60's Silverface Bandmaster ID

[Dan Lawrence]

I'm having some issues with my 60's Bandmaster silverface (Reverb). Not sure exactly what year, but I've searched dozens of schemes related to it and none seem to match exactly. Wondering if someone has a clue which model I have.

The amp's faceplate is a bit worn and missing some lettering, but has the designation TF? 5005 D (the d is questionable), has a GZ34 rectifier, two 6l6GC's for power and a total of six preamp tubes: 12AT7, 12AX7, 7025, 12AT7, 7025, 7025, in that order. The stamped serial number is 39324 and has a printed stamp of C189 on the chassis.

The scheme I found w/ closest tube set says "Vibroverb amp AB 763", but it has one more 7025 than mine. The Bandmaster Reverb Amp AA768 is also very close, but has the wrong rectifier and (I think) an extra 7025, unless the split tube is listed twice on the scheme.

Any leads would help. I have a recording session being held up on this puppy, and I'd like to start with the basics before I take it to a tech, which are REALLY hard to find where I live.

thanks

[soundguruman]

I'm having some issues with my 60's Bandmaster silverface (Reverb). Not sure exactly what year, but I've searched dozens of schemes related to it and none seem to match exactly. Wondering if someone has a clue which model I have.

The amp's faceplate is a bit worn and missing some lettering, but has the designation TF? 5005 D (the d is questionable), has a GZ34 rectifier, two 6l6GC's for power and a total of six preamp tubes: 12AT7, 12AX7, 7025, 12AT7, 7025, 7025, in that order. The stamped serial number is 39324 and has a printed stamp of C189 on the chassis.

The scheme I found w/ closest tube set says "Vibroverb amp AB 763", but it has one more 7025 than mine. The Bandmaster Reverb Amp AA768 is also very close, but has the wrong rectifier and (I think) an extra 7025, unless the split tube is listed twice on the scheme.

Any leads would help. I have a recording session being held up on this puppy, and I'd like to start with the basics before I take it to a tech, which are REALLY hard to find where I live.

thanks

The rectifier can vary, It may not be GZ34, but others will work instead.
7025 and 12AX7 are the same tube. 7025 is a low noise 12AX7, but interchangeable.
but go ahead and describe what the issue is...

[Justin Thomas]

Dan,

Schem of AA768 has a GZ34 & 2 12AT7s.

Fender Amp Heaven Schematics - Tweed Blackface Brownface Silverface Bassman Champ Deluxe Princeton Super Vibroverb Reissue

Sorry if link doesn't work, but I got the schemo @ Schematic Heaven.

Does it have the aluminum "drip edge" trim around the front of the cab? Does it have the fixed/cathode bias on the power tubes? That would be an easy way to confirm, as the "mixed bias" & trim was used on the ---68 series & didn't last long, only until early 69, maybe a tiny bit later. The faceplate should say "TFL5005D," but I only see that designation on the AA1069. Regarding the extra 12ax7 in the schematic, one tube (V4, I think) is used in two different parts of the circuit, so it's drawn on the schemo in two places. As an aside, Fenders were ALWAYS in a state of evolution. You could have a "transition" model that's between AA768 & AA1069. Someone could have put a GZ34 in an AA1069. I'd check for those cathode resistors to decide which circuit I had. If yes, I'd use the 68, if not, 1069. Also check the B+ voltages - the AA1069 should be about 40V higher. My vote? Transition model. Hope it helps,

Justin

[mort]

post the numbers from the transformers. that will take you to the most probable year.

Sounds like the recto tube has just been swapped with another. The rest of the tubes are standard and correct for that amp.


Check this layout against your amp. It's probably the right one.

[Dan Lawrence]

Thanks all y'all for the input. At least its clear why its so UNCLEAR ... OK , a few more detailed answers.

The tube rundown I listed is exactly what is posted on the old fender factory sticker on the inside. So GZ34 was the og recti ... wondering if the 5U4 is swappable ... but that's a tangent.

Justin, thanks for that link. Didn't see it on Google. It worked fine. That scheme does indeed have that 5005 number on it, but is written with the 5U4 recti, though this was clearly designed with the GZ from the getgo. Don't have the experience to know if it doesn't make any difference. I'll search that site some more. It was a great lead.

I had been realizing after writing that the 12AX7 and 7025's are considered totally swappable, and yet had to wonder why Fender would have chosen to use a mixture of both.

Yes, I do believe the amp has the aluminum drip edge of which you speak around the grill cloth. Sure likes one to me.

AS for the tranny serial numbers, Mort, F022798 is the first of the power tranny numbers followed by 606903. As for the other two, don't remember which is which (obviously, I'm not a tech, and only learned the basics of the internals) ... but the next largest is numbered 022848 followed by -606-9-08. The smaller tranny is 022699, followed by -606-9-02. The really little one, which I think is for the reverb, is numbered 022921 -606-9-03.

