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Post by Ned Ward on Mar 14, 2021 18:12:09 GMT -6
I have a 1980 Princeton Reverb I love - it's been upgraded over the years with a Deluxe Reverb output transformer, a new cap can, and a Kendrick Black Frame speaker. I was starting to hear some hum out of it, so I took it to my local amp shop. He found that the reverb drive and recovery preamp tubes had gone microphonic, and that the hum was from the tube bias at 75% of max idle. While he was in there, I had him remove all of the pull-boost circuitry and switch to a regular volume pot. He also found it still had a death cap on the polarity switch - would have thought by 1980 they had gotten rid of those... He replaced the existing 27k bias resistor with 33k resistor, and now the tube bias is 17mA@430VDC = 61% of max idle. Sounds great, no hum! Here's a pic of what came out: Attachments:
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Post by srb on Mar 14, 2021 19:37:16 GMT -6
I have a 1980 Princeton Reverb I love - it's been upgraded over the years with a Deluxe Reverb output transformer, a new cap can, and a Kendrick Black Frame speaker. I was starting to hear some hum out of it, so I took it to my local amp shop. He found that the reverb drive and recovery preamp tubes had gone microphonic, and that the hum was from the tube bias at 75% of max idle. While he was in there, I had him remove all of the pull-boost circuitry and switch to a regular volume pot. He also found it still had a death cap on the polarity switch - would have thought by 1980 they had gotten rid of those... He replaced the existing 27k bias resistor with 33k resistor, and now the tube bias is 17mA@430VDC = 61% of max idle. Sounds great, no hum! Here's a pic of what came out: Sounds like you've got a good amp guy! What tubes are you using in the output?...hell tell me all of 'em! |
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Post by EmRR on Mar 14, 2021 21:07:39 GMT -6
He also found it still had a death cap on the polarity switch - would have thought by 1980 they had gotten rid of those... Yep, surprisingly late in the game. I've seen more than a few amps with 3 prong AC cables that....surprise!...connected ground to....NOTHING. |
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Post by Ned Ward on Mar 15, 2021 11:06:58 GMT -6
I have a 1980 Princeton Reverb I love - it's been upgraded over the years with a Deluxe Reverb output transformer, a new cap can, and a Kendrick Black Frame speaker. I was starting to hear some hum out of it, so I took it to my local amp shop. He found that the reverb drive and recovery preamp tubes had gone microphonic, and that the hum was from the tube bias at 75% of max idle. While he was in there, I had him remove all of the pull-boost circuitry and switch to a regular volume pot. He also found it still had a death cap on the polarity switch - would have thought by 1980 they had gotten rid of those... He replaced the existing 27k bias resistor with 33k resistor, and now the tube bias is 17mA@430VDC = 61% of max idle. Sounds great, no hum! Here's a pic of what came out: Sounds like you've got a good amp guy! What tubes are you using in the output?...hell tell me all of 'em! Thanks! Amp guy is great. - he's worked on all my amps. Rebuilt a completely butchered 65 Bandmaster, and fixed my 65 Tremolux. For anyone in Southern California, he works through Harbor Music - harbormusic.netOn the Princeton Reverb, the Output transformer was done by a previous shop that didn't bother to take out the death cap... I haven't gone back since 2002. Tubes are from KCA NOS - Mike Kropotkin is great to deal with. Preamp tubes - JAN-Phillips 12AX7WAS Phase inverter - Mullard CV4024 Rectifier - JAN-Phillips 5U4GB Output tubes - NOS Mazda 6V6 Reverb driver, recovery - JJ - these were replaced by the amp tech this week. |
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Post by srb on Mar 15, 2021 11:12:32 GMT -6
Sounds like you've got a good amp guy! What tubes are you using in the output?...hell tell me all of 'em! Thanks! Amp guy is great. - he's worked on all my amps. Rebuilt a completely butchered 65 Bandmaster, and fixed my 65 Tremolux. For anyone in Southern California, he works through Harbor Music - harbormusic.netOn the Princeton Reverb, the Output transformer was done by a previous shop that didn't bother to take out the death cap... I haven't gone back since 2002. Tubes are from KCA NOS - Mike Kropotkin is great to deal with. Preamp tubes - JAN-Phillips 12AX7WAS Phase inverter - Mullard CV4024 Rectifier - JAN-Phillips 5U4GB Output tubes - NOS Mazda 6V6 Reverb driver, recovery - JJ - these were replaced by the amp tech this week. You've got that thing buttoned up nicely. Always have wanted to try a pair of the Mazda. Are these French and/or a re-brand? I'm a tube hound. |
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Post by Ned Ward on Mar 15, 2021 11:31:26 GMT -6
Thanks! Amp guy is great. - he's worked on all my amps. Rebuilt a completely butchered 65 Bandmaster, and fixed my 65 Tremolux. For anyone in Southern California, he works through Harbor Music - harbormusic.netOn the Princeton Reverb, the Output transformer was done by a previous shop that didn't bother to take out the death cap... I haven't gone back since 2002. Tubes are from KCA NOS - Mike Kropotkin is great to deal with. Preamp tubes - JAN-Phillips 12AX7WAS Phase inverter - Mullard CV4024 Rectifier - JAN-Phillips 5U4GB Output tubes - NOS Mazda 6V6 Reverb driver, recovery - JJ - these were replaced by the amp tech this week. You've got that thing buttoned up nicely. Always have wanted to try a pair of the Mazda. Are these French and/or a re-brand? I'm a tube hound. Good question - as NOS I believe they're the French ones, but don't know enough about tubes to be sure. Mike K recommended them and that was good enough for me. |
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