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31
Q & A / Re: Beta Lead 'both inputs' -> No Sound / No LEDs
« Last post by marvin on March 30, 2018, 11:49:57 am »
I took a closer look at the 74C04 Hex Inverter (IC103), which implements several NOT-gates. In particular the one that is needed by IC106 to sense that a plug is present in the 'both' inputs jack (Pin 11 = input and Pin 10 = output). So when a plug is present, this grounds the contact on Pin 11 and I verified that this is the case, since there is 0V on Pin 11, which means "high" or "1" in logic terms for the Hex Inverter. If this part of the Hex Inverter would work correctly as a NOT-gate, there should be around -15V on Pin 10, right? But this is not the case, it is also 0V. In fact it is 0V for every possible input jack combination, but it only matters if you use the 'both' inputs jack alone, since only then you need a logical 0 at Pin 10. If you look at the logic of IC106, this explains the behavior that I explained in my first post, and suggests that IC106 works fine.

So my best guess is a defective IC103 that does not invert the input at Pin 11, if it is a logical 1, so that Pin 10 is always logical 1. What do you guys think?

Here is a schematic, where I marked the NOT-gate in question:
https://ibb.co/fr4XZn
32
Q & A / Re: Beta Lead 'both inputs' -> No Sound / No LEDs
« Last post by marvin on March 29, 2018, 05:40:08 pm »
I verified that there is no bad connection between the jacks and the circuit board. Also the Ring of all 3 input jacks is grounded when a cable is plugged in.
33
Q & A / Re: Sunn Beta Lead Combo, Only One Channel Works
« Last post by Mr. Distortion on March 28, 2018, 11:30:28 pm »
I connect the “to” to the “from” on channel B with no luck. :/
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Q & A / Re: Sunn Beta Lead Combo, Only One Channel Works
« Last post by loudthud on March 28, 2018, 11:02:59 pm »
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Q & A / Re: Beta Lead 'both inputs' -> No Sound / No LEDs
« Last post by loudthud on March 28, 2018, 10:59:59 pm »
The input jacks on the Beta series amps are actually stereo jacks like you find on the input of just about any pedal or stomp box. The contact that would normally contact the "Ring" is grounded when a mono phone plug (normal guitar cord) in inserted. This is how the Beta amp detects which jack you plug your guitar into. Either there is a defect in the internal circuitry, or the jack is just dirty and the contact in not grounding to you guitar cord. If you do not have the training to safely work inside the amp, I strongly suggest you take the amp to someone who is qualified to work on it.
36
Q & A / Sunn Beta Lead Combo, Only One Channel Works
« Last post by Mr. Distortion on March 28, 2018, 08:37:23 pm »
Bought the amp w/ foot pedal from guitar center, had it shipped to the nearest store.  Took it home and realized that only channel A is working, channel B is just silent.  Both lights come on, so I know it’s not the fuse.  Does anyone have any idea how much it would be to fix?  I know it’s hard to tell me exactly what’s wrong without looking at the inside of the amp.  But can anyone give me a ballpark price to fix it or is it possible to do it myself?  Got it for $400 which seemed like a pretty good deal, considering average price in decent condition seems to be about $600 for the head.  I’m annoyed with guitar center, but I still would hate to return it.  Channel A sounds awesome.
37
Q & A / Re: Beta Lead 'both inputs' -> No Sound / No LEDs
« Last post by Isaac on March 28, 2018, 11:54:58 am »
My first thought is a bad connection.
38
Q & A / Beta Lead 'both inputs' -> No Sound / No LEDs
« Last post by marvin on March 27, 2018, 03:11:44 pm »
Hi folks,

first of all I am new to Sunn amps, but I had the chance to get myself a cheap beta lead combo, so I took it without thinking twice or testing the amp.
Both channels and their LEDs work fine separately, but when I use the 'both inputs' jack, there is no sound and both LEDs are off.
However, when I use a second cable to connect the channel A and channel B jacks, the channels are combined, both LEDs are on and everything (sound, knobs) works as expected.
But thats not how it is supposed to work, right?  :?

I used some contact spray on the input jacks, but that does not seem to solve the problem.  :-D

Any ideas, what might be the problem here? Thanks  :-)

39
DIY / Re: Vintage SUNN documentation
« Last post by sunn-tanned on March 21, 2018, 12:28:16 pm »
Very cool thanks! :-D
40
DIY / Vintage SUNN documentation
« Last post by Watson on March 17, 2018, 09:27:51 pm »
Unpacking, I ran across a vintage SUNN catalog from 1969.

Enjoy!
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