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7591: Old Vs Older

ivan100000

ivan100000

Well-Known Member
Gentlemen:

There are many threads discussing the new JJ/Harmonix 7591 compared to the original US-made offerings, but I'm curious about the 1960s 7591 vs the 1970s 7591/7591a.

My situation: I bought a McIntosh 225 @25 years ago in really nice condition but part of the deal was that the guy who sold it to me kept the McIntosh-branded 7591 tubes to use in something else. I knew even less then about electronics than I do now--which is still very little--but I had a quad of late-60s Sylvania 7591 that I had pulled out of a non-working receiver, and I simply plugged them into the MC225. Fast forward 25 years, and they still sound fine.

I believe the amp to be completely original (minus the output tubes, of course) and thus there's no way that the caps are still within spec being 50 years old now. I'm planning to have it recapped and re-tubed.

For years I've had 3 quads of 1961-1964 Westinghouse 7591 tubes stashed away; these have the cool-looking tall phenolic bases and all test really strong on my TV-7. Each quad came out of low-use Eico receivers: two sets are the black base, and one is the cool tan base.

At any rate, I'd figured that I'm set for life on power tubes for my 225. The tech who will be servicing the amp is a wizard who did an absolutely first-rate job on my Fisher preamp, and he advised that I go with the 7591a over the 7591, as there were upgrades made to the tube that are advantageous. Anything I've ever read about the 7591 vs the 7591a is that the latter heated up quicker, but that they are basically the same tube. It seems that at some point in the mid/late 1960s these tubes all transitioned over to the 7591a. (I have read that Westinghouse and Sylvania were the only US manufacturers of these tubes.)

Back to my original question: are the 1960-1966 issues of the 7591 better sounding/more coveted to those of you with familiarity, or are they lesser-regarded than the 1970s issues?
 
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Hi ivan,
Sounds like you trust your tech, but I'd be careful will highly desirable old tubes. I've heard of techs replacing tubes with similar but lesser grade or lower testing tubes thinking the owner wouldn't realize it. If you have some nice high testing old 7591's, I would take some detailed pictures of them including the date codes and any little specific marks and/or make some indelible marks on them (say on the bottom of the base where it's inconspicuous). Sorry to be cynical, but it's happened.

I can't offer any subjective comments on the sound of different versions. I think they sound pretty similar if they test similar.
Good luck,
John
 
Greetings John--

Thanks for your reply. This tech is actually the best I have come across in all my years of dealing with tube guitar amps and hi-fi. I was in a bad spot with my Fisher preamp, and he did an outstanding job cleaning up the previous tech's mess while charging me at @1973 rates. I know that we should generally always be wary, but I have no concerns here.
 
When Westinghouse first started producing this "just for audio output' tube, one of their main hurdles was to perfect the heat dissipating compound and figure a way to get it precisely even on the structure(s). This is why I think the tube can't be made with the same results today, that recipe is gone, and the haven't figured it out yet. I have a fascinating article on what the engineers went through designing that tube, but putting my hands on it might be a bit tricky. Are your tubes made by WH? The WH tubes seem to be in a class of their own. If you ever see a WH 7591 tube go red, the whole plate will go red evenly, not just in the middle like most tubes. That confirms to me that they were onto spreading the heat out nearly perfectly.

Love the Avatar, I NEVER missed an episode of that growing up. Poor old Lamont, Ya Big Dummy!
 
I am with Jay in that Westinghouse makes the best 7591. I am also of the opinion that the best version of almost any tube is the first of its type that was made. My reasoning is this; the tube is designed by engineers to fulfill a purpose and as such they have the say so in what is required to have it manufactured. If the demand for the tube is sufficient to have additional batches made then management will want to increase their profit margin by finding ways to do this. To wit, switching from the tan ceramic type base to black plastic. Thus cost cutting can slowly lower the quality of a tube. While I realize the "7591A" version is suppose to be improved because of controlled filament warm up, the cynic in me believes the A version is just marketing to hide a tube that has been designed to make more money for the manufacturer and still be acceptable for the market. cheers, primo
 
As an engineer, I'm too used to seeing first, and even second, tries at something have flaws that get corrected in later versions. Or, actual improvements that may not have been apparent originally. My experience is that the bean counters often foul up the first version for marketing reasons and then the flaws have to be corrected if they are bad enough. In reality, things have happened both ways, so we can both be correct.
John
 
I haven't been able to tell much difference between late production coin base and earlier high base types. I'm not sure how many companies actually made 7591a tubes. I have RCA, GE tubes that are identical. I don't have any NOS Westinghouse.

