McIntosh MC-30's, MX110 tube discussion. Perfect 6U8, 12AX7, tube? See post #43 for Steve's input.

Quick bump & grind.

Any Mac preamp users find the perfect 6U8 tube yet? Better than the RCA Black Plate?

 

Take a look. See the black part? Really just denotes a good time in RCA tube making. Especially for the famous 6L6GC output tube. The best for all Fender 40 and 80 watt guitar amps and McIntosh MC30 and 240 amplifiers.

 

Don't let tube dealers try and snow ya. "Black Plate" RCA input tubes (the little mini pin tubes that we all use) are not RARE tubes. There are zillions of them. Do not pay much for these.

Regarding McIntosh 240 or MC30: The later RCA "Clear Top" input tubes are also good. A touch less complex with more of a top end tang. I use Clear Top RCA 12AU7's in my McIntosh MC30 monoblocks to give a little flavor and air to the presentation. The 12AX7s in there are Telefunken, the 12BH7 is GE. The Tele and the Clear Top RCA are a nice duo. The Amperex "Bugle Boy" 12AU7 is a touch leaner and brighter and can work in that position but costs 15 times as much as the lowly RCA Clear Top.



The RCA Black Plate 6L6GCs on the other hand are getting rare.

 

Better late than never.

RCA 12AU7's are the best when they have clear tops. They are called (duh) RCA "Clear Tops". It is a lively sounding 12AU7 and doesn't cost much money. The tube looks unfinished because of the top but it works great if you like a dynamic and detailed sound while still retaining midband purity...

 

That's the little bugger. A great, inexpensive alternative to an expensive ECC82/12AU7 like a Telefunken, Mullard or Amperex "Bugle Boy". The RCA Clear Top 12AU7 should be 1/6 the price of these European tubes, NOS.

 

McIntosh MX-110 preamp/FM stereo info.

For those of you just joining us, there seems to be some confusion out there about your McIntosh MX-110Z and which tubes audibly effect the sound.

Tube position number 8 - muting/L&R amplifier - 12AT7. This tube SHOULD NOT BE ROLLED, it has no effect on sound quality. 'Kay? Don't bother with it, must make sure it's a fresh tube, GE, Sylvania, whatever.

Onward:

Phono stage. If you use the phono stage on your MX-110, positions 13 and 14 are the two 12AX7 tubes that shape the sound of the phono section. Use Teles if you can afford it. Get the ones rebranded FISHER, DYNACO or whatever. Same good tube, check for diamond on the bottom, don't get a fake. Original Yugo El Teles can work in a pinch. They don't cost much...

Audio tone shaping:

The 15th tube position, the L&R second audio will help shape your tonal balance. This is a 12AX7. Again, the Tele for the magic midband, or whatever you prefer. Keep GE's, SYLVANIA's and other flat sounding tubes OUT of this spot. At the very least, get a vintage RCA black plate NOS. You need the best you can afford here, NOS.

V16 and V17, these are the left and right 3rd audio amp. 6U8 here. I suggest RCA. This really changes the tone and still quite cheap. Get the best. I dislike Telefunkens in this spot, quite muddy (to me). Recently a ton of old Siemens ECF82's have been uncovered and are selling for about 45 bucks each, unmatched. I have NO idea what these sound like, probably good but you can still get RCA Black Plate 6U8s out there for one dollar each.

LAST BUT NOT LEAST, position V10 is that wacky 6D10. This is the Compactron tube. This tube does double duty as well. Part tuner stuff and part audio playback so it's an important tube. Problem is, you can't roll it because they are all GE's. It's not a rare tube, it's just not used that much in audio, it was made for Color TV's. This is used BOTH for the FM AND the audio section. This weird tube is like a Triple Hi Mu three section 12AT7 in an odd body. I believe GE invented it in 1960 or so. Back in 1997 I bought a whole bunch of them for a buck each.

So, to recapitulate: The tube spots you need to worry about sound quality issues are: V10, V15, V16, V17. That is all. Those tubes need to be of the highest musical quality. Amperex Bugle Boys, Mullards, Telefunkens, Siemens, depending on the special tone you like for your MX-110 and the rest of your vintage playback system. At the very least, NOS RCA Black Plate or Clear Tops. The GE 6D10 Compactron needs to be working in tip top shape. NOS examples are not too much money, maybe 10 to 15 dollars now. They last a long, long time though. Make sure your 6D10 is fresh in all three segments.

If you use your phono section, V13 and V14 need to be the same high quality, I always suggest Teles in that spot for maximum midrange madness.

For the FM section, etc.: Just make sure that all the countless other tubes in your unit are fresh. Cheap New Old Stock GE, Sylvania, Tung-Sol, etc. work fine in the non-critical spots..

DOES THIS HELP? The MX-110 with the proper tubes can really sing. If you play your unit a lot it is worth it to upgrade these certain tubes, trust me, especially the two 6U8 tubes.

More later if I get the chance!

 

V10, V15, V16, V17! Got it!

It's time to tweak a bit.... great thread!

I asked this in another thread but I might as well as you folks, too.... how do you distinguish between a 12AX7 and a 12AU7? When the writing is all rubbed off, of course.

 

It's true, ya know!

I remember when he deliberately let slip that Telefunken 12AX7 had the "breath of life" and that was the very beginning of my interest in McIntosh and the eventual start of "the long hunt".....

And the kicking myself in the butt for not buying all this stuff in the 1980's!

 

Yes, exactly the same..