Jay, That’s a good point, This particular amplifier is bone stock original, only thing I see is one cap changed at some point on the plate of a 6L6. It’s never been touched. I’ve done that mod once so would probably have recognized the changes. I wish I could figure out which component might do this or which area to focus on. I can read the schematic but don’t know what each component does. I verified the problem by swapping in another 530 amplifier and it was indeed louder.
Sent from my iPhone
On Aug 22, 2025, at 6:45 PM, Jay Hennigan via Jukebox-list jukebox-list@lists.netlojix.com wrote:
On 8/22/25 15:28, M De Simone via Jukebox-list wrote:
Tony, Thanks for the reply, I have the manual and enlarged schematics for the amplifier. I’m just wondering what could be pulling down my voltage. If it’s not C34 then I’d like to know if there are any other suspects before i put it back in the jukebox. I also believe it may have something to do with the AGC circuit as well, when you first turn it on the voltage is up where it should be but after a few 5 seconds or so it drops low. That’s on the bench but when I hook it up to the mech it’s starts playing loud and then diminishes to the lower level.
That indeed sounds like an AGC issue.
Note that the 530 amp for the 1900 uses a Cobra cartridge. These can be really tricky to get working properly. There's a damping compound that dries out and decent aftermarket cartridges are hit and miss. They also aren't particularly kind to stereo records.
Many of these amps have been modified to use ceramic cartridges which typically involves swapping the tonearm for a later stereo one. If yours has been modified, look at the way the modification has been done, this could be the issue.
-- Jay Hennigan - jay@west.net Network Engineering - CCIE #7880 503 897-8550 - WB6RDV
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