The Most Desirable McIntosh Amps Part 2 - A Look Inside and Bias Procedure

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The Most Desirable McIntosh Amps Part 2 - A Look Inside and Bias Procedure

Рет қаралды 9,104

Күн бұрын

We take a deep dive into the most iconic amplifier ever, the MC3500 which powered Woodstock part 2.
Link to PART 1.
studio.youtube...
Link to purchase the current MC3500 in the Tri-State area (In Store Only)
stereoexchange...
This time we take a look at the internals, circuit design and biasing.
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Пікірлер: 33

@marc49lewis 2 жыл бұрын

Ran two of these babies at The Warehouse in New Orleans in the early 70's. They were quite the monsters at the time (and still are). Ran into a few problems with the 6LQ6's going south on us. They weren't cheap tubes, even in the 70's. Ran into one problem with one of the high-voltage zener diodes leaking and it wasn't stocked at the 3 local parts houses, but were able to get them within a week. 12BH7's had to be checked carefully before installation to make sure both sections were close in transconductance. Overall, these monsters performed incredibly well. They drove 8 Seeburg twin-15 cabinets (4 each). I modified each cabinet to use 2 Altec 421A woofers and an Altec 808-8a HF driver... Yes, Seeburg - the jukebox people. The cabinets were really sturdy 1" thick composition board and simply did not resonate or rattle. At the time, it was a superb system. I'd love to see these amps up close, but I'm quite far away. Would love to put them on my bench and run response graphs on them, but the chances of that are slim, none and zero. :-) Sure wish I still had the service manuals for them.

@shanestephenson8423 2 жыл бұрын

Very interesting and a testament to just how well that amplifier was built.👍

@AllboroLCD 2 жыл бұрын

Your partner there explains this incredibly well, good stuff here!

@SkyFiAudio 2 жыл бұрын

We think so too and thanks so much for taking the time to comment.

@paulstubbs7678 2 жыл бұрын

These seem to me to be better than the new re-released models, especially being able to check all the tube biasing setting. Although I do like the micro controller they are adding that monitors all these parameters and 'saves your bacon' when something goes wrong, especially if your out of the room at the time.

@turbobird2000 2 жыл бұрын

Very cool, I have to come visit the store being in NJ also. I am Marantz person (tubes/ big SS / 9s/500). Also have Ohm Fs… do a lot of my own restores. Always looking for a trade… :)

@johnhodgson5313 2 жыл бұрын

The output transformer matches the load impedance to the tube to the speaker impedance. If a 4 ohm load was used and the switch was put to 16 ohms the anode currant on the tube would exceed the value the engineer had in mind. Tubes can handle this much better than transistors and it may not noticeably affect the tube life in normal home audio applications. However the maximum power output and the distortion and frequency response would not be as designed. If that change suits your ears is up to you, but I tend to like things running in their most linear mode. I understand speaker impedance is not one number and Tube Guru's comment on trying 8 and 4 ohm selections is right on for speakers rated at 8 ohms.

@Watcher4111 2 жыл бұрын

That great mac

@cabronesse386 2 жыл бұрын

Really nice content! Kudos!

@SkyFiAudio 2 жыл бұрын

Thank you so much!

@olinweaver8520 2 жыл бұрын

I seen on a video that Crown 300's were used to power Woodstock.

@SkyFiAudio 2 жыл бұрын

Maybe Crown was used too, but check out photos and videos of the stage and you'll see this model McIntosh without a doubt. Thanks for watching and commenting.

@billenright2788 2 жыл бұрын

great info. whatta beast.

@peebrainboy 2 жыл бұрын

Never seen that tube in amps or black/white tvs, they were made for color TVs to handle the enormous peak voltage generated during the retrace of the horizontal sweep, this voltage isn't wasted its stepped up with the flyback transformer for the 28K-32K anode crt voltage. Why mac uses it for an amp I don't know there's is nothing it does that a 6L6 cant.They are very rare so it pretty much dooms these amps for the shelf when the tubes start to go.

