First start-up/restore Luxman MB-3045

[fmriguy]

Hello,

I'm a new member, but hope I could get some advice from the experienced members of this forum. I inherited a pair of Luxman MB-3045 mono amplifiers from an audiophile friend who passed away. They have been sitting in my closet for about the past 15 years if you can believe it. I now have a bit of time to take the next step in testing/restoring them but don't want to screw up the process given their value. Given my friend's abilities, I think it is very likely that they were working when he passed, but I'm not sure, and they have just been sitting idle in my closet, so some components could have aged poorly.

I'm afraid my question is a bit broad, but if you had a pair of these fall into your lap, what would be your steps moving forward? I know my way around a soldering iron, but mostly for replacing a blown capacitor here or there in a computer motherboard, not necessarily a schematics expert. I have been doing reading online and it seems one might also need to power them up slowly (perhaps a variac?), although I'm also missing power cords for them. Also any books or reference material that you would recommend would be quite helpful.
Thanks!

 

[Blue Shadow]

Similar circumstance in that my pair sat idle for decades as I waited for the internet to show up so I could find a copy of the Luxman Modification manual to make the changes necessary to use some KT88/6550 vs. the original 8045G.

1) what power tubes are installed, to determine if the conversion has been done. There are other ways, too.
2) pull the bottom panel and verify that everything is visually in good shape the two 68K 2W resistors between the large film caps on the power tube end of the board are known to get hot. In one of mine, too hot to avoid having to do some restoration work.
3) post back the info.

If you have to move forward, I would use a variac and bring the voltage up slowly and verify the bias and balance are not so high as to cause problems. Too low isn't going to be the problem.

I'd expect most of these amps are still using their original multi-caps. I have replace the 4 caps on the board with the test points but none of the rest except as specified for the conversion.

@gadget73 helped me get mine going after the conversion so he has seen them and has an idea about them as well as a wealth of tube gear knowledge so maybe he will drop in and make some comments.

 

[Blue Shadow]

Post, drag and drop, some pictures of the guts if you want. Of course, pics of the units are welcome, too, they are nice looking amps.

 

[gadget73]

usually what I like to do with things that have been sitting a good while is to pull the tubes and clean the tube pins and tube sockets. Check the fuse, make sure its the right value and isn't blown, and give it an eyeball underneath to see what might be going on. It would be worth figuring out what has been done for the output tube situation too, whether its got originals, or has been modified. I forget what the original tube is, but the replacement should be a 6550 or KT88. If its using one of those, you'll also need to see if they set it up for triode operation or pentode. The particulars are laid out in the modification document, and it affects what the bias is set to.

If nothing looks obviously wrong, put it on the variac and give it 10v per hour or so while monitoring the current draw. Make sure the output tubes aren't drawing excessive current once they begin to conduct around 60v or so. If things start to go south, turn it off and dig deeper. Tube gear is relatively robust, but at this point we're fighting age as much as anything. If the caps are good, its pretty much going to work.

 

[UncleBingo]

Everything Gadget73 said but put a speaker/resistive load on the output terminals just to be safe. I know guys that swear that it isn't necessary, but to me if 60hz is getting past the filter caps, it's on the output transformer if the tubes are in there. No bueno.
Idea being: signal on the primary with no way to dissipate the energy on the secondary side is a problem/

 

[gadget73]

yeah, forgot to mention the load. good thing someone is paying attention