• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Ton McNally?? Help!!

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Hello, I bought a used Tom McNally built amp on A'Gon some years back it has been in and out of use, but want to stick with it now as my primary amp. I Really love it, but the right channel started intermittently cutting out with the 6550 on that side going MIA as well as far as lighting up etc. I have tried numerous times in the last 6 months or so to his email address showing on his site with no answer. Does anyone know how he may be reached? or... can anyone recommend a reasonably priced qualified repair person who may be willing to check it out for me? I live in rural SW Oregon and there is no one arounbd here seemingly and there is one fellow 3 hours away in Eugene who is a guitar amp specialist who may be able to help and I believe an audio shop or so 5+ hours away in Portland. Of course my first preference would be Tom who built it but perhaps retired or has another email now? Any and all thought on this would be most appreciated! Thank you! Let's see if the link to the original sale will post here....
Tom McNally -Wonderful 6550 tube SET amp - 8 watts per channel | Tube | Audiogon
Thanks so much folks for the replies! I will try with that link. I did pop off the bottom to inspect for anything obvious (like a broken solder joint..etc) but everything appeared good to my Totally untrained eye. I guess the heater wire would be one of them on that socket? Is there a way I would know which one? THANKS again!
Wow Thanks so much! I did take a closeup pic after seeing the replies this morning but looks look I need to have it be a URL? I guess at this point I haven't figured out how to do that yet in this darn Win 10 photo default....as I have not had to run across that the way I usually post pics. Thanks Again!!
Heaters are on pins 2 & 7 -http://www.r-type.org/exhib/aaa1348.htm like on most octal power valves. Looking at the bottom of the valve base, there is a gap between pins 1 & 8, pin one will be to the left of the gap, pin two is the next pin counting clockwise.

Try swopping the valves over first though to see if it's the valve.

Here are the pics that he sent me-


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McNally amp down...

Hi Folks, I've been traveling and will try to get some pics up asap. The first thing I did was swap valves to no avail. In looking more closely there is one pin area with two heavy wires brown/yellow that looks like it may be the problem.? It is a little hard to know as some areas get discolored on the wires jacket from the heat soldering. Thanks so very much! Rob I'm having troubles getting the photo I wanted added 3, only one took the others that showed the most likely bad spot won't load...says invalid path. Working with Google photos


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Hi, Does that socket look suspect in the second picture showing on Lingwendil's post? I guess I could try to find out how to get the proper socket (I guess it's called?) and practice soldering before hand and see how I fare...? The joint with the large brown and yellow wire looks kind of toasted? Thanks so much for any help! Rob
Alright, see if this helps you to tell what's going on.

"NC" means not connected in the picture.

Verify that each of the connections is tight. Check that none of the wire insulation has receded from the end of the wire, leaving exposed sections that can short against anything, such as the socket frame, or chassis. Check the top of the sockets, and loo into the holes where each pin goes- verify there isn't any debris, loose or broken contacts, or broken metal.

Do you have a multimeter? If you can measure the voltage at each socket pin with the amplifier powered up this would be a huge help for troubleshooting. Jiggle the tube in it's socket between powerups to see if it loses connection, which could be from a faulty socket. Also measure voltage without the tubes inserted.

Does the problem follow the tube, or is it only with that socket?


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Hi, Yes that is the only socket messing up all seems just fine otherwise. I so appreciate your trying to be so helpful, but since I have about no soldering skills yet, I just feel this needs to get to a tech to diagnose and repair as I am so limited on ability physically right now and time to pursue and practice up on soldering skills, and moreover I'm afraid I may cause more trouble than not... If anyone has someone you could point me towards that would be great! I am in SW Oregon. Have a wonderful holiday season, new year....and Happy Listening!
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