McIntosh 240 with Big Problems

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[@seeburg10]

Thank you for your attention to this wonderful piece of equipment. I've found that competent guitar amp techs are now almost the only source of service and repair for vintage hi-fi gear. We audiophiles appreciate you!

[@goodun2974]

This amp is a shoo-in for a guitar amp tech to work on because it already has a Telecaster pickup switch and knob on it!

[@g_and_kikos_studio]

My Dad has some old McIntosh equipment (pre amp, power amp) running into Klipsch Horns. I grew up listening to them. It's still my preferred way to listen to music. And now I love to play vintage tube amps. Especially my old 68 Twin. Very cool to see you working on this piece...😎🎸💡

[@michaelmoore7975]

@6:58 It's the headpiece of the Staff of Ra that Indiana Jones used in the Map room in Tanis to to find The Well of Souls where the Ark of the Covenant was kept. I bet it sounded _heavenly._

[@montygore1200]

collins radio used this type of diode clamp in their 30s1 rf power amplifier. i have not seen them used anywhere else other than this amp you're working on. Good video.

[@I.M.Guitar-Nerd]

Oh, bestill my cowering bank account, I am sooo grateful I never caught the audiophile bug.

[@edwardleaver7838]

"Looks like a multi-section can cap exploded and someone removed it. And then stopped." -- Lyle hypothesized with an audible sigh of relief. Looks like "someone" did a reasonable job of removing the blown cap, then realized he was in over his head. Kudos. One doesn't always get so lucky.

[@mrz80]

I can relate to "...and stopped" after trying to source some of those multi section electrolyics for my 275. For my 1700 receiver I eventually Dremeled open the cans of the failed caps, stuffed modern, high voltage, high temp, low ESR equivalents into the empty cans, sealed 'em all up with aluminum tape and printed nice pretty labels for 'em. Ton of work, but the resurrected cans look stock in the chassis. :)

[@TonyThomas10000]

I used to own one of those over 40 years ago. Wonderful sounding amp in its day.

[@mattjohnson6916]

Thanks for the recommendation of the Booker T and the MGs show! Man, that was a great show! I always find it interesting to see groups with gear you do not normally associate them with.

[@seeburg10]

Found on "The Stax/Volt Revue Live In London Vol. 1"

[@BenPrevo]

Some of that footage is from mainland europe - not the UK.

[@pedraw]

I remember those old McIntosh audio equipment. It was too rich for my blood back then.

[@seeburg10]

Check out the price now, used or reissue. High as a Hunter Biden meme.

[@hugeshows]

I've been watching your channel for a while. It's clear that you've touched way more guitar amps than I ever have. I was a Fender authorized tech for a while (nothing to brag about I promise) and I've seen all the Hot Rod X issues you've seen, etc. But my mainstay has always been hi-fi. Somehow, I expected you to have aome obvious weaknesses with a piece like this, but frankly you have acquitted yourself very well. My one criticism would be that I think you're underestimating the time involved to truly get that thing to a point where you'd want it as a primary listening source. I have a slightly higher suspicion level of the coupling caps but it seems to depend on moisture exposure IME. The 240 is one of the best sounding Macs out there, a very important piece historically, and if you have sensitive speakers, it will rock your world. One of the handful of amps of that era thatnhad really taut bass. Only Harmon Kardon was better in that regard (Citation II and Citation V)

[@richardlynch5632]

Looking forward to hearing this McIntosh 😃😎👍

[@jasonkirkham550]

I would have liked to have found that. I definitely would have taken the time to clean it up and make sure it was all correct. Thank you for the eye candy.

[@elshiftos]

Interesting 'patient' you have there Lyle, and of particular interest to me is how one might go about removing the surface corrosion/rust from the chassis as I have an Ampeg B15N in that the customer has asked me to do a full restoration on, no time or expense spared! As I've never gone down the rabbit hole of full chassis restoration, I was wondering if you or anyone else here has any advice on recommended products and methods for this task? Thanks!

