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Q & A / Re: Beta Lead humming / buzzing
« Last post by Dr. Gonzo on September 11, 2022, 02:58:37 am »
Thanks guys! So I'll try to find a pro who has experience with solid state amps. The amp was pretty cheap (20? including footswitch), so we can invest some money in the repair and still got a good deal.

Have a good one!
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Q & A / Re: Fisrt post... NAD Sunn Sonaro
« Last post by loudthud on September 11, 2022, 02:16:11 am »
The original switches were made by Carling. Search for Carling here, look through the threads and try to cross reference that against the Carling website and various online distributors.
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Q & A / Re: Fisrt post... NAD Sunn Sonaro
« Last post by Carlsoti on September 10, 2022, 10:27:18 pm »
IT LIVES... and I love it. My neighbors are not so fond of my new acquisition.  :evil: I did a 3-prong cord swap and "death cap" delete, swapped out the caps, even though I'm not certain it "needed" it. New cathode resistor at V1. I also found the 1K NFB resistor to be a bit crispy, despite testing OK, so I swapped that out with a 1.5K I had on hand. Additionally, I used an known good 12AX7 in V1. Overall, voltages came down a bit with the new matched tubes, which I biased to right around 60% idle dissipation; 452V and 0.031/0.032ma.

Does anyone know what kind of amp rating the stock polarity switch has or a part number I could use to find that info? I'm considering using it as a SS/Tube rectifier switch, but I'd like to know a bit more about them before committing to that mod. 
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Q & A / Re: Fisrt post... NAD Sunn Sonaro
« Last post by Carlsoti on September 10, 2022, 10:44:43 am »
EdBass, you seem to know quite a bit more than I in regards to the history and tradition of Sunn Amps. Do you think it would be hurtful to the value of this amp to install a bias balance control in addition to the bias control it came stock with? I can see both sides to this and I'm not sure which way to go. On one hand, it would allow appropriate biasing of slightly mis-matched tubes, like the vintage Mullards it came with. On the other, I can hear someone saying "Why are you using mis-matched tubes?!?!"
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Q & A / Re: Beta Lead humming / buzzing
« Last post by loudthud on September 10, 2022, 10:37:48 am »
If you look at the thread you linked on Music Electronics Forum, the first amps fixed had blown output transistors.

If your friend is self taught and can only fix tube amps, don't give the amp to him. Find someone who has been to technical school and has experience fixing solid state equipment. It is unlikely that the amp can be fixed by someone just replacing components without the technical expertise to determine what part of the amp is malfunctioning.

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Q & A / Re: Beta Lead humming / buzzing
« Last post by EdBass on September 10, 2022, 10:23:36 am »
I think so.

I don't have much experience with the Sunn transistor gear; however, I did buy a broken 4X10 Beta Lead several years ago from Guitar Center for $25. Took it to my tech and he fixed it quick, he commented that it was pretty simple early transistor technology (I think he mentioned "second phase of SS guitar amps"), but my takeaway was that it was easy peasy,
I'll bet your tech can get it back up easily.

Good Luck!
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Q & A / Re: Fisrt post... NAD Sunn Sonaro
« Last post by EdBass on September 10, 2022, 10:12:59 am »
This amp was purchased with the intent to flip it. At least, that's the story I told my girlfriend. LOL

 :-D I've gotten a whole bunch of mileage out of THAT one...
I literally have a barn stuffed full of MI gear and old cars that have showed up at our house over the years under the "flip" premise. Still works!

As you experienced, the Sunn tube stuff is pretty simple. That said, it sounds great, even compared to today's supposed cutting-edge MI gear.
The only shortfall compared to new stuff is the size/weight vs SPL challenge, which can easily be overcome with modern sound reinforcement technology, tonally the old Sunn stuff is outstanding.

Interestingly, I see the "Guitar Transducer" in the cab. I'm guessing that's a replacement; it looks like a Hartzell era driver to me. When I was in buying mode, I always wanted a nice Sonaro combo amp to add to my "flip" gear.  :wink:
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Q & A / Beta Lead humming / buzzing
« Last post by Dr. Gonzo on September 10, 2022, 05:23:18 am »
Hi guys and cheers from Berlin!

My son (13, very into Doom with his SG clone) bought his first amp himself, a broken Beta 410 combo, and now I'm the one who has to take care of fixing it. :-P

Serial number is above A-52175 so according to the service manual it has already the newer slightly changed layout.

When switched on it makes a humming / buzzing noise no matter what position the knobs are in. I recorded a short video, see Google Photos link below.
https://photos.app.goo.gl/sgx3Wq9sRsDbVpow6

I tried the line out (master and preamp) with another amp but the noise remains just the same. Only difference is (logically) that now the volume can be controlled on the other amp.

According to this post it could also be a broken OpAmp. Any other suggestions?
https://music-electronics-forum.com/forum/amplification/guitar-amps/maintenance-troubleshooting-repair/5963-sunn-beta-lead-restoration#post134912

I have a friend who is very much into repairing and building amps but he has no experience with this model. Should he just measure through all the components and replace the broken ones?

Thanks for your help and have a nice weekend!
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Q & A / Re: Demand for Rogan 0-10 knobs
« Last post by Carlsoti on September 09, 2022, 06:16:15 pm »
Any action on the new knobs?
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Q & A / Re: Fisrt post... NAD Sunn Sonaro
« Last post by Carlsoti on September 09, 2022, 05:53:15 pm »
    Thanks for the welcome, guys. My first post may have been unintentionally misleading. FWIW, I have the tools and knowledge to service this amp. Earlier this year I left the relative comfort of a menial DOD gig in favor of scraping up a living fixing music equipment in my spare room. This amp was purchased with the intent to flip it. At least, that's the story I told my girlfriend. LOL
   I saw the posting on FB marketplace listed as "make an offer." The previous owner said the tubes light up, but she didn't think the amp worked. I knew I was taking a gamble in that I might be buying a giant cabinet loaded with paperweights, but I felt it was worth the drive to check it out. The home was clean and well cared for, as was the amp, so I paid my money and carried the amp out with the side handle!
    I pulled the tubes and did some low voltage DMM capacitance tests on the electrolytics. I then stepped the voltage up through a variac and checked voltages in the amp. They were expectedly high, in accordance with today's higher line voltage. I tested all the tubes on my crappy Mighty Mite II (which I need to replace with something that does testing at "real" voltages.) I dropped the bias to it's most -, and put the tubes back in. Another quick voltage check showed everything settling in to where I was content to bias the tubes to the best of my ability. It came with an old pair of Blackburn built Mullard XF2 EL34s, certainly not a matched pair anymore, but I was able to swap them around and get one to bias just above 60% and the other just below 70%. Everything looked good on the scope and temps seemed stable, so I put it back into the cabinet for a test drive.
   I didn't get the volume up past 3. I only got to play it for a minute or a few before I heard a nasty crackly sound, followed by a rock 'n roll light-show seen through the #2 input. I immediately killed the power. With the thud of the switch, I felt my heart crash to the floor. The light show turned out to be the V1A cathode resistor going up in flames!  With the sparse layout, there was minimal collateral damage.
   I ordered new caps, plate and cathode resistors, a burned in and matched set of JJ EL34Ls, and a plug in adapter and tube to replace the 7199 with a 6GH8A. I've got good 12AX7s to swap into it, should that original GE be dead, and the MMII didn't catch it. It recently showed another 12AX7 as being good, but when driven hard, it was giving static-y/crackly noises in the Wilson 707-3 it came out of. The new parts will hopefully go in over the weekend, but I might get stuck doing yardwork instead.
   Here's a few more pics.
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