Greetings from the far north

[Pulpmillguy]

Greetings from Finland ...grew up in south Georgia, lived in FLA for a spell, Atlanta for 15 years and now call Finland home. I've been into audio my whole life, built some kit amps in high school and college and always dreamed of "someday" having that nice system.

Well, I bought a set of JBL L200s 30 years ago and now that I'm a bit older, finally got a PL700B a couple of years back to really make them sing. It was a recapped before I bought it and it worked well until it got cold...then it would sound "tinny" on the left channel until it warmed up and then presto it was good to go. It worked fine until the other night when the little woman and I were listening to them "up close and personal" and then "poof"...the left channel went back to its old tricks...but it never recovered.

Hooked it up to a signal generator and had no problems with the right channel...beautiful waveform and 53V on the output. The left channel is a little puzzling...with a 1K sine wave input, I'm getting really strange waveforms out of Q1

From the collector I get this:

and from the emitter I get this:


I'm a mechanical engineer so cut me a little slack please but I'm pretty sure that Q1 has seen better days...idle voltages are off quite a bit also...

I would greatly appreciate any kind soul reaching out with their expert opinion on this so I can get back to listening to rock 'n roll.

Looking thru some of the threads about the WOPLs...sounds killer but I think I will just try to get the old gal back up and running at 350 a side

Thanks again for any assistance you might have to offer.

 

[laatsch55]

At the least I would replace all transistors on that board. They're pretty long in the tooth. What are you running for outputs? DC protect? I would not let an amp with no DC protect within an arms reach of those L-200's...beautiful sounding speaks ya got there!!

 

[Vintage 700b]

Welcome aboard Pulpmillguy,
I agree with Lee, absolute must to add DC protection, an accident waiting to happen....soon, if not.
The L200's are fantastic speakers, and they will be toast in a short time if that non-protected 700b lights em' up !

 

[marcok]

Ciao from Italy !
Marco

 

[Pulpmillguy]

At the least I would replace all transistors on that board. They're pretty long in the tooth. What are you running for outputs? DC protect? I would not let an amp with no DC protect within an arms reach of those L-200's...beautiful sounding speaks ya got there!!

Unfortunately nothing other than the protection circuit in the PL...and I have nightmares of something happening with the amp and smoking the JBLs. I had this happen way back with one of the kit amps I built and it smoked an old JBL D-130 (still need to get that one re-coned). If you have any suggestions I'm all ears.

 

[laatsch55]

Contact "wattsabundant", that would be Don Imlay. He builds a good DC protect board. Have patience, they fly him all over the country working on UPS's. Search a few threads here with Don's board being installed and you'll have a pretty good idea what to do.

 

[Fast Forward]

Welcome from Minnesota

 

[Elite-ist]

Interesting usrname, @Pulpmillguy. I worked in a NBSK pulpmill (Woodfibre, south of Squamish, B.C., Canada) for most of my working life in many different positions. In fact, I'm still at the same site, which will become an LNG export facility. I've been at the same place for 46 years.

Nando.

 

[Pulpmillguy]

Interesting usrname, @Pulpmillguy. I worked in a NBSK pulpmill (Woodfibre, south of Squamish, B.C., Canada) for most of my working life in many different positions. In fact, I'm still at the same site, which will become an LNG export facility. I've been at the same place for 46 years.

Nando.

I do project management work for a multi-national that designs and builds pulp and paper mills...hence the name Been doing this for 40 years, know what you mean.

 

[Pulpmillguy]

Ciao from Italy !
Marco

Maybe you have seen/heard my amp before...it came from Italy!!!

 

[gene french]

welcome...

 

[J!m]

Welcome!

 

[wattsabundant]

I do project management work for a multi-national that designs and builds pulp and paper mills...hence the name Been doing this for 40 years, know what you mean.

I can count about a dozen paper mills I've worked at from Maine to Louisiana. One time I went straight to the airport after leaving the plant. Stunk up the plane with the stench from the plant. Everyone was looking around for the offender. Kept my head down.

As for the amp, the issue is most likely in the front end Q1-Q6. Try comparing transistor junction readings with the good channel.

 

[gene french]

I can count about a dozen paper mills I've worked at from Maine to Louisiana. One time I went straight to the airport after leaving the plant. Stunk up the plane with the stench from the plant. Everyone was looking around for the offender. Kept my head down.

i lived within 2 miles of pineville kraft paper mill in louisiana ....thank god i lived up wind ...they do have an unpleasant aroma...

 

[Pulpmillguy]

I can count about a dozen paper mills I've worked at from Maine to Louisiana. One time I went straight to the airport after leaving the plant. Stunk up the plane with the stench from the plant. Everyone was looking around for the offender. Kept my head down.

As for the amp, the issue is most likely in the front end Q1-Q6. Try comparing transistor junction readings with the good channel.

I have poked around a little and things get really wacky at Q1 so I have ordered some and will replace Q1 and Q2...hopefully that straightens things out...stay tuned.

 

[Pulpmillguy]

i lived within 2 miles of pineville kraft paper mill in louisiana ....thank god i lived up wind ...they do have an unpleasant aroma...

Well...I guess it all a matter of perspective...my dad was mill manager at a paper mill so I grew up thinking it smelled like money! And Like Wattsabundant, I have also gotten on an airplane right after being at a mill so I know all about the "strange" looks you get