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Bottlehead Kits => Legacy Kit Products => Paramount => Topic started by: gsharri on December 07, 2022, 06:07:33 AM

Title: Oops! Blown component on pcb
Post by: gsharri on December 07, 2022, 06:07:33 AM
I have a pair of 300b Paramounts which were modified by Paul Birkeland to use a 6LU8 driver tube. I installed a pair of NOS 6LU8s and one of them was apparently damaged in shipping (tested good before shipping). The result: a flash of light and a "snapping" sound as D1 blew it's guts across the pcb mounted below the 6LU8 tube (see pic). What type of LED do I need for replacement and how do I test for proper operation? I have no schematics or manual as I purchased these used.
Thanks
Scott
Title: Re: Oops! Blown component on pcb
Post by: Paul Birkeland on December 07, 2022, 06:18:03 AM
Just replacing the LED is rarely sufficient to perform this kind of repair.  Typically I would remove both LEDs (they are HLMP-6000), Q1, and Q2, then test R1 and R2 with the transistors removed to be sure they are still happy, then repopulate the board.
Title: Re: Oops! Blown component on pcb
Post by: gsharri on December 07, 2022, 07:32:41 AM
I will do that. Thank you sir.
Title: Re: Oops! Blown component on pcb
Post by: gsharri on December 31, 2022, 07:46:12 AM
What are the correct wattage ratings on R1 & R2 if they require replacing?
Thanks
Title: Re: Oops! Blown component on pcb
Post by: Paul Birkeland on December 31, 2022, 08:59:11 AM
R1 can be an 1/8W part.  You'd want the 90.9 RN55D to get about the same part as what's there.  R2 is a 300K 3W PR-03 resistor.  If that's not available, the RR-03 is functionally about the same.
Title: Re: Oops! Blown component on pcb
Post by: gsharri on February 04, 2023, 01:10:20 PM
Okay, a little bit of progress. I have replaced D1 & D2, R1 & R2, and Q1 & Q2 (B side of the board). After powering on with tubes installed D1 & D2 on the B side light up and D1 & D2 on the A side light up briefly and then go out. I get audio out of the speaker but at a very, very low volume.
Recommendations on what to check next?
Is it possible to obtain a manual and schematic?

Thanks, Scott
Title: Re: Oops! Blown component on pcb
Post by: Paul Birkeland on February 04, 2023, 05:25:26 PM
You really need to measure voltages before trying to use the amp.  Without knowing what the voltages are on that PC board, there aren't any recommendations that can be made.