Hello, I have a Antique Sound Lab AQ-1001DT that has a weak left channel. Right channel is perfectly fine. The sound coming out of the left is distorted, muffled, very weak. I recently noticed that if I turn off the amp the sound will be fine for that one second until the amp completely shuts down and sound fades away.
My knowledge with electronics repair is very limited please pardon any terminologies or parts names that I might get wrong. I have tried some simple test by checking the bias, switching tubes, speaker, speaker wires, RCA cables, cd players, L/R outputs from the cd players, all amp source inputs L/R and changed fuses with no luck.
I opened up the amp from below and did some visual checking. I did not notice any loose soldering, burned circuitry, leaking or bloated capacitors. I did however notice a few resistors that are darker in color than normal. I will post pictures below and add a YouTube video of how the left channel sounds like.
This is my first tube amp. I bought it from a friend for a very great price. I do like and have enjoyed it. I would like to see if this is a simple fix that I might be able to do and learn in the process. Thank you in advance!!
-Mike
VIDEO:
https://goo.gl/photos/5XF7937cdPWHQJfE9
main:
Left tubes:
Right tubes:
center plate:
My knowledge with electronics repair is very limited please pardon any terminologies or parts names that I might get wrong. I have tried some simple test by checking the bias, switching tubes, speaker, speaker wires, RCA cables, cd players, L/R outputs from the cd players, all amp source inputs L/R and changed fuses with no luck.
I opened up the amp from below and did some visual checking. I did not notice any loose soldering, burned circuitry, leaking or bloated capacitors. I did however notice a few resistors that are darker in color than normal. I will post pictures below and add a YouTube video of how the left channel sounds like.
This is my first tube amp. I bought it from a friend for a very great price. I do like and have enjoyed it. I would like to see if this is a simple fix that I might be able to do and learn in the process. Thank you in advance!!
-Mike
VIDEO:
https://goo.gl/photos/5XF7937cdPWHQJfE9
main:
An externally hosted image should be here but it was not working when we last tested it.
Left tubes:
An externally hosted image should be here but it was not working when we last tested it.
Right tubes:
An externally hosted image should be here but it was not working when we last tested it.
center plate:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Almost forgot about the resistors..
Overheated resistors???
Overheated resistors???
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Can you post the pictures here using the "Manage Attachments" feature of this site? I DO NOT sign-in to google. You have what sounds like a voltage problem in your amp. That left side could be biased to nearly cut-off. That could explain why it works for a second when it's turned off and the bias falls. Do you have a multimeter to take some measurements?
ASL images
Sorry for the Google images. I could not edit my first post since there is an expiration to do so.
@
VIDEO:
https://youtu.be/l4gS3K5z4CU
Sorry for the Google images. I could not edit my first post since there is an expiration to do so.
@
VIDEO:
https://youtu.be/l4gS3K5z4CU
Attachments
I only set the bias with the adjustment pots behind the kt88 tubes. I have multimeter, but have never checked the bias measurement internally.
aside from a faulty coupling cap, resistors that have become open,
you will be amazed to find resistors that had no signs of open,
a check with the dmm reveals them....
but make sure all caps are discharged before checking in circuit....
you will be amazed to find resistors that had no signs of open,
a check with the dmm reveals them....
but make sure all caps are discharged before checking in circuit....
I'm going to assume that the KT88s bias up correctly in the normal manor using the on-board meter. If so, this is what I would do. I would open her up and take voltage measurments with my multimeter starting with the output tubes and working back through the 12AU7s. Because you have one channel that's good, compare the readings against the good channel as you go. Measurments referenced to ground. This also assumes that you feel comfortable taking these measurments with the amp powered on. If not, get professional help.
KT88s bias voltage on pin 5 should be around negative 40 volts ±5V.
KT88s screen (pin 4) and plate (pin 5) around 475V ±20V
12AU7 driver/phase inverter plates (pins 1 and 6) around 260V
12AU7 amplifier plates (pins 6) around 165V and (pins 1) around 65V (?)
12AU7 amplifier cathodes (pins 8 and 3) 5 and 2 volts respectively.
All these values are from the basic AQ 1001 schematic below (less the IR board and other things) which the numbers are a little hard to see.
KT88s bias voltage on pin 5 should be around negative 40 volts ±5V.
KT88s screen (pin 4) and plate (pin 5) around 475V ±20V
12AU7 driver/phase inverter plates (pins 1 and 6) around 260V
12AU7 amplifier plates (pins 6) around 165V and (pins 1) around 65V (?)
12AU7 amplifier cathodes (pins 8 and 3) 5 and 2 volts respectively.
All these values are from the basic AQ 1001 schematic below (less the IR board and other things) which the numbers are a little hard to see.
Attachments
Last edited:
Same here. Google is a low-life semi-criminal organization that steals your personal information and sells it for their own profit.
Back to the main topic, those resistors that have darkened, have been overheated, due to excessive current some time in the past. They will need to be removed and have their values checked, one by one.
Sent from my phone. Please excuse any typpos.
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