1968 Fender Bandmaster Help!

[tweed_slut]

hey everyone, so I picked up a 1968 fender bandmaster head (AB763 circuit) a while back.

It's got some issues though, it starts breaking up pretty heavily around 4-5, but before that it sounds pretty damn nice. It's my understanding that bandmasters should have oodles of headroom... leading me to believe something is most likely wrong here haha.

Soooooo

I've replaced the power tubes with a matched pair of 6L6GC's, replaced V1, V2, and V3 with 12AX7 and V4 with a 12AY7 (I know that's not what's on the tube chart, it's just the only thing I had available at the time. Anyways a 12AY7 has less gain than a 12AT7 right? So that's not the problem I don't think.) The guy I bought it from had it recapped with orange sprauges (I checked too, they all brand spankin new.)

There's a pot on the circuit board, which I've been told was a balance pot but when you tweak it slightly it changes the glow of both tubes? So yeah, I need some help amigos.

Oh and I'm mainly using my neck pickup, a seymour duncan jazz, which is a fairly average output pup to my understanding so I don't think that has anything to do with it.

 

[BrianS.]

Re: 1968 Fender Bandmaster Help!

There's really nothing about the bandmaster that will make have "oodles" more headroom than any other fender amp of that lineage. The pot should be for adjusting the negative bias for the power tubes.

Sounds like your amp is functioning as normal.

 

[tweed_slut]

Re: 1968 Fender Bandmaster Help!

Hm. Honestly I hadn't thought about that haha. I've just read that the amp was clean and loud and it's loud for sure, but it doesn't sound like distortion around 4-5. It sounds real muddy and flabby and it breaks up super quickly, not gradually.

 

[autologic]

Re: 1968 Fender Bandmaster Help!

Did you check the speaker?

 

[tweed_slut]

Re: 1968 Fender Bandmaster Help!

Did you check the speaker?

actually yeah, I've got an eminence and a vintage utah speaker in the cab right now. Both are 8 ohms wired to 4 ohms. They're used but I got them from a friend of mine and he's pretty trustworthy. I still plan on replacing them both, so that might be it; I can't quite rule that out yet.

 

[Matt42]

Re: 1968 Fender Bandmaster Help!

I've got a 68 Bassman, and when I push it to 4-5 it also start breaking up. I do have to tweak the EQ a bit on it when it's pushing that hard, it does get a little muddy, but it's easy enough to dial out.

 

[Chickenwings]

Re: 1968 Fender Bandmaster Help!

could well be the 12ay7 in the phase inverter spot. thats the hardest working tube in the amp. I dont know much about 12ay7s but aside from the lower gain compared to 12ax7s, i know that 12at7s can handle roughly 10 times the voltage which is why they are often used in the PI slot. Just a thought.
The pot on a lot of silverface fender amps is hum balance, but that doesn't mean thats what yours does for sure. It could be bias too. Sorry im vague. My 69 twin has neither, but in my other fender its a hum balance. Ive also run across hum balance in a friend's sf bassman head.
Yeah ok, so basically im just guessing and probably not being much help, but might as well keep going...
Are you sure its the amp and not the speaker that is maxing out?
finally, my twin gets dirty from 5 upwards. My friend's princeton gets dirty at 4. I played an old deluxe reverb at a backline gig last week....that also got dirty above 4.

 

[jeremy]

Re: 1968 Fender Bandmaster Help!

get that 12ay7 out of the pi slot, when you crank up the amp you need to roll back the bass or its gonna get mushy. the bandmaster isnt really known for having more clean headroom.

are you running a 4 ohm load?

 

[Demanic]

Re: 1968 Fender Bandmaster Help!

If that pot is changing the glow of your power tubes, then it's a bias pot. In addition to all the other suggestions mentioned, have the bias checked. If you run the tubes cold you will get what is called "crossover distortion" which is not pleasant. Proper bias will give more headroom.

 

[jeremy]

Re: 1968 Fender Bandmaster Help!

over bias will cut headroom and cook the tubes faster too, you want it biased properly

 

[zenmindbeginner]

Re: 1968 Fender Bandmaster Help!

Bandmasters are nasty & dirty amplifiers... they offer up loads of brown sound. Whoever said they were clean, misspoke.

 

[tweed_slut]

Re: 1968 Fender Bandmaster Help!

Well damn, there goes my plan for a pedal platform amp oh well haha. I am running a 4 ohm load and the eminence is a 50 watt and the Utah is a 30 watt, so I don't think that's the problem either. So 12AT7's handle way higher plate voltages than 12AY7's? I think I have one lying around some where... That's the only thing I haven't tried!

 

[zzmoore]

Re: 1968 Fender Bandmaster Help!

