Hello, all.
I have lurked for some time and learned much, but now have a question (which I have not been able to find answered elsewhere).
What is the procedure for setting the bias on the GFA-565?
I know that with "no input" (I presume this means inputs shorted), you adjust for 24mV +/-1 after 10 minutes, then run for 10 min. at 80W output (I assume the input used to obtain this output isn't critical, though a sine wave might be simpler to manage) and readjust for 24mV (I assume with "no input" for the actual measurement).
What I don't know is which points to test at (apparently it's 301 and 401 for the 585 - are the 565 points labeled the same?), and how many locations to test (I believe it's one for the whole unit, controlled by the pot on the input board, but want to be sure it's not one for each bank of transistors, or some other grouping).
Also, how critical is the 80W figure? Can one ballpark it, or must one confirm it precisely? I'm not a tech and have only good meters (analog and electronic), a freq. generator, and non-latching, single-trace oscilloscopes.
Finally, any advice on obtaining a good schematic? I've gotten the Adcom manual from Adcom (Twice - they seem to send it in response to any question), but the scan is low-res, and some of the labels are illegible.
For those interested (go to next post, or fall into deep stupor here), my story is thus:
I've had a pair of very underutilized Infinity QLS-1's for about 15 years, which I bought at a flea market, along with a lot of other gear, over fifteen years ago. Yes, the price was right.
I ran them for many years with the GFA-1 (low side) and GAS Grandson (high side) that the previous owner had used, in a succession of rooms that were far too small to really hear them.
About two years ago, I spotted a set of four GFA-565's on e-Bay, saw that they were located within blocks of my house, and came to terms with the owner which saved both of us from the horrors of shipping. I ran four separate 20A AC lines and breakers, and used the amps happily but occasionally, as I had mostly moved to another state by then, and was just clearing out the house prior to selling.
Upon arrival at my new home, room arrangements prevented me from setting up right away, and I decided to test DC offset "for the heck of it."
Although I don't have the numbers in front of me, I found three amps with offsets between 3 and 20mV, and one around 25V. Hmmm. That would be the one that always thumped.
Upon disassembly, one had Elna caps, and a mess on the input board and three did not.
I have since bought enough good quality high-temp caps to replace all the electrolytics in all four machines (less than twenty bucks), as well as four OP97's ($2.50 each) and sockets. I was shocked to find that wire-wrap tools start at $30 (and then only for either On or Off, but not both ways) I swear they were only a few bucks the last time I saw them in Byte magazine. I have no intention of replacing any conductors with solid gold spun from Bavarian maidens' hair, or anything else with anything that costs more per gram than Bolivia's finest.
Anyway - I'm primed to rip that bad boy apart, wash up that board in Simple Green (though I wonder about such other solvents as methanol, or industrial concrete-cleaning detergents), replace parts and fire her up. It's my nature, though, to want to confirm such things as the bias adjustment when I mess around with all that stuff, so I haven't started rolling yet.
Oh - and my new venue for the QLS-1's will be our new business location - a 75 by 25 foot space in an old mill with 12 foot ceilings. Finally, a room that's big enough!
Thanks in advance for your help!
- Eric
I have lurked for some time and learned much, but now have a question (which I have not been able to find answered elsewhere).
What is the procedure for setting the bias on the GFA-565?
I know that with "no input" (I presume this means inputs shorted), you adjust for 24mV +/-1 after 10 minutes, then run for 10 min. at 80W output (I assume the input used to obtain this output isn't critical, though a sine wave might be simpler to manage) and readjust for 24mV (I assume with "no input" for the actual measurement).
What I don't know is which points to test at (apparently it's 301 and 401 for the 585 - are the 565 points labeled the same?), and how many locations to test (I believe it's one for the whole unit, controlled by the pot on the input board, but want to be sure it's not one for each bank of transistors, or some other grouping).
Also, how critical is the 80W figure? Can one ballpark it, or must one confirm it precisely? I'm not a tech and have only good meters (analog and electronic), a freq. generator, and non-latching, single-trace oscilloscopes.
Finally, any advice on obtaining a good schematic? I've gotten the Adcom manual from Adcom (Twice - they seem to send it in response to any question), but the scan is low-res, and some of the labels are illegible.
For those interested (go to next post, or fall into deep stupor here), my story is thus:
I've had a pair of very underutilized Infinity QLS-1's for about 15 years, which I bought at a flea market, along with a lot of other gear, over fifteen years ago. Yes, the price was right.
I ran them for many years with the GFA-1 (low side) and GAS Grandson (high side) that the previous owner had used, in a succession of rooms that were far too small to really hear them.
About two years ago, I spotted a set of four GFA-565's on e-Bay, saw that they were located within blocks of my house, and came to terms with the owner which saved both of us from the horrors of shipping. I ran four separate 20A AC lines and breakers, and used the amps happily but occasionally, as I had mostly moved to another state by then, and was just clearing out the house prior to selling.
Upon arrival at my new home, room arrangements prevented me from setting up right away, and I decided to test DC offset "for the heck of it."
Although I don't have the numbers in front of me, I found three amps with offsets between 3 and 20mV, and one around 25V. Hmmm. That would be the one that always thumped.
Upon disassembly, one had Elna caps, and a mess on the input board and three did not.
I have since bought enough good quality high-temp caps to replace all the electrolytics in all four machines (less than twenty bucks), as well as four OP97's ($2.50 each) and sockets. I was shocked to find that wire-wrap tools start at $30 (and then only for either On or Off, but not both ways) I swear they were only a few bucks the last time I saw them in Byte magazine. I have no intention of replacing any conductors with solid gold spun from Bavarian maidens' hair, or anything else with anything that costs more per gram than Bolivia's finest.
Anyway - I'm primed to rip that bad boy apart, wash up that board in Simple Green (though I wonder about such other solvents as methanol, or industrial concrete-cleaning detergents), replace parts and fire her up. It's my nature, though, to want to confirm such things as the bias adjustment when I mess around with all that stuff, so I haven't started rolling yet.
Oh - and my new venue for the QLS-1's will be our new business location - a 75 by 25 foot space in an old mill with 12 foot ceilings. Finally, a room that's big enough!
Thanks in advance for your help!
- Eric
