autotek 44 aka 7100bts problem with left channel

[eroc1313]

the right channel is great but left channel is crackling. the gain doesnt change the volume at all. when i turn the volume up on my radio i use for testing, the left channel cracks very loud and annoying. its ok when i turn the radio back down. the radio is the one i use to test amps and it works fine with other amps. its just the left channel of this old autotek. i moved the rca cables around and it isnt the cables.what could cause this? im kinda new to amp repair and im trying to get more knowledge.

[Perry Babin]

If the gain pot makes no difference on the noisy channel but works properly for the other channel, the pot is likely defective.

It's also possible that you have an open shield. The RCA shield should read ~0 ohms to the non-bridging speaker terminals.

[I Am An Idiot]

I think he is saying that the gain pot does not change the volume of the noise.

[mavric]

autotek xi? known for bad pots, fairly simple to fix. part # should be on the pot. parts express probally has it in stock.

[eroc1313]

i cleaned the pot with contact cleaner and moved it back and forth. i noticed it had a little catch in it and wasnt smooth.it was also at an angle. i tried to straighten it up and part of it broke off with the soldered legs on it. i then turned it and it moved very smoothly. what i gathered was that it was in a bind and was causing it to not conduct like its supposed to. i need a new pot. its the gain pot and has "820kx2" stamped on it and below that a J with a symbol and AU next to the J and symbol . i guess i can find one of these in the mouser electronics catalog and ill try to find out if i can find one.

[Perry Babin]

To prevent damaging the board, apply enough new solder to the 3 legs of each section of the pot so that you can lay the tip of the soldering iron across them and heat all 3 at once. Heat all 3 and when the solder is hot enough, the pot should pull free with very little force. Don't try to remove it until the solder is molten on all 3 legs. The vias in the board are easily pulled and if damaged, can make it difficult to get a new pot to work as it should.

[eroc1313]

i looked on the digi key website and i couldnt figure out which pot is which. the one i took out of the amp says B20k x2 . which tells me its a 2 way 20k pot. im not too familiar with the terminology on the pot specs on the digi key website. which pot should i replace it with? im not gonna try radio shack. we have a local electronics store but i dont know what to tell them when i call for the part.

[Perry Babin]

There are so many variables that you're unlikely to find a drop-in replacement unless you salvage one from another autotek (or similar) amp or preamp. If you can't find a replacement, you could move one of the other pots to the gain position. You may have to replace the missing pot with resistors (I'm not sure how they're being used in this amp). You could also replace the gain pot with resistors if you want to retain the bass/treble function.

[eroc1313]

ive called around my area and cant find a replacement. does anyone know which one to order from mouser or another mail order source. has anyone replaced one of the gain pots on one of these amps.

[1moreamp]

Autotek has them and they want $18.00 each for them + shipping. Call Autotek. They use to be located in Burlingame CA. Near the Air port . (San Francisco air port). Been there a few times in my past life and I might even have one or two myself left over from old stock. Does yours say B20K on it ?
Not cheap but its a drop in replacement from them....

I think they moved back east somewhere. Its been 5 years since i bought the last 4 pots I got off them, but I'm getting a nag that they are back east now.. Sorry for the mis-direction of their parts support ops...