Need suggestions for Fender Blackface clone repair

[mresistor]

12AU7's kind of get a bum rap - but they are good for reverb driver tubes ,,..

[eleventeen]

No argument, but after you take apart your first CONN (and most other) organ and have 36 of them, I think you have the application covered.


If you find a Schober organ for free or close, it is my strong suspicion that those use 12AX7 like most other organs use 12AU7.


A Hammond S-6 chord organ has I think ten 12AU7 and 2 12AX7 and 3 qty 12BH7 which are useful in some cases. There's one for free next town over and it's at least not a toneweeel organ so I would not feel bad dismantling it. Still, although they (used organs of various types) are unquestionably the BEST source of used parts especially tubes and/or complete working amplifier chassis you will find in 2016, I kind of don't like taking apart working organs. They also generate a tremendous amount of crud you have to haul to a dump.

[Paul1453]

eleventeen is one of my junk gear guru heros.   

I try to buy cheap junk tube gear and make great guitar amps from the parts.

PTs and OTs are the most critical parts of a tube amplifier.

I now understand that many tube junk PTs just aren't up to the job of many guitar amp circuits.

You might be able to use an oscope PT on a low voltage (+250 - +275V) low current (less than 80mA) circuit.
So there is still hope to put your PT to good use on one of those circuits.
Some other low voltage 6V6/6AQ5 circuits might fit the bill.   

Trying to power a big bottle/bigger wattage amp on a PT that isn't up to the job will leave you. 

[smackoj]

"can't wish them to have good parts in them"  amen eleventeen. exactly what the doctor tells me nowadays!

here is the pics you asked for SL. I am sure I am using the right spkr jack FYI. 

thanks mucho amigos.

[HotBluePlates]

... here is the pics you asked for SL. I am sure I am using the right spkr jack FYI.  ...

Does this mean you're plugging the speaker into the jack furthest from the power tubes (as Sluckey showed in his pic)?

The jack which has the shorting switch wired is the one away from the power tubes. If you did not use that one, you will get the extremely weak, distorted sound you're describing, because the speaker output would be mostly shorted to ground.

[smackoj]

I am using the spkr jack closest to the power tubes!  I will try the other jack and report back.... could it be something this simple?

[HotBluePlates]

I am using the spkr jack closest to the power tubes!  I will try the other jack and report back.... could it be something this simple?

Yes.

One of the jacks has a shorting switch (a la Fender's "Ext Speaker" jack). If you plug your speaker into the jack without the shorting jack, the unused jack is shorting most-all of the speaker output to ground.

This happens to folks all the time who copy a Fender layout, but don't realize there is a correct jack to use if only 1 of the 2 jacks have an actual speaker connected.

[mresistor]

Pardon me but isn't the shorting jack (12A) usually closest to the power tubes?  And isn't the main jack the one that is shorted? Why is it different on this amp?

[sluckey]

Pardon me but isn't the shorting jack (12A) usually closest to the power tubes?

Maybe with some amps. I've never seen any standard for this, nor any reason for a standard. As long as the jacks are labeled why would you need a standard?

And isn't the main jack the one that is shorted?

yes

Why is it different on this amp?

It's not different. But the jacks are not labeled on the chassis and that can make you think it doesn't matter if you don't know how to look at the wiring to determine which is which.

What I don't understand is this was brought up 6 days ago and he's just now getting around to saying he's connected to the wrong jack. Should only take 5 seconds to just move the plug to the correct jack. I even posted a pic. 

[mresistor]

I took one of his pics and blew it up and the jack closest to the power tubes (left as viewed from the back)  is a shorting jack type 12A. It is possible that when used it could still be shorting somehow. I blew up a view that shows the other jack (right as viewed from the rear) and it is hard to tell if it is a shorting jack type 12A or not. It is possible that he has 2 type 12A shorting jacks installed. And if that is the case then the OT is going to be shunted no matter what jack he uses, and would only work with two speaker plugs inserted into both jacks. 

[sluckey]

Both of the jacks are 12A switching jacks, but the one I labeled as MAIN is the only jack that has a jumper between the switch and ground. The jack closer to the output tubes has nothing wired to the switch lug so it may as well be a type 12. Look at the pic in reply #30. You can clearly see this.

[mresistor]

Oh Yeah!  I see that in pic 30. Both are 12A but only the one farthest away from power tubes is shorting. Thanks Sluckey.

[smackoj]

sorry for not writing back sooner friends. I have had to put the amp away for a week because I have my 2 toddler grand children at the condo and couldn't work on it. they go back to Nebraska on Sat. so I will try plugging it in then. I'm sorry I frustrate you SL. I absolutely do not question your knowledge senor.

jack d

[sluckey]

no frustration here.

[smackoj]

OK, after many a day away from the forum I can gladly report that using the 'correct' spkr jack does make the amp work with much more volume. However the hum and somewhat distorted guitar notes make it unusable in it's present state.

thanks amigos,  jack d