For what its worth, here is a link to a spec sheet for the Tenma 72-455A:
http://www.farnell.com/datasheets/1662398.pdf
http://www.farnell.com/datasheets/1662398.pdf
Hi wiseoldtech,
The point is, you don't have a THD meter or distortion measuring system of any kind. Do yourself a favour and pick up an HP 339A if you see one around $150. Heck, even if it's $300, it'll run rings around what you have.
You really must be able to measure distortion in order to tell if an amplifier (or any gain stage) is working properly. In other words, you can't check your work.
-Chris
The point is, you don't have a THD meter or distortion measuring system of any kind. Do yourself a favour and pick up an HP 339A if you see one around $150. Heck, even if it's $300, it'll run rings around what you have.
You really must be able to measure distortion in order to tell if an amplifier (or any gain stage) is working properly. In other words, you can't check your work.
-Chris
I'm sorry if my "standards" and equipment do not measure up to some other's ideals.
I've been doing service work for customers, some "picky" as I am, for decades, and never ever had anyone criticize my servicing, or my talent.
From "high end" McIntosh down to Sears and Kmart, I've always provided honest reliable and satisfactory service, which is more than I can say for some other service techs that I'm come across in life.
I own a full set of good servicing equipment, some brand new, have been educated professionally, have 45 years axperience under my belt, and my wall has the certificates to show my hard work.
However, it seems I fail to please the "online" cherry pickers, and that's fine, I'm not earning income from any of you anyway.
Wiseoldtech, I think you missed the very important gist of this thread in particular, where people *are* pushing for the last nth of performance. Your equipment is fine and may do exactly what you ask of it, and that's great, but it's not in the ballpark of some of the work being done here.
Hi Scott,
While I'll agree with you in some instances, a basic THD test will tell you if the amplifier is working properly after the other checks. Oscillation will typically cause high distortion in the audible range.
Hi wiseoldtech,
One tech to another, you need to do basic distortion tests. Otherwise you will never know if that repair is done right or not. Don't depend on your customers to tell you. They can't tell on average. I get equipment in that isn't working even close to okay. Some is oscillating and running hot, some has no bias and others have open emitter resistors (the measured value still seems to be in the ballpark).
I'm actually blown away that McIntosh allows you to service anything without a THD test set. Even the manuals call this equipment out where it says "required test equipment". Certainly most manuals do. How else can you compare the performance with the published limits. You can't.
I'm not crying over something that isn't needed. Testing for THD is a basic requirement of the servicing trade and you're kidding yourself that all your work has been okay over the years if you don't have that ability. I'm afraid to ask what else you don't have in relation to what you service.
In addition to the basic equipment for distortion, many of us take it further and look at the residuals (THD meter output) to determine where the problems might be. Some bias setting procedures actually have you look at the residuals to determine what the correct bias current should be. Usually at a high frequency into a 4 ohm load at low power. You are not capable of doing this, and you can't see it by looking at the sine wave, and you sure can't quantify it by listening to it.
-Chris
While I'll agree with you in some instances, a basic THD test will tell you if the amplifier is working properly after the other checks. Oscillation will typically cause high distortion in the audible range.
Hi wiseoldtech,
One tech to another, you need to do basic distortion tests. Otherwise you will never know if that repair is done right or not. Don't depend on your customers to tell you. They can't tell on average. I get equipment in that isn't working even close to okay. Some is oscillating and running hot, some has no bias and others have open emitter resistors (the measured value still seems to be in the ballpark).
I'm actually blown away that McIntosh allows you to service anything without a THD test set. Even the manuals call this equipment out where it says "required test equipment". Certainly most manuals do. How else can you compare the performance with the published limits. You can't.
I'm not crying over something that isn't needed. Testing for THD is a basic requirement of the servicing trade and you're kidding yourself that all your work has been okay over the years if you don't have that ability. I'm afraid to ask what else you don't have in relation to what you service.
In addition to the basic equipment for distortion, many of us take it further and look at the residuals (THD meter output) to determine where the problems might be. Some bias setting procedures actually have you look at the residuals to determine what the correct bias current should be. Usually at a high frequency into a 4 ohm load at low power. You are not capable of doing this, and you can't see it by looking at the sine wave, and you sure can't quantify it by listening to it.
-Chris
Yes, I'm aware of the "internet crowd" and their extremely tight, or should I say, obsessive demands, insistences, and worries.
