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I had a great sounding pair of Sylvania 3 mica 5751s running in my preamp, and I've got to admit that I used these guys far longer than what Joe's Tube Lore in the FAQ says I should have expected (the tightwad living inside me is happy). One of them went microphonic on me, and the other developed a hum/buzz that, initially, I thought was a grounding problem. It didn't dawn on me that I might have a tube that was starting to go belly up on me, but after scratching my head and futzing with cables and power cords for the better part of a day, I got the bright idea to switch the pair of tubes from one channel to the other. Yep, the hum moved to the other channel. A day or two later the other one in the pair announced it wanted to throw in the towel too.I'd bought a pair of the later production (1970s, I think) Sylvania JAN 2 mica 5751s (cheap) to keep at the ready for when this sad day came. The noise was gone, but it took me no time at all to realize that these were not anywhere near as great sounding as the ones they'd replaced. These sounded dry and grainy so, I set about to find something usable in my stash of tubes. I had an old pair of Tesla 12AX7s dating back to the sixties in there, and a few orphaned/mismatched brands, and some pairs of Telefunkens, Bugle Boys and RCAs, but after trying each of these, I came to the conclusion that I had to pull out the RCA Command 5751s I was hoping I could keep in their new boxes a little longer.
Since these usually go for a little less money, I decided that I'd look for a pair on ebay to keep in reserve. I found a pair that looked interesting enough, so I clicked the "Buy It Now" button to avoid getting into a bidding war with someone on another pair (see link below).
When they arrived, I was astonished to find that BOTH of these tubes hummed louder than the Sylvania tubes they replaced. That got me to thinking, is this ground sounding hum something common to the 5751? I don't have a tube tester, so I have to take the seller at his word. Incidentally, the seller hasn't bothered to answer my email, so I don't know what to think.
Since these tubes are hard to find (the vintage ones anyway) at reasonable prices, can anyone suggest any other places to look? I've already tried Jim McShane and Brent Jesse.
Follow Ups:
Thanks a lot for the helpful posts to my question, but the perception among all of you is that I'm limiting my search for a useful replacement to the RCA NOS variety. Nothing could be more inaccurate. Yes, indeed, I'd love to find that the Sovtek tube that Frihed89 likes would tickle my fancy too. But, alas, my own experiences with most Russian and Chinese tubes has been a little disappointing.My experiences tell me that what I would really like to find (at a reasonable price) is another pair of the Sylvania tubes just like the ones that had led a reasonably long life, and produced a sound that was maybe just a mark or two off the 100% ideal. Being an old guy who's really happy with everything (my wife is all I could hope for, my modest -- by comparison -- audio system is too), I admit to be pretty much set in my ways. I'll get a pair of these Sovteks just to satisfy curiosity, and hope for the best. Thanks too to the inmate who emailed me and volunteered to let me have a pair out of his harem. I'll be contacting him anon.
NT
I got a matched pair on the way from a dealer in CA for just under $22 with shipping. Am looking to roll these into the preamp when some friends are here for a weekend visit. And to keep my reactions to the Sovteks honest, I'll let them blindfold me then switch between a set of Sylvanias that's also on the way here (thanks to an asylum inmate with a heart of gold), and the 3 other pairs I have here right now without telling me what's what. This should make for some interesting fun and games.
The 5751 has many different voices, and a lot depends on your personal preferences for sound. The current Sovtek is not my favourite, but it does many things well and is NOT flabby-based or euphorically warm. I am glad you didn't get gouged on those Sovteks. Did you find any RCA TMBPs, or are you just interested in the illusive Command Series?
Thanks for your interest, Frihed89. As noted previously, I am not expecting great things from the Sovteks, but provided that they can produce a hint of musicality beyond some rather pedestrian sounding tubes in my stash, I'll be satisfied to use them in lieu of the more expensive Sylvanias that are on the way. The Sylvanias — along with my pristine pair of Commands — will be kept for special occasions much in the same way that I might put on a tuxedo or pour a small drink from a bottle of 24-year-old Scotch that I've had here for years. The savoring of something so special as this as if it were an every day event is just slightly too extravagant for us poor, old pensioners.I have some orphan NOS 5751s that sound quite nice: a TMBP Sylvania as well as one TMGP. Despite their differences in construction, they go quite well together. I've already mentioned the twin RCA Command TMBPs, but not one red- and one green-labeled RCAs (the green one appears to be JAN), but these, unfortunately, produce slightly different sounds, and neither can produce the lovely liquid, clear sound of the Commands.
It will be a few more weeks before my guests (both audiophiles) are here to conduct the blindfold tests, but I'll seek you out to recount the results.
Cheers from Louisiana
Don't think so. One reason people like the 5751 tube is it's generally known as being on the quiet side. I don't have any experience with the RCA command series so I can't speak for those, but my experience with other 5751s has been that they are all very quiet, even the blackplate GE's that I have from the 1950s with many, many hours on them are still very good in that department even though they test on the borderline and are starting to get weak.
I have played RCA TMBP with very good success. No buzzing. Not microphonic. Balanced, warm, smooth. But, before you get lost trying to find NOS tubes, do try the production Sovtek 5751. It sounds a lot better than some NOS 5751 GEs, but alas not like the RCA TMBP.The command series. Hum....I have enquired about these in lots of places. It's almost like no one has actually heard one before, but their brother had a girlfriend who knew someone who had....in Palestine, just after the war. Wierd stuff. And, if you look at the technology inside that tube, there is no reason for it to sound as good as legend has it.
Command series RCA's come up quite often on Ebay, just try to look for the ones that are not labeled "Command" but have the same structure, the short plate with large support bar. I have bought these in the past for reasonably cheap, and they are the same as Command Series.
Here are some...
- http://cgi.ebay.com/4-x-RCA-Tubes-5751-used-and-tested_W0QQitemZ110091625939QQihZ001QQcategoryZ67816QQrdZ1QQcmdZViewItem (Open in New Window)
I don't think the Command is your only alternative. Certainly Frihed is correct about curent production being fairly quiet or even better sonically, IMHO, recent production NOS JAN tubes. They are not prone to noise. With TMBPs you get a richer texture, layering, staging etc. but due to their age they can be pretty noisy. The Raytheon red painted 2 mica is an older production tube that is in general clean if a tad forward and hard. The red paint RCA especially the 5751WA is a generally quiet clean tube but can sound one dimensional. The white paint TMBP RCA seems to be much bigger and more holographic but may have begun to disintegrate. Unfortunately the most sought after TMBPs like the Sylvanias draw out every level of quality with sellers knowing that they can simply post emmissions data and no one seems to ask if the tube is noisy. I consider noise to represent a form of tube failure which is frequently a sign of tube wear and tear. That said sometimes it is found in NOS it is not the same as a microphonic tube.
My 5751 set up must be pretty insensitive. The 5751 is the driver. The outputs are two 12B4A. I have used a number of NOS and the current production Sovtek 5751 without a hint of noise in my headphones. I now have 3 of the RCA TMBPs, the two newest of which are either NOS or not much used.So, maybe i have just been lucky or I buy from the right sources or my headamp is extremely well designed (MapleTree Ear +).
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