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Author Topic: PL-20 Beta Preamp help needed! (with pics)  (Read 1920 times)

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Offline Andy's Junky Music

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PL-20 Beta Preamp help needed! (with pics)
« on: August 19, 2008, 04:47:18 pm »
Okay so I picked up a PL-20 on ebay the other day and I just got it tried to use it but signal isn't making to the power amp.  It turns on but neither of the channel's LED lights up and like I said signal isn't making it from the front to the back.  On the back of this there's a cable coming out with an XLR input attached.  At first I though maybe this was some sort of DI but the fact that its not labeled at all makes me think it was an addition by the previous owner...maybe some sort of footswitch splice in.  Here's a couple pics of the back of the unit.





I can't really tell where all the wires go inside but it looks like one of them is either going to the footswitch jack or the master line out on the front panel.  If anyone can help me out and let me know if this could be causing my troubles I'd really appreciate it.

Thanks,
Andy
« Last Edit: August 20, 2008, 10:22:07 am by Andy's Junky Music »
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Offline loudthud

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Re: PL-20 Beta Preamp help needed! (with pics)
« Reply #1 on: August 23, 2008, 12:17:04 am »
I have a Beta Lead that had the same symptom. The problem I found was the -15V supply was dead. All the channel switching logic runs on the -15V and ground.
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Offline loudamps

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Re: PL-20 Beta Preamp help needed! (with pics)
« Reply #2 on: August 23, 2008, 06:05:40 pm »
i ran across one like that...they had used a jack used for a mic cable for the footswitch. i had some extra parts and had my tech make it back stock. i have a lot of beta parts.
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Offline Andy's Junky Music

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Re: PL-20 Beta Preamp help needed! (with pics)
« Reply #3 on: August 23, 2008, 07:04:14 pm »
well if i happen to need a new 15v supply would you be interested in selling one...that is if you have a spare
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Offline loudamps

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Re: PL-20 Beta Preamp help needed! (with pics)
« Reply #4 on: August 24, 2008, 04:00:09 am »
sure, let me know!


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Offline Andy's Junky Music

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Re: PL-20 Beta Preamp help needed! (with pics)
« Reply #5 on: August 24, 2008, 10:10:41 am »
awesome! I'll definitely be in touch...thanks man!
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Offline george

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Re: PL-20 Beta Preamp help needed! (with pics)
« Reply #6 on: August 24, 2008, 05:27:26 pm »
Quote
well if i happen to need a new 15v supply would you be interested in selling one...that is if you have a spare

?????? The Beta amplifiers I've worked on only use bipolar transistor regulators to get + -15V. There is no seperate transformer on those designs. Typically one of the transistors either is defective (after 30 plus years of heating), there is a cold solder joint, etc. Do not have a schematic for the pre-amp though. I have to assume that Sunn used a different power supply in the pre-amp???
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Offline loudamps

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Re: PL-20 Beta Preamp help needed! (with pics)
« Reply #7 on: August 24, 2008, 06:45:19 pm »
i do have a schematic for the pre amp, i will check it.
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