2020 Monkeymatic Lassen #4 (1482)

[pompeiisneaks]

that looks great! Love the 'oh we on!' on the power light...

~Phil

[TUBEDUDE]

Good build, congrats. Progressive distortion with no artifacts is a success story. I hate the fizz.
That power lamp label is funny.
It's refreshing to see the iron was positioned for minimal hum.

[xtian]

I built out Lassen #5 today, with only minor layout improvements over #4. Powered up, and found I had a lot of hum with power tubes only installed--one screen drawing 25mA (way high) while the other only 3mA (good). I checked a bunch of things, before finally measuring the resistance of OT primary: red-blue = 213ohms (good), red-brown = ... um... OPEN.

OK, end of troubleshooting. Will have to order a replacement. Dammit, have to wait until Monday to order!

[xtian]

OT autopsy! The wire break was easy to find. Advice for repairing? Does one need to strip the varnish off that tiny wire before soldering?

IMG_4694.jpg

[pompeiisneaks]

As I recall from youtube videos on micro board repairs, the soldering iron's heat usually will melt the stuff off, but I've also seen people take a bit of sandpaper and rough up the end of the wire, I think it depends on the size of the wire though too.

I've no practical experience on it though, but I've watched tons of videos by Louis Rossman and the like that do this tiny repair work and I've been trying to learn it.

~Phil

[maxkracht]

Have done similar repairs a handful of times. Heat from your iron should do the trick but sometimes it takes a bit of time. I usually put a ball of solder on my iron and keep feeding it flux until the wire looks adequately tinned. Not as bad as repairing headphones but pretty similar, if you have ever done that. Since you cant easily get tape all the way around the core, sometimes I feed through paper or thin cardboard to get some compression force on the newly soldered wire, then glue the cardboard to itself from the other side.

[sluckey]

There was a chemical wire stripper back in the '70s and '80s called Strip_X. It was made specifically for removing the insulation from magnet wire. Small bottle with a brush in the cap. Put a gloppy bit on the end of the wire, let sit a few minutes, wipe clean. Tin and solder. Very easy to work with. But I can't find it today. MSDS probably killed it.

Nail polish remover may work. On that small wire your soldering iron will probably work.

[xtian]

Thanks for the advice and encouragement. I was able to strip the varnish with a blade. I tacked down the 18ga brown wire with UV cure adhesive so it won't wiggle. Then I was able to wrap one turn of the coil around and soldered it. Made a good connection. But still shows open to CT. Oh, well.

[angelodp]

Very cool build, love to hear it at some point. Simple effective.

Ange

[Phil_S]

Thanks for the advice and encouragement. I was able to strip the varnish with a blade. I tacked down the 18ga brown wire with UV cure adhesive so it won't wiggle. Then I was able to wrap one turn of the coil around and soldered it. Made a good connection. But still shows open to CT. Oh, well.

Eager beaver. Now you'll need to untack it and do it again. You might try abrasive paper instead of a blade.

Now, what you already know, check for continuity before you "tack it down" again. Or do you think it's toast?

[xtian]

The OT was open somewhere inside. CEdist refunded me.