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Old 13th November 2009, 06:40 PM   #21
rmyauck is offline rmyauck  Canada
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Hi, I've got 8 never used green lettering Sylvania 7236. I read somewhere they are similar to 6080. Are they good sounding? They sure are heavy duty looking and in mass. I think they are a rare tube?

Could they replace 6AS7G in tube headphone amp on the headwize.com projects site or what circuit would they be good for?

Thanks,
Randy
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Old 13th November 2009, 08:14 PM   #22
Zen Mod is offline Zen Mod  Serbia
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Originally Posted by rmyauck View Post
Hi, ......
Low-mu preamp
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Old 14th November 2009, 02:33 AM   #23
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Quote:
Hi, I've got 8 never used green lettering Sylvania 7236....I think they are a rare tube?
I bought some of those on Ebay a while back for some cathode follower experiments. They are nowhere as common as the 6080 or 6AS7 but they are not particularly rare either. They were made for use in very early didgtal computers so when you find one, there are usually more nearby.

The 7236 is a version of the 5998A designed with a special cathode material that will not suffer "poisioning" under long periods of zero current (cutoff) operation (common in a computer). Both work the same in audio applications.

The 7236 is indeed very similar to the 6080 except that the grid is wound with a tighter pitch than the 6080 resulting in a higher Mu and a higher plate resistance than the 6080. This may be good or bad in an audio application depending on your particular circuit. The higher Mu makes the 7236 easier to drive, but the higher plate resistance requires a higher load impedance. If your headphone amp design does not use an OPT, the 7236 may not be a good choice.

The 7236 and 5998A worked well in the cathode follower circuits that I was building. I used the 5998A (because I had more of them) in the DSP powered cathode follower amp that appears in the OCT 2009 issue of Circuit Cellar magazine.
Attached Files
File Type: pdf 7236.pdf (81.0 KB, 32 views)
File Type: pdf 5998_TS.pdf (192.9 KB, 22 views)
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Old 14th November 2009, 06:07 AM   #24
rmyauck is offline rmyauck  Canada
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Thanks Zen Mod! I found that site too just after posting my query, by google.

George thanks for great info!

Take care,

Randy
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Old 14th November 2009, 06:35 AM   #25
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I have to LOL, because I think many of us have made such an overkill line stage.

Cheers to you Pete for this one
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