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  #16  
Old 01-24-2012, 09:47 AM
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Wgrr -

I guess I am one of those customers!

I bought this 1910 building in 2000 for my business, and long story short, it had a new boiler then but all old pipes. Well, they have not aged well. Just put a new / new boiler, and then the condensate pipe started popping holes. While everyone was on vacation, and it was 13 deg F outside.

This is after the new flat roof, septic system and parking lot, and now shoring up some structural slumpf that I KNOW is ancient, but one of my staff is freaking out about......

Thanks for the comments on the MC-40s'

One is almost totally dis-assembled after painstakingly drawing it out so I can put it back together....





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  #17  
Old 01-24-2012, 11:00 AM
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That high voltage buzz
 
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Greetings Chinacave, sorry to hear about your heating adventures and can understand why those would take your time of late.

On the amps, I'm not sure I'd completely trust the results of the measurements just yet. What voltages are you getting on the plates of the tubes at idle and then again when your run a sine wave through it? I suspect you're going to find that those voltages will start to drop as the amp is put under more and more of a load. Did the sine wave clip symetrically? At least you know it will pass a sine wave, though.

It is sort of like an old car with low compression on the cylinders - it will idle ok but doesn't produce the horsepower when you try to drive it.

When you've got one rebuilt, though, I think you'll come back with different results!

Cheers,

David
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  #18  
Old 01-24-2012, 12:43 PM
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Dear David -

Thanks again for the comments -

I am not putting too much stock in the readings either - as I mentioned , I was measuring the AC voltage with a mid-low cost DMM, so no idea how accurate any of it is. Also not too sure of the accuracy / output of my sig. generator and my scope-fu!


I will check the delta of the plate voltage as you suggest - thanks!

I am also re-capping a Heathkit AV-3 Audio db meter and will calibrate it if THAT effort is successful.


I am still curious about a few things -

1) IS there a modern equivalent of a VTVM for measuring wide-band audio range AC? I really don't want to get involved (right now) in restoring test gear, but at least the Heathkit is the simplest of the several I have.

2) Do any of the PC (or Mac, AudioDon..) -based test programs or utilities have a VTVM mode, or are capable of measuring audio AC accurately?

3) The terminal board of the one amp I have taken apart seems pretty close to fried. Has anyone used the DIY ones from AES ( Item # P-HTUR-A )for use in Macs? Any comments or experiences?

Thanks to all for reading & commenting - Much Appreciated, as always!
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  #19  
Old 01-24-2012, 04:43 PM
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That high voltage buzz
 
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On your questions:

1) Wide-band audio (for an RF engineer, this is an oxymoron) signals can be read with most any of the better digital volt meters (DVM) these days. For instance, my Fluke 117 specs a 5Hz-50KHz bandwidth for AC volt measurements. Most all but the cheapest of the DVMs I've seen sport input impedance specs that are like what a VTVM used to carry. So, just getting a decent DVM is about all you're going to need unless you have very specific testing requirements. BTW, the Fluke 117 also has a frequency counter, too. Really reduces the number of instruments you need on the bench.

2) PC-based measuring devices usually have some sort of 'front end' box that does the A/D work needed so the software package can do its job. Since you can get a really functional DVM for less, that's the way I'd recommend mainly because you can take the DVM where you'll not likely get a laptop and the dongle/outboard box setup. One thing I do usually have, however, is a small USB or Firewire device so I can use the PC as an audio signal generator. Room EQ Wizard has a host of nice utilities for sweep frequency and other things that get interesting for a work bench.

3) How fried is the board? If it was due to the larger resistors being mounted close to the board, just mount new ones standing away from it and you're set.

Cheers,

David
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  #20  
Old 01-24-2012, 05:43 PM
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[QUOTE=chinacave;5348992]Wgrr -

I guess I am one of those customers!

I bought this 1910 building in 2000 for my business, and long story short, it had a new boiler then but all old pipes. Well, they have not aged well. Just put a new / new boiler, and then the condensate pipe started popping holes. While everyone was on vacation, and it was 13 deg F outside.

This is after the new flat roof, septic system and parking lot, and now shoring up some structural slumpf that I KNOW is ancient, but one of my staff is freaking out about......

Thanks for the comments on the MC-40s'

One is almost totally dis-assembled after painstakingly drawing it out so I can put it back together....

I feel your pain, I have rental properties and no free time. I am now looking at an old office building for my wife's law firm. It was built in the 60's with almost no updates. Hope no water pipes froze in your building. To be honest I don't know how old the steam piping is but I suspect a re-plumb may be necessary.

