Hammond AO-63 conversion
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Re: Hammond AO-63 conversion
I agree.
Re: Hammond AO-63 conversion
Hi, I got my replacement capacitors for the main power and the reverb power circuits. I replaced them all one by one keeping the exact same connections to the positive leg of each capacitor and the negative going to ground. Rechecked all my connections.
I previously purchased a new 5AR4/GZ34 rectifier and I inserted it and began bringing things up on the variac. No smoke! No crackling and there was a slight glow in rectifier. I let it sit for awhile and began testing voltages at each of the caps and on each leg of the power resistors. I am getting essentially the same voltage readings across each of the four drop-down resistors and they each go up and down depending on if I adjust the variac. Nothing is getting hot.
I previously purchased a new 5AR4/GZ34 rectifier and I inserted it and began bringing things up on the variac. No smoke! No crackling and there was a slight glow in rectifier. I let it sit for awhile and began testing voltages at each of the caps and on each leg of the power resistors. I am getting essentially the same voltage readings across each of the four drop-down resistors and they each go up and down depending on if I adjust the variac. Nothing is getting hot.
Re: Hammond AO-63 conversion
Update:
I got all new capacitors installed for the power supply circuits for the main power and reverb power supplies. I followed the suggestions from the prior post by Sluckey and first did the main power supply rectifier and then the reverb power rectifier and checked voltages on each connection for the new caps and the resistors. There was no voltage drop and the voltage reading on my DMM was the same at each connection. No heat no noise. So, I think my power supply is working for each circuit.
I would like to next try and see if the main amp is functional. Given Sluckey's kind guidance he said he had a step-by-step plan though I think I will study the schematic some more and hopefully get the next suggestion for the next step.
Thanks,
James
Kingston, WA
I got all new capacitors installed for the power supply circuits for the main power and reverb power supplies. I followed the suggestions from the prior post by Sluckey and first did the main power supply rectifier and then the reverb power rectifier and checked voltages on each connection for the new caps and the resistors. There was no voltage drop and the voltage reading on my DMM was the same at each connection. No heat no noise. So, I think my power supply is working for each circuit.
I would like to next try and see if the main amp is functional. Given Sluckey's kind guidance he said he had a step-by-step plan though I think I will study the schematic some more and hopefully get the next suggestion for the next step.
Thanks,
James
Kingston, WA
Re: Hammond AO-63 conversion
Divide and conquer...
Work on the main amp first. Plug in ONLY these tubes... V1, V2, V3, V4, and V10. Put all other tubes in a box and set aside until you are happy with the sound of the main amp. Connect a speaker to the main speaker connector. Turn on the power (no variac!) and allow to warm up for a few minutes. Turn it off if you have any alarms. Adjust the HUM BALANCE for minimum hum from the speaker. If you can't determine minimum hum with your ears, just set the pot to center of rotation. Set your meter to read a small dc voltage and connect one probe to P310 pin 1 and connect the other probe to P310 pin 3. P310 is a 3 pin test plug and the pins you want the meter connected to are the outside pins. The center pin should have -22VDC on it but you have already checked that. Now adjust the BIAS BALANCE pot for minimum voltage on the meter. Ideally, we want zero volts which will indicate that the power tubes are perfectly balanced (matched). Now disconnect the meter probes and reconnect the black probe to chassis. Connect the red probe to P310 pin 1. Voltage should be about 0.4vdc. Move the red probe to P310 pin 3. Voltage should be about 0.4vdc. Now move the red probe to P310 pin 2 (center pin). Voltage should be about -22vdc. Report all these voltage readings.
Now connect a guitar to the Organ input jack. You will need an adapter. Play the guitar some. The ORGAN LEVEL pot will control the volume but will not totally kill the guitar signal. Evaluate the sound for loudness and clean tone. The main amp is a powerful and clean sounding amp but it has no tone controls and is not voiced for guitar. If you are happy with the sound, then you are about done with the main amp, so put a pin in it, and we'll move on to evaluating the reverb amp. If the amp sounds weak or distorted then it's time to troubleshoot.
Anyhow, this is a logical stopping point. Report your findings before we move on. Don't do any drilling on the chassis at this point. We are mainly evaluating right now. All the mods, if any, will come after we have the AO-63 performing as it was intended.
