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

Posted by FlaCharlie (A) on October 13, 2016 at 19:25:15

In Reply to: RE: ". . . the O/P tubes are worked VERY hard." posted by Eli Duttman on October 13, 2016 at 12:53:54:

I was under the impression that specs listed in a tube manual are measured under quiescent conditions. Is that not the case?

I can't read the voltages on the schematic you posted. My figure regarding the S-5000 is based on the Sams which lists a voltage at the cathode pin of .5v dropped across a 12 ohm resistor to ground so 41.6 mA for the two tubes or 20.8 mA each. Plate to cathode voltage is 412.5 so dissipation would be 8.59 watts.

So are you saying the Sherwood operates in Class B? I'm not very knowledgeable about operating classes. I would have guessed it would be AB1. I was under the impression that the most common use of Class B was in PA amps, not hi-fi.

Regardless, my point was that I think the physical layout and the resultant concentration of heat plays an important role. The toasty wires around the output tubes should confirm that, don't you think? Exactly how much that affects tube life, I don't know.

Out of curiosity, I just checked the schematic of another popular and well-regarded amp - the Eico HF-81. It lists a cathode voltage of 11.5v dropped over a 165 ohm resistor. That works out to 69.7 mA per channel or 34.8 mA per tube. Plate to cathode voltage is 323.5 which gives us a plate dissipation of 11.27 watts.

So that's 31% higher plate dissipation than the Sherwood. I don't think I've ever heard anyone say the HF-81 is hard on tubes, though.

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

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