5jr rebuild original resistor not correct

bcline

I am rebuilding a set of 5jrs and opened it up today to find they both had 1.5 ohm resistors rather than the 1.0 ohm that are on the spec sheets. These have never been modified. My father purchased them back in the mid 1980s and with my parents passing, I inherited the set. Is this normal for the incorrect resistor to have been used? I had already planned on removing the polyswitch and replacing the resistor with a 1.5 ohm anyways.

xschop

Is this the non-radiator 5jr with square face?

bcline

No. It has the passive radiator. According to the spec, it should have a 1.0 ohm resistor and a 12 uF cap. It has the correct crossover and cap... just a 1.5 ohm resistor.

pitdogg2

Now you know why we state more than once to open them up to get your look on. Polk changed many many things on the fly that NEVER made it back to the schematics. More than likely it is correct, Most of us who take out the poly replace with a .5ohm resistor to account for the little resistance of the polyswitch. That 1.5 ohm might make the tweeter way too soft. then again you may find that you like that.

agfrost

Hard to know--Could have been a design update, or it could well be an 'intentional mistake' that was made to finish up your speakers/get them off the assembly line. When I went to update my RTA-11TL crossovers some years back, I found that Polk had put in a RTA-8TL crossover in one of the two (different in one resistor & one small inductor to the 11TL). So my rebuild included the spec resistor values; I also replaced both inductors with a matching pair.

I'm not a guru of reading schematics, but could someone confirm if the polyswitch is/is not in series with the 1.0ohm resistor? To my eye it looks like it may not be, in which case you'd be better off putting in a 1.0ohm Mills in place of the original resistor and then decide whether to jumper or to add a 0.5ohm resistor in place of the polyswitch.

bcline

Yes it is in series. I'm a physics instructor who teaches this stuff, so I assure you it is in series. As pittdog2 said, the polyswitch has an avg. resistance of 0.5 ohm (it can vary), so if it is taken out, most usually up the replacement resistor with one that is 0.3 to 0.5 ohms larger than the schematic in order to make up for it. Since mine is supposed to have a 1.0 ohm, I will just pull the polyswitch and put in a 1.5 Mills resistor. We will see how it goes. In reality, there probably won't be a huge difference with that 0.5 ohm change, but a some ears are a bit picky aren't they?

agfrost

Then you're good! Only got 10 hours of undergrad physics under my belt & haven't played much with circuit diagrams in the last 20 years, LOL.

The resistors are cheap enough that if you're the experimenting type, you could pick up a couple values (1.5 and 2.0?) and try them each.

Have fun.

Jay