Thanks Chris for the reply. I've learned a lot about the GFA-565, by reading the DIY threads. Yes, i have access to an oscilloscope. A good ole 1971 Tektronix, all tube. 
. Should do the job, no problem, and I will be able to detect if there is amp oscillation, with it.
So, I've already ordered a bunch of parts fron Digikey; mostly caps, and the Op amp, but i think i should have ordered the dual Lm329 zeners as well. I would have also purchased the 82ohm 1/4w 5% fusible resistor, but i'm unable to find them, unless i purchase qty 5000....
A question for Walt, regarding the zeners. Don't know if he still reads this thread. Should i buy the LM329 version with the lowest temperature coefficient (20 ppm/°C), or the one with 100ppm/°C? Not sure wich one is the best. I worry about the bias variation that may be induced by the change in temperature. Am i wrong to think 20 ppm is better than 100 ppm, but the bias voltage will swing more with the 20 ppm?
I have another question, regarding those who have not been able to clean their boards successfully, despite having cleaned their boards multiple times. Did you consider drilling a few micro holes between the most critical circuit traces, in order to remove conductivity induced by the leaked electrolyte. Obviously, this should only be done, as a last resort measure, if all else failed, and if you're ready to throw the whole thing in the garbage.
. Should do the job, no problem, and I will be able to detect if there is amp oscillation, with it. So, I've already ordered a bunch of parts fron Digikey; mostly caps, and the Op amp, but i think i should have ordered the dual Lm329 zeners as well.
I would have also purchased the 82ohm 1/4w 5% fusible resistor, but i'm unable to find them, unless i purchase qty 5000.... A question for Walt, regarding the zeners. Don't know if he still reads this thread. Should i buy the LM329 version with the lowest temperature coefficient (20 ppm/°C), or the one with 100ppm/°C? Not sure wich one is the best. I worry about the bias variation that may be induced by the change in temperature. Am i wrong to think 20 ppm is better than 100 ppm, but the bias voltage will swing more with the 20 ppm?
I have another question, regarding those who have not been able to clean their boards successfully, despite having cleaned their boards multiple times. Did you consider drilling a few micro holes between the most critical circuit traces, in order to remove conductivity induced by the leaked electrolyte. Obviously, this should only be done, as a last resort measure, if all else failed, and if you're ready to throw the whole thing in the garbage.
I was browsing the internet, recently, and i found an old thread about which capacitor yields the best results, for audio applications. They compared several brands of capacitor: Rubycon Black Gate, Panasonic FC, Elna Silmic, and 3 or 4 other brands. They rated the Elna Silmic to be the best. Does it really make that much of a difference. I mean, a capacitor is a capacitor. Any thoughts about that?? It seems that the Black Gate has been discontinued.
Hi guys;
I've ordered new caps for my GFA-565. The ovehaul of the amps went perfectly. I desoldered the main boards, and removed the relay boards. I replaced all the electrolytics capacitors and used Panasonic FC 105°c. I desoldered the OP amps and cleaned them. I cleaned the main board ultrasonically with Simple Green. I tested most of the components to see if some could be defective. Fortunately, everything was perfect. I was also pleased to see that the main board were not corroded at all, by the leaked electrolyte of the caps. Before i began, i had 19v offset at turn off in one of the amps. The other was about 500mv at turn off
When everything was cleaned up, i ended up with 50-60mv, coming down to 1-2mv after a minute or so. I'm so pleased😊. These GFA-565 are so powerful. The bass coming from these beasts is simply incredible. I will keep them for a long time, for sure
I've ordered new caps for my GFA-565. The ovehaul of the amps went perfectly. I desoldered the main boards, and removed the relay boards. I replaced all the electrolytics capacitors and used Panasonic FC 105°c. I desoldered the OP amps and cleaned them. I cleaned the main board ultrasonically with Simple Green. I tested most of the components to see if some could be defective. Fortunately, everything was perfect. I was also pleased to see that the main board were not corroded at all, by the leaked electrolyte of the caps. Before i began, i had 19v offset at turn off in one of the amps. The other was about 500mv at turn off
When everything was cleaned up, i ended up with 50-60mv, coming down to 1-2mv after a minute or so. I'm so pleased😊. These GFA-565 are so powerful. The bass coming from these beasts is simply incredible. I will keep them for a long time, for sure
Hi ypelchat,
The Adcom GFA-565 can sound really excellent with a few more capacitor type changes and a very tight match on the input diff pairs. I recently did one of these. The tight match will also reduce any DC offset.
-Chris
You poor, long suffering soul! At least the 4B wasn't used in full range or the mids / highs! Still, all that heat cooking whatever was over it.
The Adcom GFA-565 can sound really excellent with a few more capacitor type changes and a very tight match on the input diff pairs. I recently did one of these. The tight match will also reduce any DC offset.
-Chris
Working on my third GFA-565
Got it today, and ordered a bunch of capacitors so i can start rebuilding it. This one has a balanced board that looks like a mess with the leaky ELNA caps. Guy I bought it from, told me that it works perfect, but told me the balanced board has hum.. A lot of sticky goo Under the elna caps. The main board caps were replaced in the past, but i will replace them again to put Panasonic FC caps. I'll report later.
Got it today, and ordered a bunch of capacitors so i can start rebuilding it. This one has a balanced board that looks like a mess with the leaky ELNA caps. Guy I bought it from, told me that it works perfect, but told me the balanced board has hum.. A lot of sticky goo Under the elna caps. The main board caps were replaced in the past, but i will replace them again to put Panasonic FC caps. I'll report later.
