McIntosh Mc60 restoration advice...how far to go

[TriodeLuvr]

Folks here have discussed various techniques for removing rivets. They can't be simply punched out AFAIK, but maybe it's possible if you have a hydraulic press and a mandrel of exactly the right size. Some people have reported good luck drilling, then punching. The problem with drilling is that the rivets nearly always start to spin with the bit before it cuts all the way through. I seem to recall someone saying they use cyanoacrylate adhesive under the rivet to prevent spinning. Oh well, at least these aren't 21-tube receivers.

Here's one thread that discusses this issue. I'm sure there are others if you search AK.

Removing Dynaco Rivets

Jack

 

[nortoncycler]

Folks here have discussed various techniques for removing rivets. They can't be simply punched out AFAIK, but maybe it's possible if you have a hydraulic press and a mandrel of exactly the right size. Some people have reported good luck drilling, then punching. The problem with drilling is that the rivets nearly always start to spin with the bit before it cuts all the way through. I seem to recall someone saying they use cyanoacrylate adhesive under the rivet to prevent spinning. Oh well, at least these aren't 21-tube receivers.

Here's one thread that discusses this issue. I'm sure there are others if you search AK.

Removing Dynaco Rivets

Jack

Thanks Jack! That's a great thread! I appreciate you pointing me to it... looks like I'll have a bit of experimenting to do to see which method(s) work best.. This may be the one advantage of working on a corroded chassis - possibly a slightly less chance for the rivets to spin

 

[OldHvyMec]

I'm in the replace the case camp and have had to do it at least a dozen times. I've had a pair of MC240s that were nicked with sequential SN and the insurance didn't pay one extra dime for that and I didn't expect they would. But they did give me replacement cost for a C22, and a pair of MC240s at 6500.00 each. I replaced 2 pairs of
MC60s, 3 MC30s, 1 MC75 (center channel) for a MC275 I replaced the case on also.

1/2 were re-chromed cases two were new from Canada (one gold and one chrome pair) and 4 were from South Korea. The ones from Canada were like
jewelry the polish was so high. South Korea were pretty spiffy too. They use a really nice screw set that looks like rivets and are a lot easier than rivets, unless
you have made up a set of case dies for that job.

I tape off the chassis centerpunch the rivets and use a slow hand held drill. I know I've drilled out 5,000 rivets in my career as a mechanic and install 10,000
pop rivets if I've done one. I've did a lot of panel work in 23-53ft van boxes. Made a lot of metal tool boxes for drill rigs, using pop rivets.

Sharp drill bits and don't use a high speed drill. Just a fraction smaller than the actual hole for the rivet. The head should ride up the drill bit if you used the
right size.

I still have one pair of MC60s in gold. They are a lot tougher than the rose gold option too. I did the cans on one pair in anodized blue and powder coated
the transformer cases and lower case with just a little dark blue added to the black. They fetched 7800 for the pair. Samra did the rebuilds and hot rodded
them for me and I did the assembly. They aren't that hard to rebuild a weekend was kind of the norm for me when I used to rebuild a pair.
Cases add a second weekend. I'm looking for the emblems "Mcintosh 60" in gold for the pair I still have..
They make 2 or 3 different cases for the MC60s. New copper terminal strips that are a least gold plated are a nice feature to add. Soft start circuit that's
siliconed in place vs drilled and screwed is a nice feature.

I've seen a lot of people mention sequential SN but it's like saying the Beachboys used the amps, who gives a crap really. It may add value to 1 in a million
but not to the average Mac guy. Honorable mention though

I have some 565 Adcoms that are sequential, we know what that's worth. The pallet they are setting on is probably worth more than most 565s. LOL speaker
killers. 2 or 3 pairs.

Have fun.

Regards

 

[TriodeLuvr]

Sharp drill bits and don't use a high speed drill. Just a fraction smaller than the actual hole for the rivet. The head should ride up the drill bit if you used the
right size.

Yes, that works well if the damn thing doesn't spin.

Samra did the rebuilds and hot rodded them for me and I did the assembly.

How is Mikey? Haven't seen him around in a long time.

Jack

 

[gadget73]

hey use a really nice screw set that looks like rivets and are a lot easier than rivets,

stainless button head cap screws? I've used those, they do look like rivets at a glance. Usually a #4 or #6 depending if its a 9 pin or an octal socket will get the job done.

