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McIntosh - Hints and Kinks

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12AT7 in McIntosh Tuners

Most all the tubed McIntosh tuners MX110, MR65, MR67, and, MR71, use a 12AT7 in the front end of the tuner. This tube is used as an RF amplifier and mixer stage and can have a big effect on the overall performance.
Here is the problem, overall sensitivity is only 5uV and has a tendency to oscillate on the high end of the band, is very tweaky when trying to align. You have put in a new tube and expect more than this !! this is a NEW stock tube... Well take it out and use an old stock or used tube of the old design without the internal shield, all the problems will go away. It seems that the new tubes with the internal shield works fine in preamps at audio frequencies, but at RF they will not work!! The internal shield has plate to plate capacitance that will cause the tube to oscillate messing up the front end of your tuner.
This is one case where new is not necessarily better.
 
MA-5100 Transistor Help

Hello all,

I am restoring and repairing a MA-5100 with a bad right channel. I know one of the output transistors (Q220) has blown, so I want to replace both of them in this channel as a pair.

The problem is, a previous owner cleaned the chassis and wiped off the serial number!! I have a spare parts MA-5100 that is S/N 99H62, but its output transistors have different part numbers than the unknown serial number unit I am working on. I have seen some information around here on part number 032-070 transistors, which are the ones installed in my spare parts chassis. However, the transistors in my new unit are stamped "025 6-44", and I can't find out what they are. I don't know where to find out what the manufacturer part number of the transistor is so that I can order them. Help!!

-Jason
 
The replacement part for the 132-025 is the 132-070, the generic replacement for the 132-070 is the MJ15003 by ON Semiconductor (Motorola).
 
Help! Loud crackling static in MC250

I have an MC250 that has a hard to diagnose problem. After about 2-5 minutes of playing, crackling static noise will suddenly appear. The static will get louder rather rapidly where upon, after 30 seconds to a minute, there will be a loud snap/pop in the right speaker and noise will go away. The right channel then becomes extremely weak but not distorted. The left channel seems to emit some static but there is no popping sound and it maintains normal volume levels. The right channel level will come back after I unplug the amp and wait awhile. This all happens rather quickly and randomly enough that I cannot do much troubleshooting. If I pull the plug while it is crackling, the noise will just fade away until all the caps discharge and the amp goes silent. I wish I had a scope because I really don’t know between the RCA inputs and speaker screws this noise is created. Originally, the problem with the amp was just low output on the right channel. I changed most of the circuit board electrolytic caps (except for the two larger filter caps on one end of the input board) and the low output went away. I thought it was a bad NP cap at the right channel output of the driver board. This noise is new. I have not touched any of the four chassis mounted can caps. Their measured voltages seem to match the service manual. Thanks
 
Terry,

If I may ask. Having a problem at 89.7 FM...MX-110 starts to fade, signal goes about the same time in the evening each night...called the station engineer...he said could be a pirate radio station...mentioned getting in car and trying it there when it happens on the MX-110...the station jumps from 89.7 FM to about 90.1 or so...the tuning eye opens and the station vanishes, then after a bit it fades back, then back and forth.

Coudl this be an alignment issue? It only happens on this one station and mostly 10pm to 12pm or so at night?

ANy advise?

John
 
I doubt if it is the 110, a problem in the 110 would be continuous or slowly getting worse over time, especially an alignment issue.
This problem is either station related, signal path related, or caused by some type of predictable interference. The capture ratio in the 110 is being exceeded by the strong signal at 90.1, possibly a pirate station or maybe they are changing their antenna pattern at night. Remember the 110 was designed long before the crowding of the stations on todays FM band. As a side note this could be an artifact from an adjacent HD FM signal, known about but ignored by the FCC.
 
RE: MX110 and 89.7FM

Talked to the station engineer and he said go out to the car and use that unit asa the problem occurs again.

He said yes they are broadcasting in both digital HD FM and Analog BOTH but the issue is probably some sort of interference OR my MC. he asked if I has a Phase locked loop Digital set, which I do; a Grundig...fully digital and that get static but no drop out.

I have a Pioneer SA-9xxx-II analog tuner and a HK Citation 15...all of them have the problem...so therefore all a bad?

I don't think so...

he did say while the Mc is a tuner and a oldy, it could be the problem.

We'll see...oddly enough it ONLY occurs at about 10pm to midnight.

I think I agree with you and believe he is finding any reason to get me off the phone; as I am the "only" person to complain.

We'll try tonight by getting in the auto with it's brand new Honda Radio...woo hoo.

Thanks again for the diagnostic. By the way all the tuners work perfectly.

John
 
I don't know if I should post this here but since johndoe1 asked a question about the tuning eye I thought I'd ask. My MX112 tuning eye never totally closes and usually stays open about a quarter inch or so, is this normal? If not what type of antenna should be used and where can I buy one? Thanks
 
MX112 uses the AGC voltage to drive the eye, a signal strength indicator. Reason the eye will not close fully my be alignment, or a bad 6HU6 indicator tube, I don't remember ever seeing one close all of the way so I wouldn't worry.
 
RE: 89.7 and 90.1 drift and MX110 Tuning eye

Dear readers,

First thanks Terry. I spoke to the station engineer again, I only listen to 1 station ever. NPR.

He said he thinks it's the tuner(s), then he said the stuff about going to the car when it happens...guess what, last night i turned it on; all 3 tuners for grins; turned the tuning knob both directions slightly left and right of 89.7 from 8pm through midnight and no fade, no problems no nothing, nothing but muting ON and OFF switch and no extra stations.

