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I asked if he'd mind if I post it and of course it's not a problem..It talks about the 7591 tubes and an S5000 Sherwood vs a Rogue Magnum 88 so it kills two birds with one stone.Since there is a lot of talk about integrated amps lately,especially Sherwoods,I thought it would be insightful.
Mikey
I bought a matched quad of both the JJ and EH 7591's to see for myself how they compare to each other and to a good quad of vintage tubes. As expected, the EH don't fit very well in the Sherwood. There's only a sliver of space between the tubes, and that can't be good for heat dissipation. The height I don't care about since I leave the case off. They should fit well in the Scott lk72 once it's fully restored, and I hope to be able to compare the JJ and EH at that time. The really good news I wanted to pass on to you, in case you do a restoration on a s-5000II that needs tubes, is that the JJ's sound surprisingly good. They actually seem a bit brighter on the top end, which is a good thing with the speakers I run, which roll off on top a bit. They don't sound quite as lush as the vintage ones, but they are quite good. I'm surprised how good they are. I tried some about 12 years ago, and didn't like them, primarily because I had a couple of tubes short out. I've been reading that they have improved the tube, so I thought I'd give them another shot. They seem to have an improved sound, and time will tell if they have a shorting issue. I'll keep you posted.I took the vol/balance/switch assembly out of one of the amps, and should be receiving modern replacement parts for testing by the end of the week. We're going to tack in the new stuff and confirm that the control was indeed the issue. Signal tracing indicates it should be. If the new stuff corrects the issue, I'm going to order an exact NOS replacement. Expensive at $100, but worth it if it takes care of the problem. Let me know how your s-5000II restoration is going.
I received the parts needed to restore the Scott LK72 in the mail yesterday, so I'm going to try to have it fully restored and working by the end of the weekend. It will be interesting to see how it compares to the Sherwood. Love the Sherwood sound, so the plan is to restore the Scott and sell it off. If the Scott outperforms the Sherwoods, then I'll sell off the Sherwoods, but I don't expect that will be the case based on your experience with them.
Incredible how the little 35wpc Sherwood crushed the performance of the 100wpc Rogue Magnum Cronus.
John
Honest amplification is better than excessive 2nd order distortion anytime.
Edits: 04/01/14Follow Ups:
Will be interesting to hear his take. My experience is that the EH7591 and their 7868, which is essentially the same tube in the other bottle are both fantastic tubes and sound very much like old stock tubes, both American and Japanese. I have the EH7868 in my Sherwood S8000 receiver and they are wonderful and fit fine in that small space. I have installed the EH7591 in many Scott, Sherwood, Fisher, and Sansui amps and receivers and had zero failures so far. My experience with the JJ 7591 is that I have seen roughly 4 out of the 16-20 I have used short out in a relatively short time period, like the first 100 hours. Now you all know that I know what I am doing and they were all being run at conservative bias settings, well within normal limits. That was maybe 4 years ago. I have never used them since. They sounded fine, pretty much as described in the post, a little brighter, more modern sound. But the failure rate was ridiculous. The EH, on the other hand, have been totally reliable. I don't think McShane will even carry the JJ 7591 since he had too many problems. I wish the original poster good luck with his. Maybe JJ cleaned up their act in the past few years on that tube.
cheers,
Don
It has been my experience with both tube a transistor amps that when the lower powered amp has enough power, the lower powered amp sounds better (assuming good design on both). I am not sure why this is true.
Dave
Dave
I think that same way but later I realize that it wasn't so much low powered amps that sounded so much better,it was minimal output device amps that sounded so good.For instance,the Conrad Johnson premier one power amp that was 200wpc and had six 6550s per side,didn't sound as good as a pair of stock Dyna Mk3s at the time because there were so many times in them.
Honest amplification is better than excessive 2nd order distortion anytime.