 

[SaturationPt]

The rivets punch out very easily, a small pin-punch from the bottom and the peened ring shears quickly and cleanly, that's how I stripped my Mc chassis. I didn't even need a backer on the top-side, went out that easily (they're plated brass, very soft).

Regarding serial numbers etc: I have done both. If the chassis were in excellent condition, and a minimal electronic restoration were the goal, matching S/Ns are great on the original chassis.

However, if you're replacing the chassis anyway, and doing a complete rebuild (especially with any modifications) they will be a matched set when you're finished anyway. Keep a photo of the original S/Ns and if you can still find an ink-stamp, that would be cool to reproduce.

It's completely opinion and preference on replacing your chassis. I bought a pair from S. Korea, excellent workmanship and the chrome is better than original (chromed AFTER stamping and bending so the chrome covers edges and bends). The lettering is also first-rate. These original chassis were in pretty good shape and I decided that they will not gain enough value to cover the cost of the new chassis, but I wanted showpieces so I did it anyway. The problem then comes from "while I'm in there", where do you stop? I'm replacing tag-boards, all resistors and capacitors, tube-sockets, wiring, input connectors, fuseholders, repainting transformer cans, ... they'll still be matching amps when I'm finished. They will also not be original, so there are folks who will like them less than the original S/N matching chassis with slight patina, ... do what you want and you can always replace the chassis later if you want.

Also, I have found some dry-transfer lettering (a few years back) that matched the various fonts on the chassis, another option for re-lettering the deck if you refinish it (or just polish and clear-coat). I don't know where I bought it, probably still exists, and getting a silk-screen made for the chassis would be much more difficult.

Best of luck, enjoy the project!

 

[TriodeLuvr]

I didn't even need a backer on the top-side, went out that easily (they're plated brass, very soft).

Well, that changes everything. Sounds like it won't be so difficult after all.

 

[nortoncycler]

I'm in the replace the case camp and have had to do it at least a dozen times. I've had a pair of MC240s that were nicked with sequential SN and the insurance didn't pay one extra dime for that and I didn't expect they would. But they did give me replacement cost for a C22, and a pair of MC240s at 6500.00 each. I replaced 2 pairs of
MC60s, 3 MC30s, 1 MC75 (center channel) for a MC275 I replaced the case on also.

1/2 were re-chromed cases two were new from Canada (one gold and one chrome pair) and 4 were from South Korea. The ones from Canada were like
jewelry the polish was so high. South Korea were pretty spiffy too. They use a really nice screw set that looks like rivets and are a lot easier than rivets, unless
you have made up a set of case dies for that job.

I tape off the chassis centerpunch the rivets and use a slow hand held drill. I know I've drilled out 5,000 rivets in my career as a mechanic and install 10,000
pop rivets if I've done one. I've did a lot of panel work in 23-53ft van boxes. Made a lot of metal tool boxes for drill rigs, using pop rivets.

Sharp drill bits and don't use a high speed drill. Just a fraction smaller than the actual hole for the rivet. The head should ride up the drill bit if you used the
right size.

I still have one pair of MC60s in gold. They are a lot tougher than the rose gold option too. I did the cans on one pair in anodized blue and powder coated
the transformer cases and lower case with just a little dark blue added to the black. They fetched 7800 for the pair. Samra did the rebuilds and hot rodded
them for me and I did the assembly. They aren't that hard to rebuild a weekend was kind of the norm for me when I used to rebuild a pair.
Cases add a second weekend. I'm looking for the emblems "Mcintosh 60" in gold for the pair I still have..
They make 2 or 3 different cases for the MC60s. New copper terminal strips that are a least gold plated are a nice feature to add. Soft start circuit that's
siliconed in place vs drilled and screwed is a nice feature.

I've seen a lot of people mention sequential SN but it's like saying the Beachboys used the amps, who gives a crap really. It may add value to 1 in a million
but not to the average Mac guy. Honorable mention though

I have some 565 Adcoms that are sequential, we know what that's worth. The pallet they are setting on is probably worth more than most 565s. LOL speaker
killers. 2 or 3 pairs.

Have fun.

