27/37/56/76 plate dissipation - diyAudio
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Old 18th March 2009, 03:55 AM   #1
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Default 27/37/56/76 plate dissipation

Anybody have any clue what the plate dissipation is on these tubes? I've never found it on any datasheets....
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Old 18th March 2009, 06:28 AM   #2
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Default Re: 27/37/56/76 plate dissipation

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Originally posted by audiowize
Anybody have any clue what the plate dissipation is on these tubes? I've never found it on any datasheets....
These look to be small signal types, and I'd keep the Pd below about 1200mW.
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Old 18th March 2009, 03:37 PM   #3
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I have looked for this as well and like you never found a rating. I have used 76's and 37's and always kept the dissipation at 1 watt or less with no problem.

I read that they work better with grid bias, but I've had great results with cathode bias. They also work well as the bottom tube in a mu follwer configuration.

Good luck!
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Old 18th March 2009, 05:15 PM   #4
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I think that most of these tubes will be limited by filament emission rather than plate dissipation. Most of the 30's that I have tested start to saturate at 30 to 50 mA and have gone nonlinear well before that. Granted all of mine are very old and very used. I just got a few 27's at a hamfest, but haven't tried them yet.
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Old 18th March 2009, 06:07 PM   #5
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You may be correct, although the 76 and 37 (which is just a 6.3 volt version of the 27) have cathodes and are indirectly heated.

I run them in the 5 to 7 mA range.
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Old 18th March 2009, 06:46 PM   #6
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After MUCH searching

Pa Max for 56 = 1.3W
Pa Max for 76 = 1.4W

Could not find ANYTHING for 27/37 but would guess as another poster said about 1.2W.

By doing some "Forensic Acounting" I was able to justify going to say 1.4W on the 37/27.
By using spec's from same issue of Cunningham/RCA manuals I noticed that wherever I could get a PaMax rating for a specific tube and I compared that to the highest plate voltage spec the Operating point was always 88% of Pa Max. So extrapolating about 110% of the 250Vp idle current spec I get about 1.4.

Hope this helps, these tubes do not have much Mu anyway so stick with the 1.2W on all of them. There aren't many of these around.

BTW, I have a few of each in pretty good shape..interested?
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Old 18th March 2009, 07:20 PM   #7
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Thanks for digging that up.

I have many of these tubes too if anyone is interested. Many 76's, 27's and 37's. I've picked them up over the years and have way more than I'll ever use.
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Old 18th March 2009, 08:05 PM   #9
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Thanks Zibi,

Looks like my backwards math was about right (at least I did not OVERRATE the tubes!)
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Old 18th March 2009, 08:24 PM   #10
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I got some 56's I was going to use for a gain stage in front of my buffer. How would these work as a Anode follower directly coupled to a 5687 cathode follower? Or maybe 2 56's in a CCD grounded cathode amplifier like this?
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