RE: ". . . the O/P tubes are worked VERY hard."

Posted by FlaCharlie (A) on October 15, 2016 at 07:56:34

In Reply to: RE: ". . . the O/P tubes are worked VERY hard." posted by Eli Duttman on October 14, 2016 at 13:19:02:

Eli - Thanks for the explanation of how to estimate the actual working dissipation.

I understand that over 13 watts is high and would certainly be considered "hard" on the tube. But, as you said, this is at full output power.

Most users probably never run their amps at full output power. I know I never come close to that. Even with fairly low efficiency speakers (I have KLH Model 6s paired with mine at the moment) I never turn the amp up even halfway on the volume pot. Yes, I know half on the volume pot doesn't necessarily equal half power. But still. Even with fairly inefficient speakers, say 88 db/w/m, 13.2 watts output (66%) would produce over 100 db at one meter.

If the amp is being operated at 66% - 6.6 watts output per tube - and each tube needs to dissipate, let's say, 135% of 6.6 watts to produce that output, that's 8.9 watts plate dissipation. Well under the maximum specs. If plate dissipation is 135% of output, the amp would be putting out 18 wpc (90% of full power output) before the tube exceeds its 12 watt rating.

So wouldn't it be fair to say that, under what most would consider "normal" (not close to maximum) operating conditions, the tubes are not being run all that hard??

My other question is, how does this compare to the other examples I gave - both the Fisher SA-16 (13.34 W) and the Eico HF-81 (11.27 W) dissipate considerably more - at idle - than the Sherwood (8.59 W).

The Eico is supposedly 14 wpc, so less efficient (not near Class B)? I believe I read somewhere that the Fisher is about 20 wpc. Wouldn't this indicate that they are running their tubes even harder, under actual working conditions, than the Sherwood? Yet the Sherwood seems to be frequently mentioned as being hard on tubes yet one rarely hears this about other amps.

Please understand, I'm not just trying to be contentious here. I just don't understand how an amp that has its output tubes idling at what seems like a very reasonable plate dissipation (actually lower than similar amps) could be considered to be hard on tubes. And, for the record, I'm running 7189s in my S-5000.

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Follow Ups Full Thread

Topic - Did I see Gold Lion now has a EL84 - airtime 19:21:30 10/10/16 (13)

RE: Did I see Gold Lion now has a EL84 - SETdude 11:11:10 10/12/16 (0)

They've had them for at least several years - 1973shovel 08:08:08 10/12/16 (0)

RE: Did I see Gold Lion now has a EL84 - Eli Duttman 10:11:52 10/11/16 (7)

". . . the O/P tubes are worked VERY hard." - FlaCharlie 10:17:40 10/12/16 (5)

RE: ". . . the O/P tubes are worked VERY hard." - Eli Duttman 12:53:54 10/13/16 (4)

RE: ". . . the O/P tubes are worked VERY hard." - FlaCharlie 19:25:15 10/13/16 (3)

RE: ". . . the O/P tubes are worked VERY hard." - Eli Duttman 13:19:02 10/14/16 (2)

RE: ". . . the O/P tubes are worked VERY hard." - FlaCharlie 07:56:34 10/15/16 (1)

Is My Logic Flawed? Please Explain . . . - FlaCharlie 19:06:27 10/18/16 (0)

RE: Did I see Gold Lion now has a EL84 - airtime 10:13:46 10/11/16 (0)

RE: Did I see Gold Lion now has a EL84 - geezerrocket 23:58:58 10/10/16 (1)

RE: Did I see Gold Lion now has a EL84 - airtime 08:41:17 10/11/16 (0)

Wonder how this compares to the EL84M? - FenderLover 23:06:56 10/10/16 (0)

Follow Ups

RE: ". . . the O/P tubes are worked VERY hard." - FlaCharlie 07:56:34 10/15/16 (1)

Is My Logic Flawed? Please Explain . . . - FlaCharlie 19:06:27 10/18/16 (0)

RE: ". . . the O/P tubes are worked VERY hard."

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