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Old 27th April 2008, 02:12 AM   #21
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Quote:
Originally posted by itsmejto


Wow, I didn't think I'd ever see anyone who had that many, besides maybe Jim McShane.
Well, no brag...just fact. I've been collecting old tube amps for many years. In the early 80's these were available through flea markets, house sales and newspaper advertisments for about 50 to 100 dollars. Of course this was before the resurgence in tubes became popular. And back then the name brand recognition was not as big as MacIntosh or Fisher. And I also have an affinity for Ampex and Nagra tape machines as well.

Victor
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Old 27th April 2008, 02:27 AM   #22
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Quote:
Originally posted by HollowState


Well, no brag...just fact. I've been collecting old tube amps for many years. In the early 80's these were available through flea markets, house sales and newspaper advertisments for about 50 to 100 dollars. Of course this was before the resurgence in tubes became popular. And back then the name brand recognition was not as big as MacIntosh or Fisher. And I also have an affinity for Ampex and Nagra tape machines as well.

Victor
Even though I love your signature line, I dislike you intensely for the sweet toys you have. I had to sell my A80 1" and my 350 and 440C before the last move.
Sniff.....
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Old 27th April 2008, 02:31 AM   #23
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Quote:
Originally posted by ray_moth
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.
Exactly. Well said.
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Old 27th April 2008, 02:50 AM   #24
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Quote:
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.
They were watts of plate dissipation in a single ended amp with no signal present, just DC dissipation. I have tested a lot of tubes at or above their rated dissipation. I look for glow on the plate and screen grid in a dark room. I run the EH KT88 in my SimpleSE at 400 volts (plate to cathode) and 100 mA. There is no visible glow in a dark room. I have also got a big Antek toroid and I have used it to "test" my amp at 525 volts of B+ which puts about 450 across the tube. Some tubes were beginning to glow at 100 mA and all were glowing at 115 mA, some brightly.

I have built hundreds tube amps over the past 40 years. Not all of them have been successful. Many of the failures came from stuffing too much heat into too small of a package. Not only will you have problems with component and tube lifetime, there will be issues with thermally related drift and possible runaway. Component values change with time and temperature. This can lead to an amp that can behave very differently after it has been on for a while.


Quote:
maybe you forgot to back it offa little before it blew !!!
I may be known for turning things up too far, but that is how you find the limits. Once you know the limits, you can go there with your own stuff, but something that you are going to sell to a possible tube newbie shouldn't run at the limit.

I am not telling you what to do. You can build what ever you want. If you intend to build amps and sell them successfully, they better work, and keep working for a long while. That is why I test my designs at conditions far beyond where any customer may use them. I over design them, and they last.

Quote:
Very off topic.. but Tubelab im really impressed with your MiniTron!
Thanks. I haven't had any time to work on it this year, but I plan to take it further some day. I have received several positive emails, but I also got a few that were really negative. I think that I really rattled some of the "sandophobic" crowd with that one!
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Old 27th April 2008, 02:59 AM   #25
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Quote:
Originally posted by Brett
Even though I love your signature line,
Hi Brett,

That was the 2007 winning entry from an anual contest at Texas A&M University calling for the most appropriate definition of a contemporary term.

Holy mackerel... a Studer A80! What a machine! Sniff is right. I've never owned one and never will. Too much $$$ and no room.
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Old 27th April 2008, 10:28 AM   #26
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When it's finished, it's for sale on Ebay for $20.00 with free shipping.
Price includes a darn great big 5000 ohm 100 watt wire wound resistor
mounted in a seperate fan cooled box for all the weeners that want a 20 watt kt88 amp.
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Old 27th April 2008, 10:57 AM   #27
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We all know tube chassis get hot, always have, always will.
That's why there are high temperature components available for under chassis use. Some use cooling fans and extend the life and safety of these. I'm sure this thing will require some forced cooling and a well ventilated shelf. but to say the chassis is just too small may be a matter of opinion if you have seen some other high powered amps of yesteryear. Especially those used in enclosed wooden cabinets.
I considder this chassis to be large enough if the parts all fit. Afer all it's not rocket science.
Maybe a computer controlled air conditioning system would be advisable !!!!
The're tubes guys, hot is what they do.
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Old 27th April 2008, 02:16 PM   #28
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Quote:
Originally posted by itsmejto
... but to say the chassis is just too small may be a matter of opinion if you have seen some other high powered amps of yesteryear. Especially those used in enclosed wooden cabinets.
I considder this chassis to be large enough if the parts all fit. Afer all it's not rocket science.
Maybe a computer controlled air conditioning system would be advisable !!!!
The're tubes guys, hot is what they do.
All of the electrolytics in those old wood encased amps failed. From heat. And that's certainly not the only thing that happened to those old amps, I've seen the insulation melted out of a transformer or two along the way. The tubes have minimum mounting distances from each other - not just "if they fit." Without even flipping to the datasheet, I feel confident in saying the ST70 chassis is too tight for KT88s running at max dissipation. And that's not even taking in to account that they don't make them like they used to.

It doesn't matter what you put it on ebay starting at... you could put it on there for a penny and that doesn't make you a better person for selling this to some one... it's going to sell for hundreds of dollars to someone wanting a reliable amp for their stereo - someone hoping to get "the sound" without having to shell out audiophile store prices. As long as you are selling it to an unsuspecting individual, you are not going to get any props here. And yes that is all it boils down to. If you had said my latest crazy project for me (my barn, my car, my anything...) people would be saying... crank it up... but you are deliberating taking advantage of the ignorance of ebay... and it's not ok. People will not want to help you do that.
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Old 28th April 2008, 02:43 AM   #29
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Quote:
Originally posted by itsmejto
As for the power tansformer, it's an Antec 800va (5-1/4" dia. x 4" tall) toroidal mounted on it's edge and should fit fine.
Why stop at one? Can't you fit two in there...?

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Old 28th April 2008, 05:58 PM   #30
GordonW is offline GordonW  United States
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Quote:
Originally posted by HollowState
I have a pair of mono blocks that run NOS GE 6550A's in ultralinear with at least 610 volts at 60ma per tube. I can get 100 watts rms out down to 60 Hz with the Acrosound TO-600 4K P-P load. 100 ma is too much and not necessary. However, I would be very afraid to try this with todays garbage 6550/KT88 tubes.
We carry VAC (Valve Amplification Company) here at the shop... the Phi Beta 110 integrated amp reliably gets 110w/ch (MEASURED!) at the outputs, with a pair of KT88s per side.

Even in near constant use (one person who has one from us, uses it like 10 hours a DAY) tubes have lasted in excess of 3 years. That's like 7500 hours so far...

Of course, Kevin Hayes is a pretty talented designer, who knows where the limits are... and this is a $22000 (TWENTY TWO THOUSAND dollar amp)... and no, I wouldn't expect the KT88s to last as long as they would in a Citation II or Dynaco MK3... but 7500+ hours out of modern production (EH) KT88s is not bad...

However- if I was the original poster, I'd be inclined to run something in screen-drive mode (6AV5/6JE6 or something like that), to get that kind of power in that small of a space. At least then, the tubes would be idling at close to Class B, which would SEVERELY reduce the heat under normal circumstances. Would at least give them half a chance of surviving in that cramped of a space...

Regards,
Gordon.
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