McIntosh 20W2 and Ae-2 Preamp Questions

[Michiganamps]

Hello Everyone, late last December I had a chance meeting with someone who was looking to clear some "clutter" out of his attic and rafters in the garage. Long story short, the 20w2 and Ae2 preamp followed me home. I have a few questions, how are these Amps when restored? Are they good performers? I don't see to many of these online, so I assume they're fairly rare, I know that this is one of their first products they offered... cosmetically everything looks okay, except there is some "wash out" rings where the paint is completely chipped away around the volume knob and on off switch about a half an inch around each... should I try and touch it up with paint or leave as-is?
Thanks in advance!

 

[s-petersen]

I had the amplifier, the only problem is everything is potted in it, it is difficult to work on. Mine had a problem under the tar, and I traded it away

 

[zackthedog]

Hello Everyone, late last December I had a chance meeting with someone who was looking to clear some "clutter" out of his attic and rafters in the garage. Long story short, the 20w2 and Ae2 preamp followed me home. I have a few questions, how are these Amps when restored? Are they good performers? I don't see to many of these online, so I assume they're fairly rare, I know that this is one of their first products they offered... cosmetically everything looks okay, except there is some "wash out" rings where the paint is completely chipped away around the volume knob and on off switch about a half an inch around each... should I try and touch it up with paint or leave as-is?
Thanks in advance!

In 1953 the Navy ran some tests of popular amplifier amplifiers (possibly as part of their research into sonar applications) and deemed the 20-W2 the best performer of all the ones they tested. The article is here:

https://www.pearl-hifi.com/06_Lit_A...l_06/Sec_26/US_Navy_Lab_Tests_of_Pwr_Amps.pdf

I wouldn't "touch it up" but would leave it cosmetically as is. If you're experienced with tube amps it would be good to get it in working condition while making as few changes as possible. If you're not experienced you could have someone else check it out. They are rare and go for a fair amount of money.

 

[Michiganamps]

In 1953 the Navy ran some tests of popular amplifier amplifiers (possibly as part of their research into sonar applications) and deemed the 20-W2 the best performer of all the ones they tested. The article is here:

https://www.pearl-hifi.com/06_Lit_A...l_06/Sec_26/US_Navy_Lab_Tests_of_Pwr_Amps.pdf

I wouldn't "touch it up" but would leave it cosmetically as is. If you're experienced with tube amps it would be good to get it in working condition while making as few changes as possible. If you're not experienced you could have someone else check it out. They are rare and go for a fair amount of money.

I was completely blown away when I had picked up this amplifier, I know most won't believe me, but I got this amplifier For Free! So here goes, in Mid December of last year, I'm a member of a local Neighborhood app, anyhow, I also collect Tube Radios from time to time, and one day I chanced upon a listing for a Free Console Tube radio that was sitting at the curb. After messaging the Owner, he had said scrappers got the Radio, NO big deal I thought, no harm no foul, anyhow, I asked him if he had any other Tube radios, or my Favorite, Vacuum Tube Audio Equipment. He told me that yes indeed he did have a few more radios, as well as another Amplifier he was going to toss to the curb and asked if I would be interested. Thinking it would just be a typical Maggie 6v6 amp or a homebrew amp that was gutted with all tubes missing, rusted, ect. I sat on the offer for a few days, until finally I asked the gentleman what kind of amplifier he had and what kind of shape it was in. That's when I almost lost it, he told me it was a McIntosh amplifier, and I almost couldn't start my car fast enough to get over there! When I got there I saw the amp, it was in pristine condition, with all mcintosh tubes Except Ken Rad 6v6s, and he also had the PreAmp that plugs into the amplifier as well, complete and in good shape. After talking for a while he told me he couldn't remember where he had gotten the amp, (he was an older gentleman say in his late 50s early 60s) and me, being a 23 year old, he was thrilled to pass on the amp to someone who would enjoy it! So I lugged the amp and preamp home with me and she's sat while I'm doing research and gathering parts together for a proper restoration with Audiophile grade Coupling Caps and quality capacitors and resistors. I'll grab everything just in case, but with a high end preamp and amp, I've been thinking I may as well replace all parts other than if the Resistors check within spec because I know that some brands of resistors from way back when will be way higher quality than any Chinese ones I can buy today...

 

[zackthedog]

You're 23 yo? Well, welcome to the club! That's a real prize. I imagine there will be a lot of interest (and good advice) in the restoration process. Post plenty of of pics and keep us posted! Dave Gillespie is probably is great resource for these old unity-coupled amps, hopefully he'll chime in.

 

[Michiganamps]

You're 23 yo? Well, welcome to the club! That's a real prize. I imagine there will be a lot of interest (and good advice) in the restoration process. Post plenty of of pics and keep us posted! Dave Gillespie is probably is great resource for these old unity-coupled amps, hopefully he'll chime in.

