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807 Sound Quality?
807 Sound Quality?
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Old 19th October 2017, 08:01 AM   #231
VladimirK is offline VladimirK  Uzbekistan
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Quote:
Originally Posted by sser2 View Post
A very good question. Burning-in or breaking-in does not have scientific explanation. However, many (myself included) observed that sound of audio components improves with use. It is some kind of black magic.
Although there is no scientific explanation, strong belief exists, that in this case we deal with low level (hardly measurable) added noises, arising due to imperfections at various kinds of materials (wires, conducting films or foils, welded and soldered joints, tube plate and grid materials, etc.).
Burning-in is quite physically understandable effect, resulting from annealing of imperfections. I use burning-in procedure after any resoldering or parts replacement, with dummy resistors at amp output, and the procedure is much faster if output power higher. This is well described by the Annealing Activation Energy term.

Last edited by VladimirK; 19th October 2017 at 08:08 AM.
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Old 19th October 2017, 08:25 PM   #232
janos is offline janos  United States
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Quote:
Originally Posted by FullRangeMan View Post
Thanks for post your impressions
This lead me to some doubts:

What 807 are you using?
I unknew OPTs needs break-in, what break-in do in the transformer?

I suppose the core dont need any burn-in just the winding.
Thanks
Hi FullRangeMan,

The power transformer for the driver and screen high voltage has about 15 years of burn-in (about ?20K hours), the filament transformers have about 2-3000 hours, and the 700V high voltage transformer also about 2-3000 hours. I'd say they are well broken in, at least, all have well stabilized by now with the exception of the 700V transformer, which has x20 current capability compared to the demand, so will take probably a decade or longer to break in. As the idle current has been stable (thus load on PT has not changed), the changes observed are most probably due to the OPT break-in.

I had a discussion with a friend of mine who has vast experience with operating and designing tube gear and electronics (he held training courses for NASA, knows his stuff well.)
I also thought that it's the wire that needs break-in, but he said that the transformer lams also need break in - the BH loop changes with break in (it is measureable), especially in the lower frequencies. He said the bigger the iron, the bigger the change: do not expect significant base response from a big SE OPT if you are running it under a fraction of the rated idle current until it breaks in.
Burn in is a well studied phenomena at NASA, although I am not aware that much has trickled down to audio designers of that lore. For example, do you recall the NASA burn in CD? Luckily, it was available for purchase in the 90s for a brief period. That contains the signal they use to burn in the satellite transponders with before they start broadcasting. Before the burn-in, it is a fact that the satellites bandwidth is limited. (Don't know if they still do this, but has been common practice around 1990-2000. I remember finding a number of satellites with my dish with the colored lines showing, and this audio signal going on for months.) So, even solid state electronics is plagued by burn in - and of burn out as well.

I regularly run the burn-in CD, every couple months. If you have not done it in years, you will be shocked how much the imaging opens up and how more analogue-like it sounds after placing the burn-in CD on repeat for overnight. It's also great to burn-in amps and speakers, but will drive you mad - it sounds like a jumble of test signals. They are not random, they were designed to demagnetize the circuitry they are running through. Weird stuff, sounds weird, but developed by hard-core engineers driven by a critical market (communication satellites).
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Old 19th October 2017, 11:17 PM   #233
janos is offline janos  United States
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Quote:
Originally Posted by FullRangeMan View Post
Thanks for post your impressions
What 807 are you using?
Thanks
Using RCA NOS; they had about 2-3000hrs of break in in the amp with the old OPTs.
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Old 20th October 2017, 05:15 PM   #234
FullRangeMan is offline FullRangeMan  Brazil
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Wow great!!
So how many thousands hours these 807 will last in your amp?
Thanks
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Old 20th October 2017, 07:41 PM   #235
janos is offline janos  United States
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I'm using the amp a lot, it is on for at least 4 hours a day, and often I forget to turn it off at night. Usually it's on for 3-4 days at a stretch, or even a week goes by without turning the amp off. I've been running the 807 for the past year at 60-70% plate dissipation. Before the major rebuild, I used to run them at 400Vp at 85-95% plate dissipation, tubes equipped with copper cooling fins, with a pair of 12V fans blowing on them - and that way the tubes were down to 95% of their initial value after 10 years, about 10K-20K hours or so. I put that pair of tubes to rest for a while, as I replaced them with a different pair... got to do some tube rolling once in a while, shame to have a box of 807s just to collect dust ; ).

