My vintage McIntosh MX-110 preamp surprised me today. Follow up post #61!

I decided to take the plunge and I have an M-series MX-110 on its way to my house next week. I am a bit nervous as I have been a solid state guy for so long.

I had a few questions for those of you watching this thread (that have MX-110s).

What is the seller's name (on eBay?) that sells the RCA black plate 6U8s for a reasonable price?

I will not be using the FM tuner. Can I pull the tubes that power that section up or would that cause problems?

I may swap the lower front panel. How difficult is it to remove? Are the knobs easy to pull off or are there some special tricks to use or things to avoid?

Thanks,
Kevin

 

I heard back from poster Bert1 that it's easy to remove the front panel. Apparently just pull off the front panel knobs and end caps to expose a couple of screws.

I am still wondering if I can operate this thing without the FM tuner tubes. Looking at the schematic, there are at least 8 tubes I could pull out if I don't want to use the tuner if the preamp would still work well without them. Someone over on AudioKarma says it probably would work but "may raise the b+ a little". I can't see a "b+" anywhere on this schematic.

 

Well, I was figuring that all these tubes cooking away and adding heat with (for me) no added benefit, I would be better off without them. If the tuner and the audio preamp sections are somehow interconnected then I certainly wouldn't do it.

Isn't there a benefit from reducing potential noise paths in any tube circuit?

 

No, you don't want to remove tubes and leave any open circuits in your MX110, which would create more problems than it's worth. Not a good idea. Besides, you may find you enjoy the tuner. What are you swaping the front panel with?

 

Okay, I am back from the dead, or page 2 of this thread and was considering piddling with my MX110 a bit.

Judging by Steve's post (http://forums.stevehoffman.tv/threa...-follow-up-post-61.268103/page-2#post-7469223), looks like I need to find a few good tubes in key spots.

Do you know if this will work for the Compactron? http://www.tubedepot.com/nos-6d10.html
Tube Depot was originally recommended to me by Terry DeWick and I have bouhgt some 7591s from them
What does a matched set usually go for nowdays? Does anyone have any they would be willing to sell? I suspect tubes are not going to get cheaper anytime soon, so grabbing any that I can will be a good investment. I don't have a tube tester, but I do have a local guy who builds/restores guitars and he also has some old tubes for sale. I'm sure he has a tester and would be willing to help me out if needed. Here's his shop: http://www.pwogs.com/ Also notice the Mac gear in the front left.

Thanks for any advice!!

-Bart

 

Bart, Can you let us know what tubes are in your MX-110 now? You may have some good vintage tubes in there already that don't need replacing. For example, if you have some Telefunken 12AX7's in there, they are more then likely good to go! Can't say I've ever had a Telefunken 12AX7 go bad.

That said, you would be best to find RCA brand for the 6U8 and Telefunken for the 12AX7 positions. Best value for the Telefunkens are those that were rebranded as Fisher, etc. Much cheaper than getting tubes with the Telefunken logo. (Leave those for the tube collectors!) NOS RCA 6U8's are still inexpensive on eBay.

For the 6D10 compactron, the link you have to Tube Depot is probably as good a place as any to get this tube. There were lots of brands of these, but only 2 (I think) manufacturers.

Anyway, take a look at the tubes you have and post them here.

Wes

 

I heard back from restoration guru Terry DeWick that I could pull them and probably be OK because my filter caps have been replaced. His words were, "Yes and no, yes it will unload the power transformer and things will run cooler, and no because the B+ may be unloaded enough to stress the filter capacitors if they are the originals. Personally I might pull V3 to disable the tuner. Tube life is no problem in the 110. The tuner section runs them so lightly that most 110s have original tubes and still meet specs".

So basically if I wanted to do this, I should modify the circuit to load the B+ rail, something I am obviously not going to do. So, it was a good idea in theory but not so good in application.

I just ordered 5 RCA blackplate 6U8A tubes from a eBay seller for $6 a piece so I should be good to go.

Tomorrow, my Mcintosh MC240 amp is scheduled to arrive from Audio Classics. I have been thinking about this setup for about 33 years. It's about time I decided to do it.

