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The Mac 275

64.222.254.226
Posted on July 21, 2014 at 21:25:21
mark.korda@myfairpoint.net
Audiophile

Posts: 1253
Location: Maine
Joined: August 16, 2011
 Hi, A guy had this on another forum. It's really interesting. After watching this I pose a question? Can anyone repair a MacIntosh transformer, I say not...you'll see what I mean....Mark Korda

 

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RE: The Mac 275, posted on July 22, 2014 at 00:25:33
unclestu
Dealer

Posts: 5851
Joined: April 13, 2010
 Original macs used bifilar windings..still repair and replacement of cores can be done, if a bit messy.

 

RE: The Mac 275, posted on July 22, 2014 at 16:56:27
JonM
Audiophile

Posts: 292
Joined: December 29, 2000
 Some of the comments on the youtube page complain about the use of printed circuit boards instead of point-to-point wiring, claiming that printed circuit boards are less reliable in the face of the thermal cycling you get in a tube amp. Given how many Dynaco tube amps (which use circuit boards for their driver circuits) are still working, is there any validity to the complaints about McIntosh using them? (I am wondering, could ROHS-compliant, low-lead solder be a contributor to unreliability in such use cases?)

Just curious.

 

RE: The Mac 275, posted on July 22, 2014 at 18:47:09
Palustris
Audiophile

Posts: 2408
Location: Cape Cod
Joined: September 12, 2008
 When I bought my 1950s Dynaco ST 70 and Pas 2 in the 1980s they were ready for new circuit boards. I used the Triode Electronics replacement ST 70 board and for the PAS lifted up most of the tracks with an exacto knife and replaced them with wire soldered to the components leads sticking through the board.

 

RE: The Mac 275, posted on July 22, 2014 at 21:34:50
mark.korda@myfairpoint.net
Audiophile

Posts: 1253
Location: Maine
Joined: August 16, 2011
 Hi Guys, I thought that point to point soldering was the primo way to go with the heat of vacuum tubes even though Dyna amps used circuit boards. I made a headphone amp kit,the (Corda) from Germany.I made some resistor mistakes after I sent it back to Germany it was returned fixed by Jan Meier, the inventor of the amp. He told me of circuit board (lift off) of the line of wire,even though I used a 25 watt or less soldering iron. One thing that I don't get is that Lamm amps and preamps have circuit boards and cost about 40 grand? Do they ever break down?...Mark Korda

 

RE: circuit boards, posted on July 22, 2014 at 23:15:45
unclestu
Dealer

Posts: 5851
Joined: April 13, 2010
 gotta remember circuit boards were invented as a cheap way to place the proximity circuit inside of antiaircraft shells in WWII. Handwiring was too time consuming and expensive.

PCB have one major issue as I see it. Since the traces are on one plane and run adjacent to one another it is possible for arcing to occur between traces.

This is especially true if there is a lot of rosin on the boards which haven't been cleaned off. Over time and with heat the rosin, being organic, carbonizes and becomes slightly conductive. That coupled with component over heating can literally cook the boards, even the more expensive fiberglass boards. When this occurs, the carbonized board will carry leakage current, particularly with higher B+ voltages.

Normally not too much of an issue with preamp voltages (~300vdc). can definitly bE troublesome with power tubes (~600 VOLTS).

 

RE: The Mac 275, posted on July 23, 2014 at 06:22:20
Bold Eagle
Audiophile

Posts: 6936
Location: America's Heartland
Joined: May 27, 2001
 One of the problems with low wattage irons is that you have too much dwell time on the solder joint if it has more thermal mass. That is, if the joint has more massive and/or more conductive components, a low wattage iron will have to stay on the joint longer to get the solder to flow and wet the joint. This gives more time for the heat to flow down the leads and traces. In many cases, it's better to use a higher wattage iron with a higher tip temperature, and get in and out more quickly, allowing less time for the heat to flow into the leads. Obviously, some judgement is needed in this.

Jerry

 

RE: The Mac 275, posted on July 23, 2014 at 08:10:13
Hornlover
Manufacturer

Posts: 2529
Joined: March 8, 2002
 Most high end manufacturers use PCBs in their equipment. Audio Research, Conrad Johnson, etc., and have used them for decades. Dynaco used them in all of their kits (although they used the cheap phenolic boards which don't stand up as well as glass resin types, but usually still work). PC boards can handle heat you find in consumer tube equipment just fine. Any reliability issue you find isn't the result of the boards.

