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What's the current thinking on 7591's?

Rob,

I take that was 'wish'....vs 'with'...!! BTW, I have it on good authority that tube rolling should NOT be a function of the RF section. According to what I'll just call 'good authority'......the RF tubes are generally 'peaked' in their associated circuit. So, they should essentially be left alone......and if pulled and tested.....re-installed in the individual sockets from which they came. (kinda sounds like output tubes, eh?). Anyway....I learned this AFTER I'd pulled all mine out, and in reality my FM sections seem to be working wonderfully well......but I can't help but wonder how they would sound if I could find someone around here capable of doing a full-scale 'alignment' on one of these units? I do have to say I'm REALLY impressed with the 'sonics' of the 500C. Talk about 'listenable'......there is just no fatigue in having this thing 'on' and playing virtually all day! A VERY 'user-friendly' piece of audio equipment.....once properly set up!! TSD
 
Tom,

You are correct about leaving tubes alone in the RF/IF sections. Rolling there could lead to un-predictable results.

Of course if you could care less about FM/AM use whatever in those slots.

Frannie
 
On the same token though, if you don't care about the tuner part, why even change them in the first place? Generally I like to leave tuner tubes alone unless I have some solid reason for changing them. Most of what I have still has what it came with when I got it.
 
Hiya,

On the same token though, if you don't care about the tuner part, why even change them in the first place?
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Well if there are a few Tele Smooth plates in those sections ..

Frannie
 
Gadget & Frannie....this issue comes somewhat as almost being the subject for a new thread. But, quickly.......in my case, the issue was one of ignorance about 'tube' radio. For nearly 20 years I've been playing with tube amplification.... without even the remotest consideration for anything 'RF' related. After all this time, I stumbled into the 500C at a flea market.......so taking my actions from past tube amplification processes......I decided to 'test' the tubes before even plugging the unit in. If I'd had ANY idea that the RF tubes were, in a sense, 'mated' to their corresponding IF tuners......I would have at least kept track of which socket which tube came from. But.....'ignorance runs rampant'.....and I'm a victim of it! Fortunately, no major ill results seem to have come from my mistake. And, I can only assume that the RF section was set up on all good tubes, and I have 'all good tubes' still in there. It seems to work well as compared to any SS unit I have around here......even better actually!! But, I probably should have posted prior to pulling!! I might have avoided a potential problem!! I just thought I was doing the prudent thing....... Tom D.
 
PS....this unit actually got me listening to FM radio again!! I actually am considering buying a high-dollar FM antenna to get even more involved. I live in a VERY bad FM reception area.......so a better antenna will be a necessity if I plan to do any serious listening at all. But, this unit makes the idea very inviting!! TSD
 
Wharfcreek,
My opinion is only that. Your mileage may vary from mine.
No harm done.
Actually, I'm not at all afraid to expose what I don't know. How else would I learn?
I'll consider what you've said also, though my experience, so far, differs.
 
Don,

Have you tried any of these newer Chinese 12AXs? I think CE is getting all of about $5 each for them.....which by today's standard is dirt-cheap! Also, I'd make note of the fact that 'comparison' is so subjective; source material (cd, radio, Vinyl, etc), speakers, listening environment, genre of music, and even 'condition' of units being compared.....any of this can make a HUGE difference. If I'm not mistaken, you have done some further modifications to your Fisher units to be more well suited to the EH tubes....where I have not done this. My 500s are, other than coupling caps, still 'original' in stature. I don't know just how much (if any) this affects things......but who knows. Honestly, I think I may be somewhat swayed in my thinking by the sheer fact that the Chinese 12AX7s sounded as good as they did....that I may have 'lost track' of what my output sections were doing.....or 'not' doing! But, I'd like to get some further opinions about these newer Chinese 12AXs. I'm just wondering if I'm nutz or not......or if I just got lucky.....or what?!? Tom D.
 
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Wharfcreek said:
Don,

You know I have the greatest of respect for your opinions. So, for me to offer anything that may 'appear' as 'contrary' is almost painful for me. But, in the interest of 'discussion only'.....I've had almost the exact opposite experience with my 'testing' in my 2 Fisher 500Cs, the one 500B, and the 800. For me, it was the output tubes making almost all the difference, with the pre-amp tubes making little to no discernible difference. Because the units take so many 12AX7s to be functional......I ordered 30 of the Chinese 12AXs from CEDist. I then did a LOT of rolling between amps.....including the use of the old Teles, some British Mullard and Ampex tube.....and of course, some old US types. In the end, I was hearing a more 'brittle' or 'harsh' sound from use of JJ outputs, less so with the EH, and essentially NONE of that condition from old US 7591s. The 12AXs seemed to make little difference during my testing. HOWEVER, I will also note that ALL 12AXs used were either VG if old......or were NEW versions of the Cino tubes. Honestly.......I was not only surprised....but somewhat delighted. I then turned to putting some of these Chinese tubes into the integrated amps I had and I found similar results. To me, this may reflect a change for the good in the Chinese 12AX7s.......as a decade ago I would not have even attempted this test due to the poor quality of these tubes. Further, I'm a dyed-in-the-wool patriot......and use of NON-US stuff is REALLY difficult for me on general principle. But, sometimes 'economics' necessitates compromise......so I gave these things a try.....and with very satisfactory results. Now, one comment would be that of the 30 I've ordered, 3 have failed due to cracks in the glass by the pins. So, figure that into the mix. CE replaced these at NC to me......but still....that's a 10% failure ratio....which is HORRIBLE by most any production standard! But, still, figuring the cost/tube vs projected acquisition cost of 30 US or Euro tubes, and then consider the performance to be 'ok' at worst......and it becomes rather compelling. Anyway......if Rob decides to make it over here.....I'll let him do some rolling as well and see if he agrees. Tom D.
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For my Fisher 400 I had opposite effect. Rolling preamp tubes made a large difference in the clairity, focus and musical presentation. Power tubes was also a plus with RCA 7868 black plates best, Sylvania 7868s a close second. At times speakers can mask tube changes, my Klipsch Forte are very revealing.
 
