Detailed pics of Maggie 196 input wiring needed

[Sumner2020]

Hello all I need a huge favor,
I'm struggling with a Maggie 196 SE amp. I'd appreciate if someone could either reply here or send me a message with a few high res pics of the input wiring with or without the balance pot wired in doesn't matter. What I'm looking for is which pins on the 12AX7 are jumpered. If they are jumped with the resistor from input or the .01 capacitor that goes to the output tubes. Basically I just need to see how the 12AX7 should be *correctly* connected.

Also, can I replace the can cap which is 40/30/10/20uf 450/450/450/25v with all 47uf 450v caps?

Very much appreciated!
Darin

 

[FlaCharlie]

Do a search one here for Magnavox 196 and you should get plenty of results including some detailed rebuild / mod info. I have a schematic for a 197 but no 196 so I can't say how they may differ. There should be a schematic online somewhere.

The cap changes should be fine but I wouldn't use a 450v cap to replace the 25v section. If it's a cathode bypass cap I'd suggest sticking close to the original specs, so maybe 22uf 25v or 35v.

 

[Sumner2020]

I've searched endlessly both here and google images. I've found several under chassis pics but not any that are high res enough that I can zoom in on the RCA inputs to the 12AX7. Or if the balance pot is still active then it would be from the RCA inputs to the balance pot to 12AX7. I have the schematic for the 196 but since I'm struggling with reading the schematic and how to correctly make these connections at the 12AX7 with the resistors in place a detailed picture would help me finish this thing.

Thanks

 

[FlaCharlie]

. . . a few high res pics of the input wiring with or without the balance pot wired in doesn't matter. What I'm looking for is which pins on the 12AX7 are jumpered. If they are jumped with the resistor from input or the .01 capacitor that goes to the output tubes. Basically I just need to see how the 12AX7 should be *correctly* connected.

I'm not sure what you mean by jumpered - perhaps the heater? Pins 4 and 5 of the 12AX7 are tied together and one of the heater wires connects there while the other heater wire goes to Pin 9. No balance pot involved. But it sounds like you might be talking about the inputs going to the grids of the 12AX7. It would be helpful if you could post your schematic.

On my 197 schematic there are three variations with suffix -00, -10, and -20. I have the -00 but none of the versions have a balance pot between the inputs and the 12AX7 grids. The cathodes share a bias resistor and bypass cap. On my -00 they are connected directly. The -01 and -02 versions have the cathodes of the 12AX7 connected to a balance pot and then to the shared resistor and bypass cap. But this might not be the same as in the 196 model, so it would be helpful if you would post your schematic. All versions of the 197 also have a balance pot connected to the grids of the 6BQ5s.

Unless you're just replacing one or two parts, you really need to learn how to read a schematic. Think of them like a road map. The lines (wires or component leads) are the roads and the various parts (resistors, capacitors, pots) are like towns along the road. If you follow a particular "road" you will, at some point, come to the "town" shown on the schematic. Actual distance between "towns" will vary considerably so forget about whether the lines between them are short or long on the schematic. If you follow the road, though, you will eventually find the town.

 

[jebbo]

Unless you're just replacing one or two parts, you really need to learn how to read a schematic. Think of them like a road map. The lines (wires or component leads) are the roads and the various parts (resistors, capacitors, pots) are like towns along the road. If you follow a particular "road" you will, at some point, come to the "town" shown on the schematic. Actual distance between "towns" will vary considerably so forget about whether the lines between them are short or long on the schematic. If you follow the road, though, you will eventually find the town.

That is an awesome analogy!

 

[Sumner2020]

Yes I do have a lot to learn when it comes to reading schematics. That much is for sure. I've been basically replacing caps and resistors as I go. It would be a wonderful thing to completely strip the chassis and rework it from the schematic. I believe I'll be able to do that someday. Just not today.

Here's the best image I could find, along with the schematic. It still isn't clear enough for me to see the actual connections. The magenta circle on the output tube pins shows the resistor that connects to one pin but also connects to the pin beside it. That's what my jumpered reference is. The yellow circle is a jumpered connection and that one is intact on my amp. The blue circles are the 12AX7 where the 01. cap the 47k resistor & the 220k resistor. Within those pin connections are the same jumpered connection. I'm sure by looking at the schematic it's easy to see. But for me, when reading the schematic, once I get to the tube connection I get the "deer in the headlights" look. I know I'll teach myself at some point but life is really getting in the way at the moment so I'm looking for the easy way out. At least until I get the time to properly learn how to read them without all the other distractions that are inhibiting my learning retention.