@marc49lewis 2 жыл бұрын

@jerry matthers : You're right. I could never figure out why they didn't use a 6550 (or KT88) for this. Certainly WELL within their voltage/current capabilities. We had a heck of a time getting the local suppliers to have enough of them in stock when we needed to re-tube these monsters. We'd buy 16 at a time and that was the problem.

@hifijohn 2 жыл бұрын

@@marc49lewis The only thing I can think of is when you plug and unplug speakers it creates a large voltage spike in the tube, not a problem in home use where you just connect the speakers and forget about it,but in pro use where you maybe constantly connecting and reconnecting speakers (or have faulty speaker wires)for concerts this may eventually kill the tubes, 6lq6 are made to handle very large voltage spikes because they were made for the horizontal sweep section of color tvs.I maybe wrong but I cant think of anything else.

@Justplast 2 жыл бұрын

AAAAA+++++ Explanation :)

@myxplornetexperience5357 2 жыл бұрын

Uuuuugh. Can I just move half way across the world to sweep your floors or something? This is the world I want to live in.

@SkyFiAudio 2 жыл бұрын

Hahahaha! We've actually heard this a few times. Thanks for watching and commenting.

@hifijohn 2 жыл бұрын

Dont mean to contradict the tube guru but I doubt a b/w tv needed such a powerful tube they def used them in color sets,and its not that unusual to see them in audio applications they were made for tv and for audio use.

@johnhodgson5313 2 жыл бұрын

Hello, I agree with you but the guru may have taken that information from a tube manual, and my RCA Tube Manual does list that tube for b/w TV use.

@hifijohn 2 жыл бұрын

@@johnhodgson5313 They were specifically made for color tv horizontal sweep and HV generating, I've never seen them in b/w set which requires a small fraction of the power that color tv set needs, the tube has very impressive specs almost 1Kv plate voltage with a peak of 7.5Kv, also whenever the plate voltage is very high the anode is put on top to prevent arcing.they were also used in illegal CB transmitters.they stopped making them long time go so they are pretty expensive.

@johnhodgson5313 2 жыл бұрын

@@hifijohn You are right, they would have been over kill in a b/w TV and I don't think any b/w TVs were ever built with it, but the RC-29 tube manual does list this among the applications for that tube. If a younger tube enthusiast such as the tube guru mentioned were looking for information the RCA tube manuals are usually pretty good, but I agree the applications may be a little fanciful. I used the much lower power 6DQ5 in my first home built cw ham transmitter from the late 60's. I never did get it on the air, I met a girl. It took until 2006 to start using sweep tube transmitters on the air.

@michaelc.ateoate979 2 жыл бұрын

Of course it is that's a silly question..

@moodyga40 2 жыл бұрын

caps might need changing in this old amp

@stevenphillips1311 2 жыл бұрын

Need to win the lotto fly over spend the day buying

@tommasdelano2794 2 жыл бұрын

Just look at all the rust on the inside these amps they wernt sitting in someones living room they've seen some heavy duty use.My dad did electronics repair and in all the decades he has only seen one mac amp for repair.

@edd2771 2 жыл бұрын

Some Mac haters here but there is no doubt they made (and arguably make) a very high quality product But I still do not understand why this particular unit is desirable to audiophiles. It’s unattractive, noisy, not suited to at-home use, has a poor user interface in a domestic setting and is and well beyond the power requirements of even the most inefficient modern speakers. Now, if you are aguitar player and/or a Jerry Garcia or Woodstock fan, and you want this particular piece, I get it. But audiophiles? I can think of dozens of Mac products I would put into my living room ahead of these.

@hksunchaser1 2 жыл бұрын

Every Mcintosh i own is rusting badly

@garth56 2 жыл бұрын

Also I don't mean to contridict you but McIntosh are just Tosh.. The real American Hi-End community don't like this company and I agree..

@edd2771 2 жыл бұрын

Interesting. I won’t contradict you, but a few follow-up questions if I may. What do you own currently that is superior? What McIntosh amps have you owned in the past (or currently) that disappointed you, and why? Please be specific. Also, who exactly are “the real American Hi (sic) - End community”, and where do they make their equipment preferences publicly known? I would love to check it out!

@alanrogs3990 2 жыл бұрын

@@edd2771 Maybe he likes Conrad Johnson