Ok, that’s good news that I likely only have to put in a new power transistor and 2 fuses! I was reading the bias procedures in the manual but they say you need a Rockola test record. Is there something else I could use?
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On Jun 7, 2025, at 6:23 AM, Norman Macrae via Jukebox-list jukebox-list@lists.netlojix.com wrote:
I'm fairly certain that they are 2N3055 and it's not uncommon for the odd one to go short (I'm not at home right now). They're really easy to change and there's a procedure in the manual to set the bias.
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From: M De Simone via Jukebox-list jukebox-list@lists.netlojix.com
Sent: 6 June 2025 02:59:54 CEST
To: Jukebox mailing list jukebox-list@lists.netlojix.com
Cc: M De Simone m.desimone@rogers.com
Subject: [Jukebox-list] Rockola 490 Amplifier Transistor
I’m out of my “tube amp” comfort zone here but, a very good freind asked if I could help him out.
The amplifier is from a model 490 and the complaint was no sound left channel.
I have been through the amp and found 2 blown fuses F3 and F4 which relate to the left channel and 1 shorted output transistor Q15.
I know in 70’s Seeburg amps usually the drivers go with it and best to replace drivers and power transistors but in this case all others are fine, hoping someone who is familiar with this amplifier can tell me if there are any other components that would be taken out with this or if I’m good to replace the power transistor and fuses and go test?
Also what transistor would replace Q15?
Thanks for any suggestions,
Mauro
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