 

Okay, I pulled the little covers and checked. Mine are not labeled by V number, but using Steve's pic as a guide:

V10- my m serial does not have a tube in this position. Looks like a cap and is labeled MPX power it appears?
V13, 14 and 15- All are ECC with Telefunken diamond logo, made in W Germany.
V16 and 17- Telefunken branded, diamond logo, western Germany

 

If your MX110 has a "M" in the serial number, it is an early model. Does it have a horizontal control in the center of the faceplate for the balance?

If it is an "M" version, then I'm pretty sure it does not use the 6D10 tube at all. So, no need to order one of these!

Since you have Telefunken 12AX7's, then they are almost certainly good to go.

It sounds like you have Telefunken 6U8's too. These are best replaced with RCA brand 6U8 or 6U8A's.

 

Thabks for the feedback, Mr Carroll! Yes, it's an early M serial number with the horizontal knob balance control - you can see my pics on page 2: http://forums.stevehoffman.tv/threa...ised-me-today-follow-up-post-61.268103/page-2

Good to know on the 6D10.

Guess I'll leave the 12AX7s alone.

I'll look for some of those RCAs, then.

The only sound/electronic problems on mine are:

1. I have a hum from the phono section. If I wille the RCAs a bit I can make it go from tolerable to pretty loud (volume knob dependent). Sometimes this seems to get worse the longer it plyays.
2. MPX light does not come on, though stereo works fine.

Thanks for any further feedback.

 

I checked with Tube Depot and that have JAN 6U8As, but no RCA. I want to buy from a trusted seller if I am replacing anything. Thoughts on where?

 

There are a bunch of NOS 6U8A RCA's listed on eBay right now. Do a search and find a seller with good feedback.
I see some listed for for $9.75 ea from a U.S. seller with 100% feedback. This price is a little high-ish, but not bad for a safe transaction.

Or, you may try Jim McShane (very trusted seller). You can do an Internet search to find his site and email address.

Another one to try is Kevin Deal at Upscale Audio.

 

I too have a series M MX-110. You should have three phono inputs. Phono 1 Mag, Phono 1 Xtal & Phono 2. Phono 1 Mag & Phono 2 are both for magnetic cartridges. Try plugging your turntable into Phono 2 and see if the hum goes away. The reason I mention this is that my unit started humming in the Phono 1 input and when I unplugged/plugged the RCA connectors a few times (with the unit off), the hum went away. I think in my case, it was dirt/oxidation causing the problem. Yours may be too.

 

There is an MX110 and MC60s featured in a Twilight Zone episode, Sounds and Silences, starring John McGiver, which I watched on DVD recently. The stereo has a significant role in the storyline, check it out, from Season Five.

 

I bought a sleeve of 5 RCA 6U8A tubes from an eBay seller with good feedback and I got 4 pretty beat up looking tubes with cooked on dust that only tested out from 61%-68% and one tube that tested dead (38%). All were listed as NIB (new in box). When I contacted the seller, he replied in a nasty tone that he tested them all and that he would take them back and give me a refund after he verified that I didn't swap them. Needless to say, he's off my list of sellers.

I also bought a nice pair of 6U8A black plates from another eBay dealer and they were exactly as advertised. You win some, you lose some.

Next time, I'm using Brent Jessee or http://www.vacuumtubes.com/. I have a lot more trust in these guys and neither one has gone "nasty" on me. My only problem with these two dealers is that their 6L6GC prices are about 50% higher than I'm willing to pay so I'll have to continue using eBay sellers for these.

 

Have you had any luck getting the hum problem solved? Did you try the other phono input to see if that cleared it up?

 

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I've always gotten great tubes and service from The Tube Depot. Haven't bought from them in a while, but I would buy from them again anytime.

 

I switched over to phono 2 and haven't gotten any loud hum since. There is still a little, but nothing beyond normal for 2 tube units from 1962, I think. Hopefully it holds up! I do need to modify my cabinet where my TT is sitting, not ideal at the moment.

 

Been using my MX110 this week, great sounding pre-amp! I've never sorted out the issues with the tuner itself,however. My Tech had it for like 6 months, but it still won't really operate like a good Mac tuner should, won't really dial in any stations completely. Not that I use the tuner much anyway.

 

I recently bought and refurbished an original MX-110 and I am so in love with the phono preamp I will never use anything else for my needledrops.

 

I wonder how many of these old tuners this thread has sold?

 

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You could check with Terry DeWick about a possible tuner alignment.

 

Yes, I've thought of that. His backlog is pretty good right now though.