McIntosh - Hints and Kinks

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Mcintosh Meter sticks.

I recently purchased a C2200 preamp and the left meter sometimes sticks while playing music. The right side meter registers output normally, but the left will sometimes register a certain output and kind of just stay there. Other times it works normally. Is this something that has to be repaired by Mcintosh or is there something I could do to adjust the meter?
 
Shipping Boxes

McIntosh will sell you a new shipping box for most all models, better to be safe with a new box to protect vintage gear when shipping. If your old shipping box is in good condition but starting to look tired with bunches of old labels and stickers remove them and the old tape with a heat gun or hair dryer, heat will release the glue and let you peel them off without damaging the box.
 
Mac 1900 Receiver Gone Dead Now!! Please Someone Help!!

HI Terry, Hope you got my email. The mac 1900 receiver has gone dead! The line fuse is ok! I borrowed the good pwr output transistor from the good channel and placed it in the place of the shorted one the 5 a amps fuse opened again! The strange thing is that the pwr pc boards are ok because when i swapped the board from the one from the channel that the fuses were opening in the good channel to pwr pc board worked very well. My limited testing with the meter the has capcitance check on it found that one of those large can power supply GE 9300uf/50VDC cap was not showing the right cap and would not register any reading most of the time. Also what problem would there to be no sound coming from the fm section , the signal strength meter moves when the tunning dial is moved across the fm dial , the tunning meter dont moves and no sound as mentioned from the fm section. This was before the unit when dead! Do you think because one those large can power supply shows bad reading it might have to do anything with the unit to go dead?! Also should I check the diode in the 5a fuse circuit by desoldering them?!! YOUR KIND! HELP IS GREATLY APPRECIATED! Thanks! Ali
 
Looking for knobs for Mac 1500

Hello,
I have a Mac 1500 that was a gift and one of the knobs is missing. It is a Base control with double knobs on the same contorl. If any one has a source for these knods I would appricate any feed back.
Thanks,
Jesse
 
Knobs are hard to find, McIntosh has very few older model ones, sometimes Audio Classics has some so give them a call to find out. I hate to say it but the last resort for odd parts can be eBay, one never knows what will show up.
 
Hi everyone. Since I rebuilt my MC240, I have been wanting to make sure that I wasn't overdriving any tubes. Replacing the old diodes with new HEXFREDs changed the voltages a little bit so I have been verifying in several ways that the changes are ok. I thought a DIY rebuilder would be interested in this information and/or would like to add to it.

I have 3 different schematics for MC240, two of which have different voltages listed. I used the IXYS DSEI 8-06A HexFRED instead of the 4007 diode and the IXYS is very close to the original one except for a bump in the negative grid voltage of the 12ax7 drivers. This was the main thing I was worried about so I set off to find out if it was a problem.

One schematic shows the following plate voltages:
split 12ax7: 103
12au7: 205
12BH7: 350
driver 12ax7: 430
6L6: 430

The other one shows
split 12ax7: 108
12au7: 275
12BH7: 355
driver 12ax7: 430
6L6: 430

Note the large difference on the 12au7s. Both schematics show the negative grid voltages for the 12ax7 and 6L6 to be -46V. Mine measure at -51V with no load and the new diodes. Data sheets show that some 12ax7s are limited to -50. However, EH 12ax7as and 5751s are good to -55. Also, the MC40 amps run the 12ax7s even harder than the 240: the negative grid voltage is set at -52. So it looks like the IXYS is an excellent choice since it doesn't need any voltage adjustment and you get the benefits of latest technology.
 
MC-30 questions

Burned R19 and R20 12K's, fried R17 1.2 cathode resistor and half the 12bh7 gone- Terry warned about the 12k's going bad. So have rebuilt the power supply filter. Put in the IN4007 diode and series 9.1K resistor. Decided C13 10uF on the serial number 15329 and above schematic is the bias filter capacitor he refers to in recommending replacement with a 22uF. Replacing the burned and low resistors seems to have gone well. Bought Hovland Musicaps and between the red and green leads on them, the banding and orientaion of the original bumlebees ,(most of which fail testing with a Heath IT-11) and the schematic there seems to be places where there are conflicts in how to orientate the red high end of the Hovlands. So I figure the designers orientated the caps right so which end of the Hovlands red or green correlates with the banding on the Spragues? Advice appreciated-really miss listening to this thing. Did not want to mess with this either. Was hoping to have more time to work my way up to it.
 
