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Could I use those with my Sherwood S-5000.
I have to say that Gold Lion is proving to make a lot of darn good tubes.
charles
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They have been around a while an I preferred them to many old production. They cannot be run hard.
They sound great in my Dynaco SCA-35, but I did the EFB modification to it, which makes the amp less abusive to the output tubes.
New Sensor's "reissue" Gold Lion N709 EL84/6BQ5 equivalent is a very nice tube. However, it can't take abuse.
Your Sherwood S5000 must be equipped with 7189 equivalents, as the O/P tubes are worked VERY hard. These days, "the only game in town" is the EL84M (6p14p-ev). Be grateful that good sounding tubes appropriate to the unit are being produced and sold at reasonable cost. A lot of nice, vintage, amps would be "parted out", if not for the EL84M.
Eli D.
". . . the O/P tubes are worked VERY hard."
When I rebuilt one of my S-5000s a couple of months back I was rather surprised that, according to the schematic, the 7189s were run at a plate dissipation of only 8.59 watts. Since both the 7189 and the EL84 have a dissipation rating of 12 watts, that doesn't seem particularly abusive.
In contrast, I just finished rebuilding a Fisher SA-16 amp that was pulled from a console. According to the schematic, and from my actual measurements, that amp was running the output tubes at a dissipation of 13.34 watts. I should note that it had two dead (white getter) output tubes that had to be removed in pieces! While I made some adjustments to bring it down under 12w, it's still running them harder than my S-5000 despite the fact that the voltages are lower.
It makes me wonder if the physical design of the amp makes more of a contribution to the amp's reputation (which is constantly repeated on here) for being tough on tubes. I don't think I've ever seen (not saying there aren't any) another design where four output tubes and a rectifier tube were placed in such close proximity. On top of that, they added a heat shield whose main purpose seems to be to keep the cabinet cooler to the touch, yet it probably serves to concentrate even more heat around the tubes.
One result of this is that the wiring around the output tubes is often fairly well toasted. If you take a close look at some of the pics of rebuilt S-5000s that have been posted here, you can see how some of the wiring in that area looks somewhat charred. While none of the wiring on mine seemed to be at the point of shorting out, I was concerned about how well it would fare in the future so I rewired that area with mil-spec teflon wire.
The S-5000 may be a tough environment for output tubes but I question how much the circuit's operating points contribute to this.
Look at the voltages the schematic shows. They are "tall". The dissipation you quote makes sense for a near Class "B" operating conditions set, where "idle" and peak dissipation are quite different. You don't get 20 W. from a 7189 pair, unless the tubes are "humping".
Eli D.
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.
Edits: 10/13/16 10/13/16 10/13/16
Work backwards from 20 W. The max. theoretical efficiency for Class "B" is 78.5%. In the real world, the efficiency will be lower. For sake of argument, we'll use 78.5%. 10 W./tube leads to 12.9 W. being dissipated.
Yes, the S5000 works the O/P tubes hard . Factoring near Class "B" (prevents cross over distortion) and real world losses into the calculus, both of which reduce the efficiency, means over 13 W. being dissipated/tube, at full power O/P. Don't think of anything other than EL84Ms in an S5000.
Eli D.
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.
Am I incorrect in saying that at 66% power output - which most people would consider closer to "normal" operating conditions than full output power - the plate dissipation of each output tube in the Sherwood S-5000 would be about 8.9 watts?Is running a tube rated at 12 watts dissipation at under 9 watts "hard" on the tube?
If my logic is flawed please correct me and explain.
Edits: 10/19/16
Hey no worries. Those 7189 equivalents are quite good and I have NO complaints about them.
Just curious after I saw those on Jim's site.
Charles;
If the Gold Lion is a true EL84, then you could use it in your Sherwood, but not for long.
El84 can handle about 300 volts on the plates, where as a 7189 can go over 400 volts, while some of the Russian variants (6P14EV) and 7189a can go a little higher yet.
You can sub a 7189 for a 6BQ5/EL84, but not a 6BQ5/el84 for a 7189......At least not for long.
Meat; It's the right thing to do. Romans 14:2
I had a feeling that was the case but thanks.
A very good tube with years of reliable use, under its belt.
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