Regards

Hi OldHvyMec, thanks for the reply and the great insights... I'm in a similar camp of not attributing much in the way of actual value to the sequential number... its just more of the "oh cool" factor for me .
I did see the ones from Korea you mentioned ... and saw what looks like the screw set alone as well... I do not foresee myself even trying to put new rivets back in...
So I was thinking on stripping these down trying the chrome power coating and see how the really rough one looks first (I called around this morning and saw a place not too too far from me that does it..and they recommended the place next to them to redo the lettering... if this turns out not so good then I think the SS chassis will probably be in order...
I appreciate the tips on removing the rivets...never at all would have thought of using a hand drill on them... I'm thinking this will be a big challenge and that I may mess up the chassis in the process... I'll give it a shot though... nothing tried nothing gained.
The soft start is definitely 100% what I'll add to these... I can not think of a reason NOT to do it...

Just curious what kinda of Hot Roddin?? Upgraded caps or something else?

Thanks Again!!!!!!!

 

[nortoncycler]

The rivets punch out very easily, a small pin-punch from the bottom and the peened ring shears quickly and cleanly, that's how I stripped my Mc chassis. I didn't even need a backer on the top-side, went out that easily (they're plated brass, very soft).

Regarding serial numbers etc: I have done both. If the chassis were in excellent condition, and a minimal electronic restoration were the goal, matching S/Ns are great on the original chassis.

However, if you're replacing the chassis anyway, and doing a complete rebuild (especially with any modifications) they will be a matched set when you're finished anyway. Keep a photo of the original S/Ns and if you can still find an ink-stamp, that would be cool to reproduce.

It's completely opinion and preference on replacing your chassis. I bought a pair from S. Korea, excellent workmanship and the chrome is better than original (chromed AFTER stamping and bending so the chrome covers edges and bends). The lettering is also first-rate. These original chassis were in pretty good shape and I decided that they will not gain enough value to cover the cost of the new chassis, but I wanted showpieces so I did it anyway. The problem then comes from "while I'm in there", where do you stop? I'm replacing tag-boards, all resistors and capacitors, tube-sockets, wiring, input connectors, fuseholders, repainting transformer cans, ... they'll still be matching amps when I'm finished. They will also not be original, so there are folks who will like them less than the original S/N matching chassis with slight patina, ... do what you want and you can always replace the chassis later if you want.

Also, I have found some dry-transfer lettering (a few years back) that matched the various fonts on the chassis, another option for re-lettering the deck if you refinish it (or just polish and clear-coat). I don't know where I bought it, probably still exists, and getting a silk-screen made for the chassis would be much more difficult.

Best of luck, enjoy the project!

Thanks SaturationPT! Sounds like there are a few good options out there for getting those rivets out and gone... I never heard of peened ring shears... Amazon here I come
The While I'm in there is what always gets me... I think for these I'm leaning towards checking the components and replacing just those tat are out of spec. These have the "black beauty Coupling caps.. so I'm hoping they test out good in which case I'll leave them. Most everyone says the bumblebee's need to go...so I'm guessing that will be the case here as well as the bias rectifier and electrolytic's.
I was thinking of the dry transfer route... I could probably pull if off on the top, but I'm thinking replacing all the lettering on the back would be a challenge at my skill set... I did find a place locally that said they could do it ..but I haven't had a chance yet to get a few pics over to them to validate ..and as importantly find out the cost... so TBD.

Always fun to try new approaches and ideas so I appreciate your help and everyone on here! I can't express how much I appreciate you all for the great information and guidance!


Thanks Again!
-Kevin

 

[nortoncycler]

Well, that changes everything. Sounds like it won't be so difficult after all.

Yea I completely agree! My stress level is going down a notch or two on trying to strip these with all the help and suggestions

 

[SaturationPt]

When you install these rivets, you “peen” the hollow end and it flares out into a “ring” of metal. That is what I am referring to, sorry if I wasn’t clear. Giving the rivet a firm tap with a pin-punch (or even a finishing nail if you don’t have an appropriate-size punch I suppose) will quickly shear off that thin ring of brass, cleanly driving the rivet back out.

The problem that I found with my own restorations is that it is so tedious to unsolder, then unwrap each of these components so that the value of each component can be properly measured out-of-circuit, then order just the ones you find out of spec, replace all of them just for other aging components to drift out of spec later in the year, ... it’s easier (in my opinion) and not much more money to just order all of the passive parts for replacement before starting on the restoration. If I’m going in to un-solder everything it’s easier to just snip leads first and then un-solder, and install all new matching age & design parts. Plus, not many people have the equipment to properly test components. Easier sometimes is better.

