edster00 Posted April 14, 2004 Share Posted April 14, 2004 I know there are others on the BB who are sending Mac gear to Terry DeWick to be serviced and/or repaired. I am going to be sending a Mac tuner or two myself, just to have them cleaned if nothing else. Here is a link to info for Terry-click on "DeWick Repairs" if you are interested in contacting him. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted April 14, 2004 Share Posted April 14, 2004 Hey, Randy: Did you ever try switching tubes? In addition to open filter capacitors being a possible cause for motoboating -- and that didn't help -- another cause can be an open grid pin/grid circuit. These can sometimes be carefully heated on the exterior to once again 'make' the delicate internal connection, but if you've got spare tubes, try them first. There will also be a grid (sometimes grid-leak) resistor that can 'open' and cause this problem. The grid circuits of the tubes can be gone through one at a time, but I hate to hear what the cost of this might become for you. No way am I a Mac expert, but I've heard and read about this problem many times in many different sources. Low frequency oscillation like this is a fairly common problem encountered by antique radio collectors, and it shouldn't be too difficult or costly to fix! Do you have an ohm-meter and a schematic! DON'T DO ANYTHING! I'm just thinking about ways we could maybe cure this thing without having to spend the cost of a brand new component on the replacement one grid resistor. I need to go back and reread your initial post, but is this in one channel only. Have you tried shorting the input to the amp (speaker connected)to see if the problem persists, or is it only when the preamp is connected? Do you know how to short the inputs, and do you have a shorting jack to test this? I can tell you how to make one from a single Radio Shack jack -- it's nothing at all to do! Erik Erik Quote Link to comment Share on other sites More sharing options...
NOSValves Posted April 14, 2004 Share Posted April 14, 2004 Randy, Just send it here $100 and I'll fix it ! Geeezz this stuff isn't rocket science work its just another tube amp McIntosh or not. Craig Quote Link to comment Share on other sites More sharing options...
edster00 Posted April 14, 2004 Share Posted April 14, 2004 My pleasure mdeneen! I just got that link a few days ago from Audible Nectar, he is having a MX-110 checked out by Terry as we type. I'll never be able to give back 1/10 of what I have gained from the BB. Quote Link to comment Share on other sites More sharing options...
rtaylor Posted April 14, 2004 Author Share Posted April 14, 2004 ---------------- On 4/14/2004 8:11:19 PM Erik Mandaville wrote: Hey, Randy: Did you ever try switching tubes? In addition to open filter capacitors being a possible cause for motoboating -- and that didn't help -- another cause can be an open grid pin/grid circuit. These can sometimes be carefully heated on the exterior to once again 'make' the delicate internal connection, but if you've got spare tubes, try them first. There will also be a grid (sometimes grid-leak) resistor that can 'open' and cause this problem. The grid circuits of the tubes can be gone through one at a time, but I hate to hear what the cost of this might become for you. No way am I a Mac expert, but I've heard and read about this problem many times in many different sources. Low frequency oscillation like this is a fairly common problem encountered by antique radio collectors, and it shouldn't be too difficult or costly to fix! Do you have an ohm-meter and a schematic! DON'T DO ANYTHING! I'm just thinking about ways we could maybe cure this thing without having to spend the cost of a brand new component on the replacement one grid resistor. I need to go back and reread your initial post, but is this in one channel only. Have you tried shorting the input to the amp (speaker connected)to see if the problem persists, or is it only when the preamp is connected? Do you know how to short the inputs, and do you have a shorting jack to test this? I can tell you how to make one from a single Radio Shack jack -- it's nothing at all to do! Erik Erik ---------------- Yup, tried switching tubes and it doesn't follow the tubes. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted April 14, 2004 Share Posted April 14, 2004 Those 2 gentlemen do have a nice website for sure. They must be partners or something. Craig Quote Link to comment Share on other sites More sharing options...
Cleve Posted April 14, 2004 Share Posted April 14, 2004 ---------------- On 4/14/2004 7:08:57 PM rtaylor wrote: ---------------- On 4/12/2004 7:20:18 PM Cleve wrote: Perhaps this is too obvious, but when you said you 'got them back' I'm assuming you had them serviced by an authorized McIntosh tech to correct the motorboating. Won't the service facility stand behind their work? It's not like the problem resurfaced weeks or months later, after the implied warranty has ended. If it were me, I'd ask the service facility to make it right. Also, in the worst case, the Binghamton factory will repair ANY McIntosh product. Good luck! ---------------- Cleve,just received a reply from Mac and they will not due any servicing on my Mac's, they did say they thought it the price was high. They gave me some recommended shops and none of them are close. ---------------- I am shocked! One of McIntosh's traditional strong points was that the factory will service ANY McIntosh product, regardless of age. I was concerned about Mac's integrity - first with the Clarion takeover - then the recent aquisition by Denon's parent company. Now I am even more concerned! Dave O'Brien used to conduct the famous Mac amplifier clinics across the country - http://www.roger-russell.com/clinics.htm - he's now retired, but Roger Russell lists Dave's e-mail at his website. It's obriendh75@msn.com Perhaps he might know what's wrong with the amp, or suggest someone that can repair it? I wish you the very best of luck! Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted April 15, 2004 Share Posted April 15, 2004 Ok. That means that the problem probably doesn't reside within the tube in relation grids. This is one step closer to solving the problem. Do you happen to know what resistor was replaced? If the put in new power supply filter capacitors, they may have also installed a new dropping resistor at the same time. However, that's not the type or application of resistor that can cause motorboating. ...time is getting away from me, and I've got lesson plans to do for the rest of the week. You'll get this worked out! Erik Quote Link to comment Share on other sites More sharing options...
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