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tubes 6082 Raytheon

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Posted on May 8, 2020 at 11:16:08
sprussog
Audiophile

Posts: 5
Location: east germany by silicon saxony
Joined: October 23, 2013



Hello dear people, I built the Macovski OTL. The power supply is more modern and I built a reliable speaker protection. A small hum is annoying me, for which I cannot find the cause. For all tubes i have a DC heather.
The preamp power supply is separate from the end stage power supply. I installed another preamp stage ( JJ828 ), the hum became less. Is it the many different tensions in the preamp stage that cause this?
Lots of 6082 tubes have been broken lately. They are now 53 years old, NOS, in best quality. Thats normal for this Raytheon tubes? Sometimes I can see some rust on the bases. Best greetings from Steffen

 

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RE: tubes 6082 Raytheon, posted on May 12, 2020 at 22:36:37
djn
Audiophile

Posts: 1954
Location: michigan
Joined: January 15, 2003
Would the 6AS7 be a drop in replacement?

 

What is the value of the current limiting resistors in the output section?, posted on May 13, 2020 at 11:54:58
Ralph
Manufacturer

Posts: 3910
Location: Minnesota
Joined: April 24, 2002
Also, how are the grid and cathode resistors of the input voltage amplifiers grounded?

If they are not tied to exactly the same point and then a single wire to ground, you'll likely get a hum even though you have DC filaments.

 

RE: tubes 6082 Raytheon, posted on May 13, 2020 at 13:18:39
cpotl
Audiophile

Posts: 947
Location: Texas
Joined: December 6, 2009
Nice looking amps! I also built the Dickie-Macovski OTL a few years ago, and it's been working nicely since. I followed the original power supply design, so there really is no transformer anywhere in the amplifier. I do have a slight hum, because of the necessity, given the power arrangements, of half-wave rectification. I've never got around to trying to deal with that but I assume I could moderate it with extra smoothing capacitors. I use AC for the heaters, and I don't think that is a significant source of hum. (I put the input tubes at the bottom end of the 120V heater chain and the 6082 output tubes at the "live" end.)

To answer djn the 6082 is not a drop-in replacement for a 6AS7 because it has a 26V heater. I think a 6080, differing only in having a 6.3V heater, is essentially equivalent to a 6AS7, though.

 

If it lacks current limiting resistors in the output section, power tubes will fail easily., posted on May 14, 2020 at 09:46:57
Ralph
Manufacturer

Posts: 3910
Location: Minnesota
Joined: April 24, 2002
The best place to place the resistors is in the cathode circuit of each section. We use 5 ohm 5 watt devices and what might sound weird here is that they will actually lower the output impedance of the amplifier because they will cause the power tubes to work more harmoniously together. If a power tube is hogging current it will limit the output power and it will be more likely to fail.

So this is a common sense improvement to the original circuit.

The other thing I would do is pre-condition the power tubes. 6080s and 6082s need about 4 days and 4 nights of pre-conditioning prior to use. You can't precondition a used tube- this only applies to new tubes or NOS. Pre-conditioning is essentially running the filament circuit and no B+ whatsoever during the process. It can double the life of the tube and vastly reduce arcing due to flaking of the cathode coating.

 

Ralph, What about my 7241s?, posted on May 23, 2020 at 18:36:04
Lew
Audiophile

Posts: 10366
Location: Bethesda, Maryland
Joined: December 11, 2000
I just re-tubed one monoblock with all new 7241s. Do you recommend for whole days for pre-conditioning the filaments of that tube type. I did it for 6 hours or so and then was impatient to hear music. So, listening now, but could go back and do more conditioning. Thanks.

 

RE: Ralph, What about my 7241s?, posted on May 23, 2020 at 18:55:56
pictureguy
Audiophile

Posts: 13005
Location: SoCal
Joined: October 19, 2008
Isn't it 'conditioning' (whatever that is) even as you listen?

It's not like the filaments shut off when you turn on the music.


Too much is never enough

 

RE: Ralph, What about my 7241s?, posted on May 24, 2020 at 09:06:32
Lew
Audiophile

Posts: 10366
Location: Bethesda, Maryland
Joined: December 11, 2000
Well actually, the goal is to condition the filaments before you apply B+ from plate to cathode. So while you are applying B+, the filaments are having to do their job of producing electrons, and therefore at least in theory they are not ".conditioning".That's the way I think about it. It's kind of like letting your car idle until the oil and water warm up sufficiently before asking it to perform at a high-level. I could be off base. But in researching this topic online, and with respect to a generic triode, the recommendation of another expert was 5 to 6 hours. But Ralph has vast experience with the particular power triodes used in his amplifiers, and I have no doubt that his recommendation to do it for 4-5 days is based on his long-term results. My question is whether that applies to the type 7241 power triode, which can pass many times more current than a 6AS7.

 

RE: Ralph, What about my 7241s?, posted on May 24, 2020 at 16:50:50
pictureguy
Audiophile

Posts: 13005
Location: SoCal
Joined: October 19, 2008
I have no idea what that means, but if it makes you happy, carry on.

The metals from which the various conductive parts of a tube are made MAY benefit in some fashion, perhaps increase lifetime, from the stress relief of heating and cooling, but I have not idea.
Also? once the getter has done its work and the vacuum in the tube is as good as it will get, than THAT should be it on that front, too.
Too much is never enough

 

RE: Ralph, What about my 7241s?, posted on May 25, 2020 at 07:29:21
Lew
Audiophile

Posts: 10366
Location: Bethesda, Maryland
Joined: December 11, 2000
I have no dog in the fight for filament conditioning. You asked a question and I tried to respond based on my own poor understanding. This is the sort of topic where even EEs might disagree.

 

RE: Ralph, What about my 7241s?, posted on May 25, 2020 at 09:57:08
pictureguy
Audiophile

Posts: 13005
Location: SoCal
Joined: October 19, 2008
The vacuum tubes I currently own, and I DO have a few, are in a 1950s Zenith Trans Oceanic Radio.

And they are difficult to source tubes, I'm told. But also last 'forever'.

I'd love for an EE to weigh in. Lot's of points in modern hi-end audio which are less than accessible to many people. And I think works to the detrement of the hobby as a whole when somebody goes to a store and is told they need XX for cables and the tubes in the amp 'are OK' and 'you should upgreade them ASAP'......

I'd love to compile a list....
Too much is never enough

 

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