I like the new ones coming out of Russia. I've built a few guitar amps using these. I think they are too wide for 1960's stereos. They almost touch each other when in the sockets. They sound real good.
 
The latest Russian 7591 is a proper sized 7591. I have EH7591's in my Scott 340B, luckily the sockets have plenty of room around them for their large size but many integrated amps and receivers are better off with the smaller tube.
 
My understanding is that the 7591A rotated the plates for better heat dissipation, since the originals had the hottest sides facing each other when the sockets were placed for best wiring layout. And most 7591s were used in a close pattern where this makes a difference.
 
Perhaps I'm low man on the totem pole here as far as knowledge goes in this topic. Just some observations. Both the WH and the WHA have stood the test of time. 60 years later we like both even if we have our preferences. Macs don't run tubes at the ragged edge of the operating envelope.(note the 225 only puts out 25wpc as most PP 7591 put out 35 wpc. (I'll even qualify that in, the 25wpc is probably conservative) .
I guess what I'm driving at. While your tech may be right. I believe any good old stock would be equally good (you'd be hard pressed to tell a sonic difference regardless of brand, new or old stock tubes).
I'm not sure how Mac does it but tube rolling (at least in my limited experiments has no effect on sonics)
Therefore going back to your other statement. You very likely are set for life with your current stash. My 2c
 
Thanks for the responses. I did come across a non-internet source--and a nice guy--with a fair price on a matched-at-load quad of NOS/in-box GE 7591a with the same production codes that I will send along with the MC225. As NJ Phoenix above said, my own experience has been that different brands of old tubes don't make an appreciable difference sonically, though of course I am abiding by my tech's recommendation with regard to the 7591a.
 
nerdorama said:
As an engineer, I'm too used to seeing first, and even second, tries at something have flaws that get corrected in later versions. Or, actual improvements that may not have been apparent originally. My experience is that the bean counters often foul up the first version for marketing reasons and then the flaws have to be corrected if they are bad enough. In reality, things have happened both ways, so we can both be correct.
John
Click to expand...

I couldn't agree more John. I wish I could point you guys to an article I read years ago about the development of this tube. They wanted high power in a small package, which IMHO they achieved (WH that is). They battled the heat thing in the lab back then more than they do know I think. Now they do a lot of testing in the consumer market, while back then they did it in the lab, and would not put the tube into production until the issues had been solved. Ahh the good old days huh?

Interesting point Tom B makes, I had never heard that before, but it makes sense. I learned from reading Jone's "Building Valve Amplifiers" that when putting in power tube sockets you want to orient them so they are not radiating heat into each other. Tubes cool primarily by radiation, so it's fairly important if you want max life from expensive power tubes. Great thread we got going here.
 
Yep, great thread, paid a pricey amount for NIB quad of Westies about a year or so ago, Doing duty in my 800C now and hope I dont have to find another set for awhile. If I do see another set I will snatch them up for my X202B later on. Al
 
I've been running the new Tung-sol 7591A tubes in my Scott 299C with good results. Lets me save my Westinghouse tubes (12) for those special occasions.
 
I've become quite a fan of that tube...... the 7591 in general that is. And, I've used about every 'brand' I could get my hands on in one amp or another. Note my avatar, which is an old 7868 juke-box amp 'converted' to 7591s, and using the JJ types. However, I've used the EH versions, the Westies, GEs, and others, and in reality, I find it hard to distinguish whether or not it's the 'tubes' that might be making any difference, or if it's the amp itself. I guess what I'm saying is that what is coming out of the factories today just isn't all that bad! I know some of these tubes earned a pretty bad reputation some years ago.....particularly the JJs when used in some of the Fisher stuff (like the 500 receiver). But, I've used a set in my 500 for the past 2 years, and for the first year that amp was run almost daily without a glitch..... AND, it sounded pretty good....at least to me. I wouldn't deny that perhaps the EH version is a bit more 'stout' in build quality. But, like Andy alluded to...... when only being run at 25 watts for a PP Pair...... that's NOT really pushing them any. I'd think most any 7591 would hold up. And, for what it costs for a NOS set of 7591A....you could probably buy 4 quads of JJs.... or 3 of the EH tubes.....and still not burn them up in your life time!! And, I think if you did an 'honest' A\B blind sound test between your Westies and the 'new' stuff..... you might find that you can't hear any difference, particularly in that Mac amp! Might be worth a try with a set from someone else you might know. BTW, does you 225 have any kind of 'individual bias' adjustability? If not, you might have a talk with your Tech friend about adding that capability to your amp. Even a good matched quad can benefit from that. Oh, those new Tung Sol repros' are probably the best deal going as far as trying to keep that 'vintage' look and sound but at 'new' tube prices. FWIW WC
 