Discussing a plethora of subjects ad nauseam, like a bunch of high-level surgeons prior to some critical life-threatening operation.
Picking at every micro-crumb of information and dissecting it.
Indeed, I know this well.
However, fortunately, in the real world, most people do not have this going on in their lives, and as such are more inclined to being reasonable about things.
That is where I spent 45 years providing, dare I say it..... Top Notch Service to people.
The widowed grandmother wanting her beloved stereo console serviced that her dead husband bought for their anniversary - I doubt she cared about such things as THD, stylus pressure, etc etc.
The guy with the Marantz 2275 with a blown right channel...
Or another guy with a huge Pioneer SX-1250 that took it to a butcher before finding me...
And thousands of others through the decades....
They all were enormously appreciative, even to this day, I get Christmas cards from past customers, emails of thanks, and referrals.
But lord forbid I ever have some snotty insistant internet self-proclaimed "expert" to deal with - I've tossed some of them right out of my shop when they attempted to challenge my skills and capability.
The internet crowd can be a strange bunch, and thank the lord they're on the other side of my screen and easily dealt with.
This thread is and always was about creating the highest performing oscillators possible for distortion measurements. It’s not about servicing equipment or what the bare minimum that will suffice is.
I’d invite you to skim the thread because there are a lot of good tidbits of information here. It’s not going to be that relevant to your day job - we understand that grandma just wants her stuff to work and not grossly distort.
The initial reaction you got was probably because it appeared you hadn’t read any of the thread, unless you just have an axe to grind with people who care about measurements and want to learn. If you take a step back, you might see why you appeared to be that same snotty expert in someone else’s shop.
Point taken.
But I'm not about to wander through 740 pages of comments discussing the Holy Grail Oscillator.
I merely pointed out the one I use which more than suffices for a technician's purposes, and right away got hit with questions regarding specifications.
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There probably are multiple threads on the forum somewhere about test gear for service purposes, or best procedures to diagnose stuff, and if you had posted it there the reaction would have been different.
You just were unlucky to pick the thread about super low distortion oscillators and challenge us all ;-)
Like walking into the Hells Angels clubhouse and starting to discuss your mountain bike
Not a good career move.Jan
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80+ year old Sidney Simon (no relation) was a retired college art professor who used to frequent a biker bar where he liked the bands. Normal clientele just called him pops and treated him with respect. Of course he was about 5' 6" and 120 pounds. No points given for bullying a tiny old guy.
Besides he could tell tales of his good friends like Andy Warhol and Nico.
So folks can we quit beating up on someone who just took a wrong turn?
Besides he could tell tales of his good friends like Andy Warhol and Nico.
So folks can we quit beating up on someone who just took a wrong turn?
+1
Head over to xrk971's excellent thread; performance is good enough for R&R and the cost is close to $0. I also have good experience with ARTA, DiAna & Visual Analyzer.
Really, the hardest part is to overcome the initial reluctance to things that have no knobs; if successful, then the second hardest part is to get rid of all those old gear.
Head over to xrk971's excellent thread; performance is good enough for R&R and the cost is close to $0. I also have good experience with ARTA, DiAna & Visual Analyzer.
Really, the hardest part is to overcome the initial reluctance to things that have no knobs; if successful, then the second hardest part is to get rid of all those old gear.
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hello Wiseoldtech,
Using a square wave can tell you lots of how your amplifier is operating, in some cases it provides more information than a sine wave will. I used a home made XR2206 (from a Popular Electronic article) for years until I could afford better gear. More like better gear came down to affordability in a hobby sense.
Sounds like you do good honest work, I will recommend you to anyone that is in your area asking for service.
Service a SX-1250 or any receiver/tuner, does include testing/adjusting the tuner and for that you do need some specialized RF gear. Most discriminators have a zero/null and a linearity adjustment requirement.
P.S. these small precision oscillators are very economical to put together yourself.
Cheers Rick
Using a square wave can tell you lots of how your amplifier is operating, in some cases it provides more information than a sine wave will. I used a home made XR2206 (from a Popular Electronic article) for years until I could afford better gear. More like better gear came down to affordability in a hobby sense.
Sounds like you do good honest work, I will recommend you to anyone that is in your area asking for service.
Service a SX-1250 or any receiver/tuner, does include testing/adjusting the tuner and for that you do need some specialized RF gear. Most discriminators have a zero/null and a linearity adjustment requirement.
P.S. these small precision oscillators are very economical to put together yourself.
Cheers Rick
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