Good news = I got a 71 Bandmaster for $40! (Clips added)

[infiniteposse]

Hi all-

Last night this amp popped up on CL and I couldn't resist. A dead silverface bandmaster for $40. I figured for parts alone it was well worth the 30 minute round-trip drive. It appears that the OT may be dead...

Just got it open. It appears Lee Jackson "worked" on the amp at some point. It has received his thorough attention. It now has an effects loop, push/pull Vol on channel 2, mid selector switch, reverb has been relocated and I'm going to guess has been changed significantly, extra 12ax7 installed and god only knows what else...

I guess my question would be, what do you gentlemen know about what was done to this amp and is it worth trying to make it function as-is? Allen makes a drop in transformer for $70 that should work perfectly for the OT if it is indeed blown. I was figuring maybe I get that working and then see how it sounds. My expectations are low:)

Any feedback appreciated.

[IMG:640:427]http://i18.photobucket.com/albums/b149/ ... mods18.jpg[/img]

[IMG:640:427]http://i18.photobucket.com/albums/b149/ ... mods20.jpg[/img]

[IMG:640:427]http://i18.photobucket.com/albums/b149/ ... mods16.jpg[/img]

[IMG:640:427]http://i18.photobucket.com/albums/b149/ ... mods14.jpg[/img]

[IMG:640:427]http://i18.photobucket.com/albums/b149/ ... mods10.jpg[/img]

[IMG:640:427]http://i18.photobucket.com/albums/b149/ ... mods12.jpg[/img]

[IMG:640:427]http://i18.photobucket.com/albums/b149/ ... nmods9.jpg[/img]

[IMG:640:427]http://i18.photobucket.com/albums/b149/ ... nmods4.jpg[/img]

[IMG:640:427]http://i18.photobucket.com/albums/b149/ ... nmods3.jpg[/img]

[IMG:640:427]http://i18.photobucket.com/albums/b149/ ... nmods2.jpg[/img]

[Phil_S]

$40? That's a steal! Even with problems it's dirt cheap. Congratulations.

Well, I'm the wrong guy to give any advice on how it might sound or what to do about a modded vintage amp. I just don't know enough.

Regarding your basic question about the OT, this is simple enough to test and there is more than one way to do it.

For starters, I'd pull the power tubes. This effectively disconnects the primary leads so you can clip onto the approprate tube pins to see the number ohms on the primary. You will need to lift the primary center tap from the B+ rail to get a proper reading. This simple continuity check will tell you if it is open (infinite)or if there is a short (0). I don't know this OT, but I'd expect something between 20 and 200 ohms.

Next, I'd do a continuity check on the secondary. You can go to the output jack (speaker unplugged) and meter for ohms on the secondary. This is usually a very small number, less than 1-2 ohms. If there is a chassis ground, it needs to be lifted so you just have the OT leads on the meter.

Provided there is continuity on both sides, I'd go for the low voltage test. Run a low AC voltage thorugh the secondary and measure what comes out the primary. From this, you can compute the turns ratio. This amp is supposed to have secondary impedance of 8 ohms. I don't know what the primary is supposed to be, but I'll guess at 4K and you can adjust your calculations as appropriate when you find the correct number. The turns ratio is the square root of the impedance ratio. So 4000/8=500. Sqrt (500) = ~22. So, I think you are looking for a turns ratio of about 22:1.

If you have no other source of low AC voltage, pull all the tubes and put jumpers from the filament supply to the OT secondary (no wires to ground!). 6.3VAC into the secondary should give you about 22x that coming out on the primary or about 140VAC. If you get anywhere close, I think your OT is probably OK.

Wait a bit. Someone might have another/better suggestion.

Good luck.

[jaysg]

The chassis is worth at least $40!

Any number of people would like you to document the circuit, even if it's just to jeer at Lee Jackson in the end. Not much is known about his mods.

[David Root]

Interesting find all right. Just curious but what makes you think it's a '71? The OT is clearly marked 606-616, which would be '76. Could be a replacement of course, what's the EIA code on the PT? Faceplate does look OK for early '70s though.

[FYL]

Just curious but what makes you think it's a '71? The OT is clearly marked 606-616, which would be '76. Could be a replacement of course, what's the EIA code on the PT? Faceplate does look OK for early '70s though.

MV version, wich shipped from '76 to '80 only. So this is probably a '76 or early '77 model.

[FYL]

Not much is known about his mods.

And that's better that way. Wonder who is the numero uno Fender amp butcher: Jackson, Torres or Weber? Their mods make a pre-Mesa Smith-modded Princeton the paragon of neat wiring...

[Cliff Schecht]

I know Lee, he's up at the Paia offices quite often. I'm not on Austin anymore but I
could email him those pics and get his thoughts if you are interested.[/url]

[David Root]

FYL, that's right, I missed the MV because the original position is not used. Need to slow down a bit! Probably a '76 as it was worked on in March '77, see the cap cover.

[infiniteposse]

Interesting find all right. Just curious but what makes you think it's a '71? The OT is clearly marked 606-616, which would be '76. Could be a replacement of course, what's the EIA code on the PT? Faceplate does look OK for early '70s though.

Thanks for all of the feedback all!

You are correct re: the date. I simply misread the tranny code. My back went out on Friday and the pain isn't helping me think straight:(

Re: actually asking Mr. Jackson about the mods, I would be very appreciative. I emailed the contact email on his page, but it's for distribution, not directly to him. I have no idea if he'd ever get that message...

Thanks again.

[FUCHSAUDIO]

Not much is known about his mods.

And that's better that way. Wonder who is the numero uno Fender amp butcher: Jackson, Torres or Weber? Their mods make a pre-Mesa Smith-modded Princeton the paragon of neat wiring...

Beat me to it.....

[Bob-I]

Personally I'd gut that thing and either rebuild it to an AB763 or build something else in the chassis. There may be some components you can use, but that rats nest looks like trouble.

I picked up a 70's Bassman that looked similar to this mess, with a blown PT. I put in a PT I had around and built a Trainwreck Rocket preamp with EL34 power, it's simply a great clean amp.

Good luck.

[Kazooman]

Geez.... It looks like someone got a new hot glue gun for Christmas and couldn't wait to try it out.

40 bucks!!! You have got to be kidding me! I troll several regional CL listings hoping for a find like this. You got a great bargain.

That said, if your OT is really toast it is no surprise given the mods that seem to have befallen this amp.

I agree with other posters. Document carefully with pics and schematics the current state of affairs and then rebuild the amp to original specs or something with a few time-proven mods. I fear that just spending the money for a new OT and throwing it into the rats nest you have may be asking for trouble.

[Structo]

That looks a hell of a lot better than the Torrez amps I've seen.

A lot of guys glue the orange drops down because of the radial mount.
Also helps microphonics of the cap.

Not saying that amp doesn't need help, just that I've seen worse.

[Cliff Schecht]

Yeah, who knows what has happened to that amp over the years. Even if Lee did touch it, we don't know that all of what we see is his handiwork. It could be a great sounding amp in its own right with just a bit of work and preventative maintenance.

I don't know what you guys have against Lee (or at least seem to) but he's always been pleasant to me and definitely knows his stuff. I honestly don't need to vouch for him, he's consulted for more manufacturers than any of you guys .

[FYL]

I don't know what you guys have against Lee (or at least seem to) but he's always been pleasant to me and definitely knows his stuff. I honestly don't need to vouch for him, he's consulted for more manufacturers than any of you guys .

Mr. Jackson could be a nice and knowledgeable person, but a butchered amp is a butchered amp.