• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Balance pot on magnavox amp

hogdaddy

hogdaddy

AK Subscriber
Subscriber
I have a couple questions regarding the balance pot on this amp.

"Does your amp have a balance pot? If not, it needs a pair of 390 Ohm resistors to sub for that (some versions had the pot in the amp, some in the tuner)."

Mine has the balance pot in the Tuner well except its not marked balance see pic. It says meter zero. I assume this is it?

If this is the balance pot would it be better to use than the resistors?
Also, it will fill that empty hole in my chasis where the balance pot would go except its missing a knob to turn it with.
 

Attachments

  • 002.jpg
    002.jpg
    128.8 KB · Views: 80
  • 001.jpg
    001.jpg
    109.3 KB · Views: 58
Last edited:
Register to hide this ad
If your tuner has an S-meter, that pot is most likely used to set the s meter needle to rest at zero, w/ no antenna or signal present. The manual might give specific instructions.

That other pot on the amp is probably just adjusted w/ a small flat bladed screwdriver. No need for a knob, I suspect.
 
Elrick said:
If your tuner has an S-meter, that pot is most likely used to set the s meter needle to rest at zero, w/ no antenna or signal present. The manual might give specific instructions.

That other pot on the amp is probably just adjusted w/ a small flat bladed screwdriver. No need for a knob, I suspect.
Click to expand...

Its the same pot on the tuner just 2 different views. It is the S-meter I see now. Thanks!

The only pot on my amp is Hum pot.
 
The balance control is probably on the front panel, maybe a concentric deal behind another control.
 
gadget73 said:
The balance control is probably on the front panel, maybe a concentric deal behind another control.
Click to expand...

I don't see it on front panel unless its behind one these :scratch2:

This is a pic of diagram that was inside console.

I am somewhat confused...If my amp does not have a balance pot on the amp chassis then I need the two 390ohm resistors or I don't?
 

Attachments

  • 003.jpg
    003.jpg
    56.3 KB · Views: 54
  • 22.jpg
    22.jpg
    72.2 KB · Views: 53
Last edited:
The balance pot is mounted to the back of the bass control. To adjust it you remove the bass knob and insert a flat jewelers screwdriver into the shaft and rotate.

Yes, it is a crazy system.

You only need the 390 ohm resistors if you plan on running the power amp without the tuner attached. If you do use the tuner there's no need for the balancing resistors.
The way I recently solved this on my 8802 was to gently pry the balance pot off the back of the bass control and then remount it on the power amp deck in the spot already marked ........... balance. It will fit there with no mods to the chassis or the pot. The wiring is very straightforward but some knowledge of the Negative Feedback Circuit, upon which this balance scheme is built, is required. Or the other way to look at it, once you figure this out you will know all about Neg Fdbk!
The nice thing about the pot being relocated to the power amp is that now the balance control is still functional in both the standalone and with tuner modes.

RWood
 
Last edited:
RWood said:
The balance pot is mounted to the back of the bass control. To adjust it you remove the bass knob and insert a flat jewelers screwdriver into the shaft and rotate.

Yes, it is a crazy system.

You only need the 390 ohm resistors if you plan on running the power amp without the tuner attached. If you do use the tuner there's no need for the balancing resistors.
The way I recently solved this on my 8802 was to gently pry the balance pot off the back of the bass control and then remount it on the power amp deck in the spot already marked ........... balance. It will fit there with no mods to the chassis or the pot. The wiring is very straightforward but some knowledge of the Negative Feedback Circuit, upon which this balance scheme is built, is required. Or the other way to look at it, once you figure this out you will know all about Neg Fdbk!
The nice thing about the pot being relocated to the power amp is that now the balance control is still functional in both the standalone and with tuner modes.

RWood
Click to expand...

OK I removed the pot like you said but there was no attachment tabs on it so I attached this from the bass pot on tuner (I am making a stand alone amp).
It works the same as before with a screwdriver.

Lots of info on NFC'S when I searched and it seems that this is a desireable feature in an amp.

I just hope I can figure out how to make it work on this amp looking at other similar amps and trying read schematics of which I sux at but slowly getting better.

I also installed the binding post for the speakers earlier and I need to polish the chassis up.
 

Attachments

  • 001.jpg
    001.jpg
    88.7 KB · Views: 55
Last edited:
always thought that was a really kooky scheme to adjust balance. Most systems do it by adjusting signal input to the amp. This one does it by adjusting the gain of the amplifier, which can also change the frequency response due to how its done. Kind of dumb really. I suppose they had their reasons, but I don't know what they are.
 
Hogdaddy - it looks like you moved the entire bass pot + balance pot over to the power amp. What I was talking about was removing the balance pot from the back of the bass pot. It is held in by the two tabs that will now secure it to the power amp chassis. I used a putty knife to gently pry the balance pot away from the bass pot. Then I straightened the tabs and inserted it into the 8802 chassis and bent the tabs over to secure it.

Of course you are welcome to keep yours as is, but if you plan on using the preamp/tuner, you will not be able to adjust the bass response. But if you want to do as I did you still can.

