MC30 tubes
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sloober
Super Member
hey Vendo81- As I told you so far, I am running 7581a GE/RCA outputs. So far so good. I am running Telefunkens for the 12AX7s and 12AU7, an RCA 12BH7 (a?). After reading a whole bunch on the subject, many seem to feel the Teles are perfect in the 12AX7 positions. The RCA is great for the 12BH7. People mentioned that the 12AU7 is where you want to experiment. They recommend RCA, Bugle Boy etc., but say a Tele does not sound good here. Could have fooled me! I will try other tubes I have in that position to see what happens. I know I have some JAN tubes and some I got from HP test gear marked HP. Not sure who made these.
Can't wait to see what yours look like, and to see your restoration!
John
Can't wait to see what yours look like, and to see your restoration!
John
bricktop
Couch woofer
The MC30 shouldn't need too premium of output tubes because of the unity coupled configuration (they only have a gain of ~2 because of the split-load). Low-distortion driver tubes are the key part of the circuit, since they have to swing a lot of voltage for the output stage.
Thanks for all your responses. It will be a while until these are done,I haven't even picked them up yet,but I'm trying to get an idea what works for other MC30 owners so I can look for a few tubes while restoring them.
Sounds like CarlV really likes the KT66's. I do have some 50's grey glass Genalex KT66 tubes I bought as extras for my W5M's that I can try. I have two NOS gold lion KT66's from 1961, but like CarlV I don't really want to buy another set. The 7581a tubes that Sloober is using are a great sounding tube and I've used them in the past.
I've read that most people like the RCA 12BH7 tube. I looked and have a few of them but none are black plates. Anyone know how the grey plates sound? I've read that many like the Brimar black plate 12BH7 as well.
I be able to roll all the different 12AX7's and 12AU7's I have until I go crazy :screwy:
Sounds like CarlV really likes the KT66's. I do have some 50's grey glass Genalex KT66 tubes I bought as extras for my W5M's that I can try. I have two NOS gold lion KT66's from 1961, but like CarlV I don't really want to buy another set. The 7581a tubes that Sloober is using are a great sounding tube and I've used them in the past.
I've read that most people like the RCA 12BH7 tube. I looked and have a few of them but none are black plates. Anyone know how the grey plates sound? I've read that many like the Brimar black plate 12BH7 as well.
I be able to roll all the different 12AX7's and 12AU7's I have until I go crazy :screwy:
vinylisfinal
Super Member
i like the grey glass genelex kt66's. i have run them in w-5m's and tried them in my brothers mc-30's. but i think the real cats ass was the quad of tungsol orange/brown based military 5881's.... so musical.. the high end sound stage came to life, the bass was solid and not muddy. my favorite by far for the mc30's.
vinylisfinal
Super Member
as far as a 12au7 i recommend rca clear-tops....my #1 choice.
sloober
Super Member
Well I tried a few things last night, but it is hard to say. I just don't have the best listening location. I replaced the 12AU7s with some NOS JAN 5814a tubes I had. Can't be sure, but it did seem a little tighter. I am lucky that the 2 12BH7a tubes I have are RCA black plates (thanks Don) and my 12AX7s are Teles. I think this combo is about as good as it gets. Now I can keep on the hunt for clear top RCA tubes... John
Hi Vinylisfinal...I have several brown based Tung-Sol 5881's so I'll try them out. I'll have to see if any of my RCA 12AU7's are cleartops.
Sloober...I'll have to buy a set of black plate 12BH7's. I have NOS Tele 12AX7's so I'm OK there.....Sounds like you are almost dialed in!
Sloober...I'll have to buy a set of black plate 12BH7's. I have NOS Tele 12AX7's so I'm OK there.....Sounds like you are almost dialed in!
I suppose this comment may be more system dependent, but in my experience tube complement in MC30s makes a difference on my horns....in fact I consider the MC30 to be wanting of good tubes for best performance in my systems. The general body of an MC30 remains similar with most tube setups, but the finishing touches can certainly vary.
12AX7 - Telefunken smooth. Very midrange oriented with a hint of a euphonic nature that really make an MC30 for me. This tube goes with MC30s like peanut butter goes with jelly, pizza with beer, and tubes with vinyl. For a more linear sound, try Amperex/Philips, or an early 60's greyplate RCA for a more dynamic sound.
