perspective, you should be more responsible with your design (and ultimately your customer) and from a customer standpoint - no one wants to buy something that breaks or requires fixing / maintenance...
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Old 26th April 2008, 05:18 PM   #13
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Quote:
Originally posted by itsmejto
oh my, such negativity.
Guess none of you ever saw a Harmon Kardon Citation II then.
Oh yes. I happen to own five of them. I did have six but I just sold one to a good friend last week. JAN GE 6550As and Tektronix matched 12BY7A drivers.
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Old 26th April 2008, 05:30 PM   #14
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Quote:
Jeb, I have a set of the EH, I'll let you know when it's working.
Please do. I've been considering them for a while.
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Old 26th April 2008, 05:54 PM   #15
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Quote:
Originally posted by tubelab.com


Lets see, 60 watts of dissipation per tube, 240 watts total in the output tubes. The whole amp will melt if the rectifier tube doesn't blow up first! I have been known to bend some tube specs a bit (OK a lot) but I haven't found a KT88 that can deal with 60 watts. The best are EH KT88's and they glow dimly at 45 watts, brightly at 50 watts. They wouldn't last long (a few hours maybe) at 60 watts.

Power transformer? No, you are going to need a nuclear reactor.
Is that plate dissipation or audio watts rms your quoting, either way, if your EH's are glowing at that level I'd think there was a problem.

maybe you forgot to back it offa little before it blew !!!
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Old 26th April 2008, 06:16 PM   #16
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Very off topic.. but Tubelab im really impressed with your MiniTron!
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Old 26th April 2008, 07:36 PM   #17
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Quote:
Originally posted by itsmejto
Is that plate dissipation or audio watts rms your quoting, either way, if your EH's are glowing at that level I'd think there was a problem.

maybe you forgot to back it offa little before it blew !!!
There is a difference between "negativity" and exceeding a KT88's 46W ABSOLUTE MAXIMUM plate + SG dissipation rating by 14 watts. In any case, it is of course up to you how you build your amps, but please consider this a warning in case something blows up, that's all.

reference:
http://www.mif.pg.gda.pl/homepages/f...086/k/KT88.pdf
(and that's for the "real deal" Genalex tubes. don't expect any leeway with new production)
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Old 26th April 2008, 08:43 PM   #18
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Quote:
Originally posted by sorenj07

There is a difference between "negativity" and exceeding a KT88's 46W ABSOLUTE MAXIMUM plate + SG dissipation rating by 14 watts. In any case, it is of course up to you how you build your amps, but please consider this a warning in case something blows up, that's all.

reference:
http://www.mif.pg.gda.pl/homepages/f...086/k/KT88.pdf
(and that's for the "real deal" Genalex tubes. don't expect any leeway with new production)
If you absolutely insist on turning this into a p!$$!ng contest :

The older kt88's though a fine quality tube are not up to modern kt90 standards like the EI or EH currently available.

Besides which, you are quoting plate currents for a single tube.

Having said all that, I built a similar amp way back in 1959 for a local dance hall driving two 18" EV speakers which had to be re-coned because the wern't powerfull enough to handle the output of that amp (mono). yes they were GE tubes at the time.


"KT90 is a beam-power pentode primarly designed for use in audio frequency power amplifier applications. Anode dissipation rate is 50W, which provides for push-pull amplifiers utilization up to 110W output per pair, with 550V on the anode. Up to 160W per pair may be achieved with anode voltage of 750V and screen grid voltage of 600V."

Dangerous, yes I agree, but feasable enough.
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Old 26th April 2008, 09:02 PM   #19
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Quote:
Originally posted by HollowState


Oh yes. I happen to own five of them. I did have six but I just sold one to a good friend last week. JAN GE 6550As and Tektronix matched 12BY7A drivers.
Wow, I didn't think I'd ever see anyone who had that many, besides maybe Jim McShane.
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Old 27th April 2008, 01:31 AM   #20
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itsmejto,

When you start off a thread with a statement like: "Yes, tube life will be limited, but it's for Ebay when done," you give a clear impression that you have a cavalier attitude toward the fate of an amp that you intend to build and then sell. This is bound to attract criticism from responsible forum members, especially if some aspects of your plan appear to be unrealistic.

It is not a "p!$$!ng contest", just common sense. If you don't like other people's comments in a public forum, then I suggest you keep your ideas to yourself.
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