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02-01-2009, 05:53 PM
| #1 |
| Senior Member  Join Date: Jun 2006 Location: Palermo, Italy (right at the Crossroad...)
Posts: 376
|  Weak tremolo due to low grid voltage off tremolo tube?
I am overhauling a Silvertone 1472 amp. It's very similar to the more common 1482 with just less volume (maybe due to lower voltages in the power supply section?). This amp has a weak tremolo: I can barely hear it even with the strength pot set at 12. Also, there is a 4-5 seconds delay when I turn the strength pot to max before I can hear the effect. Voltages are in specs all over the chassis, EXCEPT on pin 6 (grid 2), where I have 42 instead of 75 VDC. Can this explain the weak tremolo? What can cause such lower-than-expected voltage? I have tried a different NOS 6AU6 to no avail. I have also replaced all the components around pin 6 (R30, R31, R32, C14 and C15).Schematic is attached. TIA, Carlo
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02-01-2009, 08:05 PM
| #2 | |
| Supporting Member Join Date: Feb 2007 Location: Wellington NZ
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__________________ Building a better world (one tube amp at a time) | |
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02-01-2009, 08:57 PM
| #3 | |
| Senior Member Join Date: Jun 2006 Location: Palermo, Italy (right at the Crossroad...)
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I have already replaced C14 (leaky) and C12 (with a smaller cap for speeder trem rate). Carlo
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02-01-2009, 09:08 PM
| #4 | |
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__________________ Building a better world (one tube amp at a time) | |
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02-03-2009, 02:04 AM
| #5 |
| Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA
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How old is this thing? Pretty old, right? You have alreasdy had to replace some caps, so REPLACE THEM ALL. Your trem doesn;t wake up instantly - that means it is not oscillating. C10,11,12 need to be new. And if all those needed to go, why wouldn't we expect C13,14,15,16 needed to be replaced? Actually C13 is likely the only one in there that is OK. Pin 6 voltage? What are the resistances of R31,R32? You got the 250v B+ up at the top of R31, R30? How far off have R26,27,29 drifted from their value? Turn the trem strength to zero, not measure the voltage at the grids of hte 6V6s - pins 5. Is there any positive voltage there at all? That would be leakage voltage coming through C7,C8. WHich brings me back to have you replaced all the caps yet?
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02-05-2009, 06:32 PM
| #6 |
| Senior Member Join Date: Jun 2006 Location: Palermo, Italy (right at the Crossroad...)
Posts: 376
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I replaced the caps that I hadn't replaced before... Now the tremolo is strong and bold as it can be...  I had already replaced a few drifted resistors. Thank you!
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