Blackfaced 68 super reverb with JBL's

[jelle]

If those cathode caps are black spragues, replace them. I have had bad batches of those and stopped using them altogether for cathodes.

[jelle]

And check if the mica caps in the tonestack do not leak DC to the pots.

[redshark]

Thanks a lot Jelle!! but...sorry for my ignorance....how do a test for cap leakage???? I know, it's bad not to be a professional tech!!

New pic with the annoying components replaced!!

Also a 5751, new recto, better bias, carbon films all together made it sound much better and clean with a LP @ 4 in volume vs. dirty with 3 in volume....Any way super reverbs aren't squeaky clean like twins are they?

[jelle]

They are not squeaky clean like twins. And I would test with a strat.

Nice work. I still see those pesky TVA bypass caps... axe them.

Leakage, Set the voltmeter to mV. Lowest scale. Ground probe to ground. Red probe test the decoupled or potentiometer side of the caps. It should be very low, like below 25mV.

Let us know, and have fun!!!

Jelle

[redshark]

Thanks for the lesson man!!!

I just spent one hour with the amp. I played it and I think what I've done is enough to please the owner.

If he still wants me to go forward I will replace the TVAs and test for leakage but for now, is cleaner, not as harsh and the distortion has a better character.

I hate being spoiled by trainwreck!!!! all this fenders with the exception of the tweeds sound aweful to me!!
All my blues jam friends put the blackface deluxe reverbs in a pedestal and to me uhmm...they sound boring!!!!

[redshark]

Actually now you are making me think Jelle...

what would be the effect of those TVA's not performing right???

cathode is what sets the bias of the preamp tube, correct?

Could that cause that first gain stage to be harsh and more distorted that usual? the schematic calls for plate voltage there to be 270 and I have 280, nothing out of the ordinary....what do you think?

thanks!!

[jelle]

Five minute swap....

In my case it made the amp sound middy, lifeless and lame. Not the powerful lows and highs that I am used to hearing. Perception of distortion? Maybe...

Five minute swap...

[redshark]

Yes!! 5 minute swap!!! after 10 minutes of chassis removing and before 45 minutes of putting it back together!! LOL

I will see if I have some CDE's of that value!!!

[jelle]

If customer likes it, I would leave it then. Jelle

[Roe]

Metal oxide resistors can sound pretty good.

Has the amp ever been recapped?

All voltages ok?

Personally I hate the sound of MO resistors. Try AB CCs for an authentic fender sound

[Roe]

...
Power tubes(general electric 6L6GC's) tested fine, 5mA apart 40mA and 45mA with bias probes.

I'm picky and I like them to be matched within 2-3mA apart and although this ones are not 5mA is not an scandalous mismatch!!
...

personally, I often prefer around 5mA. A slight mismatch gives more harmonic overtones

[redshark]

Thanks guys, actually it was a succesful project. The owner loved it!

[Zippy]

Also a 5751, new recto, better bias, carbon films all together made it sound much better and clean...

I know it'd be a pain to do, but aren't you the least bit curious to know which of those changes made it better?

I wonder if the tube swap and bias adjustment would have done the trick.

Regardless, congrats on getting the job done!

[redshark]

Also a 5751, new recto, better bias, carbon films all together made it sound much better and clean...

I know it'd be a pain to do, but aren't you the least bit curious to know which of those changes made it better?

I wonder if the tube swap and bias adjustment would have done the trick.

Regardless, congrats on getting the job done!

I think every little change you make to an amp has some impact. All together according to the owner made a night and day improvement so as long as he is happy I am too!!

[vibratoking]

Glad the owner loves it...he would adore it if those orange drops were gone.