12AU7 - This one varies a bit, I have several preferred 12AU7 in MC30s, seems to depend on the internal cap choice to see what "jives"/has synergy. My best Amperex/Philips have a home in my "wide open" MC30 pair, and I enjoy early Mullard or early RCA long greyplate in my PIO built pair. There are a bunch of 12AU7 that I don't care for; Amperex, RCA and Mullard seem a good menu of choices. I also make sure to use strong and balanced tubes here (phase splitter).
12BH7 - I don't know if I've ever seen a BAD 12BH7 amongst the popular vintage brands, it's a matter of the 15% or so of flavor that this tube in the audio path imparts. RCA blackplate for warmest, smoothest sound, Tungsol and GE in the middle, and RCA greys and Sylvania being more "open" and energetic up top. LOTS of good ones - choose one!
12AX7 - (again) I again use Tele smooth, having them in both slots gives the amp that special magic I like. It seems with both 12AX7 the same (like both Tele sm or rib, both Amperex, both RCA, etc) the "sound" of that tube becomes more evident - so if you like what the first input tube does for the sound, using the same tube in the last will "lock in" that tube's sound in the signature that much more. It is a point worth making that this last driver tube gets WORKED: That's another reason I like Teles, because that's one tough 12AX7 and you need one here. This is NOT the place for weaker marginal strength tubes - bring 'em strong for this duty!
OUTPUTS: I've used an array of 6L6GCs, including the SED winged C (clean, balanced presentation with good bass punch that's a great value), RCA 6L6GC (can be a really nice smooth tube, especially with PIO caps, but not so well balanced with more modern parts packs IME), GE, which is a very nice classic tube for these with a very nice midrange carriage......then there's the "neighborhood" tubes such as GEC KT66 which are phenomenal sounding in these, albeit a bit more work for the transformer.
I have oft wondered if real vintage Tung-Sol 5881 are OK in these, not sure on that one, but it is a curiosity. It seems some DO use them, including here, but I must admit I hadn't considered this tube much. It seems maybe I should?
Of course, YMMV and all that, but listening on fully horn loaded high efficiency speakers has me very sensitive to tube complements - and even different parts packages that can be used in MC30s. Both 12AX7s, the 12AU7, and the 12BH7 are all in the signal path and do impart some differences in "finish" and signature. Also true of the outputs. The general presentation of the MC30 remains the same using most in spec tubes, but there are a host of nuances and refinements that lie therein.
I do leave the following caveat: I'm not a big fan of continuous "rolling" on my MC30s. Once I find what I like - I leave. Every roll does introduce the small possibility of having an issue (and the value of your tube testing equipment and sources are realized in spades here), and frequent rolling can wear out the sockets in time. I did do some experimenting with them upon the initial rebuilds, but once I found the solution I left them - in the interest of stability as well as wear. I also had my amps scoped on my tech's bench with my tube choices to be double-plus sure.....
12AX7 - Telefunken smooth. Very midrange oriented with a hint of a euphonic nature that really make an MC30 for me. This tube goes with MC30s like peanut butter goes with jelly, pizza with beer, and tubes with vinyl. For a more linear sound, try Amperex/Philips, or an early 60's greyplate RCA for a more dynamic sound.
12AU7 - This one varies a bit, I have several preferred 12AU7 in MC30s, seems to depend on the internal cap choice to see what "jives"/has synergy. My best Amperex/Philips have a home in my "wide open" MC30 pair, and I enjoy early Mullard or early RCA long greyplate in my PIO built pair. There are a bunch of 12AU7 that I don't care for; Amperex, RCA and Mullard seem a good menu of choices. I also make sure to use strong and balanced tubes here (phase splitter).
12BH7 - I don't know if I've ever seen a BAD 12BH7 amongst the popular vintage brands, it's a matter of the 15% or so of flavor that this tube in the audio path imparts. RCA blackplate for warmest, smoothest sound, Tungsol and GE in the middle, and RCA greys and Sylvania being more "open" and energetic up top. LOTS of good ones - choose one!
12AX7 - (again) I again use Tele smooth, having them in both slots gives the amp that special magic I like. It seems with both 12AX7 the same (like both Tele sm or rib, both Amperex, both RCA, etc) the "sound" of that tube becomes more evident - so if you like what the first input tube does for the sound, using the same tube in the last will "lock in" that tube's sound in the signature that much more. It is a point worth making that this last driver tube gets WORKED: That's another reason I like Teles, because that's one tough 12AX7 and you need one here. This is NOT the place for weaker marginal strength tubes - bring 'em strong for this duty!