Don, I started my journey into 'home audio' as a 'tube amp' convert from the guitar amp world. I guess it's been about 10 years now....give or take..... since I purchased my first ST-70. I had a 'tube' Jolida amp several years prior to that....but that was kind of a 'cookie cutter' unit.....and not what I'd call 'hard core'. But, my experience in the guitar amp world was all 6L6, 6V6, and EL84. When I switched to home audio and bought the ST-70, I got my first real chance to appreciate that tube. Now, perhaps 50 or so ST-70s later, I love the amp and the tube. BUT. having been through countless Dynaco amps, all encompassing the EL-34, EL-84, and 6550 world, I got 'hooked' on 7591s as a function of Fisher and Scott amps! My Dynaco stuff now just sits on the shelves.....and were it not for my latest love affair with D. Gillespie's little Single Ended amp, I'd be listening to my Scott 299C.... or my converted Juke Box amp...both with 7591 tubes..... and just lovin' the sound! They're a great audio tube, and I'm convinced now that I'll probably never go back. I just wish I'd kept the 7591 tubes I'd come across over the years. I probably let several dozen go back when I thought I'd never use them. I kick myself in the tail for that......... Tom D.
 
Hi Wharfcreek--

Thanks for your tips, and it's good to know that the reliability of the new tubes has improved; that seemed to have been a common complaint. I think availability of these new-production tubes have played a big part in the renewed interest in--and escalating prices of--the 1960s Fisher receivers, and they also seem to have leveled off the NOS 7591 market. I have no first-hand experience with the new tubes, and you may well be right that I wouldn't hear a difference A/B'ing the Russian tubes with the old Westinghouse or Sylvanias. It's completely irrational, I admit, but I just like the old tubes.

I too share your affinity for the 7591. When paring down my guitar amplifiers to 1, sentimentality won out and I stayed with the first amp I ever acquired: a 1965 Ampeg Jet. I've always liked oddball tubes, and the Jet does not disappoint in that regard: two now-unobtainium 6BK11 compactron preamp tubes to go along with two 7591 (not common in guitar amps) and the garden variety 5Y3 rectifier. The white Fender Bassman shall always be the barometer by which all others are measured, but this 7591-equipped little Ampeg jazzer is fine for my needs these days.

My own hands-on experience with tube gear has been that tubes last for years in guitar amplifiers, and for decades in hi-fi and jukebox applications. I've gotten 25 years out of the 7591 Sylvania quad in my 225--that were used when I put them in there to begin with--and the price I just paid for an NOS quad of 7591a is very reasonable when I consider how many years of service they will give me in the 225 once it has been electronically restored by an expert tech.
 
Ivan, I cut my teeth in the tube amp world all on Guitar amps. That was some 20+ years ago.....and now I too have eliminated 'most' of my collection (which numbered over 100 guitars and 100 amps at one point!). At the 'peak' of my guitar amp interest, I went into work one day where we had a really nice copy machine! I photo copied blown up sections from the old 5F4 Tween Bassman amp (final output section), the 'reverb' section from a black face Super Reverb amp, the Tone Control section of a Bandmaster, and the power supply section from the old Piggy-Back black face Bassman. I then when home and played 'cut & paste' with all the photo copies, and drew lines from one point to another where I thought the connections should be, and ended up with a complete schematic. Then, I built it! A 'hybrid' of all the favorite aspects of the Fender amp line that I'd grown to love over the years of playing. And, it worked! I built 2 actually......one I sold, and one still resides out in the garage, alone and sad....but there to give to my Grandson some day (he'll really get a lot of Crap from Grand-dad....like guitars, amps, motorcycles, boats, and maybe even my old Jeep Wrangler!!!......lol....not to mention 'stereo' stuff......).

Anyway....we'll have to compare notes on Juke Box amps some time. I've built several 'home audio' amps from the re-purposing of old tube Juke Box amps. I'm convinced they used pretty good iron in some of that stuff. Maybe not all of it, but the Rowe amps in particular captured my interest.....and now I've built several of those into 'home' units, as well as Rock-Ola amps, and one other I can't remember right now......Oh, Wurlitzer! Anyway...... fun stuff!

Tom D.
 
Wharf, one of these days I'm going to find one of those D Gillespie 5 watt amps... don't have the skills to build it but hope to find one. I've seen Dave's in person and it sounds great! Al
 
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