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I know this is a well-trodden path on the 'ticking' Fender Tremolo circuit using the neon-LDR circuit. In this case, it's a re-issue '65 Fender Deluxe Reverb, where I'm just beginning Preventative Maintenance work on 13 of them in our rental inventory. While listening to this first amp, there was that all-too-familiar low level ticking that wouldn't shut up. Yes, you can, of course turn it off with the foot pedal, but I remembered having dealt with that problem a few years ago on one of the Fender amps.
After not finding it highlighted in any of my Fender notes, I found it in an email with David Lamkins back in 2010 where I was servicing a Vibro-King...same amp he had written his notes on. This being a re-issue of the '65 Deluxe Reverb, apart from the short leads off the tube socket to the PCB, there's no lead dress to fiddle with. After trying 22nF across the lamp, as well as from the top of the lamp/100k resistor R47 (to the HT supply) to ground, neither of those eliminated the ticking, though did lower it and took the sharp edge off the conductive spike when the lamp turned on or off. Next, not really wanting to pull the PCB up to get to the back side of the PCB to do the surgery, I decided to cut the HT side of the 10M plate resistor R45, and take it to ground, as well as add a 68k resistor from the junction of the top of the lamp and R47 (100k), effectively putting a voltage divider between that 100k and ground, where the neon lamp is the current path to the plate of V5B.....which was David's approach David Lamkins - Guitarist - Vibro-King "Ticking Tremolo" Fix.
I heard a substantial reduction of the ticking....I could hear it in the phones thru my analyzer, but not thru the speaker, while with signal applied, I had plenty of intensity control. When I looked at the tacked-in 68k shunt, I discovered I had NOT connected it to the top of the lamp, but to HT (other side of R47). When I corrected it's placement, the ticking was once again very noticeable. Interesting. I then removed the 68k resistor and also the 10M from the circuit, so the only current path for V5B was thru the 100k & lamp. The ticking couldn't be heard in the speaker, as it behaved when I made the mistake.
I thought I had read somewhere that Fender had, at one point, NO 10M in the plate circuit across the lamp/100k resistor. I couldn't find it anywhere in all my Fender schematics. I did read in a long thread from 2009 "Fender AB763 Style Optocoupled Tremolo Circuit Question" started by Wilder Amplification, where Enzo stated that the 10M resistor was added to help eliminate the ticking. In this once instance with the Deluxe Reverb I have on the bench, it may just be a fluke. I'll know more tomorrow as I roll in more of the amps for scrutiny.
The 22nF cap that I had tried never eliminated the ticking, only lowered and altered it some. Things that I haven't tried is lifting the connection to HT & Ground from where they are placed on the PCB, if it happens to be coupling the ticking by either of those paths.
After not finding it highlighted in any of my Fender notes, I found it in an email with David Lamkins back in 2010 where I was servicing a Vibro-King...same amp he had written his notes on. This being a re-issue of the '65 Deluxe Reverb, apart from the short leads off the tube socket to the PCB, there's no lead dress to fiddle with. After trying 22nF across the lamp, as well as from the top of the lamp/100k resistor R47 (to the HT supply) to ground, neither of those eliminated the ticking, though did lower it and took the sharp edge off the conductive spike when the lamp turned on or off. Next, not really wanting to pull the PCB up to get to the back side of the PCB to do the surgery, I decided to cut the HT side of the 10M plate resistor R45, and take it to ground, as well as add a 68k resistor from the junction of the top of the lamp and R47 (100k), effectively putting a voltage divider between that 100k and ground, where the neon lamp is the current path to the plate of V5B.....which was David's approach David Lamkins - Guitarist - Vibro-King "Ticking Tremolo" Fix.
I heard a substantial reduction of the ticking....I could hear it in the phones thru my analyzer, but not thru the speaker, while with signal applied, I had plenty of intensity control. When I looked at the tacked-in 68k shunt, I discovered I had NOT connected it to the top of the lamp, but to HT (other side of R47). When I corrected it's placement, the ticking was once again very noticeable. Interesting. I then removed the 68k resistor and also the 10M from the circuit, so the only current path for V5B was thru the 100k & lamp. The ticking couldn't be heard in the speaker, as it behaved when I made the mistake.
I thought I had read somewhere that Fender had, at one point, NO 10M in the plate circuit across the lamp/100k resistor. I couldn't find it anywhere in all my Fender schematics. I did read in a long thread from 2009 "Fender AB763 Style Optocoupled Tremolo Circuit Question" started by Wilder Amplification, where Enzo stated that the 10M resistor was added to help eliminate the ticking. In this once instance with the Deluxe Reverb I have on the bench, it may just be a fluke. I'll know more tomorrow as I roll in more of the amps for scrutiny.
The 22nF cap that I had tried never eliminated the ticking, only lowered and altered it some. Things that I haven't tried is lifting the connection to HT & Ground from where they are placed on the PCB, if it happens to be coupling the ticking by either of those paths.
Ha, if I stay on this track I'll be ready for the Sumo Ski Jump pretty soon.
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