[MCC]

Update 1/25/12, for those getting here via search
My 1500's still going strong since I created this thread a few years back. Since then I've replaced the two burnt out resistors in the power supply with Dale CW-5 12k 6.5w resistors. I've also bypassed the rectifier diodes and larger capacitors with Vishay MKP 630v 0.01uF capacitors. This noticeably quieted the noise floor with headphones.
 
The RCA jacks were starting to go bad for me so I replaced 3 sets with gold plated ones from Ebay. This isn't a reversible operation- the existing jacks need to be smashed with a pair of pliers and eased out of their home. I also had to widen the holes a bit with a circular file to get the new ones to fit. Since this change I've added a turntable to my rig so I'll need to change those next- I have a channel that keeps going out due to the old jacks.

One word of caution: by design, the 1500 drives the 7591s very hot- beyond, in fact, the specs of modern replacements. I kept burning them up (red glow) until I made a few adjustments. I now run the 1500 with a 114V wall voltage and I keep the test voltage for the bias on the 7591s at less than 0.6v. I haven't had one die on me since I made these changes almost a year ago. I went through more than I care to count beforehand.
 
 

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Update: 5mp pics of the insides in post 8
 

A few months ago I dug up an old Mac 1500 amp in my grandparents' basement and forgot all about it when I found the electrical condition to be, well... not good.

Today I dug it up again and played around with it, nothings changed but this thing weighs a TON!

Front panel, off (it has a nice blue glow when on)

Back panel

Interior

Closeup of audio section

So, how does it sound? In its current state, pretty bad. For the first few minutes, it doesn't sound that bad at all. But, turning any knob on the front makes loud staticy noises and sometimes causes the left channel to go out. It can take a lot of effort but I can usually get it working again for a minute or two before it starts to fade away. After it warms up, everything gets muddy and pretty much turns into one big blur. Also, the left channel develops a rather annoying hum after some time.

So, it's obvious that at least one tube is bad, but this thing has 13 of 'em and I don't have a tester. Many have the McIntosh logo on them and may be original! I've heard that old McIntosh amps like this are pretty good, but how much real potential do you think this guy has? It's rated @180w but I have no idea when it was made. I don't know how much I should invest in it for repair or if at all.

Finally, what would be the resale value of this amp in its current state vs. repaired?

I have a feeling I have something with good potential on my hands, but I don't really know to what extent as I hail from the digital generation.

Edit:
I just tried it again after a few cycles spread out over the past several hours. It still hums but I think it just woke up! The sound has greatly improved after probably decades of unuse, and I don't have any problems with the stability of the audio anymore. It sounds pretty decent now, but I can tell that it's still not back to prime.

Edit 2: I think I just found the stability problem. Some of the switches on the front don't like being touched. I'll have to take a look if I can stay away from it long enough to let it cool down.

 

[jamato8]

It should be nice sounding but would need an overhaul of the caps and the tubes, which are original would need some real checking. The volume control needs to be cleaned or replaced and the tuner section tuned. I would imagine the iron for the transformers is pretty good and with some work you could have a nice sounding amp but it will take some money. It all depends upon what you want. If you could do the work yourself it could be worth it but some people just like to have restored gear. Most of the tubes aren't that expensive.

I would do a google for Mac 1500 tuner here is a site for price:

http://www.classicaudio.com/value/mac/index.html

 

[tjohnusa]

Sounds like it needs some overhauling....probably caps and resistors, maybe some tubes also. It could be quite expensive to get in working order again but you will have a very fine amp when done. In present condition you should be able to get at least $200 but repaired it could fetch over $500 I didn't check the specs but it looks to be in very good cosmetic shape....of course if you don't want the hassle I could give you mmmm maybeeee $50.....cause you have an honest face....lol

 

[JadeEast]

Wahoooo!!!!!

Nice score. A classic amp like that is going to need a freshening
up. If your not sure of what your doing find a tech that does or
start slow and learn what your doing. Get it refurbished and
you'll be passing it on to your grandkids.!!!!

The amp is a hybrid and I think that the headphone output is
wired out of the output transformer so it should have nice
tubeyness.

 

[003]

I would seriously recap the whole amp and check all the tubes and resistors before you hook it up to anything expensive, if it's anything like old tube radios at least.

 

[vcoheda]

that thing is ancient, but it looks pretty cool. 13 tubes!

 

[braillediver]

looks like it has 15 tubes in it.

Check out special features D

Mitch

 

[MCC]

I just opened up the bottom. WOW, there is MUCH more to this thing than I thought! Oh, and Sprague caps! I'm uploading new pics now, this time full-res 10mp.

Edit:

Excellent feedback, thanks!

Edit 2: Here they are, sorry for the huge size but this receiver is so complex I thought it warranted it. I did halve the size though since bayimg has problems showing 10mp pictures, but 5mp is still huge.

Entire inside
Top left
Top right
Bottom right
Bottom left

As you can see in the last picture, I also have a broken resistor... now to find where it came from.

Edit 3: Oh, duh... right above the shell.
Edit 4: The broken resistor appears to be wirewound, leading me to believe all of them are.

 

[GAD]

Man I miss those days, and I'm only 42!

GAD

 

[jamato8]

The carbons may have drifted, which may or may not be a problem depending upon where they are and caps may or may not be any good. There are normally much better caps than what are in there and for sound some of the silicon really needs to be replaced. So it is a transformer coupled amp for the headhones. That could be a lot of fun with really good drive. I would put the money or time into that section.

 

[F107plus5]

Quote:

Originally Posted by GAD /img/forum/go_quote.gif Man I miss those days, and I'm only 42! GAD

Man I REALLY miss those days and I'm only sixty......uh,
never mind

...yeah; me too!

 

[MCC]

Looks like it's time to buy a tube tester, dig up my multimeter, and get to work!

At the time I turned it off for cooldown before I opened it up, it had already greatly improved. It's going through a sort of hyper speed re-burn-in. I'm only trusting it with KSC-75s but the sound is already blowing me away. I'm hooked. To think I actually let this receiver sit for more than a day.

 

[JadeEast]

Do you know how to discharge a capacitor???
Sorry but I just want you to be safe there is a lot
of pop in these tube amps.

And you may need this.

http://www.pmillett.com/file_downloa...ice_manual.pdf

 

[MCC]

Yes, I do. Thanks for the concern, these caps probably can indeed give quite a shock.

Thanks for the service manual link. I actually just bid on one but someone else has a higher max, so no wasted cash.

 

[joelk]

Paul of Bizzy Bee Audio is a champ with old Fisher gear, and even if he won't work on it could guide you someone who might. He's redone a Fisher 400 and 500 for me, and they sound quite wonderful and with enough power to drive almost anything.

I think that you've found a real diamond in the rough.