On last thing, the balance pot on mine needed several rounds of cleaning before it would work well. As quirky as this balance scheme is, it is not half bad at fine tuning the left-to-right. It is only when it is turned to the extremes that the volume jumps on that particular channel and forces you to readjust the Volume as well. But for me, when I was running bench speakers, it was fairly effective for me with minor adjustments not far off the center.

RWood
 
gadget73 said:
always thought that was a really kooky scheme to adjust balance. Most systems do it by adjusting signal input to the amp. This one does it by adjusting the gain of the amplifier, which can also change the frequency response due to how its done. Kind of dumb really. I suppose they had their reasons, but I don't know what they are.
Click to expand...

So IYHO would you use the balance pot or replace it with the 2 resistors having no adjustment?
 
RWood said:
Hogdaddy - it looks like you moved the entire bass pot + balance pot over to the power amp. What I was talking about was removing the balance pot from the back of the bass pot. It is held in by the two tabs that will now secure it to the power amp chassis. I used a putty knife to gently pry the balance pot away from the bass pot. Then I straightened the tabs and inserted it into the 8802 chassis and bent the tabs over to secure it.

Of course you are welcome to keep yours as is, but if you plan on using the preamp/tuner, you will not be able to adjust the bass response. But if you want to do as I did you still can.

On last thing, the balance pot on mine needed several rounds of cleaning before it would work well. As quirky as this balance scheme is, it is not half bad at fine tuning the left-to-right. It is only when it is turned to the extremes that the volume jumps on that particular channel and forces you to readjust the Volume as well. But for me, when I was running bench speakers, it was fairly effective for me with minor adjustments not far off the center.

RWood
Click to expand...

I removed one attaching piece from the bass pot only...the threaded piece and attached it to the Bal. pot.
My Bal. pot had no tabs on it to attach it on the chassis.

I metered the Bal pot and it appears to work fine.
 
Last edited:
hogdaddy said:
So IYHO would you use the balance pot or replace it with the 2 resistors having no adjustment?
Click to expand...

well, functionally it doesn't matter a lot if you have fixed resistors vs the balance pot set in the center. Electrically speaking, its the same thing. Fixed resistors might be quieter than a 50 year old pot though. If you have the pot mounted and wired, run with it.

I just wouldn't have designed the amplifier with that particular balance scheme to begin with if it were up to me. I'm sure they had a reason for it but I don't claim to know what it was.
 
gadget73 said:
well, functionally it doesn't matter a lot if you have fixed resistors vs the balance pot set in the center. Electrically speaking, its the same thing. Fixed resistors might be quieter than a 50 year old pot though. If you have the pot mounted and wired, run with it.

I just wouldn't have designed the amplifier with that particular balance scheme to begin with if it were up to me. I'm sure they had a reason for it but I don't claim to know what it was.
Click to expand...

You make a good case for not using the pot and I haven't wired it up yet.
 
6DZ7 said:
The balance pot is there for a good reason. The true balance between the channels is never found exactly at the center of the pot. If it were that easy they would have saved themselves the cost of a pot and just used two resistors in the circuit. The pot is on the 9302 chassis so that a technician can makw the best adjustment and not the consumer. It's then used when repairs or tube changes are done. If the pot works, keep it. Or find the values on each side of the center that give the best balance then try to find the exact fixed resistors to use.

Have fun,

6
Click to expand...

This makes good sense also :scratch2:.
TBH the 50 year old pot (I disassembled it and re-assembled) was in surprisingly nice condition.
I guess it was not used much in the first place.

If I can figure out how to wire it easy enough I just may use it and could if desired remove it later .

I am awaiting caps & resistors but installed this switch after filing the hole slightly bigger.

I am gonna use a Mundorf dual 50/50 cap w/ clamp to fill the multi filter cap hole and put the other filter and cathode caps underneath chassis.

Here's the IEC plug installed also. Lots hand filing.
 

Attachments

  • 003.jpg
    003.jpg
    82.7 KB · Views: 20
  • 004.jpg
    004.jpg
    106.6 KB · Views: 23
  • 005.jpg
    005.jpg
    83.1 KB · Views: 18
Last edited:
6DZ7 said:
The balance pot is there for a good reason. The true balance between the channels is never found exactly at the center of the pot. If it were that easy they would have saved themselves the cost of a pot and just used two resistors in the circuit. The pot is on the 9302 chassis so that a technician can makw the best adjustment and not the consumer. It's then used when repairs or tube changes are done. If the pot works, keep it. Or find the values on each side of the center that give the best balance then try to find the exact fixed resistors to use.

Have fun,

6
Click to expand...

I understand the point of having a balance pot, I just don't know why they implemented it in this particular manner. Monkeying with the feedback loop in order to alter the gain of the channel seems like a dodgey way of doing things. Most everything else just shunted some input signal to ground and let the gain of the stages be fixed at whatever it was.
 
You must log in or register to reply here.
Back
Top Bottom