My guess is either they fixed something OR it's interference from somewhere. Is it possible that someone could be broadcasting an iPOD via one of those little tiny FM Transmitters? I have one Griffin and it's at 88.6 as a std. I wonder?

Anyway, MT restored tuner and the other tuners worked flawlessly for 4+ hours not a change rock steady.

Now as for the tuning EYE, mine uses the 6 tube Terry indicated v. what you have...mine originally did not close right nor did the MPX Light fade and function properly. I had it aligned per the Service Manual and then restored and aligned it again by myself...yes it can be done.

My version has every knob and POT one could ask for with the exception of the T4 being a tunable transformer, mine has the old style TOP - rounded no adjustment.

I did find that without a NOS 12AT7 and then without a very good 6GH8 in the back left position for the MPX...the thing just would not adj. properly. Once I went with all NOS tubes, Telefunkens, Valvo and Amperex Bugle Boys...yes used were very cheap where I live...the tuner came alive...this was some 8 years ago and I have had not one problem.

At 120V or higher AC line coming in, the transformer is HOT but not as Terry says hot enough to burn.

I did put HEXFREDS in the diode section for the PT and added nice solen caps, the big non-polarized ones for the old might mite paper covered jobs.

I replaced all the coupling caps, the RED ones on the inside support rail to ASC custom made 1% Mil spec teflon and polyprop...600VDC...I got some samples from my work.

I've lost only one tube in 10 years due to age...

I DO NOT use the PHONO Section so I removed the tubes. I use a diff. Left Right amplifier tube, can't recall the euro version but it's for a higher DC filament voltage to offset what comes out or the wall...get back to you on that...it's in a cabinet.

Bottom line on the Tuning eye, once aligned, properly mine closes and then I find the widest OVERLAP after the beams come together and that is the strongest signal and best MPX Light.

As I said it's flawless...but this pesky non-sense on NPR was driving me crazy.

I do use a cheap - Radio Shack TERK like square coax connected antenna - in house on a 8 foot tether...converted from 75 Ohms to 300 ohms via balun n the antenna IN on MX-110.

I have tried my rooftop antenna, old ARCHER job...on a mast...no diff.

For what it's worth.

John
 
Update

Helpers,

It could be interference...it started again at 5pm last night and I jumped in my car and nothing, works just fine.

Maybe the old non digital tuners are the problem.

It took fiddling again at the 89.7 dial to more like almost 90 to get a muted station in.

I think it's a neighbor maybe...not sure.

Oh well.

John
 
MC275 Farting noise

Hi Terry,
Sad day for me. My mc 275 started making a loud farting noise.
I quickly switched it off and let it cool down and put it back on after about 30 min. It played fine for about 5 min then the sound came back.
the noise is coming from the right speaker. it is very loud and sounds like it is in motion
all the tubes light up and noting seems amiss other than the loud noise
the amp is an original 275 and is still in its original state.
 
First place to look is at the tubes, swap good channel tubes into the bad one and see if the problem moves with the tubes or stays with the channel. If the problem stays with the same channel it is time to trouble shoot, if it moves wit the tubes swap them back one at a time to find the bad one that carries the problem with it.
A MC275 in original condition is due for updates, bumble bee capacitors need replacement, power supply needs a rebuild, and all resistors need to be checked foe correct value.
 
MC275 Farting noise

Hi Terry thanks for getting back so soon.

i tried swapping the tubes. On the first attempt i noticed the sound started on the left side and then when i switched off the amp the sound stopped on the left and came out of the right while the amp was powering down.

i swapped the tubes back to their original position and the noises did not change. started on the left and then moved to the right while powering down after i switched off the amp.

on another attempt without further tube rotation the initial sound came out of both speakers and on power down came out on the left speaker.

thanks for the help. i cant concentrate on anything else. and i am hoping it is not the transformer. would like to have an idea before i have to send it off for repair and full service.
 
hi i just purchase a c-39 without the 6 channel upgrade my question is (i'm a bit confused) is will this unit still function as a 6 channel surround without the upgrade
 
help with my 2205 when i turn the volume to about 6 oclock the lights on the meters start to blink is this something to be concerned about? also the transformers get quite warm not hot but quite warm
 
Hi,

Does your MAC 1900 emit a horrible squeal? Is it most noticeable at the top of the dial? Check the soldering of the 2 capacitors near the tuning capacitor and if the solder joint is cold or debatable, reflow the joint. Cured this problem on my late version with impedance switch.
 
Terry good day,
can you help me with a question?
my name is Lev and i live in Israel i have purchased mcintosh amplifier mc 352 and mcintosh preamplifier c2200 new. I have a problem with 352: it doesnt output bass and it feels like it doesnt work at all its possible power.
in Israel i couldnt find anyone who can fix mcintosh (technician ).
This is mine equipment :
1.amplifier mc 352
2.preamplifier c2200
3.cd DCD 700AE
4.cables by "monster cable"
5. speakers KEF aq9
could you help me to diagnose the problem? why its doesnt work properly?
thank you
my email : vlk@zahav.net.il
 
You didn't mention your speakers, possibly they do not like an autoformer amplifier like the 352, assuming they do, try changing the speaker output tap to another value, some speakers that are rated 8 ohms like the 4 ohm tap better.
A lack of bass can also be caused by having the speakers out of phase, reverse the leads to one of the speakers and listen again...
 
Terry, thank you for your quick answer.
my speakers are KEF aq9, i tried all options 8 ohm, 4 ohm and 2 ohm.
i tried to replace speakers for TANNOY mercury F3 and for another kind but the same problem remaind.
the same about the bass, no change.
In generally there is no drive at the sound of music.
thank you
 
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