OUTPUTS: I've used an array of 6L6GCs, including the SED winged C (clean, balanced presentation with good bass punch that's a great value), RCA 6L6GC (can be a really nice smooth tube, especially with PIO caps, but not so well balanced with more modern parts packs IME), GE, which is a very nice classic tube for these with a very nice midrange carriage......then there's the "neighborhood" tubes such as GEC KT66 which are phenomenal sounding in these, albeit a bit more work for the transformer.
I have oft wondered if real vintage Tung-Sol 5881 are OK in these, not sure on that one, but it is a curiosity. It seems some DO use them, including here, but I must admit I hadn't considered this tube much. It seems maybe I should?
Of course, YMMV and all that, but listening on fully horn loaded high efficiency speakers has me very sensitive to tube complements - and even different parts packages that can be used in MC30s. Both 12AX7s, the 12AU7, and the 12BH7 are all in the signal path and do impart some differences in "finish" and signature. Also true of the outputs. The general presentation of the MC30 remains the same using most in spec tubes, but there are a host of nuances and refinements that lie therein.
I do leave the following caveat: I'm not a big fan of continuous "rolling" on my MC30s. Once I find what I like - I leave. Every roll does introduce the small possibility of having an issue (and the value of your tube testing equipment and sources are realized in spades here), and frequent rolling can wear out the sockets in time. I did do some experimenting with them upon the initial rebuilds, but once I found the solution I left them - in the interest of stability as well as wear. I also had my amps scoped on my tech's bench with my tube choices to be double-plus sure.....
I know this is a very old thread, and I've thrown this out on a more recent thread but perhaps I can get @vinylisfinal to comment if he's still around. I received a pair of TS 5881's from Audio Classics with my MC30's, and used them a bit before switching to RCA GC's. But I love the look of the 5881's, and now that I read that the sound is great, just want to confirm once and for all that there is no problem using them as a sub for the GC's in the MC30's.
The relevant point is that the 5881 has a maximum plate dissipation of 23W and the 6L6GC has a maximum plate dissipation of 30W. That's a huge difference. You will need to compute the output tube plate dissipation for your MC30 and see if the 5881 is safe in your unit.
Ei black plate 12bh7 in the driver spot.
Finding American NOS with matched sides have been problematic for me at least. Don’t know why.
Tend to use Mullard or Telefunken all other 9 pin.
Wouldn’t use anything other than 6L6GC in mine.
Between the NOS GE 6L6GC and Jim McShane Tung-Sol Reissue, could not hear enough difference.
I guess saving the GE’s for later.
The ultimate which I will never be able to afford would be real GEC.
Finding American NOS with matched sides have been problematic for me at least. Don’t know why.
Tend to use Mullard or Telefunken all other 9 pin.
Wouldn’t use anything other than 6L6GC in mine.
Between the NOS GE 6L6GC and Jim McShane Tung-Sol Reissue, could not hear enough difference.
I guess saving the GE’s for later.
The ultimate which I will never be able to afford would be real GEC.
I suppose I'll ask Audio Classics, but wouldn't it make some kind of sense that they when they sent me the amps that one of the had 5881's inserted in them?
The 5881s are not a sub for 6L6GCs. They are an acceptable sub for the 1614s that the Mc30 were designed for. 6L6GCs will work just fine in the Mc30 but the extra plate dissipation is not needed. The tech who installed them at Audio Classics knew what he was doing.
I use NOS GE 6L6GC's or, JJ 6L6GC's which are remarkably good, too. I personally wouldn't use 5881's since my household voltage runs between 121 to 124 volts on a given day. I have a nice stash of USA made NOS Sylvania 12BH7A which I use now that I am low on RCA's. It is very hard to find 12BH7A's with tightly matched sections but I haven't found that to be a huge issue. I currently use GE 12AX7A's but have found the JJ 12AX7S (box grid type) to be good sounding and long lasting. USA made NOS 12AU7A's (GE, Sylvania/Philips) are still fairly easy to find so I use those as well. Amperex's are nice, too, in that tube type.
Now there’s a tube I’ve never heard of, looks like a beast!
