bf Bassman question: phase inverter

[justinbelshe]

Hey Fender gurus...

I've been overhauling my '67 Bassman to follow Andy Ruhl's AA864/AB165 hybrid recipe...

I've tried to make the phase inverter look like the AA864, but I've run into a snag...

See where I've put the question mark? There should be a jumper from that point to... where, exactly?



AB165 board layout:



AA864 board layout:



Let me know what you think, and if you spot anything else I might have missed...

[Tom Phillips]

That looks like point "X" to me. ("X in a box")
There are two of them on the parts board and they connect together. Fender did it with a wire on top of the board that was twisted with the "Y" wire and ran above the parts. It's the signal from the second channel pre-amp to the PI.
Tom

[justinbelshe]

I copied the jumpers from the AB165 circuit and it's obvious that I'm going to have to change... something.

[justinbelshe]

Okay, I just redid my jumpers, copying the AA864 layout.

What do you think, will this work?

[Tom Phillips]

All I can say is "Maybe". That last jumper was a connection that was missing but you are creating your own version of the wiring dress. That will introduce additional variables. I looked for a photo of the inside of an AA864 for you but I don't have one in my records.

Without reading through Andy Ruhl's article and trying to figure out what deviations / mods you are implementing I can't say much more.
Bottom line is that you need to trace out your wiring and verify that the final connections match the circuit you are trying to create.

[justinbelshe]

Just found this on eBay, guess it's important to twist these jumpers, eh?

[Tom Phillips]

I think the twist on those particular jumpers was just a convenient way to hold them together. They are not twisted for the same reason that you twist the AC heater wires to reduce the radiated field around them. Your method may work just fine. As I said, it is just another variable.

[justinbelshe]

Submitted for your perusal. I already know it won't work as it is, I'm just not sure why. I'm not even going to plug it in until I'm reasonably certain that I've got everything arranged correctly...



Here's the color code for wires coming out of the doghouse:



Here's the filter board:

[justinbelshe]

[justinbelshe]

Thanks to everyone for playing, but today's winner is JERRY SHAW! He wins my eternal gratification for sending me about 30 pages of notes, among which was this diagram:



I looked at it, and it suddenly made sense. I ran out to the shop and pulled that pair of 220K resistors and put in a .001uf cap. I plugged it in, biased the tubes, turned it on and it was DEAD QUIET! I was afraid that maybe it wasn't passing signal, there didn't seem to be any hiss. I plugged my "Test Probe" guitar in was blown away!

http://youtube.com/watch?v=GnS4KEFMQKI

(Yes, I know the guitar is out of tune...)

The normal channel seems to have more gain than the bass channel, but I only played through each one for a minute (it was 1:30 in the morning).

[Satamax]

Same post copy pasted, mate you're doing everything you can to save your energy! http://music-electronics-forum.com/s...8628#post28628 Same applies withe the layout, it all came back to me now, i've done it in the past, long time ago, and i didn't have a layout. You could have worked it out yourself withe the schemo and the notes. (i didn't even have the notes at the time, and i did the 864 conversion) . Well hope life is good for you, but please, get better at schemo reading.

[justinbelshe]

get better at schemo reading.

What a novel idea, I'll take that under advisement...

[Satamax]

I know i might sound harsh or else, but frankly, don't you think you could have done it by yourself? I admit i didn't remember how i did it before seeing Jerry's layout, and obviously mine was pure AA864, but still, i didn't have anything else than the two schemos at the time. And i wasn't the best of shemo readers either. And when i read "Thanks to everyone for playing, but today's winner is JERRY SHAW!" that sent me off, as if there's something for us to gain. Realy, i could have worked it out, but said to myself, why bother and waist time. Ok, i'm not always like this, and try to help from time to time; but i thought it had to be said. Nevermind my rant, i'm sure you're a good guy.

Bye.

Max.

[justinbelshe]

I know i might sound harsh or else, but frankly, don't you think you could have done it by yourself? I admit i didn't remember how i did it before seeing Jerry's layout, and obviously mine was pure AA864, but still, i didn't have anything else than the two schemos at the time. And i wasn't the best of shemo readers either. And when i read "Thanks to everyone for playing, but today's winner is JERRY SHAW!" that sent me off, as if there's something for us to gain. Realy, i could have worked it out, but said to myself, why bother and waist time. Ok, i'm not always like this, and try to help from time to time; but i thought it had to be said. Nevermind my rant, i'm sure you're a good guy.

Bye.

Max.

How are you with math, Max? You do well with it?

I have some learning disabilities. I have enough credits for a Masters degree, years and years of college education, but no degree because I couldn't fulfill the math requirement (and believe me, I've tried over and over.) I don't seek to make excuses here, but to explain myself. I look at schematics and all the lines start to jumble together. I'm better at it than I used to be, but it's still a challenge for me. I learn by doing.

You might think that I have no business messing about with amplifiers, yet I've refurbished and modified many, many amps for professional musicians. Those players are all happy, too.

Perhaps you're able to do whatever you set out to do. Congratulations, but you would do well to remember that not everyone is wired the same way.

As for "Jerry's the winner" and "thanks for playing"... that was a joke, my little attempt at humor. I'm sorry you didn't appreciate it.

And yes, I'm a great guy.

[soundmasterg]

Justin, the trick with schematics and learning how to read them is that you need to remember that they are a map. Just like if you are reading a map about how to get from one place to another in your car, you don't read the whole thing at once. You pick where you are, and then where you want to go, and you trace it out until you get there. Same with electrical schematics. You need to start at one point and follow that through the circuit instead of trying to read the whole thing at once. You don't need to be able to know any math to read a schematic either, except maybe how to convert from one value to another as far as the units are concerned. (uf to nf to pf for example)

One thing that really helped me was taking an amp that I had no schematic or layout for and drawing up a layout and schematic for myself from looking at it and comparing to existing amps like a Fender where you can get access to a layout and a schematic. It took forever and I had many errors the first time, but it helped me to do it immensly. Don't give up...just keep working at it and you'll get it.

Greg