SE408S Transducer Energizer Failing

[dougzilla]

I am original owner of v 1969 Lancer 99 speaker system with the enclosed SE408S Transducer Energizer. After 34+ years of faithful service (other than replacing some bias adjustment trim pots, as I recall), the amp has developed an annoying AC hum even with shorted inputs and makes unpleasant crackling noises when input is moderately high.

I love this old thing and want to get it fixed, right. No longer have an oscilloscope, so cant do much testing. I suspect the power supply filter caps, but not sure.

1) Where can I find a circuit diagram and/or service guide/bulletins. I've searched the LH web site without success.

2) Who does good repair work in the Bay Area of California?

Any and all advice is appreciated.

[dougzilla]

I have found the circuit diagram I was looking for and the compete service manual, at this website, maintained by JBL http://www.jblproservice.com/navigat...ectronics.html

There are lots of old diagrams and manuals there, including one for my SG520 preamp.

Also, following the advice of Mr. Widget, I have taken the SE408 to The Sound Well in Berkeley for repair, with a printout of the manual. I'll let y'all know how it comes out.

Doug(zilla)

[dougzilla]

It was the big filter caps, as I suspected.

The Sound Well replaced all four (with over-spec units, but not lookalikes) and all is well. Total tab was $200 including $80 for the caps. Smooth, clean and silent when it should be. Tested THD 'okay' at 50W/ch which is 10 over nameplate power.

[Rafael]

dougzilla,

the equalizer boards installed in the 408-s have several numbers for different speaker systems. I couldn´t find out what number stays for what speaker. Maybe you can help me. The se 408´s are very fine amps, i wonder why the idea of fine tuning a system with EQ cards in the amps was not a broader success.

Rafael

[dougzilla]

That's right, the SE408S manual shows poor quality pictures of 16 different versions, but I've never been able to determine which ones were designed for systems other than the L99, nor can I find schematics. JBL did state in its catalogues that the amp could be ordered in the internal mount version with their various system/enclosure combinations, optimized for each one.

I wish I could get more info, since I am considering building some larger cabinets and converting to an LE14a + horn + super-tweeter config, but I would like to keep using the SE408S, optimized for those components. I realize I can go to 'flat' operation merely by flipping the boards I have around to use the contacts on the opposite end, but the optimization posibilities are intriguing.

Anybody have more info???

[script56]

Any info on replacement transistors for Jbl se408s?