 

[nortoncycler]

When you install these rivets, you “peen” the hollow end and it flares out into a “ring” of metal. That is what I am referring to, sorry if I wasn’t clear. Giving the rivet a firm tap with a pin-punch (or even a finishing nail if you don’t have an appropriate-size punch I suppose) will quickly shear off that thin ring of brass, cleanly driving the rivet back out.

The problem that I found with my own restorations is that it is so tedious to unsolder, then unwrap each of these components so that the value of each component can be properly measured out-of-circuit, then order just the ones you find out of spec, replace all of them just for other aging components to drift out of spec later in the year, ... it’s easier (in my opinion) and not much more money to just order all of the passive parts for replacement before starting on the restoration. If I’m going in to un-solder everything it’s easier to just snip leads first and then un-solder, and install all new matching age & design parts. Plus, not many people have the equipment to properly test components. Easier sometimes is better.

Hi Jeff.... Ok Cool thanks for the clarification... I was thinking it was along the line of using a pin punch to loosen it then there was a special snipper / shear that I could use from the top side to cut through the rivet
I see people commenting on retaining a few of the original components to keep the "sound" ... specifically the coupling caps, although some mention the carbon resistors are important to this too? The resistors are easy enough to find new replacements for, but wondering about the caps? I guess on the flip side its only a few caps for this so seems easy enough to swap out and in...

Thanks Again!
-Kevin

 

[Lavane]

The only problems I've ever had with a few things being powder coated is it can be kind of thick? I had to carefully ream out some holes in some rims so the studs on the hub would fit through. Small bo

Yes, that works well if the damn thing doesn't spin.

How is Mikey? Haven't seen him around in a long time.

Jack

I've had the best luck as well drilling rivets out. A slow drilling is the key. If they spin, that even helps sometimes as the bit and chassis itself tends to ground the rivet down some if not all the way. If it doesn't, they at leased get loose enough I can either clip the head off the rivet, or peal the edges of the bottom side of the rivet up enough using aide cutters I can then easily punch it out.

 

[nortoncycler]

The only problems I've ever had with a few things being powder coated is it can be kind of thick? I had to carefully ream out some holes in some rims so the studs on the hub would fit through. Small bo

I've had the best luck as well drilling rivets out. A slow drilling is the key. If they spin, that even helps sometimes as the bit and chassis itself tends to ground the rivet down some if not all the way. If it doesn't, they at leased get loose enough I can either clip the head off the rivet, or peal the edges of the bottom side of the rivet up enough using aide cutters I can then easily punch it out.

I'm planning on wandering by the place that does the coating here in the next few days and take a looksee firsthand at how the chrome coating looks...also check out some colors while I'm there (either for these or maybe if I do another amp down the road). I saw a bunch of images online and it seems a bit hit and miss for the chrome so figure out I better check... likewise I'll pop over next door to them and check out the place the recommended for the lettering.

I also think I'm going to order both the pin punch and also see if i can find a small hand drill just so I have them handy and see how things play out

I'm looking forward to this, I feel like I'm in a lot better place armed with all the information so far... I'm so glad I came out of the "lurker" state and posted!
Everyone has been so amazing!

Thanks!!
-Kevin

 

[SaturationPt]

Hi Jeff.... Ok Cool thanks for the clarification... I was thinking it was along the line of using a pin punch to loosen it then there was a special snipper / shear that I could use from the top side to cut through the rivet
I see people commenting on retaining a few of the original components to keep the "sound" ... specifically the coupling caps, although some mention the carbon resistors are important to this too? The resistors are easy enough to find new replacements for, but wondering about the caps? I guess on the flip side its only a few caps for this so seems easy enough to swap out and in...

Thanks Again!
-Kevin

I think that there is some truth to the thought that changing components can alter the sound. Changing from an old carbon-comp resistor to a new carbon-comp resistor shouldn’t change anything but maybe from carbon-comp to film (different delta-T) has the potential to change, ... something? Same with changing from electrolytic to film, etc. it has the potential to make something different.

There are many people who claim that changing every cap to film will make it better, ... which begs the question why McIntosh Engineers who had plenty of access to film caps (and used many of them) didn’t do that if there were improvements to be had (the answer is obvious: it didn’t improve anything).