I think you are correct that the number of output devices is a major factor. I did know someone who used a CJ Premier One to drive Acoustat 3's to good effect. If you need the power, you have to bite the bullet.
Dave
As far as transistor amps go, Bob Carver commented on much the same thing a long time ago. His point was once you raise the power to the point where you need parallel outputs; the amp is more difficult to design and sound often suffers. He felt that the amps he'd listened to at 60 wats/ch and lower all performed well and didn't exhibit odd behavior.
Tubes are somewhat similar, I think. As power rises, voltages go up, the drivers and phase splitters get more difficult, and the power supply needs to be beefed up - a lot. It's also more difficult to design the output transformers. Back in the late 60's, early 70's, when I was working with tube amps, I preferred those with 50 watts/ch or less.
Jerry
Coincidentally, my current favorite amp, the Threshold CAS-1 is a 60 watt amp. Maybe it is not a coincidence. 60 watts or less does seem to be the right place for good sound. Fortunately, with a little headroom, 60 watts can be quite powerful. For tubes, a pair of 6550/KT88 or EL34 per side can be quite satisfying. I lean more towards the EL34's.
Dave
Dave,
All good tubes; but if going for 60 W/ch I'd much prefer the KT88's. I really like EL34's; but after 50 watts/ch their life is too short. rather poor life I thought in the Eico HF60. Dynaco was right in going to KT88's in the Mk III. The lower plate voltage in the Mk II was fine with EL34's and they lasted very well. Of course, that was with Mullard EL34's.
The 6550 is an industrial tube, and to my ears, it sounds like it. But it is rugged.
Jerry
Hi Jerry,
I would agree that if you want 60 watts continuous, KT88/6550's are the way to go. However, I did have Dynaco Mark IV's for a while and even though they are rated at the same power as a stereo 70, in real world performance they seemed more powerful. It was enough power for me driving ADS 500 speakers. I would expect similar results with a Mark II. Didn't you own Mark II's at one point?
Dave
Dave,
I always liked the Mk IV. The ST70's biggest issue in my opinion was too small a power supply transformer and only one GZ34. Two Mk IV's got around that nicely.
Yes, I did have Mk II's in the late 60's and up until late '71. Oddly, one was a real Mk II, the other was an early Mk III converted back to Mk II with EL34's. Both used GZ34's and gave right at 52 W/ch from about 40 Hz to 17k Hz. I carefully re-matched the matched pairs of resistors and harmonic distortion on the verge of clipping was 0.3% I was driving KLH 17's at that time, and I still have them, although they were with a friend and then his son for years. Now they are refurbished, fitted with Morel MDT20 tweeters and a new crossover and sound really good again.
Back in that era I also had a much worked over Eico HF20 with a huge Chicago transformer that overhung the chassis, GZ34 rectifier, EL34's, and the output stage rebuilt as a Dyna-like common cathode resistor; but retaining the Eico voltage amplifier and drivers. That got 48 W/ch at 0.5% THD and sounded almost exactly like the Mk II, and i used them as a pair until I got the Mk III, and then I picked up a McIntosh MC225, which I wish I still had.
Jerry
Hi Jerry,
That is an interesting history. I'll bet the KLH 17's sounded good driven by the Mark II's. I never had a chance to own McIntosh gear, but I can still hope!
Dave
Citation II baby.... about 65 watts/ch on the bench when rebuilt with the McShane level II+ power supply.... You would have to have incredibly misbehaved and inefficient speakers in a huge room where you would need more of an amp....
If the betting Window is open, my money is on the Sherwood. In reality from experience it should boil down to personal preference as each is voiced quite differently. Not as much a matter of better vs not as good but flavor such as AR3a vs Klipschorn.
Don Brian Levy, J.D.
Toronto ON Canada
when he tells you, please. And details of what he did to it if he doesn't mind sharing. I have a Scott 233 in the queue somewhere and, without looking, believe it's the same thing or at least very similar. Always good to get input!
Thanks,
John
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