[@Satchmoeddie]

They probably removed that FP cap, went to look for a new FP cap and couldn't find one anywhere. There are two film and foil in oil black beauty caps in there and the rest are paper & foil in oil bumblebee caps. The part that came apart looks like a Workman or an Oneida thermistor. Those things were very commonly sold in a set with a pair of varistors for old analog CRT TV set repair. It was for the automatic degaussing. Odds are that one in the Mc40 just keeps the current inrush down a little. It's a thermistor because there no reason to have a varistor over there. With the set of 3 your old boob tube television set would degauss itself a little bit every time you turned the set on from a cold start.

[@mrz80]

That is indeed a 25ohm thermistor, to ease the inrush current and help that godawful expensive power transformer to last as long as humanly possible. :D Oh, and the fuse is a Slo-blow, so the inrush current doesn't eat fuses.

[@valleywoodstudio7345]

What a piece! I've an old Pioneer SX-34B receiver/amp from the late 60's that melted a hole in one of its output tubes about 10 years ago. I did replace with another to see if it powered up and it still worked, but have not used it since for fear that there is an internal problem that caused this fail. No idea where to start with it and finding someone in my locale is difficult!

[@goodun2974]

Tube type Pioneer hifi equipment is very uncommon here in the States. I've seen a couple old Sansui and Trio/Kenwood receivers and integrated amps that used tubes.

[@valleywoodstudio7345]

@@goodun2974 Pioneer also made a branded version of the SX-34B called the Allied 333 for the US.

[@goodun2974]

@@valleywoodstudio7345 , interesting, I vaguely remember having seen one of those a long long time ago. Most tube equipment branded "Allied" in the States was part of the Allied/ Knight (Knight-kit) conglomeration. There was a lot of that going on in the early Sixties, such as the merger of Heathkit and Daystrom.

[@tedmich]

Nice project Lyle, while possibly "in name only" McIntosh is said to provide a optional high end stereo for a new Jeep, an odd paring if ever there was one. Big VU meters and all!

[@PsionicAudio]

Saw that ad. Threw up a little.

[@seeburg10]

Mcintosh did make high quality solid state car audio for a while, not sure if they still do. I had one of their amps from the early 2000's.

[@goodun2974]

@@seeburg10 , the company has been bought and sold a couple times; McIntosh was even owned by Japanese car-stereo manufacturer Clarion for a while.

[@goodun2974]

I'm guessing those "VU meters" aren't actually analog meters but instead some sort of cellphone style screen that simulates the VU meters digitally. As if people with money who drive expensive cars need more blinking lights and gee-gaws in their vehicles to distract them from the business of driving the damn thing safely and responsibly....

[@mrz80]

@@goodun2974 Yep, that's where the Mc car audio came from They sold (and maybe still sell?) a head unit, a couple amplifiers, and some speakers. They have also at various times done complete factory systems for Subaru (Outback and Legacy for several years ), Ford (the GT reissue a few years back), and now Jeep.

[@mrz80]

I had to pause the video at 8:53 and address a point in case you don't bring it up further along. According to the 240 schematic those speaker terminals are floating. Don't ground the amp by tying to one of the speaker terminal common lugs. Use one of the barrier strip *mounting* screws to get a connection to the chassis. I could scan my 240 service manual/schematic and email it to you if you need it, and I unearthed a half dozen or so NOS Mc-labeled 6L6GCs that I'd be willing to part with if you need any.

[@PsionicAudio]

Yeah, I noticed after this. Thanks. But there are other points to tie a non-invasive ground to.

[@alexanderlindback2519]

That photo of Cropper & Dunn is from Oslo, Norway

[@alexanderlindback2519]

kzbin.info/www/bejne/oYbOYoqKdreYr6c

[@jannatinkarlen8702]

Hi lyle, some grounding in the world are not wired properly. Sometimes, the ground is HOT. Shouldn't it be safer not to ground the amp? Although the regulations say that they should be grounded

[@PsionicAudio]

Regulations come after injuries/deaths. Have properly grounded equipment and ensure your outlets are correctly wired. No excuses.

