UREI 813 crossover rebuild

[kwingylee]

Guys
I finally got around to semi-restoring my UREI 813s (serial numbers 101 and 119) with the Altec 604-8G drivers. In the process of recapping the crossovers, I noticed a discrepancy between the "original" crossovers as I purchased them and the schematics that I pulled off the 813 owners manual in the JBL PRO website. The schematics showed a 10uF capacitor C8 in series with a 50 ohm resistor R1 interconnecting the 604 LF driver and the Eminence LF woofer. In the crossovers that I have, there is no 10uF capacitor and the 50 ohm resistor is connected across the terminals of the Eminence woofer. Does anyone on this forum know the purpose of C8/R1 as they are shown in the schematics. Looks like a low frequency signal is capacitively coupled into the Altec woofer to improve the bass response perhaps? Appreciate any analysis on this. I am not sure about any audible benefits.

Another issue is the UREI blue horn mounted to the 604-8G. All of the foam has disappeared and I want to replace them. Does anyone know a good source for the foam?

All signal paths to the Eminence, 604 LP and 604 HP drivers go through 3 different sets of light bulbs. I plan to by pass all of the bulbs. I cant imagine this being good for the sound. Any opinions?

Other than these issues. I am pretty close to being done. I recapped the crossovers using Soniccap, Jensen, Jantzen Z series, crosscap and AXON film caps (there are a lot of caps). I left all of the aircore inductors (5) in place. Cant wait to fire these up hopefully in the next couple of weeks.

Kwing

[Earl K]

Hi,

I thought that only the 813A or 813B or 813C ( versions had the added foam on the horn ).

No-matter, you could do something like this ( using felt ).

[kwingylee]

Hi,

I thought that only the 813A or 813B or 813C ( versions had the added foam on the horn ).

No-matter, you could do something like this ( using felt ).

You could be correct. The felt looks great! I finished the crossover rebuild today. Adding some terminals and adding the 10uF capacitor as per the 813 manual. I then tested them with some cheap drivers I had lying around and the seem to work ok. I need to get a few missing screws before I can reassemble the whole system. A couple ideas I have include installing Altec 411 woofers in lieu of the eminence to improve the bass response (probably need to modify the cabinet to provide the seal enclosure it needs and to add a super tweeters but that will be at some point in the future.

[bowtie427ss]

No foam on the lips, and no slots on the first version blue horns. I'm no expert, but i think i recall the earliest versions of 811 and 813 using the factory Altec sectoral horn on the 604.

Consider a 416 for a helper woofer, the 411's sensitivity is too low to couple it passively.

[C.DARRELL FREEMAN]

hello,could the light bulbs possibly be for driver protection from excessive power input to the system as a whole.i have not looked myself,but did the schematic show the light bulbs in the three passbands to the three different drivers.if they are not on the schematic or any updated tech bulletins,in all probability they were added aftermarket or customized by the owners/users.there may not be any significant loss of quality from the light bulbs other than the slight resistance they might add to the circuits.others on the board may have a more in depth analysis on this modification.just thought i would throw that out there.

[bowtie427ss]

I missed the bit about the bulbs.

Light bulbs in a crossover network are almost always there for the purpose of current limiting. High acoustic output, and high power handling were important design goals in the Urei monitors.

I'd want to be reasonably certain about what i was doing before bypassing any of them.

[kwingylee]

hello,could the light bulbs possibly be for driver protection from excessive power input to the system as a whole.i have not looked myself,but did the schematic show the light bulbs in the three passbands to the three different drivers.if they are not on the schematic or any updated tech bulletins,in all probability they were added aftermarket or customized by the owners/users.there may not be any significant loss of quality from the light bulbs other than the slight resistance they might add to the circuits.others on the board may have a more in depth analysis on this modification.just thought i would throw that out there.

Appreciate the ad. It clearly shows no foam on the horns. Very cool.
The bulbs are in the schematic. One bulb for each pass band.
I plan to drive the system with a 45W/ch tube amp. I dont plan to ever light the bulbs but seems the removal of the additional filament resistance would change the system's voicing.
I completely mounting of the crossovers last week, plan to mount the drivers this weekend and fire them up.