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The Chinese are not a monolith. Not with 1.2 Billion people or more.
Many Chinese are awaking to the sensual delight of good audio and I expect great things from an inventive corner of the world that was dormant for the better part of a century.
I haven't seen or heard anything from Psvane that wasn't excellent. Shugang stuff (the parent of Psvane) is also good. I would expect others will also be good.

As far as output tube sonic sampling, that's something that has to be one of the very last things you do, after coupling cap noodling and preamp tube noodling and power supply stuff. Output tube changes are best heard when the upstream stuff is taken care of first.

An exception to that rule of minor impact is with genuinely crappy sounding tubes like the GE manufactured 7868s. Now there are rebranded 7868s that say GE but are Sylvanias. They're fine. I think, but can't corroborate, that the Sylvania branded GE tubes were a toe in the water test for GE. But when GE jumped in and manufactured, they didn't make a big splash with their entry, which is an inferior sounding output tube.
 
I may just re-perform all my testing.....just to see if maybe I alter my prior position. WC
 
audiodon said:
The Chinese are not a monolith. Not with 1.2 Billion people or more.
Many Chinese are awaking to the sensual delight of good audio and I expect great things from an inventive corner of the world that was dormant for the better part of a century.
I haven't seen or heard anything from Psvane that wasn't excellent. Shugang stuff (the parent of Psvane) is also good. I would expect others will also be good.

As far as output tube sonic sampling, that's something that has to be one of the very last things you do, after coupling cap noodling and preamp tube noodling and power supply stuff. Output tube changes are best heard when the upstream stuff is taken care of first.

An exception to that rule of minor impact is with genuinely crappy sounding tubes like the GE manufactured 7868s. Now there are rebranded 7868s that say GE but are Sylvanias. They're fine. I think, but can't corroborate, that the Sylvania branded GE tubes were a toe in the water test for GE. But when GE jumped in and manufactured, they didn't make a big splash with their entry, which is an inferior sounding output tube.
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GE have a place, a little soft sounding in my Fisher. GE could be just the ticket for a bright sounding amp. Tubes in different circuits sound different.
 
moving the tuner tubes around won't ruin it by a long shot. I'd probably make the argument that 50 years later, the tuner isn't dead on alignment anyway and playing with the tubes has the potential to push it closer to correct. If you really want to do tube rolling in the tuner and compare them honestly for best performance and sound, you need to do a full on alignment after each change to be absolutely sure its smack dead on. I would expect that improvements to tuner performance can be had by just doing an alignment with whatever tubes are currently in the thing, provided they are good.
 
If I had alignment questions, I'd talk to PunkerX. That said, the Dynaco FM3 build manual has some creative ideas on aligning with an eye tube. It's an awfully simple tuner though.
 
most FM stereo rigs align with a sweep generator for the IF strip and an FM stereo generator for the multiplex decoder along with a scope for readout. Specifics about hookups and whatnot should be in the service manual but it requires some specialty equipment to get it right. You can do a basic alignment for satisfactory mono performance with just a signal generator and a VTVM in the right spot but for optimal performance and especially for good stereo you need a symmetrical IF passband, which is really only obtainable with a sweep generator.
 
sony6060 said:
For my Fisher 400 I had opposite effect. Rolling preamp tubes made a large difference in the clairity, focus and musical presentation. Power tubes was also a plus with RCA 7868 black plates best, Sylvania 7868s a close second. At times speakers can mask tube changes, my Klipsch Forte are very revealing.
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The sound is in the ear of the beholder. I too have had much more luck changing the sound of a push/pull amp by changing the small signal tubes. You are also right about the speakers. I have always used Klipsh and currently have Cornwall's. If an amp has a flaw it shows up with remarkable clarity.

My experience is with mostly McIntosh. My MC40's did not care if it had Ruby 6l6GC's's or RCA black plates. They both sounded the same. I tried many different 12AX7's, The best were the original Tele smooth plates and, believe it or not Sovteks with the 1999 date code. I sold the amps a year ago to a friend and we put in Tung-Sol reissue 6L6G's (I am keeping my black plates :yes:) and I did hear a positive sound difference; not to mention they look fantastic. The speakers are Klipsch Chorus II's.

As far as the 7591's go it is the tube in my 299D. I have been looking for a red based Scott 7591 tube to go with the other three I have that test very strong. No luck so far. White and black is no problem. Probably a Sylvania tube. The JJ tubes are fine but, I put almost no hours on the amp. I need to do more research, and posting, since posts here have piqued my interest concerning grid resistors, coupling caps, and biasing.

Did I read correctly. Does EH now offer a small bottle 7591A. The coin base tube is too tall to put it back into its case. If I ran the amp as a daily user, I would simply leave the case off. This is a project to keep the amp as original as it was when my father in law purchased it in the 60's. He loved music.
 
I saw the title of this thread, and my first thought was "about 30 to 35 milliamps each". :D

Regards,
Gordon.
 
wgrr said:
Did I read correctly. Does EH now offer a small bottle 7591A. The coin base tube is too tall to put it back into its case.
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I would like a small bottle but unless they developped something new in the recent weeks, they have a big (too big in some cases) bottle 7591A.
 
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