[@edwardleaver7838]

@@PsionicAudio And keep a socket polarity tester in your gig bag. And use it. Every. .damn. .time. Dan Torres recounts when he was a gigging Bay Area musician he'd check each stage socket and found about half of them mis-wired. Attributed the half that were wired correctly to random luck.

[@mrz80]

Looking at the 240's schematic, I don't think there's any reason NOT to ground the chassis. Just don't do it from one of the speaker commons; they're floating. Use a mounting screw somewhere like one of the speaker terminal barrier strip mounts.

[@ctcards2636]

I use to actually own one their power amps. Nothing quite like them sound wise. A Twin Preamp thru one of these = bliss. :-) . Now a days I use a SMS Classic Tube Preamp rack into ART SLA-1 power amp for my guitar work. That signal goes into my JBL e120's. But these def have a sound unlike others in a good way when these are healthy and working right. :-)

[@mrz80]

Les Paul and Jerry Garcia were both fans. Everyone knows about Garcia's 2300 and the stacks of 2300s the Dead used in their PA; not everyone knows that Les Paul used a Mc amp along with I think it was n EV speaker (go check out his interview video on the Mc website) in his homemade combo amp.

[@williambock1821]

So a grounded power cord CAN interfere with sound quality from ground loops in hifi equipment?

[@stevencraig]

The capacitor in the centre of the board at 6:19 (between the leaking electrolytic and the clamp mounted diode) to me looks like it would be a line cap. But if I'm not mistaken...there's only one? I would expect to see another one for the other side of the AC line. Is there another side to that little board? I didn't notice one near the like cord, fuse, or the thermistor. Has anyone started producing reproduction black "death caps" but in X1Y2 rating? I'd hate to see the price...

[@srenalwan4829]

Actually the footage of Booker T & the MGs playing Marshalls is recorded in Norway🤓🥸🕺🏻

[@PsionicAudio]

It was the UK/Europe tour in '67. That photo was from Oslo but they got the Marshall backline in the UK. Same snazzy suits for all the shows.

[@roncarter2188]

So is this the model that Jerry Garcia used as part of his rig? Would the sound change very much if this amp's output transformer was changed to a say a 100 watt guitar amp ot? Being that these were designed for hi-fi use. Thanks - great video!

[@goodun2974]

To answer your question in one word: yes. McIntosh amps use very high quality, labor-intensive, bifilar-wound transformers which they made themselves. A guitar amp output transformer is rather crude by comparison.

[@searing7549]

No. Jerry used an MC 2300. A solid state amp.

[@mrz80]

@@searing7549 He drove it with a tap taken from the preamp circuit of some or other old Fender amp, at least until Alembic started making preamps for him.

[@searing7549]

@@mrz80 it was a silverface Twin. Blackface as a backup. Modified.

[@goodun2974]

The worst thing about working on any piece of Mac gear is, they have sharp edges underneath and they're very heavy, hard to get a good grip on when moving them around or flipping them upside down on the bench. Also, it's easy to scratch the paint on top of the transformers if there's any metal debris, swarf or solder-balls, on the bench. Best to mask off the transformers with painter's tape, use a piece of kitchen carpet under the amp when it's upside down on the bench, and wear thin Kevlar workgloves.The process of refurbishing a Mac amp will beat the heck out of your hands.....

[@mrz80]

And all of that weight is lined up along the backside of the chassis, which always surprises people the first time they pick one up. There is a LOT of iron in those transformer cans (also a lot of tar, so God help you if you ever have to rewind one :D )

[@goodun2974]

@@mrz80 Most if not all of the McIntosh output transformers are supposedly bifilar wound and so I don't think it's really practical to rewind them, as far as I know. McIntosh has or at least had their own transformer manufacturing facility and I'll bet they had some fancy equipment to wind those Transformers. It couldn't possibly have been done by hand , could it?. I've watched videos online of Toroidal transformers being wound by specialized machines and that's a whole another level of complexity in itself.

