[MCC]

Quote:

Originally Posted by ziplock /img/forum/go_quote.gif Something to keep in mind when taking your readings. You should probably de-solder the components for accurate results; at least one contact anyway. You could be measuring lesser/greater resistance/capacitance while the part is still in circuit. When you find a component that is still within it's tolerance spec, you can use it temporarily to take readings from the various sections that use the same values. That way you'll know which sections are good or bad according to the manual. What I am getting at is, you don't want your readings skewed due to faulty components from the get go. Do you follow me? ~Zip

I did as you said and now get 8.13k and 7.30k. Still way out of either spec. I don't quite know how reliable the schematic is since it's labeled as being for an earlier serial # series, so I can't even do the math to determine the resistance I need. Who knows, the final output voltages on the schematic might be different than what my model needs.

McIntosh is sending a copy of the manual via UPS. If this doesn't have what I need, I'm going to have to forget the schematic and replace them with 12k as used in the circuit.

For the second part, what you're saying is that I should test a component in and out of the circuit and, if it falls in spec out of the circuit, use the in-circuit value to test other same-resistance components. Correct?

 

[ziplock]

Quote:

Originally Posted by MCC /img/forum/go_quote.gif For the second part, what you're saying is that I should test a component in and out of the circuit and, if it falls in spec out of the circuit, use the in-circuit value to test other same-resistance components. Correct?

Close but not quite. My suggestion was along the lines of physically putting the good component in place of the bad to see if the rest of the circuit checks out.

Example.. R12 on PCB 1 is bad. R12 on PCB 2 is good. Are there other problems with PCB1 or is it just the resistor? Put the good resistor from PCB 2 on PCB 1. If the value reflects what is stated in the manual.. OK. If not, then you need to test other components on PCB 1.

This is just a process of elimination and controlling how many variables you have to work with while troubleshooting. This methodology has worked well for me while repairing electronics in the past. It may or may not work for you. After all, we are all wired differently.

~Zip

 

[Herandu]

I just picked up on this thread, and all I can say is: great find!

As you pointed out, your serial number is outside the range of what the circuit manual indicates. That means that there was at last a MK-2 version of your receiver, which is underscored by the differences in component values. Forget the meter readings for a 2nd and look instead to see if you can find any component values indicated on the components themselves. That is the way to go about it.
The change in resistors design could be for some very good reason. There might have been an issue identified with the earlier versions, which were corrected in yours. So going backwards to the original components might do more harm than good.

 

[MCC]

Alright! Thanks. I'll go with component values then and tack a pair of 12k resistors onto my next order. Brown and orange look almost the same from the heat but that's really the only reasonable value.

 

[tbonner1]

You may want to ask MAC guru Terry Dewick:

http://www.mcintoshaudio.com/dewick_repairs.htm

 

[MCC]

I'm finished with the first wave of improvements, and just got the final temp tube in the mail...

I'm currently running it through the cheapest tubes I could find on ebay as temporary stand-ins for the telefunkens. No caps have yet been replaced even though the 50-50-50-50mfd can cap is leaking, that's definitely next. My new variac is outputting exacly 117v. My ears have led me to bias the output tubes to a .55v reading at the testpoints, since I'm not going to risk them at the full .7v as spec'd. Any lower and the transparency suffers.

It's incredible. I can't pull myself away so I'm writing this on a laptop next to it on the floor. The sound has literally brought tears to my eyes, there's just no describing it. And this is through KSC75s with an X5 as a source. Going on memory only, I'd say it murders my HeadFive for synergy with my KSC75s. I'm not risking my Senns yet, so that'll come later.

The hum is totally gone, the background is black as I can imagine a tube receiver getting, and the layers in the sound... incredible. And with crap tubes at that.

The guitar in the live version of Hotel California jumps out of the black, it seems to bite into my ears. The bass is tight but not overpowering. Overall, it sounds incredibly clean and balanced for so few part replacements.

So far, I've replaced all of the power resistors w/ Vishay silicon metals, all rectifiers are now Fairchild stealth soft hyperfast, 4 output resistors are now Holcos, and I'm halfway done replacing the wiring with Neotech 18awg OCC copper. I'm using Cardas quad-eutectic solder to make all connections and everything that makes any kind of contact has been doused with Deoxit DN5. Other than rerouting the headphone/speaker return cable away from AC, that's it.

