18W SL TMB--ticking only with single coils

[ViperDoc]

I just wired up a new 18W "Superlite TMB" that sounds great and is fully operational. The only issue I see is when I select a single coil pickup on any guitar I use, there is a faint high-speed ticking in the background, along with what I can only describe as a "swirly" background noise, also very faint. When playing I don't notice it. I can only find amp ticking threads relating to Fender tremolo circuits. Is there a common reason why this occurs? Thanks.

[xtian]

Only with single coil pickups? Then you answered your own question: ticking is coming from OUTSIDE the amp. See if ticking changes as you rotate/reposition your guitar. Try in another room.

Great looking build, man!

[ViperDoc]

Thanks for the hot tip, xtian, I’ll check that out.

[thetragichero]

how close is your phone/wifi router when this is happening?

[ViperDoc]

how close is your phone/wifi router when this is happening?

It's upstairs on the second floor where it's always been. I've never noted that particular issue with any of the other amps I've built, though, FTR. I'll check it out.

[thetragichero]

okay just ruling out something that can be maddening when tracking down a noise, only to find the cell phone on your front pocket is the cause of it

[ViperDoc]

I'm using 7189 power tubes on this amp and I want to maximize the PT plate voltage. This amp has a SS rectifier with a 100R sag resistor (bypassable) before the reservoir cap. See the attached schematic. The voltage just after the rectifier diodes is highest at around 370 (my 290 HT secondary puts out 305V). I have the OT CT tapped on the far end of the sag resistor to be continuous with the reservoir cap via a wire lead. That A Node voltage changes depending on the sag bypass switch setting. Could I tap the OT CT right after the diodes, before the sag resistor such that the OT CT voltage doesn't change with the switch? I wondered if having a lower reservoir cap voltage when the sag resistor is in the path would be problematic. Thanks.

18W OT TAP OPTIONS.pdf

[Colossal]

No comment on your application, but you do show both the Load and Neutral fused. Remove F2.

[ViperDoc]

No comment on your application, but you do show both the Load and Neutral fused. Remove F2.

Thanks, Colossal. In this build I used a Schaffner AC power module that has room for two fuses inside, one for hot and neutral if I'm reading the datasheet correctly:

https://www.mouser.com/datasheet/2/355/ ... 608605.pdf

Is this bad? If it ought to be removed from the circuit, I could either replace the neutral fuse in the holder with a highly-rated fuse, like 20 A if they make them that small, or is there a cartridge out there that just serves as a non-fused connection?

[ViperDoc]

I boneheaded the obvious variable--the 220K resistor to ground on the reservoir cap--when deciding on my A node B+. I doubled it to 440K and got an additional 10 VDC when my sag resistor is bypassed, but I get the same 365 VDC when I switch it back in with either shunt resistor value. I picked up some varistors to play around with other values.

I couldn't find a 5 x 20 mm fuse-style connector to eliminate my neutral fuse in my AC power module, so I picked up some 20A ceramic fuses to put in. I figure if one is going to blow, it will be the 2A on the hot side. Have you seen a fuse-sized connector anywhere? I thought of making a solid stand-in connector, but didn't take the time to make/test one.