[@mrz80]

@@goodun2974 Yep, Mc still winds and tar-pots all their transformers in-house. At least the tar is kept in a sealed vessel now so it doesn't stink up the place like it did when I was a kid! :) I think I ran across a reference to a company that can unpot and rewind the Mc output transformers. It's a rather laborious process, and the bifilar (or in later cases trifilar or more complex) windings add to the joy of the job.

[@basspig]

A blown PTC thermistor, in conjunction with evidence that a cap may have shorted out necessitates checking the power transformer windings to make sure that they haven't shorted as well. Before investing a large amount of Labor and time and money into repair.

[@amoruzz]

👍👍

[@goodun2974]

Yes, the broken disc thing at 7:00 is a thermistor, to limit inrush current at turn-on. Not unusual when compared to the *surgistors* that were used for this purpose in the days before thermistors were developed. I'm somewhat surprised you didn't point out the selenium bias diode!

[@PsionicAudio]

Didn’t want to get too info-dumpy in one video. I know a few bias changes will be happening and wanted to address that in a separate video after I get the electrolytics sorted. I figured it was a thermistor but confirmed it with the schematic. Didn’t want to assume.

[@sgt.grinch3299]

That’s a dusty mess. Can’t wait until this is restored to a better than new condition.

[@mrz80]

There was a chap named Terry DeWick out of Knoxville, TN, who could do miraculous things to Mc amps in the WORST shape. He once had a pair of MC-30s on his bench that he ended up having to strip completely, and ship the chassis out for sandblasting and re-chroming, then find someone who could make the silkscreens and reletter them. By the time he was done, they look like they were ready to ship from the factory.

[@goodun2974]

The silkscreening is fragile on these, especially where the plating speckled with rust and pitting. I use NeverDull polishing wadding on them; your WD40 technique might work. Note that Mac amps ran the tubes very conservatively, and at fairly low plate current; and even with today's high wall voltages I expect you'll have B+ that is well below 500 volts. Be aware that their grounding scenario is not the best ---- riveted grounds abound, and note the RCA'S that are riveted directly to the chassis ---- and so the likelihood of ground loops is very high. Try not to breathe in that powdery white chassis-corrosion product; clean the amp outside and wear a mask. The octal socket connections (once used for a McIntosh preamp that didn't have its own power suoply) are plugged with mud, like something a mud dauber or other wasp-like insect would do to encapsulate its eggs!

[@mrz80]

Ditto the delicate silk screening. Many years back my mother decided to get "all those awful fingerprints" off the pretty chrome chassis on the MC-275 in the living room. Couple minutes with some 409 and all the fingerprints were gone. Alas, so were all the tube labels, and most of the serial number. OY Mom! :P Once in a while I still think about calling Mc to see if they still have the silkscreen for the OG 275. :D Plate voltage on the 6L6s in the -240 is 430V. Voltages on the preamp tubes run from 430 down to 108.

[@goodun2974]

@@mrz80 , even Windex will remove the silkscreening from old Mac amps (probably due to the ammonia content) but Formula 409 is terribly harsh stuff. My wife is a clean freak and uses 409 way too much on surfaces that she probably shouldn't, including toilets and even glass sometimes. The directions tell you not to use it on those! I can always tell when she's been out and about with the 409 because I walk into the bathroom and I start gagging and choking from the 409 fumes, which smell pretty much like sodium hydroxide/lye-based oven cleaner..... My wife is under strict orders not to clean any of my audio or stereo equipment, not ever. She broke the stylus on my Linn turntable once and I was pretty ticked off. By the way, I have had to cleaned the backside of the glass frequency-scale on Mac tuners and receivers from time to time, and that stuff is even more fragile than the silk screening on the chrome amps. You end up cleaning it with Q tips and distilled/deonized water and working around the lettering as carefully as you can, And since the Q tips tend to leave a whitish haze behind then you have to go behind back over everything carefully again with a lint free lens wipe or silicon eyeglass cleaning cloth. If you touch the dial lettering with anything, wet or dry, it will probably flake off or dissolve and smear.

[@goodun2974]

@@mrz80 , ps, I'd Love to see Lyle post to follow up to this video but I know hes super busy and he works for himself first and foremost, and not for us.