Work on the main amp first. Plug in ONLY these tubes... V1, V2, V3, V4, and V10. Put all other tubes in a box and set aside until you are happy with the sound of the main amp. Connect a speaker to the main speaker connector. Turn on the power (no variac!) and allow to warm up for a few minutes. Turn it off if you have any alarms. Adjust the HUM BALANCE for minimum hum from the speaker. If you can't determine minimum hum with your ears, just set the pot to center of rotation. Set your meter to read a small dc voltage and connect one probe to P310 pin 1 and connect the other probe to P310 pin 3. P310 is a 3 pin test plug and the pins you want the meter connected to are the outside pins. The center pin should have -22VDC on it but you have already checked that. Now adjust the BIAS BALANCE pot for minimum voltage on the meter. Ideally, we want zero volts which will indicate that the power tubes are perfectly balanced (matched). Now disconnect the meter probes and reconnect the black probe to chassis. Connect the red probe to P310 pin 1. Voltage should be about 0.4vdc. Move the red probe to P310 pin 3. Voltage should be about 0.4vdc. Now move the red probe to P310 pin 2 (center pin). Voltage should be about -22vdc. Report all these voltage readings.
Now connect a guitar to the Organ input jack. You will need an adapter. Play the guitar some. The ORGAN LEVEL pot will control the volume but will not totally kill the guitar signal. Evaluate the sound for loudness and clean tone. The main amp is a powerful and clean sounding amp but it has no tone controls and is not voiced for guitar. If you are happy with the sound, then you are about done with the main amp, so put a pin in it, and we'll move on to evaluating the reverb amp. If the amp sounds weak or distorted then it's time to troubleshoot.
Anyhow, this is a logical stopping point. Report your findings before we move on. Don't do any drilling on the chassis at this point. We are mainly evaluating right now. All the mods, if any, will come after we have the AO-63 performing as it was intended.
Re: Hammond AO-63 conversion
Thanks Sluckey!
While I was typing this up the update from Sluckey came up. Here is what I have done thus far this afternoon. I will go back and follow Sluckey's advice.
I left the amp on for about an hour with zero issues. I wanted to test the power amp side so I had only the V10 rectifier, the two V3/V4 power tubes and V2 phase inverter installed. I turned it off and attached a speaker. I then inserted an alligator preamp signal onto Pin 7 of V2 from my little FiiO digital player with a preamp out - my reasoning was since it was a preamp signal I could bypass V1.
Brought up the power and there is no motorboating, no hum from the speaker and it is playing clean and loud albeit a mono signal. It sounds terrific actually. This is just the main power side I have not as yet tested the reverb circuit.
Now, I will go back and do it right by following Sluckey's instructions.
While I was typing this up the update from Sluckey came up. Here is what I have done thus far this afternoon. I will go back and follow Sluckey's advice.
I left the amp on for about an hour with zero issues. I wanted to test the power amp side so I had only the V10 rectifier, the two V3/V4 power tubes and V2 phase inverter installed. I turned it off and attached a speaker. I then inserted an alligator preamp signal onto Pin 7 of V2 from my little FiiO digital player with a preamp out - my reasoning was since it was a preamp signal I could bypass V1.
Brought up the power and there is no motorboating, no hum from the speaker and it is playing clean and loud albeit a mono signal. It sounds terrific actually. This is just the main power side I have not as yet tested the reverb circuit.
Now, I will go back and do it right by following Sluckey's instructions.
Re: Hammond AO-63 conversion
Sorry about going right to the conquer part earlier. I have done exactly as you indicated below. Before I was running off of the variac when I tested the audio and running it through a cheapo stereo test speaker.
This time I am running off of the wall socket. I set the bias to 0.00v pretty easily and each of pins 1 and 3 measure .4v. Pin 2 measures right on -22.0v
I dug around in my adapter jar and found a 1/4" to RCA adapter (garage sale one of those you never know purchases). I monkeyed around with the organ level control and was getting some static (note to self to clean it out). I found that the hum reduced a lot when I turned it all the way up. I then hooked all up to one of the organ speakers and the hum while there is very tolerable. Especially after I plugged in the guitar.
I am quite happy with the sound even without a proper guitar preamp in between my guitar and the amp. The tone is very clean and almost crisp. I did put a 12AX7 in V1 (couldn't help myself). Volume is pretty loud but I can see it getting louder with a proper guitar preamp ahead of this.