 

RE: The Mac 275, posted on July 23, 2014 at 08:16:31
Crazy Dave
Audiophile

Posts: 14371
Location: East Coast
Joined: October 4, 2001
 I agree on both counts. Lots of great equipment uses circuit boards and modern glass resin boards can take the heat. I have seen a lot of Dynaco boards, but a lot of them had repairs to there traces.

Dave

 

RE: The Mac 275, posted on July 23, 2014 at 08:19:33
Crazy Dave
Audiophile

Posts: 14371
Location: East Coast
Joined: October 4, 2001
 That is why I like screwdriver tips. The get the heat to the target faster.

Dave

 

RE: The Mac 275, posted on July 23, 2014 at 09:38:59
elflow
Audiophile

Posts: 354
Location: Indiana
Joined: November 1, 2005
 I'm with you 100% on this issue! The quicker you can heat the connection to the point the solder flows, then reomove the heat the better.

 

RE: The Mac 275, posted on July 23, 2014 at 13:10:19
adam@denderapartners.com
Audiophile

Posts: 282
Location: So. Oregon, State of Jefferson
Joined: October 1, 2007
 Mark, when I was working in Grants Pass, Oregon years ago, I saw PCBs at my local PCB shop being fabbed for Conrad Johnson preamps. The traces on these boards were fat and thick--2 ounce copper. AND gold plated when they were done. I doubt those traces would lift easily....

 

RE: The Mac 275, posted on July 23, 2014 at 21:33:08
mark.korda@myfairpoint.net
Audiophile

Posts: 1253
Location: Maine
Joined: August 16, 2011
 Hi, thanks all you guys for your input. I always learn stuff from your answers. When I saw on that video that they poured hot tar in the Mac's transformers I thought that was it,if it does not work, replacement automatic. I'm a Heathkit and Dyna nut. One amp seen on Ebay a lot was the Heathkit AA-32 integrated amp. It came out in 1963 or 1964. My father built one and I remember hearing Light my Fire by the Doors when it just came out, about 1967. I have a good example of that amp now, and it is hard wired. There was a Heath amp made before this ,1962, with an alligator type cabinet exactly like the AA-32 but with a circuit board covering the whole chassis. Heath must have had failures pile up and learned the lesson in 1963 about power tubes, even small like EL-84's might cause problems with circuit boards with heat. Thanks guys...Mark K.

 

Circuit Boards, posted on July 24, 2014 at 05:40:50
briggs
Audiophile

Posts: 1674
Location: Connecticut
Joined: April 16, 2002
 I expect the Mac 275 is made in Binghamton. It may be worth noting that that area abounds in circuit board expertise. IBM's former main circuit card and board plant, and center of competence, was just down the road in Endicott.

 

RE: The Mac 275, posted on July 25, 2014 at 05:54:15
dls123
Dealer

Posts: 1214
Location: Beautiful B.C.
Joined: April 15, 2003
 Yep Jerry, I am with you on this one. I have my soldering station dialed way up. Hot and fast is the way to go. Also you have to use good solder. I use some nice Qualitek stuff that Jim McShane turned me on to. 60/38 with 2% silver and fairly high flux content. If flows very quickly and makes very nice joints. Never had bad ones since I started using it 3 or 4 years ago.
don

 

RE: The Mac 275, posted on July 25, 2014 at 08:43:29
Crazy Dave
Audiophile

Posts: 14371
Location: East Coast
Joined: October 4, 2001
 Hi Don,

Anything Jim recommends, I'm interested in. What is the part number of this solder? Is it leaded or unleaded. TIA!

Dave

 

RE: The Mac 275, posted on August 4, 2014 at 21:20:04
dls123
Dealer

Posts: 1214
Location: Beautiful B.C.
Joined: April 15, 2003
 Sorry, I didn't check this thread for a while.
Qualitek 32021 is what I buy. I usually get it from this guy, but you can get it from other places I am sure:

http://www.phonetechsupply.com/p658/Qualitek-50-32021-1-lb-Roll-Silver-Solder-62/36/2-RA300/product_info.html

I think it comes in larger rolls, larger diameters etc... I find this size works well in point to point tube gear. It is really good solder and a bit cheaper than the boutique brands.

cheers,
Don

 

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