Hopefully I've made some sense.
Thanks
Darin

 

[FlaCharlie]

OK, I was able to download a readable schematic and I see the 196 does have a balance pot at the input. I'm still unclear as to what you mean by "jumpered" though.

Schematic shows (on each channel) a 100k resistor between the input and one side of the pot and a 47k going from that side of the pot to the grid of one of the 12AX7 sections. The wiper (center connection) of the pot goes to ground.

FWIW, the 197 just has a 47k between the input and the grid. No 100k or pot. So if you just want to eliminate the balance pot, that's the way to go. On mine, I installed a 100k stereo volume pot so I could connect a CD player directly to the amp without having to use a preamp. So, if you want to install a volume pot, the input is connected to one end, the other end goes to ground, and the wiper goes to the 47k which is connected to the grid of the 12AX7. The volume pot takes the place of the 100k resistor and balance pot on the 196 version. Radio Shack used to carry an inexpensive 100k stereo volume pot made by Alps. If there's still one nearby you might want to check to see if they still have them.

 

[FlaCharlie]

I see you uploaded stuff while I was writing. I'll take a look and compare it to the schematic.

 

[FlaCharlie]

Here's the best image I could find, along with the schematic. It still isn't clear enough for me to see the actual connections. The magenta circle on the output tube pins shows the resistor that connects to one pin but also connects to the pin beside it. That's what my jumpered reference is. The yellow circle is a jumpered connection and that one is intact on my amp. The blue circles are the 12AX7 where the 01. cap the 47k resistor & the 220k resistor. Within those pin connections are the same jumpered connection. I'm sure by looking at the schematic it's easy to see. But for me, when reading the schematic, once I get to the tube connection I get the "deer in the headlights" look. I know I'll teach myself at some point

Well, there's no time like the present and this is a pretty simple schematic.

I assume the pic is something you found online, not a pic of your amp, correct? I also assume that some of the parts are missing from your amp and that's why you can't just replace them one by one?

You talk about pins but you don't make reference to the pin numbers, which are shown on the schematic. In case you don't know how they are arranged, it's pretty simple. Both the 12AX7 and the 6BQ5 are 9 pin tubes. Looking from the bottom, you'll see a gap between pin 1 and pin 9. Starting from the gap move clockwise, the first pin you come to is pin 1 and so forth.

So, which pins of which tube are you wondering about?

 

[FlaCharlie]

Here are data sheets for the two tubes that list the pin connections. You can ignore all the data numbers, just look at the pin diagram. All the pins on the 12AX7 are used so the only two that should be jumpered are pins 4 and 5 which are the heater. Usually they're just bent over and soldered together.

http://tubedata.milbert.com/sheets/093/1/12AX7A.pdf
http://tubedata.milbert.com/sheets/093/6/6BQ5.pdf

 

[Sumner2020]

The amps at home and I'm not. It may be a day or so before I get time to sit down with the amp and computer and get the specific pin numbers I'm struggling with.

I really appreciate your patience. And I love that sig line. If you could see my basement (bachelor after 21 years of marriage) it is filled with speakers and receivers and amps and shells of what used to be all three. My oldest child lives with me and has his room downstairs. He mentions about once a month how cool it would be if the living room downstairs could actually BE a living room! I reply the same every time "There's a living room upstairs, how many you need?"

I'll reply back as soon as I can.
Thanks again
Darin

 

[Sumner2020]

I had some time to look this over tonight and post my ignorance. So here goes. I'm bypassing the balance pot. So in place of the 100k & 47k resistors I'll have. 470k resistor directly coming off my left and right channel inputs.
Pin 1 12AX7 has the .01 cap (C2) that connects to pin 1 of the EL84. Along with the .01 cap on pin 1 EL84 there is a 470K resistor (R7) to ground. One of those leads is also attached to pin 2. But which lead is it?

Going back to 12AX7 that same question applies. Pin 1 12AX7 has the .01 cap (C2) and the 220k resistor (R5) one of those leads continues on to pin 2 (grid) where my 470k resistor from input will also be attached. Which lead continues onto pin 2?