This has been a really fun process. So, I am putting a pin in the main amp. I will have the tubes tested as well. Everything in this is what came with it. Thanks again for your guidance.
I am ready to move to the reverb amp. I hope this has not been too much trouble.
James
This time I am running off of the wall socket. I set the bias to 0.00v pretty easily and each of pins 1 and 3 measure .4v. Pin 2 measures right on -22.0v
I dug around in my adapter jar and found a 1/4" to RCA adapter (garage sale one of those you never know purchases). I monkeyed around with the organ level control and was getting some static (note to self to clean it out). I found that the hum reduced a lot when I turned it all the way up. I then hooked all up to one of the organ speakers and the hum while there is very tolerable. Especially after I plugged in the guitar.
I am quite happy with the sound even without a proper guitar preamp in between my guitar and the amp. The tone is very clean and almost crisp. I did put a 12AX7 in V1 (couldn't help myself). Volume is pretty loud but I can see it getting louder with a proper guitar preamp ahead of this.
This has been a really fun process. So, I am putting a pin in the main amp. I will have the tubes tested as well. Everything in this is what came with it. Thanks again for your guidance.
I am ready to move to the reverb amp. I hope this has not been too much trouble.
James
sluckey wrote: ↑Sun Mar 04, 2018 10:59 pm Divide and conquer...
Work on the main amp first. Plug in ONLY these tubes... V1, V2, V3, V4, and V10. Put all other tubes in a box and set aside until you are happy with the sound of the main amp. Connect a speaker to the main speaker connector. Turn on the power (no variac!) and allow to warm up for a few minutes. Turn it off if you have any alarms. Adjust the HUM BALANCE for minimum hum from the speaker. If you can't determine minimum hum with your ears, just set the pot to center of rotation. Set your meter to read a small dc voltage and connect one probe to P310 pin 1 and connect the other probe to P310 pin 3. P310 is a 3 pin test plug and the pins you want the meter connected to are the outside pins. The center pin should have -22VDC on it but you have already checked that. Now adjust the BIAS BALANCE pot for minimum voltage on the meter. Ideally, we want zero volts which will indicate that the power tubes are perfectly balanced (matched). Now disconnect the meter probes and reconnect the black probe to chassis. Connect the red probe to P310 pin 1. Voltage should be about 0.4vdc. Move the red probe to P310 pin 3. Voltage should be about 0.4vdc. Now move the red probe to P310 pin 2 (center pin). Voltage should be about -22vdc. Report all these voltage readings.
Now connect a guitar to the Organ input jack. You will need an adapter. Play the guitar some. The ORGAN LEVEL pot will control the volume but will not totally kill the guitar signal. Evaluate the sound for loudness and clean tone. The main amp is a powerful and clean sounding amp but it has no tone controls and is not voiced for guitar. If you are happy with the sound, then you are about done with the main amp, so put a pin in it, and we'll move on to evaluating the reverb amp. If the amp sounds weak or distorted then it's time to troubleshoot.
Anyhow, this is a logical stopping point. Report your findings before we move on. Don't do any drilling on the chassis at this point. We are mainly evaluating right now. All the mods, if any, will come after we have the AO-63 performing as it was intended.
Re: Hammond AO-63 conversion
Sounds like you have a pretty good idea where I'm headed with this.
OK, on to the reverb amp... I want to proceed cautiously because of those two burned resistors in the reverb power supply. They didn't just fail for no reason. Something else failed, causing excessive current to flow through those resistors, causing them to burn up. Hopefully that cap can C336 was the culprit. But still keep an eye on those resistors throughout this next test. If you see any sign of overheating, STOP. We will need to change from eval mode to troubleshooting mode. I'd like to see an updated photo showing how you replaced all the caps and those two resistors. A big pic showing the entire guts would be nice.
Divide and conquer... Remove V10 GZ34. We don't need that for now. Install V7, V8, and V9. Connect a speaker to the reverb speaker connector P307. Use alligator clip leads to connect your little FiiO digital player to the REVERB LEVEL pot (or P302 pin 3). Turn the power on. Remember to watch for smoke! You should get a clean moderately loud signal through the speaker. May not be as loud as the main amp. If satisfied, move on...
