Blonde/brown Bandmaster issues... wonky vibrato!

[J Moose]

So I've got a '62 or '63 blonde/brownface Bandmaster head that I loaned to a buddy as a reference for his newly aquired brown tolex Concert... got it back & loaned to another buddy who promptly called me to say it was "bonked" and promptly got it back to me...

Never checked it out between loans...

DOH!

It also sat for like, I dunno... 6 or 7 months without any use what-so-ever.

Anywhoo... long story short... found & replaced bad tubes so now it at least sounds mostly right aside from some rice crispies.

Bad news is that for some reason, the vibrato is pretty fukked. It's doing a motorboat thing... LF oscillation of sorts when the intensity hits 3 or 4...

Largely unusable really.

I had it recapped & gone through after I purchased it 2-3 years back... when I got it back the motorboat thang was happening but only when the intensity hit 8 or 9... not "perfect" but still largely usable IMO.

I've given up on it for the time being but I want to get back in there before the weekend.

There's still some "krunchy" things happening, mostly some random noise that's coming from (I think) power tube land since it's not affected by the volumes & doesn't matter if anything is plugged into an input jack on either channel.

Thanx!

 

[CapoFirstFret]

Re: Blonde/brown Bandmaster issues... wonky vibrato!

sounds like the optical sensor is "bonked" and you're gonna hvae to replace it. The Fender tremolo/vibrato relies on an optical light for it's pulse...without it, it just does screwy things. maybe someone who has more technical knowledge can explain it better.

In other words, it happens man. Old parts and all

 

[B Bent]

Re: Blonde/brown Bandmaster issues... wonky vibrato!

Sounds like it is time to give up and sell it to someone else. (me)

 

[J Moose]

Re: Blonde/brown Bandmaster issues... wonky vibrato!

Sounds like it is time to give up and sell it to someone else. (me)

Riiiiiiiiigggggghhhhht.





I haven't dug out a schematic for it yet, but don't the brownface Fenders have a 'tube' driven trem... bias driven is it?

It could be an opto sensor that needs cleaning/replacing, that'd be too easy!

I think this is a bit deeper though...

 

[Vasshu the humanoid typhoon]

Re: Blonde/brown Bandmaster issues... wonky vibrato!

Motorboating...well some values are off for sure then

 

[ES350]

Re: Blonde/brown Bandmaster issues... wonky vibrato!

no roach in the 6G7 or 6G7A...bias modulated tremolo. Check for drifted values in the trem circuit...

 

[the guy who invented fire]

Re: Blonde/brown Bandmaster issues... wonky vibrato!

You guys crack me up...a blond Bandmaster (and the rare brown Bandmaster for that matter) have an all tube harmonic vibrato that has nothing to do wiht bias modulation or an optocoupler.

Moose: If you're getting motorboating out of it something had drifted way to far out of spec. That is actually pretty common in those harmonic vibrato amps...it's a picky design and even Leo had problems with it...thats one of the reasons it only lasted a few years...that and the fact that it used 2-2.5 12AX7's to make it work!

Your best bet is to take it to a tech and have it looked over and fixed up...it more than likely won't take much to fix it once the problem is found.

 

[ES350]

Re: Blonde/brown Bandmaster issues... wonky vibrato!

yep--you're right. I was looking at the schematic trying to figure what all that glass and wire was for...forgot all about the harmonic vibrato thing.
Glad we made your day...

 

[J Moose]

Re: Blonde/brown Bandmaster issues... wonky vibrato!

Moose: If you're getting motorboating out of it something had drifted way to far out of spec. That is actually pretty common in those harmonic vibrato amps...it's a picky design and even Leo had problems with it...thats one of the reasons it only lasted a few years...that and the fact that it used 2-2.5 12AX7's to make it work!

Your best bet is to take it to a tech and have it looked over and fixed up...it more than likely won't take much to fix it once the problem is found.

Yeah... but it's such a juicy vibrato! More like a vibe really.

Anyway... yeah, I figure something has drifted or pulled out of whack... I've tried some tube swapping which seems to help things a hair bit... but doesn't "solve" the problem.

At this point I have more time on my hands then money & I'm comfertable delving into amps & audio gear with a soldering iron...

I figure I'm looking for resistors that have drifted out of tolerance?

 

[the guy who invented fire]

Re: Blonde/brown Bandmaster issues... wonky vibrato!

Yeah... but it's such a juicy vibrato! More like a vibe really.
Anyway... yeah, I figure something has drifted or pulled out of whack... I've tried some tube swapping which seems to help things a hair bit... but doesn't "solve" the problem.
At this point I have more time on my hands then money & I'm comfertable delving into amps & audio gear with a soldering iron...
I figure I'm looking for resistors that have drifted out of tolerance?

W/O seeing it I'd be taking a shot in the dark to be honest...ya should hold off until you can get it to a tech, it'll save a lot of time and trouble, and you just trying different resistors in the old hunt and peck method will for sure be a long road that could end up in you having more issues that you do now...

 

[J Moose]

Re: Blonde/brown Bandmaster issues... wonky vibrato!

and you just trying different resistors in the old hunt and peck method will for sure be a long road that could end up in you having more issues that you do now...

Indeed!

That's why I was hoping that someone would know a place to start... heheheheh

I'll look up a schematic for this thing & give it a look see...

Where's Scott at these days?!