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Sunn Solid state amp not repairable?
- Thread starter TFM94
- Start date
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- Tags
- amp repair sunn beta lead
- Feb 16, 2008
- 21,240
- 23,638
- Disclosures
- John K Custom Basses
Wow, that's a doozy of a logic circuit. Amusing features: The logic chips can be powered by 15 V, and the whole logic circuit is positive ground so that the control signals to the JFET switches can be negative.
Last edited:
- Feb 12, 2006
- 61,067
- 5
- 221,115
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- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Yes, that's the primary tricky part. Those days are long gone, except that I just designed a logic switching circuit based on similar era type components (but current parts) for an unrelated product.
Another cool feature is using a CMOS logic inverter as a linear amplifier. All of those things were reasonable design options at the time.
- Feb 12, 2006
- 61,067
- 5
- 221,115
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Yes, Craig Anderton was a big fan of this at the time.
Here is the page for the MC14506 IC workaround, remove chip and install socket, install 2 x CD4011 IC's on top of another socket and install it.
https://forum.sunnstillshines.online/index.php?topic=6864.msg29374#msg29374
(Thanks Loudthud )
https://forum.sunnstillshines.online/index.php?topic=6864.msg29374#msg29374
(Thanks Loudthud )
This is a link to my build and PCB of the Sunn Beta Bass/Lead, Thanks to Fishhead Joe for taking the time to measure and photograph his SUNN BETA for me to get the dimensions fairly close to the original.
Sunn Beta PCB
Sunn Beta PCB
Following this thread just because all of you dudes are so super cool to help out the OP.
Plus, I dig old Sunn amps and cabs and want to see this one live again!
Plus, I dig old Sunn amps and cabs and want to see this one live again!
Good news! I got a message from the tech today. He has a diagnosis and he said that he can repair it, just waiting for me to give the go-ahead. He even has all necessary parts in stock and repair cost is very reasonable. I'm very relieved!
As to what's wrong with this amp, he wrote: "There is several failures, in power amplifier and driving section for the signal to power amplifier."
- Feb 12, 2006
- 61,067
- 5
- 221,115
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
You have now experienced the difference between an under-qualified tech and one that knows their trade.
So, I got the amp back last week. It works and sounds glorious. I'm still experimenting with settings, but I already got some very useful sounds out of it, both with guitar and bass. I was hoping that it would have a bit more gain on tap, but the gain that is there is very nice, fuzzy and thick. And it's loud...very loud.
Now that it's in good condition again, I had to build a headshell for it. It originally came out of a combo, but I don't have the speakers for it. Now I'm using it as a head, which I prefer anyway. I know that the original Sunns have black tolex, but that seemed a bit boring to me, so I went with british racing green instead. The enclosure is pine, 18mm with finger joints. This way it doesn't add too much weight and it still offers good protection.
and some vents on the bottom side:
Thanks again for all the support and knowledge shared during the repair process. You guys rock!
Now that it's in good condition again, I had to build a headshell for it. It originally came out of a combo, but I don't have the speakers for it. Now I'm using it as a head, which I prefer anyway. I know that the original Sunns have black tolex, but that seemed a bit boring to me, so I went with british racing green instead. The enclosure is pine, 18mm with finger joints. This way it doesn't add too much weight and it still offers good protection.
and some vents on the bottom side:
Thanks again for all the support and knowledge shared during the repair process. You guys rock!
- Feb 12, 2006
- 61,067
- 5
- 221,115
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Nicely doneSo, I got the amp back last week. It works and sounds glorious. I'm still experimenting with settings, but I already got some very useful sounds out of it, both with guitar and bass. I was hoping that it would have a bit more gain on tap, but the gain that is there is very nice, fuzzy and thick. And it's loud...very loud.
Now that it's in good condition again, I had to build a headshell for it. It originally came out of a combo, but I don't have the speakers for it. Now I'm using it as a head, which I prefer anyway. I know that the original Sunns have black tolex, but that seemed a bit boring to me, so I went with british racing green instead. The enclosure is pine, 18mm with finger joints. This way it doesn't add too much weight and it still offers good protection.
View attachment 5140600
View attachment 5140599
and some vents on the bottom side:
View attachment 5140582
Thanks again for all the support and knowledge shared during the repair process. You guys rock!
Wow, excellent work, absolutely stunning!So, I got the amp back last week. It works and sounds glorious. I'm still experimenting with settings, but I already got some very useful sounds out of it, both with guitar and bass. I was hoping that it would have a bit more gain on tap, but the gain that is there is very nice, fuzzy and thick. And it's loud...very loud.
Now that it's in good condition again, I had to build a headshell for it. It originally came out of a combo, but I don't have the speakers for it. Now I'm using it as a head, which I prefer anyway. I know that the original Sunns have black tolex, but that seemed a bit boring to me, so I went with british racing green instead. The enclosure is pine, 18mm with finger joints. This way it doesn't add too much weight and it still offers good protection.
View attachment 5140600
View attachment 5140599
and some vents on the bottom side:
View attachment 5140582
Thanks again for all the support and knowledge shared during the repair process. You guys rock!
So, I got the amp back last week. It works and sounds glorious. I'm still experimenting with settings, but I already got some very useful sounds out of it, both with guitar and bass. I was hoping that it would have a bit more gain on tap, but the gain that is there is very nice, fuzzy and thick. And it's loud...very loud.
Now that it's in good condition again, I had to build a headshell for it. It originally came out of a combo, but I don't have the speakers for it. Now I'm using it as a head, which I prefer anyway. I know that the original Sunns have black tolex, but that seemed a bit boring to me, so I went with british racing green instead. The enclosure is pine, 18mm with finger joints. This way it doesn't add too much weight and it still offers good protection.
View attachment 5140600
View attachment 5140599
and some vents on the bottom side:
View attachment 5140582
Thanks again for all the support and knowledge shared during the repair process. You guys rock!
So clean! That looks legit! Nice work! Glad I followed this thread and got to see the end result and read the happiness in your post! Now go ROCK that thing!
Only if by "recent years" you mean starting in the 1960s
The power transistors are on sockets. You don't find that often these days. Automation and pick and place for manufacturing. And transistors and many other components are just more reliable these days.