Next step... Putting it all together. Put a jumper wire between P302 pins 1 and 3. This bypasses the console switches and connects the reverb preamp to the reverb power amp. Connect the reverb tank. If unsure which connector is which, use your ohm meter to check the resistance between the center pin and the shell of the RCA jacks on the tank. The jack with the lowest resistance will connect to P303. And the other connects to P304. Plug in all tubes, including V10, the GZ34. Connect a guitar to the ORGAN input, P306. You should have guitar signal at the main speaker and you should have reverb signal at the reverb speaker. Report... Hopefully you will have good news.
BTW, now is a good time to mention the main speaker connection. Notice that the OT secondary has a center tap connected to ground? You can't change that. This means that the two wires that actually connect to the speaker are floating above ground. And this means that if you decide to use a more guitar friendly speaker connection such as a 1/4" phone plug, you will have to isolate the jack from chassis. That's easy with a cliff jack because they are already isolated, but to use a Switchcraft jack you will need two fiber insulating bushings.
OK, on to the reverb amp... I want to proceed cautiously because of those two burned resistors in the reverb power supply. They didn't just fail for no reason. Something else failed, causing excessive current to flow through those resistors, causing them to burn up. Hopefully that cap can C336 was the culprit. But still keep an eye on those resistors throughout this next test. If you see any sign of overheating, STOP. We will need to change from eval mode to troubleshooting mode. I'd like to see an updated photo showing how you replaced all the caps and those two resistors. A big pic showing the entire guts would be nice.
Divide and conquer... Remove V10 GZ34. We don't need that for now. Install V7, V8, and V9. Connect a speaker to the reverb speaker connector P307. Use alligator clip leads to connect your little FiiO digital player to the REVERB LEVEL pot (or P302 pin 3). Turn the power on. Remember to watch for smoke! You should get a clean moderately loud signal through the speaker. May not be as loud as the main amp. If satisfied, move on...
Next step... Putting it all together. Put a jumper wire between P302 pins 1 and 3. This bypasses the console switches and connects the reverb preamp to the reverb power amp. Connect the reverb tank. If unsure which connector is which, use your ohm meter to check the resistance between the center pin and the shell of the RCA jacks on the tank. The jack with the lowest resistance will connect to P303. And the other connects to P304. Plug in all tubes, including V10, the GZ34. Connect a guitar to the ORGAN input, P306. You should have guitar signal at the main speaker and you should have reverb signal at the reverb speaker. Report... Hopefully you will have good news.
BTW, now is a good time to mention the main speaker connection. Notice that the OT secondary has a center tap connected to ground? You can't change that. This means that the two wires that actually connect to the speaker are floating above ground. And this means that if you decide to use a more guitar friendly speaker connection such as a 1/4" phone plug, you will have to isolate the jack from chassis. That's easy with a cliff jack because they are already isolated, but to use a Switchcraft jack you will need two fiber insulating bushings.
Re: Hammond AO-63 conversion
Thanks Sluckey. When I get out to my office/studio I will anxiously take a picture of the bottom. My soldering skills are not perfect. Kind of like how my wife describes things when I cook dinner - it sure tastes good but God you make a mess! It will be about an hour or so I think.
I will follow your instructions as well.
I will follow your instructions as well.
Re: Hammond AO-63 conversion
I'm on jury duty this week so my replies may not be as timely as usual. But I will be checking the forum daily, probably more in the early evening. And I may get released early if they decide they don't want a very opinionated old man! 
Re: Hammond AO-63 conversion
Hey Sluckey,
I am an attorney and have never managed to get on a jury though I would love it. I work/live in a rather small community and the last time I got called I actually made it into the jury room for the first time. I walked in and I knew one of the attorneys. It went like this: "Hi Jeanette. Hi James." Judge points finger to the door. I did not even get to sit down.
Anyway, I did the first part of your suggestions and got no smoke, no unusual noises, all components stayed pretty cool, good glow on power tubes. I inserted the FiiO at the reverb pot and got good strong clean audio from the reverb amp.
Ready to move on but I need to get some work done first.
Here are the pics. The main power caps were these long things that I had to canoodle with to get installed. Two of them are under the power resistors laying against the chassis steel and another one is laid cross-wise. I did bend the tabs for the can caps down so they would not be in the way too much. I will hot glue them all in place before I am all done with this.
The reverb power caps I just laid out in a circle as best I could.
