Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: antfarmer on April 25, 2011, 07:00:00 pm
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:help:Well I just finished installing a Hoffman AB763 built up board and Mercury Magnetics trans. and choke set in a friends deluxe rev RI. It is super quiet(yeah!) and sounds great, but the trem does not work. When I hit a note and turn the power off I here it working as the signal dies out. Voltage problem? Any ideas on a solution would be great. Thanks. Phil
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Does this use a fender optocoupler? If so are you sure you installed the optocoupler the right way?
Scratch that question. I dont see one in the layout. All i can say is double check your wiring. I still make the simplest mistakes my self
What are the cathode voltage of pins 3 & 8 of V5? Pin 8 voltage might tell you if theres a problem
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Hi Plexi50, Thanks for responding . Pin 3 is ok (2.3v) but you were right pin 8 is 221v (geez). I checked my wiring for the 5th time and every thing looks good. There are some different values of resistors and caps on the board than on the drawing but I was told the changes were to make the trem more blackface than brownface. I'm scratching my head, any other thoughts? Thanks, Phil
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Hi antfarmer
Pin 8 of the cathode follower stage in the trem circuit is supposed to be high (its sittin' on top of a 470k resistor after all and the plate (pin 6) is connected straight to the HT). I'd work through the term ciruit wiring myself (e.g.: check with your R-meter to see it you have you depth pot wired up properly and that it is making connections etc). Also what are the idle voltages thru-out the trem stage (with the trem footswitch shutting the trem off)?
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210v on pin 8 is okay.
Take a look at this schematic... See the voltages around the tremolo circuit? Check against your amp.
http://www.el34world.com/charts/Schematics/files/fender/tremolux_6g9a_h-fa.pdf
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Finally was able to get back to problem. Checked my wiring again to drawing, checked to schematic of 6G9-A. nothing seemed obvious or wrong. The voltages at idle w/trem off are Pin#1-210v, #2-1.4mv,#3-2.3v,#6-448v,#7-210v, and #8-221v. I discovered something else weird besides getting trem effect when I put amp on standby or shut off power before signal dies out, using a single coil guitar the single coil hum modulates according to the speed setting of the trem. Does this spawn any other ideas. Oh the intensity pot is wired correctly and I reflowed all pot connections in trem circuit. ????
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Check your bias, it may be set too hot... Make it cold and see if anything happens.
The bias setting and the tremolo depend on each other to do thier stuff.
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Check your bias, it may be set too hot... Make it cold and see if anything happens.
The bias setting and the tremolo depend on each other to do thier stuff.
Also you may try changing the .1 trem caps to .047. I have never seen .1 caps in a trem before. .022 is common for me. Or paralleled .022 to get near a .047 value. I dont have any experience with this schematic build using .1 trem caps. It could be possable that the .1 caps are IMO are taking the trem to such a low rate of speed that it wont work or can hear any trem action using .1 trem caps. Try .022 and tell us what happens. Ive messed around a bit with slowing and speeding up trem circuits by changing the trem caps value. Some times for weird reasons things work differently then expected. This might also explain when you turn the amp off as the voltage bleeds down you can all of a sudden hear the trem for a second. It could be those .1 caps bleeding out the voltage and in a way changing the cap value for just a split second. But not really
Now after having said all this i see i am looking at the wrong caps in the trem circuit. Hey it's Friday! Sorry /
Try changing the .01 trem caps out to .022 And this is on my first beer
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Hey Guys, Thanks for all the ideas on solving my issue. It was the bias (too hot), I changed the bias resistor back to the original 470 ohm and adjusted the bias til the trem was throbbing just right.
Thanks again
Phil