Tubes for a Hammond Model M

[ArnoldLayne]

http://img19.imagevenue.com/loc1127/th_16530_Hammond_Model_M_amplifier_122_1127lo.jpg

 

I was wondering if anyone had any advice on what to do for this problem I am having. I fire up this organ and it sounds great for about 15 minutes and then starts to slowly distort and the volume starts to fade.

 

The side of the amp says Type M-C

 

I pulled all the tubes and the prongs and sockets all look clean. The tube in the picture marked GE 7 prong has a burn mark at the top, I can't read any numbers on it.

 

I'm thinking about buying a whole set of replacments if anyone knows the best place to go.

 

Any other suggestions would be appreciated.

 

Thanks,

[B3bluesman59]

fire up this organ and it sounds great for about 15 minutes and then starts to slowly distort and the volume starts to fade.

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As the heat builds up the performance of the faulty components starts to fail. This could also be a capacitor and or a resistor problem. If the tubes are old go ahead and change them and see if that solves the problem. If not, be ready for some trouble-shootin'......

 

[retrokeys]

I've had good luck with BB Organ and they do have a tube set for the M3. I suspect Goff professional can also set you up. If you know a good electronics tech you might take the the amp over to him/her. Disconnecting it is not that tough. Just draw a good diagram so you can hook it back up. B3bluesman is right. This could be something other than tubes. A good tech can answer these questions before you have to go too deep in the wallet on something you might not need.

[Jim Alfredson]

Doesn't necessarily sound like a tube issue to me. Probably a capacitor problem. Those old can-style caps go dry out. Unfortunately they are a bear to replace if you want another can.

 

That said, before you replace the tubes, get a good contact cleaner and spray that into the sockets (with the tubes out and the organ unplugged, obviously). Wait an hour, plug the tubes in, and see if that fixes it.

[B3Nut]

The 7-pin tube between the 5U4 and the 6V6's is a 6BA6. You can find a schematic for the Model M at www.captain-foldback.com (there are schems there for the M, M-2, and M-3 as well as lots of other models.) I second B3-er's thought that you have a capacitor issue. Your Model M was made in 1949, and is relatively rare (they were in production for a month, then revised with split vibrato as the M-2.) A full recapping of the amplifier will greatly improve the organ's function and tone.

[ArnoldLayne]

Thanks for the advice.

 

I have a local tech I found at www.mitatechs.com coming out next week. He says he has all the tubes and what not I may need.

 

I feel better having someone smart look at this anyways since my new Leslie speakers will be arriving soon (from post below).

 

https://forums.musicplayer.com/ubbthreads.php?ubb=showflat&Board=18&Number=1922634&Searchpage=1&Main=138107&Words=&topic=0&Search=true#Post1922634

 

Don't need to be blowing them up right away...

 

Thanks again,

 

Arnold