The MC40's are coming along nicely though.
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  #21  
Old 02-05-2012, 01:15 PM
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Quote:
Originally Posted by dshoaf View Post
On your questions:

1) Wide-band audio (for an RF engineer, this is an oxymoron) signals can be read with most any of the better digital volt meters (DVM) these days. For instance, my Fluke 117 specs a 5Hz-50KHz bandwidth for AC volt measurements. Most all but the cheapest of the DVMs I've seen sport input impedance specs that are like what a VTVM used to carry. So, just getting a decent DVM is about all you're going to need unless you have very specific testing requirements. BTW, the Fluke 117 also has a frequency counter, too. Really reduces the number of instruments you need on the bench.

2) PC-based measuring devices usually have some sort of 'front end' box that does the A/D work needed so the software package can do its job. Since you can get a really functional DVM for less, that's the way I'd recommend mainly because you can take the DVM where you'll not likely get a laptop and the dongle/outboard box setup. One thing I do usually have, however, is a small USB or Firewire device so I can use the PC as an audio signal generator. Room EQ Wizard has a host of nice utilities for sweep frequency and other things that get interesting for a work bench.

3) How fried is the board? If it was due to the larger resistors being mounted close to the board, just mount new ones standing away from it and you're set.

Cheers,

David
Hi David - Thanks again for your responses -

1) Looked up the specs of the 'best' DVM I have, and the AC response is 40-400Hz. Looks like I will be looking for a better one soon. The Fluke 117 you mentioned looks good - what should I be looking for in terms of input impedance, or is it ohms/volt? As I recall , VTVM's have a very high impedance. On my cheap DVM's this is not even listed. Is there a recommended minimum figure for accurate readings with tube circuits?

2) I think you are right - I feel I am spending too much time learning and obsessing about test instruments (right now), distracting me from the task at hand of re-building the amps. I will get a better DVM and look into PC based test-ware later.

3) Once stripped of all components, the board does not look half bad, just a lot of soot. Seems perfectly re-usable, even after ham-fisted de-soldering. Man they really wrapped the leads around the terminals in a death-grip! I found a purpose-built solder-iron with integral solder-sucker - $7.95 from MP Jones, I think - seems to work pretty well.

Thanks Again!
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  #22  
Old 02-05-2012, 01:19 PM
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[QUOTE=wgrr;5350386]
Quote:
Originally Posted by chinacave View Post
Wgrr -

I feel your pain, I have rental properties and no free time. I am now looking at an old office building for my wife's law firm. It was built in the 60's with almost no updates. Hope no water pipes froze in your building. To be honest I don't know how old the steam piping is but I suspect a re-plumb may be necessary.

The MC40's are coming along nicely though.
Wgrr -

Thanks - a re-plumb WOULD be a good idea, but a logistic and financial nightmare. The pipes above the condensate line seem healthy enough. The jacking and shoring went well enough, now I have some monster cracks in plaster and doors that worked fine in tilted frames, now cannot be closed......

Next weekend I have all to myself, will get MC-40 #1 back together - more progress pix soon!
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Last edited by chinacave; 02-06-2012 at 08:02 AM.
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  #23  
Old 02-09-2012, 05:40 PM
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The Horror......

More deconstructive progress.













1) I was thinking about re-painting the two transformers, but A) Its a pain, there is that nice logo plate on the top and the paint was not THAT bad, and B) I tried a little wet metal polish on one side & it looks great, and I think I'll go with the "cleaned up, but with the real patina of age" look rather than totally pimp it out. C) It will save time on the other two. Plus its too cold here to paint outside. Plus lets face it, these deserve better than a spray can job.

2) I included the last photo to show that the serial number is stamped not only on one lip on the bottom of the chrome chassis, but also twice on the top, one under each transformer. I wonder why?

3) Not sure what to do about the rust, will try some gentle polish / wax I guess unless anyone has any suggestions. Would like to minimize it and stabilize it if possible. That ugly strip of tape on the top mostly came off with a overnight soak in Goo-Gone, will have to try more or some more nasty solvents.

I have the whole weekend free, will strive to get this one wired up and running.
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  #24  
Old 02-13-2012, 09:00 AM
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A little more progress

Sockets wired for filaments & several misc. wires that might as well be done now:


Re-swadgeing the eyelets that had loosened up:


Soak in Goo-Gone to get rid of masking tape residue & soot...


Cleaned & ready for solder:


Delicate little arms - must make de-soldering less traumatic!
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  #25  
Old 02-13-2012, 09:19 AM
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Quote:
Originally Posted by chinacave View Post
...3) Not sure what to do about the rust, will try some gentle polish / wax I guess unless anyone has any suggestions. Would like to minimize it and stabilize it if possible. That ugly strip of tape on the top mostly came off with a overnight soak in Goo-Gone, will have to try more or some more nasty solvents...
For cosmetics, I use naphta spirits which can be bought in bulk as golf club grip solvent or lighter fluid. Naphta is a gentle solvent which in my experience works on metal, wood, and clear plastic dial covers. Naphta will dissolve rust, tape residue of all sorts, candle wax soaked into wood veneer, and sometimes Magic Marker. It is not caustic and will eventually evaporate within an hour or two leaving behind almost no residue. And it is fast working.
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  #26  
Old 02-13-2012, 09:19 AM
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Components placed and wrapped for fit:


"Almost Done" -or so I thought -Also noticed that the two electrolytics are 400v when they should be 450.. Will change before applying any juice. I have had a few issues with miss-labeled parts in recent orders, as well as a bunch of 68 ohm resistors that were marked perfectly, but ALL measured at 45ohms..... guess thats why they were surplus!


