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

The reason that so many amps, preamps, tuners, etc. made in the USA from the Golden Age used Telefunken tubes is because (so I've been told) the USA distributor practically gave them away for publicity. It just so happened that they were (and are) amazing sounding tubes.

Fanatic tube collecting nuts only want Tele tubes with perfect ink lettering on them, so the rest of us can get the exact same tube branded Fisher, McIntosh, Dynaco, etc. Also they were used in radar and all sorts of other non audio applications and many of those have been yanked and sold for not much money.

If you see NOS Telefunken tubes in pristine boxes on eBay for not that much money, they are fakes. Better to get a FISHER or DYNACO branded Telefunken 12AX7. That way you know for sure you're getting the right thing and not an Asian fake job.

If it has the diamond on the bottom, it's a good one.

If you have the Telefunken 12AX7 tube and nothing to put it in, find something.

 

Thanks! Mine takes 12AX7 and 12AU7's........ and I have tele's hanging around for both. Fun. Wow.

 

Yeah, that's funny.

I actually had to go and fire mine up after working on this thread. I've decided to move the MX-110 to my mastering room anyway. For that vintage smell and sound when I'm in the mood..

I paid 900 bucks for my current working version, mint, restored, all correct tubes. Some old doctor dude on eBay sold it. Even had the wooden case. Can't beat that price for a fun preamp/FM.

Of course it sounds nothing like a modern tube pre. It also sounds nothing like a vintage Marantz 7 which is much more accurate for such an old design. But for under a grand the McIntosh MX-110 does a lot of things pretty neat and has quite a 3-D sound on the right material. Fun to look at, like looking at the Hi-Fi gear in those old Allied Radio catalogs from 1965 when we were kids and couldn't afford anything and couldn't talk our parents into anything...

 

Yes, it was a great machine back in the day and I think one could buy it as late as 1968 in some markets...

I enjoy the 3-D holographic sound it gives the midrange. Not exactly accurate but fun and quite musical.. It works wonders on sterile solid state recordings like ELO "Out Of The Blue" that needs some midrange magic..

 

Eh, who knew? My first expensive (well, over a grand) amp was a giant watt Solid State baby that sounded dry and thick. I found out quickly that power wasn't everything and for the tube stuff, rolling REALLY could change the tone. Never looked back.

I found this pair of RCA 6U8 black plates on the bay for 30 bucks (which is way too much) but they match so I grabbed them. 10 years ago they were 3 bucks..

 

I've never tried a sub in my MX110 being that the actual 6U8 tube is not rare and is not hard to find. I've heard that unless it is an exact sub for a 6U8, forget it in the Mac..

 

An old crusty TV repair guy just told me in an email that in a tubed color TV set, 6EA8 and 6GH8 are direct replacements for the 6U8A.

He wasn't sure about McIntosh ("Never owned one in m' life")...

He did volunteer this: "World's lousiest radio and TV tubes: 6EA8 and 6U8."

Also, this from the rado archive:

"Comparing 6EA8 to 6U8A/6KD8 there is little difference in the RCA tube
manual except that the 6EA8 has a bit more gain. The 6EA8 triode has a
bit less plate dissipation rating while the pentode has a bit greater
plate and screen dissipation.

I don't see differences great enough to be audible, possibly just enough
to be able to measure a difference in a laboratory setting, providing a
large sample of each type is tested.

It is probable that any 6U8 without suffix or dual label 6U8A/6KD8 were
made a decade earlier than any 6EA8. That added storage (and pin seal
leakage time may have contaminated the cathodes to lead to shorter life.
It is possible that had the tubes been operated with heater power alone
for a day or two to clean up the cathode and the vacuum that they may
have lasted better, and its possible they were always not very good,
heading for a short life whenever put into service. Many a TV had 6U8, I
don't recall any suggestions that the 6EA8 was preferable for
replacements."

So, there you go.

I heard a pair of these Siemens today. Not bad! Better than the more expensive Telefunken version IMO.. More open..

 

I was actually told the answer to that when I first got into the MX-110 design specs about 14 years ago. Ashamed to say I have forgotten what I was told about the reason they used a 6U8.

Sorry!

At any rate, they used that particular tube and it strongly affects the audio signal tone and quality so we have to grab the good ones, no matter how much of a pain it is..

 

The quest for the perfect 6U8 still goes on. Valvos stink. Don't like 'em. What's next?

 

I don't believe that for a minute. One guy (CountD, I think he was thrown off of here) said on AudioKarma that his MX-110 ran cooler with an earlier version of the RCA 6U8 and all of a sudden I'm hearing it all over the 'Net EVEN THOUGH TERRY DW said it was not possible for such a thing to be. He's the McIntosh Fix-It God so I believe him...

At any rate, carry on, y'all!