Dead Bass Channel JR-20

[Dutch]

I’ve been a member of this great forum for a while, but this is my first post.

I have a JR-20 Tone Cabinet, circa 1956, that has a dead bass channel. No sound comes from the bass speakers; all else works fine. All tubes (except one that I'm not sure about) have a '56 date code on them, and I don’t know of any source within 300 miles that can check themfor me, so I’m pretty much on my own. I do know some electronics, and I have a DVOM. I also have the wiring diagram for the amp. Rather that waste a bunch of time, I thought I’d ask for your help.

I know many of you would say why bother, JR-20s are crap. Well, it was given to me for free (I think the guy who gave it to me thought it was fully functional) and it is absolutely pristine, not a scratch on it anywhere. So, if I can fix it cheaply enough, I would like to add it to my present set-up, a D-150 with a 122.

So, my question is HOW to diagnose what the problem is. I can tell you all the tubes glow nicely when it’s powered-up, at least the glass ones that I can actually see. What should I check for next?

[paulj0557]

This tone cabinet is certainly worth keeping and USING for sure. In fact listen to this JR-20 http://youtu.be/WBh5urg7Ex0 I also have just picked up a JR-20 that I will be getting into soon enough. I've seen many of these cabinets appear with Hammond organs over the years as an added bonus to the sale, but presented more like a burden. The fact is that a plain old Leslie on a Hammond can get a little bit boring from my personal experience. Although I've not had a Hammond tone cabinet per say up until now I have learned the benefit of other non-Leslie cabinets to fill out a sound along with a Leslie.

I hope someone helps you figure out your problem. Anyone reading this who can help, lets keep this top priority for Dutch I'm signing off right now, but I'll look at a schematic when I get a moment and see what I can find that might help. In the meantime see if you can unhook your bass speakers and put your ohms meter on 'ohms' and put the leads on the speakers two terminals and see if you get a reading. If no reading then maybe the speaker is blown. If you aren't sure about your ohms meter then unhook the speaker wire from the speaker and get a flashlight battery (1.5 volt) and touch briefly the +/- of the battery to the +/- (either direction they needn't match) and you should get speaker movement provided the battery is good. If nothing happens then there is a good chance the speaker is blown. You can always get the speakers reconed if that is the problem, but for the price of used Hammond speakers you can probably just get them replaced. Of course the speakers might not even be the issue. For now try that and anyone else jump in here.