Your a younger member too? I will definitely keep everyone updated when I start in on this amplifier and Preamp, I'll start a proper thread when I get all the parts together and have the time to start in on her! there's a couple things I'm not sure of yet, like if I should try and reform the Electrolytics or just shotgun replace them, and when I replace them, if for an amplifier like this, if I should go ahead and restuff the cans (which I have plenty of experience on from working with tube radios) or if I should just bite the bullet and buy New custom Mallory Can capacitors with the right specs.

Looking at the Schematic definitely had me scratching my head for a minute... I've never seen a tube amplifier start out with a Phase inverter right off the bat, and then go right into a driver tube (in this case a pair of 6J5's for each 6v6) and then having some interesting coupling for the output transformer...very interesting indeed. Whoever had this amplifier replaced the old 12ax7 with a Telefunken ECC83 tube. I checked the date code and it gave me a hit for Nov, 1962 so I believe the amplifier was in service until at least 1962 granted the tube wasn't replaced at a later date. I haven't checked the date codes for the Ken-Rad tubes because I know they aren't as common as say Tung Sol or Sylvania tubes... The other 3 tubes are McIntosh originals though, the 5y3gt, and 6J5 pair.

Interestingly enough, I think this is an "early production" 20W2 amplifier, the rectifier tube is stamped as a 5V4gt on the chassis, but it's an original branded 5y3gt so I know that came that way from the factory with a 5y3. And then, where the 12ax7 tube is, the chassis is cut out for an Octal tube socket, instead of the 9 pin socket. As if they were planning on using a 6SL7 or 6SN7, but at the last minute decided on the 12AX7.. I just thought that was fairly interesting, because I've never seen an Octal Sized 9 pin socket before I came across this amplifier...

I haven't opened up the Ae-2 Preamp yet, so I'm not sure what goodies are waiting inside for me but I know for sure that the 12AX7s are safe and sound inside. I can tell the Metal Cover hasn't ever been opened before, there aren't any of the "scratch" marks you usually see from star washers scraping the cover plate, which is always a good sign... The Amp is the same way, I always like to see an All Original Unmolested Amplifier, untouched by any servicemen or interested child or teenager. So that made me real happy to see that the amplifier and Preamplifier hasn't ever been serviced or tampered with. The only thing that was kind of a bummer was finding out that the Amplifier might have came with a Cage from the Factory. Granted I'm not totally sure if it was an accessory or not, looking online I haven't seen one photo of this amp with one. But I did see ads for this amps younger brother, the 15W2 that had the cage.

Back to the technical side of things, I think that the only modification I'm going to make to the Amplifier is adding a Thermistor to the hot leg, or both legs of the power transformer. Im still not sure though, since this amp may actually draw a large amount of current, since its also powering up a Preamp too. And I'll probably add a fuse inside the Preamp too, right after the On-Off switch, but only if there isn't one already. Just so I can keep the amplifier chassis clean and original. Because the Preamplifier chassis isn't going to be checked out quite as much as the power Amp chassis. I have the perfect fuse holder from the '50's to use for this Project. In this day and age, there's no reason to risk burning up this unobtainium equipment.

Adding a Thermistor might make the Amp have a longer warm up time, but for me, the low cost of less than $3 a piece to add 1 or 2 Thermistors is a no brainer. And with that, I have the peace of mind (no pun intended ) knowing I'm not adding stress to the Tubes, Transformers, or the passives like resistors and capacitors. I added one to a Japanese Layfayette Tube Receiver i use in my bedroom. It doesn't have a rectifier tube, so as soon as the power switch was turned on, the tubes would get a dose of 275VDC on Cold Cathodes and Plates. But now, the thermistor gives a slow start up instead of throwing HVDC across cold tubes that aren't warmed up yet. I could tell that the EL84 tubes and Drivers didn't like that, because those were the only 4 tubes replaced in the whole Stereo, so I swapped out the Groove Tubes (never been a fan of the Chinese tubes, but that's just me) and installed GE tubes instead.

Sorry with my ADHD, coupled with a few brews and a joint or two, sometimes i get a bit off track and a little long winded. My apologies.. anyhow that's the reason why I always add thermistors to my equipment because you really can't beat prolonging the life of your tubes for less than $7 worth of parts. So I always try and install them whenever I can because just so long as they're in a place where heat isn't an issue they really can't cause any damage to anything. Anyhow it's getting late here where I'm at! Rock on man

 

[zackthedog]

No, I'm an old guy, I just meant welcome to the Tube Club. ;-) Your enthusiam is refreshing!

There are pix online of models with that octal-sized 9-pin socket, maybe it was an early design choice to creat a look of consistency. The 5V4 marking is interesting, though. You may be right about it being a very early model, which would increase the rarity factor, I would think. Please post some pix when you get a chance!

ETA: More browsing reveals that there was a 5Z4 version as well...