MC-30 questions

Problem resolved. The old Mc-30 is singing away as I type. Correlated the schematic to the capacitor orientation-tied myself up in knots trying to do otherwise plus a good nights sleep doesn't hurt.. Checked the original can 15/35/80uf and they were above 90%. The 15 didn't show any leakage but the 35 and 80uF sections did. Seems to like the new Spague atoms in the power filter.
 
Mc30

Don't worry about the C12c, the 15uF section, it is only used if you plug in a C8 into the preamp socket.
 
Question For Terry Stereo Light Mcintosh Mx114

HI Terry! My McIntosh MX114 Stereo light does not stay on it light bright breifly and then goes off! I have the service manual. There is a part called LDR on the MPX board with a resistor attached to one of its four legs do you think this part is causing the stereo light and stereo sound to not function properly?!! The MX 114 is without question one of the finest! FM tuner I have ever heard even with its mono sound at present is sound fantastic! the sound is absolutely stunning! and I have at one point also owned a MR 78 and couple of Marantz 10B both in mint condition but for some reason! the sound from the MX 114 Fmtuner/pre-amp to my ears sound much better. Any kind help to fix the stereo and the stereo light problem in the beauty will be much appreciated! Thanks Terry! With Best Regards! Ali
:music:
 
Resistor Tolerance and Matching

Here is a tip on resistors used in McIntosh tube amplifiers.
If a pair is marked 1% in the schematic this means to each other not the listed value.
When purchasing resistors here is something to remember -
When resistors are made the 1% ones are removed from the batch first, then the 5%, then the 10%, and what is remaining is called 20%. Think about this process,a batch of 10% resistors will have NO values closer than 5% as the 1% and 5% values have been removed already. This doesn't say you will not find resistors of the same value within 1% or less, just that none of them will be closer than 5% of the nominal value.
 
Speaking of resistors... The MC225 schematic shows 10 or so resistors that are to be 5% tolerance. What are all of the other, unmarked resistors supposed to be?
 
MC224 hot 12BH7 and 22K, 1W resistors.

If your MC225 has cooked the two 22K, 1W resistors and the 4.7K, 1/2W resistor, replace the pair of .047uF bumble bee capacitors feeding the grids of the 12BH7 at the same time you replace the resistors. When the .047uF caps get leakage they will raise the grid voltage of the 12BH7, I have seen 96V on the grids, replaced the caps and had it go down to 33V, close enough to get the tube running in spec. The second thing this will do is raise your output power from a sad 22W to a happy 30W+ as it did for me on a customers 225 that was running all original McIntosh tubes.
 
Hi everybody,
I have a 6100 in 110V, bought in the US.
I'm wandering whether the transfo can be modified to provide 220V? I did it on my 7270 and it works perfectly, the transfo was designed to work with 220V with a small modification.
Is anyone knows if it's the same on the 6100?
Thanks for your answer :)
 
Adding a quick note about a the 1% matched resistors - check them even if they look fine. I did that to my 240 last week and found the ones powering the power tubes were off 20%! I don't know how it happened (voltages were ok before and after) but replacing them improved focus tremendously. All the other pairs were still matched but I replaced them while I was at it. The amp now sounds more "hifi" than I ever thought possible.
 
Hints/Kinks?: Dewick: How 2 bias/offset MC-2002

Dear Sir,

Can you advise the process to bias and balance the MC2002?

I've searched the net for a manual, service. I am an EE and can do this if provided the process. May end up buying a service manual from Mc. I have all tools, scope, freq. generator, variac, etc.

Any kinks with this one, the amp.? The amp sounds fine, no issues, says on back stickers that it went to clinic and serviced fine 1999 - 8 years ago.

In addition, no feet for the amp, Mc wants $2 per foot and recommend 1 inch from bottom without mounting in the walnut panloc cabinet I have. I'm currently using in shelf with clearance above at 8 inches, sides 4, bottom less than .5 inches. - using rubber bump on 3M feet on the panloc rails. It gets hotter on the front meter top of chassis than near heat sinks.

It hums quite a bit as a unit, not specific to the speakers, dead quite...chassis humm...probably just solid state and the power supply transofrmer...it's in pretty tight acoustic space, maple ent. system...please advise any airflow issues, what should the sound of the chassis make - hummm....

Please advise as a courtesy.

Thank you for a prompt and kind reply with guidance or exact answer(s) to my ?'s. I appreciate it.

John
 
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Here is a scan from the manual, have Bias set and meter only, no offset.
 

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