John Warren
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Posts posted by John Warren
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Here's something you don't see, a %THD v. power plot for a pair of MC30s. The output tubes are new make, matched pairs from JJ (6L6GC), rectifier is also new make JJ 5U4GB. The small signal tubes (preamp 12AX7, phase inverter 12AU7, voltage amp 12BH7 and driver tube 12AX7) are all vintage. The amp pair is shown. Load is 8 Ohm non-inductive power resistor. Plot shows that both amps produce about 30W RMS with <0.4% THD.
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22 hours ago, frt8dog said:
Very nice work John! I’m always amazed with folks like yourself. Meticulous with attention to detail, and it shows in your labor. Excellent! I had a pair many moons ago driving a pair of ‘78 Klipschorns! Terry DeWick did his magic with them. Sounded wonderful, typical McIntosh with Klipsch! Awesome combo!
Thanks!
I too owned MC30s which I sold many, many years ago. I liked them enough but really didn't use them and, at the time, preferred having the cash (June 1988). I've reworked a few pair of MC30s and have done a few chassis replacements on other McIntosh amps, but this was the first MC30 with a chassis replacement. I have a pair of MC40s in the que for the same.
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On 4/29/2024 at 4:03 AM, Woofers and Tweeters said:
Is there a way to tell if the original covers have been replaced?
Take the bottom cover off, the factory units are dull, bare metal finish on the underside with ink stamped codes. The new make are mirror like on the underside and no codes.
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Thanks Dave.
For the amps here, the bottom sections needed refinishing. There's an autobody nearby that will refinish (paint, powder coat) anything made of metal. The paint used here is an acrylic urethane automotive paint (a satin topcoat). After paint is applied, the parts are hung in a benchtop IR oven. Tougher than what a rattle can applied paint provides.
The difference between this method and a rattle can approach is the hardness of the paint. Even using a rattle can, an hour or so under the IR improves the durability of the paint.
I like the paint shop but I've found another that specializes in small jobs like this and the turnaround is a few days rather than a few weeks. I'll be bringing a set of transformers from a Citation II to them to powder coat in that oddly cool brown color. They match paints using fancy machines and lasers.
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On 4/23/2024 at 5:25 PM, Woofers and Tweeters said:
All I got was Once Upon a Time, The End. 😁 You have a lot of work turning them into what they are from what they were. I want to see more (for a personal reason).
In the first post, there's a link to a thread showing photos.
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Don't be amazed, the chassis tops are reproductions sourced from Korea. The quality is excellent. The bottom sections were reworked at a local metal refinisher I use. Does enamels, powder coat, anodize, acrylics.
And the Korean supplier does make a chrome on stainless chassis top section for the MC225. They have a large collection of top sections reproductions. They've been making them for some time.
Fair amount of work goes into the restoration. Most of the hardware is replaced which it should be it's over 60 years old!
Good to see the amps in use! Interesting song selection.
jw
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Thanks gents!
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Quite pleased with the end results.
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Working an interesting project which I'll detail in the link below.
MC30 pair for restoration (northreadingeng.com)
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Agree with your assessment.
I would not purchase a McIntosh product today. McIntosh's best days are behind them.
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A few photos of a tube amp project completed recently. Two channels, about 20WRMS/ch into 8Ohms. Based somewhat on the Scott 299C output stage but using a solid-state, HV power supply design capable of substantially more power than is required for the push-pull 7591 pairs.
Chassis CAD files were sent out for quote, the supplier (New England based) responded with pricing for larger quantities than I was considering. Placed an order for a small lot of chassis assemblies. All metal chassis assemblies are best for RFI/EMI/noise immunity. The chassis assembly is the high-cost item in the build. Uses oversized Hammond or Lundahl output transformers. Still waiting on a few finishing touches (knobs, graphics). Was considering silk screening the top plate but perhaps some other time.
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Water should be either deionized or distilled.
A friend of mine uses distilled water and Simple Green surfactant solution. It's alcohol based. Chemical smell.
The u/s cleaners that sweep the frequency clean better than those that sit at a single frequency. With the surfactant and swept frequency embedded particles can usually be extracted.
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18 hours ago, HenningO said:
Hi Marvel, do you think another tweeter or diaphragm will fit my Palladium P-37f?
That would be awesome.
It may be possible to remove the transducers from the plastic horn section and find ones that would fit.
Can you provide photos of the rear of the assembly and, if possible, remove the transducers so we can have a peek?
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The WSJ had an article that talks to the concept of "health-span" rather than life-span. Health-span is the years one lives with good health and free of diseases that impact your quality of life and state of mind. The years past when the health-span ends are the years spent managing disease. Most medical interventions, especially for the 75+ crowd, increase life-span but not health-span.
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3 hours ago, hron61 said:
Interesting, never saw a portable GFCI before.
Common in industrial locations. If you have a portable water pump, wet-vac or using power tools in wet areas this is what you want.
If you work on vintage, old and/or faulty electronics, lots of "gotchas" and surprises. Here's my take, connect chassis directly to panel Earth.
Regarding Variac, the red, Chinese Amazon units are the POS. Can't run at rated kVA without getting hot AF. Wipers aren't accurate or don't function until the wick is turned halfway up then wham! The internal winding is likely a better fuse than the fuse.
A Staco 12A variable transformer runs about $650 and will source 1.4kVA all day and barely get warm.
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On 12/16/2023 at 9:45 AM, henry4841 said:
If you look at the price of a Pass Lab phono stage $12,075 for the XP-27 and $4,500 for the XP-17 you will understand the quality of sound you can expect from a phono stage designed by Wayne Colburn.
Texas Instruments published a 2-stage, phono preamplifier design based on the LM833. Flat RIAA response with noise floor lower than -100dBV. Can be fabricated for about 60 USD at the board level.
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On 2/1/2020 at 11:59 PM, rplace said:
I need balanced connections
Are you running long cables at line level signals?
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It's Damping, not Dampening.
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On 7/1/2023 at 6:59 PM, henry4841 said:
That said Mac transformers are more complicated to wind but I understand others are doing it the same way now. Found that out on this forum from our great members.
The unity coupled transformer offers improved performance for CL-B vacuum tube operation only. CL-B amplifiers are somewhat higher efficiency than CL-AB.
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4 hours ago, Marvel said:
She's on blood pressure meds, a statins, and I could see the future.
High BP can have nothing to do with weight. I recall a statistic that ~20% of the people on BP meds are at a good weight (i.e. BMI <24).
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It's dB (capital B for Bell as in Alexander Graham).
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18 hours ago, babadono said:
Ask your doctor to do a fasting insulin test, not a fasting blood glucose level test
A1C is the gold standard, most docs will prescribe an A1C if a couple of 12h fasting BG ratings are 105-115 (at least that was my experience). The correlation coefficient between BMI and A1C for the 50+y/o crowd is basically =1.0 so if you're heavy or obese you're most likely prediabetic or diabetic.
To your point, you can live into your early 90s with all sorts of metabolic issues. I've got family members there now.
And they're depressed, immobile (really crippled), fatigued, constantly panting and vision impaired. And that started 10-15 years ago. Not saying I won't experience same fate but if there's any opportunity to avoid it, I'll try.
Genetics loads the pistol but it's lifestyle that pulls the trigger.
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MC30 pair
in Talkin' Tubes
Posted
Thanks.
They sound like they measure, undistorted.