Next up, I'm going to replace all resistors in the circuits I'm concerned with with PRPs. It turns out that they are carbons, not wirewound as in the case of the broken one. They've drifted quite a bit, in some cases up to 40%. I'm also going to put in Sonicaps and Black Gates where appropriate and bypass the LF/HF filter "module" and associated switches. I've decided to let go of all budgetary restraints and do it right the first time, even if it does mean doubling my work hours. The improvement I've had is just that amazing.

Edit: Almost forgot to check. The FM works again, and only seems to be slightly out of alignment if the reading I've done has left me a good impression of what alignment issues sound like.

Edit 2: I have 12 Vishay MKP .01uf polypropylenes to bypass the sonicaps with when I get them.

 

[tbonner1]

FM alignment is a tough and vanishing art to get right. You need an FM generator and other test gear to zero out everything just right before you can bring the tuner into alignment.

If you are serious about bringing the FM section into spec, you really need to do this with the needed test gear.

 

[ziplock]

Good job so far. Glad to hear you got it working. I need to go hit up some estate sales and land one of these beauties...

~Zip

 

[MCC]

Quote:

Originally Posted by ziplock /img/forum/go_quote.gif I need to go hit up some estate sales and land one of these beauties... ~Zip

There's one on ebay.. it's expensive though.

Now that I've gained confidence after several hours on KSC75s and cheapo bookshelf speakers, I felt it OK to hook it up to our Energy RVS system, the best in the house. I've routed the signal through the sub then to the speakers since, obviously, the 1500 doesn't have an LFE out.

Dad said, and I quote, "We should throw the Pioneer in the river". This is referring to a Pioneer Elite VSX-90, well regarded at the time. 'Nuff said.

I've listened for pretty much 14 hours straight now with the last 4 hours on the Telefunkens when I deemed it safe. I didn't have the energy to tear myself away unless it was to change speakers or tubes. It's like listening to the music for the first time all over again; it's so good that he's actually considering buying another for himself some day.

 

[MCC]

Done!

New Electro Harmonix 7591 tubes (2 stock tubes were bad) and a pearl cooler for the 12AX7.

This is the preamp, now outfitted with PRP resistors, auricaps, and Black Gate NX caps (phono section is BG Standard). It might look like the auricaps were positioned randomly but in fact I did follow the guide. The top right auricap isn't attached to the PCB so it appears to be backwards.



(Click for large version)

Power:

1. Vishay silicone (and 1 heatsinked) power resistors
2. Fairchild Stealth Soft Hyperfast rectifiers
3. BG Standard caps bypassed w/ Vishay MKP
4. On Semiconductor zener
5. A few PRPs here and there

Audio section:

1. Auricaps and original AMC films for coupling (see below)
2. PRP and Vishay resistors
3. Black Gate NX, silver micas, and Relcaps
4. Neotech 20awg solid OCC copper wire
5. HF and rumble module bypassed

Not shown: After I took this picture, I repurposed the LF cutoff switch to act as an input switch. I now have 3 inputs that can be switched as follows:

Tape monitor off: AUX
Tape monitor on, LF switch off: Input 2
Tape monitor on, LF switch on: Input 3

You're probably wondering why the original films were left in the direct signal path. The answer is that auricaps in this position made the receiver sound detailed, but the layered warmth was gone. Placing the original caps back where they were gave me the warmth I wanted without sacrificing much of the detail provided by the auricapped preamp upstream.

Finally, its new home in the listening room:

I've been planning on replacing the filter caps but the only person I found that makes them custom seems to have fallen off the planet. I'm probably going to have to rig up standard caps underneath at some point, but for now I'm not having any issues. As long as they don't blow up between now and then that is.

The sound is very well balanced now, almost the perfect combination of detail and musicality. As expected, my modifications did make the receiver lose some warmth. This was done to make it sound just as good with rock/metal as it does with classical and I feel I've succeeded in doing that.

Deoxit DN5 really did a great job of killing the scratchiness I had before. If you need a contact cleaner, Deoxit is a great choice for the job.

About the financing: Although I did all the work, the receiver ended up in Dad's listening room since I don't have the space. As a result it was agreed that he would pay for all the parts.

Without this funding the receiver probably never would have gotten auricaps, relcaps, new wiring, etc.

 

[augustwest]

That Mac receiver is a great find and in nice condition too. Definately worth bring up to spec!

- augustwest