Back from deployment, time for some MC240/MX110 fun

smartin53

Well-Known Member
So now that I am back from the sandbox, I was able to toy with the MX110 and MC240 I got off eBay 5 months ago.

Out of the box, both were a bit dirty with the MC240 having some rust and a mishmash of tubes, while the MX110 was just dusty and had its original complement of Telefunken/McIntosh branded tubes. Also did a basic inspection that showed all was physically good with no burns or leaking caps.

I brought both up with a variac with no issues while doing some cleaning to each. I also did a test rust removal on the MC240 with good results, but it will end up with pitting. The MX110 just needs some new foam.

As for functionality, I hooked up the MC240 first and to my amazement the thing has zero issues. It was dead silent and pushes audio with no problems. After that I plopped in the Gold Lion KT66 power tubes along with Gold Lion 12AU7/12AX7 and EH Gold 12BH7 Input tubes. These made a marked improvement with the sound and worked great. The power supply only got warm, and the output transformers stayed cold (I wasn't exactly pushing it hard). No problems with caps getting hot either. All the pots worked with no crackling.

As for the MX110, it needs a bit more work though I think its mostly related to dirty pots. I had some issues with channels being quiet/noisy at some volume levels. At other points they are fine though. To be safe I pulled the existing tubes and installed a new set of tubes to ensure I wasn't dealing with problems compounded by worn tubes. Luckily it looks like the original tubes are sound so I'll likely reinstall those.

For now I had to stash everything for a few weeks. I intend to do a full capacitor swap on both since the good behavior is likely chance only. In the meantime I'll be doing a quick recap on a Dynaco ST-70.
 

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I'm just happy your home safely but I can see your in heaven playing with your gear.
 
Welcome back and thanks for the sacrifice...If you go on patrols, do you think of the gear?
 
Z - has concentric on/off and balance controls; M has thumbwheel balance control. OP's is a Z.

Classic Mc combo. Good luck with the restoration.
 
Welcome back and thanks for the sacrifice...If you go on patrols, do you think of the gear?

Luckily no patrols, but plenty of desk time to research. There have been a lot of MC240 threads I've noticed as of late so lots to think about.

For the others, yea the MX110 is a Z series.

In the meantime I should get to refresh my rebuild skills on the ST-70. I bought one of those Hakko desoldering guns which should hopefully simplify the work. There are lots of caps to replace on the MC240 and desoldering was always my biggest pain.
 
Well I finally got back to the amp at least. Did a full swap of all the caps. Hadn't quite intended to do the whole thing in a day but I got in one of those modes. Got slowed up a bit after accidentally crossing a couple wires in the power supply. Luckily no damage but a lot of confusion initially. I went the full orange drop route and used some F&T electrolytics for the non-can caps. Quite a pain getting the stuff desoldered on that board but my Hakko 808 desoldering vac helped a lot.

Everything is working great and my voltages are good. I just have to swap the selenium rectifier with a diode and resistor and I forgot to order a cap for that bumblebee in there so I'll do that since I doubt radio shack has poly caps. I tried just a diode alone and my bias was sitting at -49V which was outside what I was comfy with. Reading around, I need a 470 ohm resistor to drop in series with the diode correct?

Right now I'm letting everything burn in along with this set of XL1 speakers I just refoamed. Now I get to look into the MX110 and also have a set of ML-1C speakers that I am refinishing in the garage.
 

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Thank you very much!

the very reason I get to sit up all nite listening to music that made the hairs stand up on my narrow fee neck, is incredible, people like you. Honestly I am feeling far more thankful, today, than yesterday, and you are the reason. I hope you remain healthy and welcome home.
 
Amazing, welcome back - it proves that we are all just men or boys (I mean, you come back and play with your toys) even though some of us do things that most of us see only, in the movies - Thank you, can tell us about the sandbox? how was it? how long did you stay?
 
can tell us about the sandbox? how was it? how long did you stay?

It is what it is. I was actually in Afghanistan so in most places there isn't actually much sand (just lots of dirt) but we all still call it the sandbox. Twas there about 6 months. It certainly is trying with limited comforts and occasional rockets attacks (at least where I was) but you make the best of it. I just did IT work myself so it wasn't like I was in the thick of it every day.

More on topic, started doing some rust removal on the amp. It looks like a cake right now as I slathered a paste made from Barkeeper's Friend over the control side. It's doing its thing eating up all the rust as we speak. I also got rid of the selenium rectifier finally. Ended up that a 330 ohm resistor in series with the diode got me to the -46V bias I needed.
 

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I'm not ashamed to say that I work at a VA Hospital. Especially thank you for your service! Hope you will find AK as helpful as I did........ I dearly hope the care at t he VA will deserve the respect of your consideration: ..... this is a a great forum to address your audio questions...
 
Welcome home. Thanks for what you do and you have some pretty nice toys.:thmbsp:
 
Welcome home. Thanks for what you do and you have some pretty nice toys.:thmbsp:

Thanks. Pilot type I take it? I'm heading to OTS myself in Feb next year but I'll be doing Space Ops (not sure which shredout yet).

In relation to the amp, anyone have any idea what would cause a slight red plate at one edge seam of the plates of a Gold Lion KT66 Reissue? All 4 seems to be doing it on the same edge side. I thought I saw something when it was dark, but after a few hours it was definitely there. My bias seemed to be stable at about -46V but I admit I never tried to measure it over a long term period beyond 30 minutes. Aside from the red plate everything else seems to be working fine.

In the attached pic, you can kind of see it to the left side on tubes 1 and 3, and the right side on tubes 3 and 4. Originally I thought it was just a reflection in the exposure but like mentioned, it definitely was not a reflection a few hours later.
 

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Welcome Back, and thanks for your service.

I've got to get a new soldering iron also......and get to work on projects.

Have fun!
 
Hell no. I had to work for living.Backshop EW/ECM wizard!:thmbsp:

Ah wasn't sure from the avatar. I've been doing IT comms (with a bit of aircraft sat comms on this last deployment) so far but I decided to take the chair force route and steer some satellites or something :D

I always get picked on from my brother as he does engine MX himself so this was the first time I got to not be a "nonner" as he put it.
 
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