Already got my parts from Digikey. Gees these guys are fast. Ordered yesterday, at about 10h00pm, and the box was waiting for me when i got home today.
So, I've started the work on the 565, but will get more serious about it next week, as i'll be off work for 3 days. Like i said in my previous post.. The low Z board is a mess, but the main board is looking great, no acidic damage to the board. Board looks pretty clean, but i'll take no chances, and will do a through ultrasonic cleaning. Caps on the main board were replaced, but 40c caps were installed, instead of the 85c or 105c caps. So, i'll replace them with Panasonic FC series caps. In fact, i've ordered each of the 565 caps (but the main power supply caps), QTY 15. So i've got plenty of them.
I did not turn the amp on, yet, but given the state of the main board, i'm pretty sure the sellers word that it was functioning well, is correct. Main board is very clean. (Even though acidic liquid from the leaky caps can be translucid, i can tell you that the ELNA caps still present on the low Z board leaked a very evident brownish color goo).... However, I will find out when the Simple Green ultrasonic cleaning and recap is done. I'm a real fan of the 565. I don't know how the Krell amps are sounding, but i can tell you i'm getting goose bumps listening to Stan Getz, Miles Davis, Viola Beach or any kind of music. I'll use the 3rd 565 as my bass amp.
So, I've started the work on the 565, but will get more serious about it next week, as i'll be off work for 3 days. Like i said in my previous post.. The low Z board is a mess, but the main board is looking great, no acidic damage to the board. Board looks pretty clean, but i'll take no chances, and will do a through ultrasonic cleaning. Caps on the main board were replaced, but 40c caps were installed, instead of the 85c or 105c caps. So, i'll replace them with Panasonic FC series caps. In fact, i've ordered each of the 565 caps (but the main power supply caps), QTY 15. So i've got plenty of them.
I did not turn the amp on, yet, but given the state of the main board, i'm pretty sure the sellers word that it was functioning well, is correct. Main board is very clean. (Even though acidic liquid from the leaky caps can be translucid, i can tell you that the ELNA caps still present on the low Z board leaked a very evident brownish color goo).... However, I will find out when the Simple Green ultrasonic cleaning and recap is done.
I'm a real fan of the 565. I don't know how the Krell amps are sounding, but i can tell you i'm getting goose bumps listening to Stan Getz, Miles Davis, Viola Beach or any kind of music. I'll use the 3rd 565 as my bass amp.
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Ooops.... I need help
Anatech, i think i need your help. The schematics of the GFA-565 service manual that i have, is quite low quality, and i'm not able to see correctly where main board terminal 5 - 11 and 10 - 6 are connected. These are the four wire wrapped wires. I chopped the wires, but forgot to mark where they were connected. They are the same color. Theres a red-orange wire pair that goes to the main supply filter capacitor, and the other red-orange pair, goes to the two fuse holder on the back panel.
Can I also assume the lone white wire (small wire), goes to terminal 7 on the main board? I'm ok with location of the other wires. I have two other GFA-565, that i could use to check for the location of the wires, however, that are rack mounted, and i dont feel like pulling them out of the rack..
Thanks.
Anatech, i think i need your help. The schematics of the GFA-565 service manual that i have, is quite low quality, and i'm not able to see correctly where main board terminal 5 - 11 and 10 - 6 are connected. These are the four wire wrapped wires. I chopped the wires, but forgot to mark where they were connected.
They are the same color. Theres a red-orange wire pair that goes to the main supply filter capacitor, and the other red-orange pair, goes to the two fuse holder on the back panel. Can I also assume the lone white wire (small wire), goes to terminal 7 on the main board? I'm ok with location of the other wires. I have two other GFA-565, that i could use to check for the location of the wires, however, that are rack mounted, and i dont feel like pulling them out of the rack..
Thanks.
Was able to find out where the wires are connected. Amp is functioning beautifully now. My 3rd 565, successfully rebuilt. And i've got parts for many others. Most difficult part was the low z board, which was a mess, due to the 4 ELNA caps leaking and one of the two transistors had badly corroded pins, + a defective 2w 2.7k resistor. Had to fabricate 3 pin extensions for one of the transistors, due to corrosion. These transistors are not available anymore, so i had no choice but to try to repair the one that was damaged. Simple Green + ultrasonic cleaning does wonder to these ELNA damaged boards. . Bias is perfect, and the amp sounds great with the new Panasonic FC series caps. I will use this 565 along with my Yamaha PB1 preamp, as my main bass amp, driving my Peavey 3620 cabinet. 565's are bass monsters.
My 3rd 565, successfully rebuilt. And i've got parts for many others. Most difficult part was the low z board, which was a mess, due to the 4 ELNA caps leaking and one of the two transistors had badly corroded pins, + a defective 2w 2.7k resistor. Had to fabricate 3 pin extensions for one of the transistors, due to corrosion. These transistors are not available anymore, so i had no choice but to try to repair the one that was damaged. Simple Green + ultrasonic cleaning does wonder to these ELNA damaged boards. . Bias is perfect, and the amp sounds great with the new Panasonic FC series caps. I will use this 565 along with my Yamaha PB1 preamp, as my main bass amp, driving my Peavey 3620 cabinet. 565's are bass monsters.
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