As for checking the B+ voltage I must admit I've forgotten where to check that.

So, Soundguruman, thanks for asking about the issues. I'll run by 'em best as I can.:

I got the amp ten years ago, and it had supposedly just been serviced by a "qualified tech." That could have been the only guy in the store with a screwdriver, for all I know. Cuz it worked fine for a few hours of playing it, be began to develop intermittant spitting and hissing. I did alot of moving since then, and rarely played through it. Pulled it out last summer, and remembered exactly why I'd bought it. Used it as the go-to amp for a weekend festival where I worked sound, and everyone who played through it loved it. Didn't seem to have to many issues then, as I recall. But perhaps by the end of the gig, or at least by the time I got it home, that intermittent thing came back.

Then it got more consistent just as I began this recording project, and at one point, the reverb went out all together. Lately I've only been using the normal channel, but that developed enough of an audible hiss to nuke some otherwise good tracks.

I do have a tube tester, and all tubes seemed to check out at about 80 percent good.

As for the condition, I've opened it up and pulled the chassis since my first post, because I noticed the pins of the 12AX7 had a fair amount of corrosion. I cleaned them, but need to get some De-oxit to properly due the socket. (I've dissapated all the latent voltage) None of the other sockets or parts of the amp have any corrosion at all, and there is no sign anything was spilled in it. The particular 12AT7 is a tube (right next to the reverb tranny) which ties tabs of pin sockets 3 and 8 together w/ just a solder bead. and that point had the worst corrosion on the inside of the chassis. Most of the rest was on the tube side (outside)

I noticed one other thing that seemed strange to me, but it may mean nothing. While checking the voltage on pin sockets to varify I drained everything, I noticed that all the preamp tubes had the same leftover voltage reading on pins 4 and 9 (about 6 volts when I first checked), all EXCEPT the 12AX7 socket, which always read half the voltage on pin 4 socket, but pin 9 socket had the same as all the other sockets points w/voltage. Could this be a sign that one of the component values leading to that socket has been compromised?

I will also confess that I realize caps can come and go in there performance, only to re-emerge some time later, then seem to miraculously heal themselves for a time, then go out again just when you thought you were in the clear. I 've resisted finding competent help until I've eliminated all other possibilities.

I should add that I've done a visual inspection, with no signs of caps w/ busted guts, cold solder joints, or breaks. The wires coming out of the output tranny look a little greasy. I did see one two-prong termination lug ground to the chassis, but w/o any wires connected to it. Probably means nothing. I see no wires to go there.

Lastly, I am wondering about Ext speaker jack. I could seem to get any sound out of it. I suspected that it might be wired for one jack or the other, not "either or both", but didn't get any sound out of it w/ or w/o the normal speaker jack plugged.

Sure love this puppy. Currently using it to drive an Eden 2x10 for an Alembic bass for a fast country swing tune. It sound really good when it's not acting up.

Thats all the info I can think to add for now. I don't dare hope that a little De-ox and a scrub will solve all my probs, but ??? I'll let y'all know. Where does one buy De-oxit. Radio Shack?

Thanks again to all.

Dan

[Justin Thomas]

Hey Dan,

Your amp is an early to mid 69. Don't use the tube chart to figure out what circuit the amp is. Fender was notorious for not wasting anything, and since yours straddles the fence between two circuits, it's even more "important" to use power supply voltages and whether or not it's got the cathode resistors on the 6L6's to know which schematic to use. As far as swapping rectifier tubes, other more experienced guys will have to say.

Back in the day, the 7025 was a low-noise tube compared to a "regular" 12AX7. So they specified 7025s in the actual preamp stages and 12AX7s in the "function" stages. In 1969 it made a difference, not so much any more.

Ten years in storage, effectively, can take a toll - resistors drift, caps dry up... regarding the speaker jacks, you have to have a speaker plugged into the main jack to get sound; if not, any signal is grounded out. It's supposed to help protect the OT in case you forget to plug in a speaker cab. Personally, I don't test that theory...

[Dan Lawrence]

Justin, I just wanted to say thanks again. Come to think of it, "69 sounds familiar (the used tag at the music store). I did some tinkering and cleaned up the corrosion on the one tube, and I got tons of tonal and s/n ratio improvement. I did figure that out about the jack, but thanks for mentioning it. I still can't recover the reverb though, and the tube which I suspect is primarily responsible for it makes a lot of noise when I tap it lightly. All other tubes seems pretty quiet on the tap test. So I'll check the circuits on the opposite side of that tube.

Thanks again to all

dd