It’s your amp, if you want to change the type of cap and/or resistor it likely won’t hurt anything, just don’t expect some magical improvement because the capacitors have an expensive name on the side. I stick with high-quality commercial resistors and capacitors as nobody will ever open my amplifiers to see if there are fancy names on the caps. Good enough for McIntosh is a pretty good endorsement.

 

[TriodeLuvr]

So I was thinking on stripping these down trying the chrome power coating

The chrome powder coat I've seen was easily distinguishable from real chrome. I would move all the major parts to a new, unblemished SS chassis rather than do that. Some of the PC colors are excellent, but then it's less of a restoration and more of a "restomod."

The problem that I found with my own restorations is that it is so tedious to unsolder, then unwrap each of these components so that the value of each component can be properly measured out-of-circuit, then order just the ones you find out of spec, replace all of them just for other aging components to drift out of spec later in the year, ... it’s easier (in my opinion) and not much more money to just order all of the passive parts for replacement before starting on the restoration. If I’m going in to un-solder everything it’s easier to just snip leads first and then un-solder, and install all new matching age & design parts. Plus, not many people have the equipment to properly test components. Easier sometimes is better.

Trying to save parts with leads crimped onto tube socket lugs and terminal strips is a major PITA. I won't do it unless a component is irreplaceable. Matter of fact, this is one advantage to replacing the tube sockets. Just rip everything out - including the attached resistors and caps - and toss it all.

Jack

 

[TriodeLuvr]

There are many people who claim that changing every cap to film will make it better, ... which begs the question why McIntosh Engineers who had plenty of access to film caps (and used many of them) didn’t do that if there were improvements to be had (the answer is obvious: it didn’t improve anything).

I strongly disagree with this conclusion. Film caps weren't readily available (or affordable) in the physical/electrical sizes that are common today. It's also questionable whether McIntosh engineers would have prioritized characteristics such as dielectric absorption at that time. This was a rather esoteric concept for audio gear in the '60s and '70s. Manufacturers select component types for many reasons, and the choices back then were much more limited than today. We all know the sound quality of products from that era can be improved with newer components, and not just because the old ones have "worn out." We have superior dielectrics and manufacturing processes today, and there's no reason not to take advantage of it. The only value to carbon comp resistors is their non-inductive nature, and they belong in our amps as grid stoppers. The most transparent dielectrics are polypropylene, polystyrene and teflon. Will it change the sound if you replace 20 mylar coupling/EQ caps with polypropylene and polystyrene? Absolutely, and for the better.

Jack

 

[PakProtector]

Right on Jack. That brings me to a simple improvement to the MC-series, the 12AU7 phase splitter stage. Couple things; it has a resistive tail, and imbalanced plate loads in an attempt to correct this. Then there is the 12AU7 itself. Rigging its heater circuit for a 6CG7 is a very fine idea, so is installing a current regulator in place of that tail load. Along with that, install a matched pair of 27kOhm plate loads( or 33k ).

The 12AU7 allowed simpler manufacture, and was cheaper than a 6CG7. Good current regs( like the cascode, depletion mode MOSFET circuits ) were totally unavailable.

That is 'tip of the iceberg' stuff to do to them. You want some more fun, increase the value of the first 12AX7 cathode resistor a bit and sub in a 12AY7( don't worry, there are plenty of 12AY7 to experiment with, and their ruggedized variant the 6072). I do admit rolling input stage tubes can be fun. But...what the heck is up with a circuit so sensitive to tube variations that this is worth doing? Perfection? my backside...

There is plenty of NFB delivered in the output transformer. That split-load design reduces the gain of the output stage to about 1.7 from something more like 12.

If I ever find some more of these, rest assured they will get modified... The idea that these were as good as they can possibly be is easy to counter; McIntosh made money on them over a significant timeframe. They were good for sure...but so good they can not be improved?...get a grip people...LOL

Douglas

 

[AudioAvarice]

I'm thinking of using film caps in the PSU on my tube amp restore, the are a couple of brands offering these caps, things have a 100,000 hour rating

 

[gadget73]

Manufacturers select component types for many reasons,

I always found the notion that a group of engineers or golden-ears or whomever sat around rolling capacitors and resistors after the engineers had selected the values to get "The Sound" to be fairly silly. I strongly suspect that given the components available today, the choices in 195x wouldn't have been the same.