Thanks
Darn

 

[Sumner2020]

Why remove those resistors when all you need to do is swap in the 470K at the juction where the pot connected?

I followed other members directions from previous posts on how to bypass the balance pot.

 

[FlaCharlie]

I had some time to look this over tonight and post my ignorance. So here goes. I'm bypassing the balance pot. So in place of the 100k & 47k resistors I'll have. 470k resistor directly coming off my left and right channel inputs.
Pin 1 12AX7 has the .01 cap (C2) that connects to pin 1 of the EL84. Along with the .01 cap on pin 1 EL84 there is a 470K resistor (R7) to ground. One of those leads is also attached to pin 2. But which lead is it?

Don't have much time now but . . . as I said earlier, the 197 model has no balance pot and it just has a 47k (not 470k) between the input and Pin 2 (the grid) of the 12AX7. If you don't need a volume pot and want to remove the balance that's what I'd suggest. See my post above if you want to install a volume pot. Obviously, if you're using a preamp you don't need one. Are you using a preamp? Is that why you want to bypass the balance pot?

Again, I'd suggest you follow the schematic and think of it like a road map. Follow the road from Pin 1 of the 12AX7. There are two parts connected to Pin 1. They might be connected directly to the pin or they might be further away with a wire between them. One is a 220k resistor (R5) which connects to the 180v section of the power supply and the second is the .01 uf cap (C2) which connects to Pin 1 of the 6BQ5. The 470k (R7) goes to ground. It might be connected to Pin 1 or Pin 2 of the 6BQ5. Those pins are connected internally (inside the tube) so connecting to either is functionally the same. That's why it shows 1-2 on the schematic instead of just 1 or just 2.

Going back to 12AX7 that same question applies. Pin 1 12AX7 has the .01 cap (C2) and the 220k resistor (R5) one of those leads continues on to pin 2 (grid) where my 470k resistor from input will also be attached. Which lead continues onto pin 2?

Again, look at the schematic. There is no connection between Pin 1 (the plate) of the 12AX7 and Pin 2 of the 12AX7 (the grid). The only connection to Pin 2 is whatever connection you choose to make with the input.

 

[FlaCharlie]

....and they said the 47K grid stoppers should go? Those provide a different function than the balance pot. A fixed 470K in place of the pot won't make those redundant.

Hi - I suggested earlier that he might follow the model 197 schematic on the input since it's essentially the same amp. If so he would keep only the 47k grid stopper and eliminate the pot and the 100k.

If he wanted to duplicate the 196 version, you are correct. He could just put a 470k to ground from the junction of the 100k and the 47k on each input.

 

[Sumner2020]

Thank you both. I "think" I'm clear now. Here's a pic of what I think it should be.

Thanks again
Darin

 

[FlaCharlie]

Thank you both. I "think" I'm clear now. Here's a pic of what I think it should be.

Thanks again
Darin

No, 470k is too high for the grid stopper. My earlier suggestion was to use 47k in that position with no resistor going to ground. That's what the input is on the 197 model, which doesn't have a balance pot on the inputs.

Some Magnavox schematics do have a 470k to ground but it goes on the other side of the 47k - between the input and the 47k instead of after the 47k as your diagram shows. This would be the similar to your 196 schematic - again, take a look - with the difference being that you just eliminate the 100k. Either way should be fine.

So, you haven't explained why you want to eliminate the balance pot. Are you using a preamp with this that already has a volume and balance function?

 

[Sumner2020]

So, you haven't explained why you want to eliminate the balance pot. Are you using a preamp with this that already has a volume and balance function?

Yes I'm using a preamp.

So remove the 470k and replace it with a 47k and remove the 47k to ground also? Like the following.

 

[FlaCharlie]

Yes I'm using a preamp.

So remove the 470k and replace it with a 47k and remove the 47k to ground also? Like the following.

Yeah, that should work fine. It's the same as the input on the 197 model. Typically a grid stopper like this 47k is mounted right on the tube socket with as short a lead as possible rather than soldered to the input jack. While that's important for some tubes, it probably makes less difference with 12AX7s. Another option, since you already have the 470k resistors is to put them to ground from the input side of the 47k rather than the tube side as in your earlier diagram.

 

[Sumner2020]

Got it all wired last night. Very low volume output. I tried it direct from an iPad, Sansui AU-555A, Pioneer SA-600 and a PS Audio 4.5. Any ideas?