I am an attorney and have never managed to get on a jury though I would love it. I work/live in a rather small community and the last time I got called I actually made it into the jury room for the first time. I walked in and I knew one of the attorneys. It went like this: "Hi Jeanette. Hi James." Judge points finger to the door. I did not even get to sit down.
Anyway, I did the first part of your suggestions and got no smoke, no unusual noises, all components stayed pretty cool, good glow on power tubes. I inserted the FiiO at the reverb pot and got good strong clean audio from the reverb amp.
Ready to move on but I need to get some work done first.
Here are the pics. The main power caps were these long things that I had to canoodle with to get installed. Two of them are under the power resistors laying against the chassis steel and another one is laid cross-wise. I did bend the tabs for the can caps down so they would not be in the way too much. I will hot glue them all in place before I am all done with this.
The reverb power caps I just laid out in a circle as best I could.
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Re: Hammond AO-63 conversion
Be sure none of those cap leads or resistor leads touch any of the original cap can terminals. If you want a neater solution, consider buying this can from AES. It will mount exactly like the old can.The reverb power caps I just laid out in a circle as best I could.
https://www.tubesandmore.com/products/c ... ectrolytic
Re: Hammond AO-63 conversion
Hi, thanks for the link. I will bend those tabs down better and anchor the other caps away from it with hot glue. No jury duty?
Re: Hammond AO-63 conversion
Still in the selection process. I'm heading out right now.
Re: Hammond AO-63 conversion
Update:
I tested as you suggested and made all the connections you described. First try did not work except for the reverb speaker hummed but the main did not. There was no response from playing the guitar but the reverb twanged when I tapped on the reverb tank. That told me that the reverb circuit was working. I plugged the guitar into the reverb input and it was amplified. So, basic troubleshooting mode I first switched speakers and got the same result. I went all the way down to the basic power amp with only its rectifier and tubes in. Then, I got signal from the guitar. I then went back again one by one with the reverb circuit tubes and it worked. No connections changed but maybe I just nudged a connection somewhere when I did all this.
I am getting reverb from the reverb speaker and guitar from the main speaker. The reverb speaker is quite a bit hummier than the main. Kind of a crackling almost staticy hum but it is outputting reverb! I wonder if one of the 7247 tubes is out of whack a bit. I have yet to clean all the pins on the tubes as well.
The main is louder. The reverb level goes up and down with the reverb level pot.
My first step is to go in and DeOxit all the potentiometers.
I tested as you suggested and made all the connections you described. First try did not work except for the reverb speaker hummed but the main did not. There was no response from playing the guitar but the reverb twanged when I tapped on the reverb tank. That told me that the reverb circuit was working. I plugged the guitar into the reverb input and it was amplified. So, basic troubleshooting mode I first switched speakers and got the same result. I went all the way down to the basic power amp with only its rectifier and tubes in. Then, I got signal from the guitar. I then went back again one by one with the reverb circuit tubes and it worked. No connections changed but maybe I just nudged a connection somewhere when I did all this.
I am getting reverb from the reverb speaker and guitar from the main speaker. The reverb speaker is quite a bit hummier than the main. Kind of a crackling almost staticy hum but it is outputting reverb! I wonder if one of the 7247 tubes is out of whack a bit. I have yet to clean all the pins on the tubes as well.
The main is louder. The reverb level goes up and down with the reverb level pot.
My first step is to go in and DeOxit all the potentiometers.
Re: Hammond AO-63 conversion
Update ad infinitum (that's Latin for a lot):
Cleaned all pins on tubes, tube sockets and potentiometers. I am getting better sound now but there is a significant 60 cycle hum coming from the reverb speaker. V6 was microphonic when I touched it with a chopstick. I moved the tubes around and the microphonics stopped but the hum remained. The hum goes up and down with the reverb level.
I have tried grounding the reverb tank with an alligator cable - no change. I notice if I touch/move V6 it makes a scratchy kind of whooshy noise.
Thoughts?
James
Cleaned all pins on tubes, tube sockets and potentiometers. I am getting better sound now but there is a significant 60 cycle hum coming from the reverb speaker. V6 was microphonic when I touched it with a chopstick. I moved the tubes around and the microphonics stopped but the hum remained. The hum goes up and down with the reverb level.
I have tried grounding the reverb tank with an alligator cable - no change. I notice if I touch/move V6 it makes a scratchy kind of whooshy noise.
Thoughts?
James