I tried to keep the original color-coded wire scheme - note to self - SOLID WIRE, not stranded. And 20ga. rather than 18 or 16.... Sheesh.


Input pot and bits...



Power supply assembly - I used two caps to make the 150uf / 250v units for the voltage doubler & increased the voltage rating to 400v. I may re-stuff the salvaged cans...
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  #27  
Old 02-13-2012, 09:55 AM
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Top side of power supply unit:



Part of OCD re-building - cleaned all the screws and nuts etc in a tumbler with walnut shell media and a bit of case cleaner - Scrubbed the output terminals with a old toothbrush....(I am somewhat in the nuts & bolts biz, so its sort of a must do for me..)


Starting assembly and fit- nothing soldered yet.


I am realizing the virtues of pure point-to point rather than this crazy hybrid!


An opposing point of view:



I had hoped to get this one running, or at least tested for basic voltages this weekend, it was not to be.

Also, in poking and tracing wires on the amp in back, #02500, I had lifted several caps and connections to test and view better, naturally, when I buttoned it up to play / test it, it has massive distortion, and the amp meter on my variac bounces with the beat a LOT more than normal - I am sure that this suggests something specific to experts - if you know what I may have missed, please don't be shy!
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  #28  
Old 02-14-2012, 04:33 AM
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looking really good. I wish I had time for large audio projects. It seems like all I do is work on my house when I have free time. That usually breaks down to posting here when the weather is bad because I am lazy and don't like cold weather.

We got a massive 1 inch snow storm yesterday morning that melted off by evening. Funny thing is about this time last year we got well over two feet of snow and temps at -18 *F. This Winter I don't think I have scrapped the windshield on my service truck even one time. We are back in the upper 50's by tomorrow. Fine with me.

I meant to add that AES Tubesandmore has the can caps for these amps. I believe that is what Terry posted. It looks like they are all new on the amps he rebuilt for me. Some folks say the CPE caps made on the original Mallory equipment are not that good. Terry has posted he has had no trouble with them. Another thing. The can cap closest to to front of the amp is a can common positive I believe. The original had a paper insulator cap and the one Terry installed in my old amp is covered with black duct tape. He had to make a minor adjustment on the mounting to get it to fit into the case. I no longer have my MC40's to look at or I would.
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Last edited by wgrr; 02-14-2012 at 04:47 AM.
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  #29  
Old 02-15-2012, 09:55 AM
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Quote:
Originally Posted by SoCal Sam View Post
For cosmetics, I use naphta spirits which can be bought in bulk as golf club grip solvent or lighter fluid. Naphta is a gentle solvent which in my experience works on metal, wood, and clear plastic dial covers. Naphta will dissolve rust, tape residue of all sorts, candle wax soaked into wood veneer, and sometimes Magic Marker. It is not caustic and will eventually evaporate within an hour or two leaving behind almost no residue. And it is fast working.
Great Suggestion - I will try some - never heard that Naptha would remove rust, and I am in the decorative metal industry - good info!

Thanks
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Old 02-15-2012, 10:06 AM
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Originally Posted by wgrr View Post
looking really good. I wish I had time for large audio projects.

I meant to add that AES Tubesandmore has the can caps for these amps. I believe that is what Terry posted. It looks like they are all new on the amps he rebuilt for me. Some folks say the CPE caps made on the original Mallory equipment are not that good. Terry has posted he has had no trouble with them. Another thing. The can cap closest to to front of the amp is a can common positive I believe. The original had a paper insulator cap and the one Terry installed in my old amp is covered with black duct tape. He had to make a minor adjustment on the mounting to get it to fit into the case. I no longer have my MC40's to look at or I would.
Thanks - By any reasonable measure, I don't have time for this, just a singular opportunity that came up to help a friend and get to work on some gear I might never otherwise have a chance to experience - also to try and do the very highest quality job I can, regardless of time input!

Your recall is correct - the second 150uf cap in the voltage doubler is positive to ground - and that is why it is on the lone phenolic washer - I used an AES can cap for the quad, I did not see that they still have single units in cans - I could have used the 50/50/50/50 µF @ 350 VDC @ $35.00, also I am trying to keep the $$ outlay for my friend reasonable.

Parenthetically, or O/T - I have seen Many pictures of Mac amps with the little studs to hold / locate a tube cover / cage (sim to the one on the Marantz 8B,) but I have never seen the cages themselves - were they an accessory that was never bought? (seems unlikely) - were they lost? - Aliens? .gov conspiracy?
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