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91

Q & A / Re: New to the group, question about Beta Lead output problem

« Last post by engineco16 on April 21, 2023, 03:15:40 pm »

A common problem with Beta amps is that either the Plus 15V or Minus 15V regulator transistors on the power amp PCB fail. Q1 is the Plus 15V regulator, Q11 is the minus 15V regulator.

Well I'm no repair guy, but is this fixable on my end? I would really like to get this working, but if not I'll sell it as is and buy a Marshall DSL20. I really appreciate the help.

92

Q & A / Re: New to the group, question about Beta Lead output problem

« Last post by loudthud on April 20, 2023, 03:42:21 am »

A common problem with Beta amps is that either the Plus 15V or Minus 15V regulator transistors on the power amp PCB fail. Q1 is the Plus 15V regulator, Q11 is the minus 15V regulator.

93

Q & A / Re: New to the group, question about Beta Lead output problem

« Last post by engineco16 on April 19, 2023, 04:34:50 pm »

Something else I thought of. The footswitch doesn't have a both channel switch anymore, been trying to find a replacement and I tried one, didn't work. Then I left the two wires disconnected, then reconnected them as they were since the 80s probably. Right now the footswitch is connected, when I power it on, guitar plugged into both channels and the switch goes between them. Now I disconnected the footswitch, unplugged the guitar and the B green channel is lit up but goes off after short time. If I plug the guitar into A channel slowly, the B channel lits up for 2 seconds then goes off. IDK if any of this means anything, but I think the amp has been that way forever.

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Q & A / Re: New to the group, question about Beta Lead output problem

« Last post by engineco16 on April 19, 2023, 04:21:52 pm »

This might help: https://www.audioservicemanuals.com/s/sunn/sunn-beta/5017163-sunn-beta-partial-sm

I tried everything you said and no sounds anywhere, anyway, just the 'pop' when turning it off. I don't think I'm a good enough repair guy to tear it apart, and it's not cost effective to have someone to repair it. 

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Q & A / Re: New to the group, question about Beta Lead output problem

« Last post by engineco16 on April 19, 2023, 03:53:05 pm »

Just real quick, I'm looking at it right now. I double checked that all the jacks are clean. I then plugged it in normal again, had to try, nothing. Then I plugged my guitar into the Power Line In, no sound, but when I turned it off I got the infamous Sunn speaker pop. I'll try running it into the other amps clean channel. Thanks again for the help.

96

Q & A / Re: New to the group, question about Beta Lead output problem

« Last post by Isaac on April 19, 2023, 11:48:21 am »

This might help: https://www.audioservicemanuals.com/s/sunn/sunn-beta/5017163-sunn-beta-partial-sm

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Q & A / Re: New to the group, question about Beta Lead output problem

« Last post by Isaac on April 19, 2023, 11:47:25 am »

Here's what I think I'd do.

You know that the speakers work. You have another amp on hand.

I'd start by running a cord from the MASTER LINE OUT to your other amp. Use a line in if the other amp has one, but the regular input is okay, too. Just make sure it's turned down, because, if this works, you'll be putting in a pretty hot signal. If the preamp is good, then you'll get sound from the other amp. Might be distorted, but that's from the hot input signal overloading the input. Don't worry about that, at least not at this point.

If that doesn't work, then do the same thing with the individual channel LINE OUTs.

If those all work, then you know the preamp is not the problem. You already know that it's not the speakers, so that leaves the power amp and interconnecting wiring. Never forget that it might just be a cord!

Loudthud suggested plugging your guitar into the POWER AMP LINE IN. I've tried that before and got nothing, even on known good amps. Might be that your guitar doesn't have a strong enough signal to drive the power amp to an audible level. If you know that you're getting a good signal from the MASTER LINE OUT, then running a short cord from that to the POWER AMP LINE IN gives you a good signal into the power amp. Thud suggested that, but I'm not clear from your answer whether or not you tried it. If you have another, known good amp with a line out, go from that line out to the Beta's POWER AMP IN. That's to prove that the problem is in the power amp.

Doing all that should tell you where the problem is. Once you know that, you'll have to decide how to proceed. If you have the technical skills, you might be able to fix it yourself. Otherwise, you'd have to take it to a tech. Only you can decide whether or not that's worth the cost.

98

Q & A / Re: New to the group, question about Beta Lead output problem

« Last post by engineco16 on April 17, 2023, 01:41:24 pm »

Tried what you said, nothing. I literally took the old speakers out, with the power off and put the new ones right in. Six months ago when I pulled it out of the closet I totally went through the head and cleaned all connections and pots, much needed and it sounded much better. I plugged my the speakers into my VS265 and they worked fine and sounded so much better than the Marshall speakers in it.

I'm baffled. I took the amp out, looked inside and everything looks fine, clean, nothing burned, no smells, no loose wires. Everything looks fine from the outside. I got this amp and my Gibson "The Paul" for my 16th birthday/Xmas, I still have both and now that I'm into playing again it means a lot to have this amp working. Thanks for the help so far.

99

Q & A / Re: Help with Sunn concert bass

« Last post by Isaac on April 17, 2023, 11:12:41 am »

400w sounds high to me.

The original Concert Bass amp was 150w into 4 ohms. The next generation was rated at 2 ohms, but some knowledgeable people have advised against running it at 2 ohms. As you mentioned 2 ohms, I'm assuming that you have the newer (late 70s) version. Figure 200w at 4 ohms, not much more at 2 ohms. I wouldn't risk it.

For myself, I'd run one 4 ohm cabinet or two 8 ohm cabs.

As for the Celestion K15T, this conversation on TalkBass doesn't speak highly of it: https://www.talkbass.com/threads/celestion-speaker-specs.607781/

100

Q & A / Help with Sunn concert bass

« Last post by Oliv on April 17, 2023, 07:31:31 am »

Hi,
I am new here !
I have a Sunn Concert Bass head (red knobs), and have several questions.

The seller told me it runs 400 watts with 2 ohms, and I read this somewhere on the web, but I mostly read that it is 200 with 4 ohms and 160 with 8 ohms? Is it right ?

I used an ampeg cab with celestion k15t 100 - 4 ohms. Was it a good match, technically speaking (ohms, RMS etc) ?
I think the sound was too mid and not low enough.

I am looking for another 1x15 cab. What would fit with the concert head ?
I play bass (rock / metal) and am looking for something punchy with low frequencies.

Thanks a lot for your help !!