Getting Started on SSS 002

[Vertigo]

Thanks for the tip! That's so simple and clever it should be obvious...but wasn't. That method will definitely be in the back of my mind for next time, but I've already done the front panel the hard way. I don't mind it though, since I have no aspirations to ever try to make money doing this, it's a perfect diversion and the high level of concentration required to make everything "just so" is exactly what I need right now.

[Vertigo]

ugh, the 10K/push pull pot I installed for the FET last week had junk threads that fell apart immediately and the replacement that I've been waiting on is a SPST.

I made a lot of progress last night and got the PT, OT, power board and driver board all wired up last night. I was hoping to get the reverb and preamp wired up tonight but want to have the FET and pot in place before doing them so I can easily run the relay wiring to the DIN. This pot/switch is giving me a cramp. Someone please tell me that I can wire up the SPST switch and still use the relay.

[martin manning]

Someone please tell me that I can wire up the SPST switch and still use the relay.

Ok, you can. Wire the SPST pull switch to ground the relay coil, and connect the foot switch direct to the ground side of the relay coil. Keep the 100n cap across the pull switch; it will function as intended.

[Vertigo]

Thank you, Martin. If I wire it this way, I have to wire the FET footswitch different from normal. My hope was to use the same foot switch as my ODS and just swap it as needed since it lives on my pedalboard. I was initially just going to make an extra deep nut for the borked up pot, but it's got some goofy 7x.75 thread pitch.

I appreciate your advice, thank you.

BTW, what's the purpose of the 100n cap? I don't have it on my ODS and haven't noticed anything unusual when switching

[martin manning]

If I wire it this way, I have to wire the FET footswitch different from normal. My hope was to use the same foot switch as my ODS and just swap it as needed since it lives on my pedalboard.

I don't think so, as long as your foot switch is wired in the usual way.

BTW, what's the purpose of the 100n cap? I don't have it on my ODS and haven't noticed anything unusual when switching

It's there to keep the switch contacts from arcing.

[Vertigo]

If I wire it this way, I have to wire the FET footswitch different from normal. My hope was to use the same foot switch as my ODS and just swap it as needed since it lives on my pedalboard.

I don't think so, as long as your foot switch is wired in the usual way.

BTW, what's the purpose of the 100n cap? I don't have it on my ODS and haven't noticed anything unusual when switching

It's there to keep the switch contacts from arcing.

So I must not be understanding it then. I admire how easily you seem to solve these problems. My brain is cramping and I'm going to make a few drawings to try to understand this better...and then put a cap in my ODS to prevent arcing

[Vertigo]

OK, if I'm understanding this, when the knob on the Pull-On switch is pulled, it connects the relay to ground, rendering the foot switch ineffective, but routing the signal through the FET. When the switch is pushed, the relay is energized and the footswitch will function.

Is this correct?

FET SPST.png

[martin manning]

That looks correct. Grounding the relay with the pull switch energizes it, and it routes the signal through the FET. The foot switch does not function, but its FET LED will stay on (and I'd call that a feature, not a bug). When the FET relay is not grounded by the pull switch, the foot switch controls it. I'd draw it like this:

[Vertigo]

Ready for power after I give it another thorough lookover. Caught a ground on the preamp that I missed earlier. Fingers crossed that this comes up as easily as the last one did.

5C026FAF-38DA-4529-AED9-2BA7927C50E3_1_105_c by Sean Chaney, on Flickr

[Vertigo]

Set it up on the bulb limiter and the bulb didn't turn on. Starting where the power comes in, I've got ~110V on the plug and across the power switch.

I've got 300V on each secondary wire on the bias board
416DC on the B+ output on the bias board and at the other end of the wire on the PS board
The heaters are reading 3.1V

I'm still not feeling confident with this part, but this is looking good so far, right?

edit: I just realized that the bulb IS turning on, but it's so dim that I can't see it when my shop lights are on. There's no bright instantaneous burst when I turn the amp on though...is that cause for concern?

[erwin_ve]

Set it up on the bulb limiter and the bulb didn't turn on. Starting where the power comes in, I've got ~110V on the plug and across the power switch.

I've got 300V on each secondary wire on the bias board
416DC on the B+ output on the bias board and at the other end of the wire on the PS board
The heaters are reading 3.1V

I'm still not feeling confident with this part, but this is looking good so far, right?

edit: I just realized that the bulb IS turning on, but it's so dim that I can't see it when my shop lights are on. There's no bright instantaneous burst when I turn the amp on though...is that cause for concern?

Tubes are in?
Heaters are measured from 1 leg to ground? If so this looks fine.


Erwin

[Vertigo]

Tubes are in?
Heaters are measured from 1 leg to ground? If so this looks fine.


Erwin

Heaters were measured from each leg to ground. No tubes installed though

[pompeiisneaks]

Tubes are in?
Heaters are measured from 1 leg to ground? If so this looks fine.


Erwin

Heaters were measured from each leg to ground. No tubes installed though

With no tubes installed the amp will draw almost 0 current due to nothing to conduct it. the caps will charge up, of course but that's on the milliseconds level before fully charged I think so if you weren't staring at it first time you probably missed the glow. Subsequent startups may have happened before they discharged fully. Either way, putting in the tubes with the lamp in is a smart first step after checking you have a reasonable negative bias to the power tube grids, and that the negative bias is turned to the maximum negative value to keep the tubes cold/shutoff until you can adjust the bias. Then fire away.

~Phil

[Vertigo]

OK, another check

only power tubes installed at this point

Heaters - 3.33
All below are on the power board
B+ STB - 460
B+ rvb - 456
B+ can - 454

I'm getting 0 or -0 when trying to read the bias, regardless of how the pot is clocked. In going back and forth between the layout and my build, I can't find anything amiss.

[martin manning]

You won't get a reasonable bias voltage until you install the driver tube. It should be equal to your raw negative voltage now. Put the driver in and see if you can bias the power tubes.