Just some thoughts;
1. The orange caps Are Not what gets changed in a "cap job".
Most of them (B+) you cannot see, they are under the (dog house) cap cover on the other side of the chassis. I cannot over emphasize the importance of a caps of in an amp of that age. The Bias Cap and By-Pass caps are also Very Important to change/check
2. The bias Really Needs to be checked when you replace power tubes.
3. Try getting rid of (temporarily) that AY. You need to try an AX or AT in the phase inverter.
4. Make sure the speakers are good.
good luck.....those are wonderful amps

 

[Matt42]

Re: 1968 Fender Bandmaster Help!

Bandmasters are nasty & dirty amplifiers... they offer up loads of brown sound. Whoever said they were clean, misspoke.

I think people often associate vintage Fender's with a super clean sound without looking at the actual model of amp.

 

[zzmoore]

Re: 1968 Fender Bandmaster Help!

Bandmasters are nasty & dirty amplifiers... they offer up loads of brown sound. Whoever said they were clean, misspoke.

It is AB763.
The same circuit used in the :
Deluxe Reverb
Super Reverb
Twin Reverb
I have heard/worked on a lot of Bandmasters. I would not use Dirty or Nasty to describe them.
They are a fairly loud and clean amp.......:dunno:

 

[Matt42]

Re: 1968 Fender Bandmaster Help!

It is AB763.
The same circuit used in the :
Deluxe Reverb
Super Reverb
Twin Reverb
I have heard/worked on a lot of Bandmasters. I would not use Dirty or Nasty to describe them.
They are a fairly loud and clean amp.......:dunno:

They aren't the same circuit. It might be similar, but all of those amps use different tube sections and different sized transformers, both of which can affect the output and sound dramatically.

 

[Matt42]

Re: 1968 Fender Bandmaster Help!

Well damn, there goes my plan for a pedal platform amp oh well haha. I am running a 4 ohm load and the eminence is a 50 watt and the Utah is a 30 watt, so I don't think that's the problem either. So 12AT7's handle way higher plate voltages than 12AY7's? I think I have one lying around some where... That's the only thing I haven't tried!

I use a 68 Bassman as a pedal platform, and it does a wonderful job. The Bandmaster and Bassman are fairly similar, the Bandmaster just has a smaller transformer. You should be able to use it as a nice pedal platform if you can get the other issues figure out. (assuming there are other issues)

 

[philthis]

Re: 1968 Fender Bandmaster Help!

VanHalen has a bandmaster in his basement and said it has glorious tone when cranked ......I wouldnt trust the clean headroom thing. If I remember correctly they were known for going to a certain loudness and then almost everything after that was just adding distortion as you turn it up further with very little volume increase. I have a book somewhere that talks about all this for vintage amps.

 

[zzmoore]

Re: 1968 Fender Bandmaster Help!

They aren't the same circuit. It might be similar, but all of those amps use different tube sections and different sized transformers, both of which can affect the output and sound dramatically.

Yes they use a different tranny set... and a somewhat smaller OT (the band master). The Band has 440 VDC on the plates...the Super 460. They both have The Same B+ Filtering and phase inverter.
440 Volts and a pair of 6L6 makes for a fairly clean amp.
My point is, your description of an AB763 Band being "Nasty and Dirty" is not what a AB763 Bandmaster sounds like.
I have never heard one that I would put in that category.
If his amp is sounding like that....with no headroom, there is something amiss with the amp/speakers.

 

[zenmindbeginner]

Re: 1968 Fender Bandmaster Help!

Yes they use a different tranny set... and a somewhat smaller OT (the band master). The Band has 440 VDC on the plates...the Super 460. They both have The Same B+ Filtering and phase inverter.
440 Volts and a pair of 6L6 makes for a fairly clean amp.
My point is, your description of an AB763 Band being "Nasty and Dirty" is not what a AB763 Bandmaster sounds like.
I have never heard one that I would put in that category.
If his amp is sounding like that....with no headroom, there is something amiss with the amp/speakers.

I'm the one who described it as nasty and dirty, not Matt42.

You are describing a perfectly maintained Bandmaster or going back in time to when they were fairly new. My Bandmaster is exactly as described... starts to break up around 4.

Properly maintained Fender amps are very expensive... I am picking up my Super Reverb and Princeton Reverb from the repair guy today as a matter of fact. I'm $500 less wealthy.

Yes, I can't do my own maintenance like you can... that's pretty rare, most players just play and don't have the ability to tinker around with our amps.

Every vintage amp YOU own, might be operating at maximum efficiency, but most are not and get sent in for repair only when they finally catastrophically break down or start emitting smoke.

Will I take my bandmaster in to be repaired anytime soon? No, it operates smoothly and beautifully the way it does now. It's dirty and nasty as is every bandmaster or bassman from that era I've ever played was.

Could every one of those bandmasters and bassman I've played use some maintenance and could get louder and cleaner? Most likely yes.

When I talk about old Fender amps, I am talking about them as "aging objects in use" not as perfectly or well maintained collector's items