 

[trainbuftony]

Congratulations on the incredible find.
Young folks like you and I need to learn how to maintain this gear correctly. Restoring it properly is going to be a challenge, but it sounds like you have experience working on tube amplifiers and the ability to level out with a joint, my guess is you're the perfect person, and this amp landed with you because you're fated to be the person who brings it back to service and eventually finds it a life partner...
You're eventually going to give us some photos as well right?

 

[Michiganamps]

No, I'm an old guy, I just meant welcome to the Tube Club. ;-) Your enthusiam is refreshing!

There are pix online of models with that octal-sized 9-pin socket, maybe it was an early design choice to creat a look of consistency. The 5V4 marking is interesting, though. You may be right about it being a very early model, which would increase the rarity factor, I would think. Please post some pix when you get a chance!

ETA: More browsing reveals that there was a 5Z4 version as well...

Thanks Zack! Growing up I always hung out with the older crowd when I was younger I was fascinated with history, and I used to take things apart, and put them back together again. So for me it was only a matter of time before I got into Tube Radios, and from there, Audio Equipment. Ive just always enjoyed talking with friends that were older than me because I'm like a sponge, always absorbing information and that's how I've learned a lot of tips and tricks over the years!

I didn't know there was also a 5V4 model, so now I'm interested in seeing if this was a factory 5y3 swap or maybe a dealership swap. Aren't the 5y3 and 5v4 very similar tubes? I think I remember reading somewhere, but I'm not entirely sure, that a 5v4 can swap for a 5y3, but a 5y3 can only swap for a 5v4 if it can handle the current, or something like that... I will go ahead and post some photos in a few minutes!

 

[Michiganamps]

Congratulations on the incredible find.
Young folks like you and I need to learn how to maintain this gear correctly. Restoring it properly is going to be a challenge, but it sounds like you have experience working on tube amplifiers and the ability to level out with a joint, my guess is you're the perfect person, and this amp landed with you because you're fated to be the person who brings it back to service and eventually finds it a life partner...
You're eventually going to give us some photos as well right?

Thank you! I was thrilled to take this amplifier home with me! Never in a million years did I think I would come across an amp like this, let alone in good condition too! I'm thinking about putting a period correct "HiFi" setup together, with period Tube Tuner, 1950s turn table, a nice full range 12-15" speaker, and maybe a few more goodies as well. I don't mind that the amp is a MonoBlock setup, I was actually getting ready to restore another mono 6v6 PP homebrew amplifier when i came across this one! I plan on using this Eico HFT-90 FM mono Tube tuner. I had bought this tuner a while back, and I feel like this would be perfect for this setup! Here's a few photos, and I'll have more photos of the amp and preamp as promised!

 

[zackthedog]

Thanks Zack! Growing up I always hung out with the older crowd when I was younger I was fascinated with history, and I used to take things apart, and put them back together again. So for me it was only a matter of time before I got into Tube Radios, and from there, Audio Equipment. Ive just always enjoyed talking with friends that were older than me because I'm like a sponge, always absorbing information and that's how I've learned a lot of tips and tricks over the years!

I didn't know there was also a 5V4 model, so now I'm interested in seeing if this was a factory 5y3 swap or maybe a dealership swap. Aren't the 5y3 and 5v4 very similar tubes? I think I remember reading somewhere, but I'm not entirely sure, that a 5v4 can swap for a 5y3, but a 5y3 can only swap for a 5v4 if it can handle the current, or something like that... I will go ahead and post some photos in a few minutes!

5Z4 is similar to 5Y3. 5V4 is a slow-warm-up rectifier with lower voltage drop common in early Williamsons. Rated at 375-0-375 but easily capable of 400-0-400 or more at 175 mA.

https://www.usaudiomart.com/details/649673740-mcintosh-collectors-tube-mono-block-20w-2/

 

[Michiganamps]

5Z4 is similar to 5Y3. 5V4 is a slow-warm-up rectifier with lower voltage drop common in early Williamsons. Rated at 375-0-375 but easily capable of 400-0-400 or more at 175 mA.

https://www.usaudiomart.com/details/649673740-mcintosh-collectors-tube-mono-block-20w-2/

I'm sorry it had been a while since I took a look at this Amplifier, it is a 5Z4 and not a 5v4. As promised here are some photos finally! The Preamp has definitely seen some better days cosmetically, but for a free amp and preamp I really can't complain... Woodworking is also another hobby I've been into for some time, so hopefully I can wick some of the old lacquer into the scratches and make them less noticeable... I've never had an "exclusive" piece of high end equipment before, like a HH Scott, Marantz, Fisher, McIntosh, ect. So I don't want to go too invasive with the preamp, come to find out like cleaning an old gun or coin, repairing the scratches and dents, I've hurt the value.. As you guys can see, I've left the Units in their "As found" state, dust and all, I havent done anything to them yet, not even given them a good cleaning from their spot up in the attic, where they were before I came across them! Let me know what you guys think!
~John