A #102 Attempt - First amp

[martin manning]

the footswitch toggle caps are probably to stop pops but I've never used them and had no problems.

Caps across the footswitch will suppress arcing, protecting the switch and relay contacts. The voltage and current are pretty low, though, and the diodes across the relay coils will also help.

[martin manning]

Is this looking OK?

You have an error in connecting the left ends of the lower two 22u caps together.

No reason to duplicate the eyelet board templates posted here, though (https://ampgarage.com/forum/viewtopic.php?f=5&t=29630). They are good to go, except I would ground the B+3 cap with the B+2 cap. All of the axial preamp caps are 22u 500V. The same template can be adapted for radial caps by drilling some extra holes.

[rootz]

I always thought those caps were there to prevent switch bouncing! Arcing with such a low voltage? Oh well, I learn something new every day.

[Vertigo]

You have an error in connecting the left ends of the lower two 22u caps together.

No reason to duplicate the eyelet board templates posted here, though (https://ampgarage.com/forum/viewtopic.php?f=5&t=29630). They are good to go, except I would ground the B+3 cap with the B+2 cap. All of the axial preamp caps are 22u 500V. The same template can be adapted for radial caps by drilling some extra holes.

Thanks Martin for pointing that out. I had actually removed the wire on the lowest 22uF cap, but posted the wrong screengrab. I'll swap the ground wire from B+3 too.

[Vertigo]

For the 6-0-6 filament transformer, is the Hammond P-T166G6 being used? (https://www.amplifiedparts.com/products ... pen-63-vct)

[martin manning]

For the 6-0-6 filament transformer, is the Hammond P-T166G6 being used? (https://www.amplifiedparts.com/products ... pen-63-vct)

That transformer will work with the relay supply shown in the #102 layout, which is a voltage doubler circuit feeding 12V relays. Note that it's secondary is "6V CT" which can also be described as 3-0-3. Is your relay supply board a doubler or a full wave bridge?

[Vertigo]

That transformer will work with the relay supply shown in the #102 layout, which is a voltage doubler circuit feeding 12V relays. Note that it's secondary is "6V CT" which can also be described as 3-0-3. Is your relay supply board a doubler or a full wave bridge?

Martin, I'm using the eyelet board layout you linked above. Like this:

Screen Shot 2020-01-31 at 9.51.53 AM.png

[martin manning]

Ok, FWB. You need a 12V PT if you use 12V relays. Hammond 166F12C, available from the same source.

[Vertigo]

Ok, FWB. You need a 12V PT if you use 12V relays. Hammond 166F12C, available from the same source.

Thank you, Martin!

[Vertigo]

After diverting my attention from this build for way too long...

I've read a lot of information about the footswitchable FET but I seem to be coming up short on solutions. I found this the other day, but the thread where I found it, I don't believe anyone verified it. Will this work? A recurring theme of my FET searches seems leads me to believe that it needs an L114b jack, so I'm confused as ever.

Followup question: is the shield from V1a connected to the other side of the 1M resistor?

Footswtichable FET Boost Layout.jpg

[martin manning]

Switchable FET schematic is here: https://ampgarage.com/forum/viewtopic.php?f=5&t=31084

[pompeiisneaks]

A recurring theme of my FET searches seems leads me to believe that it needs an L114b jack, so I'm confused as ever.

Followup question: is the shield from V1a connected to the other side of the 1M resistor?

That special jack is used to allow the 'switching' to happen based upon if you use the normal jack or the FET jack. If you're using footswitchable FET, then you don't need a special input jack.

As the schematic Martin linked shows, the shield connects to the ground side of the 1M resistor, yes.

~Phil

[Vertigo]

thanks gents!

Phil, that makes perfect sense after thinking about it a little bit. Those shunted terminals allow the signal to pass without needing to be plugged in. Thanks for pointing me in the right dirrection.

[Vertigo]

I did the 9V FET bias trick today (thanks Martin) but before I solder in the Rs resistor, does it matter much if the voltage it a little high or low at the drain? Voltage is 9.4V with a 3k3 and 8.6V with a 3k. If it matters, my batteries started at 19V when in series and quickly dropped as I was goofing around with resistors so I switched to a benchtop power supply set at exactly 18V and verified by my meter.

[Synchu]

Should be close to half the input voltage which is your case and I'd go with 9.4
Just finished a 2nd gen hybrid and the FET boost sounds absolutely phenomenal with this one.
I highly recommend going with the adjustable FET option (i.e. mounting a 10k pot in place of the FET jack, i.e. lifting the trimmer of the board).
Niki