I'd say when they have the copper cooling fins, they last forever when run at 80% dissipation... can't imagine how long they will last with 65%

Also, I used to bake them once a year. (There's a special heating procedure to activate the getter to eliminate gas.) Now I use demagnetization instead of baking, I suspect it works better than baking. (Demagnetize the tubes with a tape demagnetizer when the amp is on.)

In brief: keep the tubes cool and keep the vacuum tight, and a pair of 807s will outlast you ; ).
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Old 20th October 2017, 08:35 PM   #236
FullRangeMan is offline FullRangeMan  Brazil
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WOw Thanks for your first hand experience.
Do you would say the Russian G807 Ulianovsk would lasts this much?
Thankyou again,
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Old 21st October 2017, 04:05 AM   #237
janos is offline janos  United States
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Don't have any experience with those tubes, but I assume they will last a very long while if you keep plate dissipation at 80% max, and help with cooling - with either sticky aluminum tape or copper tape. (Plus, make sure the screens are kept strictly under 300V.)
I'll try to post a picture with what I do with my power tubes; )
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Old 1st July 2018, 08:05 AM   #238
Topace is offline Topace
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From Post 107
"As long as plate voltages are kept in the 400V range UL should be OK. The strict 300V screen grid rating applies ONLY for tetrode mode. In triode or UL you can run it higher, provided that the screen is ALWAYS at a lower potential than the plate - which it always is in triode or UL mode."

Actually, I have measured the screen voltage to be higher than the plate voltage in my Ultra linear connected 807. There is a 343V screen and a 337V plate Voltage. This makes sense as the screen tap it closer to the B+. There is no screen stopper resistor. I will have to add one which should get the screen voltage under the plate voltage. Also in triode mode, wouldn't the voltages be the same for the screen and grid without a screen stopper resistor?

It was this thread mostly that convinced me to buy the Old buffalo amp. OldBuffalo 807 fu7 tube amplifier

Although from the only review I was expecting a 480 supply voltage, it is only 337 volts.

The sound is unbelievable clear compared to the mid priced transistor amps I have. Such as the NAD C320BEE. The depth and definition of reverb is astounding. And the bass definition is the best I have ever heard. Led zeppelin II was one of the first albums I ever bought and it is the first time I can hear every bass note super clear. But it feels lacking in dynamics and weight in the lower frequencies. I am sure this amp has plenty of room to tweak it up.

I will update on the progress. Next step is the screen stopper resistor.
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Old 3rd July 2018, 02:02 PM   #239
Kay Pirinha is offline Kay Pirinha  Germany
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Please don't get me wrong, I really like LZ's 2nd album. But I don't think it is apt for judging the sound quality of electroacoustic gear.


Best regards!
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Old 9th July 2018, 01:10 PM   #240
Topace is offline Topace
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Continuing from post 238.
The screen voltage was still higher than the plate voltage after installing the 100ohm stopper resistor on the screen. I did not feel comfortable with this and with further research found these tubes are not ultra linear friendly, so I converted the amp to triode mode.
It sounds much better now. In ultra linear mode the high frequencies were too emphasised and lacked dynamics. This did make listening to reverbs facinating, but the amp sounds much more relaxed and balanced now with a more present and deeper sound stage. I don't know why anyone could say a bad thing about single ended zero feedback tube amps.

There is not much to mod on this amp. Just some capacitor upgrades really, perhaps a larger choke. That's it. I will let you know when I do these upgrades. But at the moment it sounds very nice. There is no going back to transistors now.
One thing to note is the original Chinese tubes sound a bit fuzzy. I have installed NOS Sylvania and Russian tubes which have better focus and sound stage.
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