Wiring up a Hammond 1620?

[studiodunn]

I have this wreck build started in another thread, but thought I would ask this question over here in case anyone else might need help.

I'm guessing this OT has been used by a few on the forum and wondered if anyone had a wiring diagram for this Ot using 4, 8 and 16 ohm outputs.
I'm admittedly a novice here, but I can't wrap my head around wiring the secondaries up using 3 jacks. I wasn't planning on using a impedance switch and I'm thinking that is my first problem.

If anyone has a napkin doodle to share I 'd appreciate it.

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[Phil_S]

I think this is what you want. I'm reasonably sure someone here gave me this diagram. I don't remember who it was. It dates from 2012. I have a similar OT. It's still in the box, but I do have a rotary switch for it! I find anything more than a SPST switch to be challenging.

Spud at AX84 gave me this written explanation:

You can do this a few different ways, one way would be to find a 5 pole 3 position rotary switch - good luck with that - both in finding one and also with the cost. It would be pretty straight fwd with one of those since you have 5 wires coming out of the OT - just connect them to the common side then using the switch side, strap them like the diagram shows. But as I said, good luck finding one and even if you can it will be pretty pricey and probably gigantic as well.

A more reasonable way is to use a more common, smaller rotary (6 x 2 or 4 x 2/3) and a SPDT switch in combination. A 6 pole 2 position rotary (using only 4 of the 6 poles) or a 4 pole 2/3 position (for 3 poles just wire 2 of the positions the same). In addition, you will need a SPDT switch.

Take the 4 main wires (ignore the Yellow one for now) and solder them to the "common" side of the rotary switch working from positions 1 - 4 use G/Y for 1, BL/Y for 2, G for 3, BL for 4. On a 6 pole switch, use the first 4 and ignore the rest. On the switch side for position one, strap poles 1 + 3 and 2 + 4 like in your diagram. This is your 4 ohm (and 8 ohm) position, then strap 2 + 3 on position 2 for our 16 ohm setting. If you have 3 positions, choose either the 4 ohm or 16 ohm and strap them the same as one of those - your choice, doesn't matter. (So you will have 4-4-16 or 4-16-16 ohm on the switched side of the rotary.)

Now run a 2 wires from the common side of rotary switch - one from position 1 (G/Y) to one of the outer poles of the SPDT switch (we'll call it SPDT position 1). Run the other wire from rotary position 4 (Black) to the GND side of your speaker jack (sleeve).

On the SPDT switch, attach the yellow wire we ignored earlier to the opposite side from the G/Y jumper you just attached (this will be Pos 2 of the SPDT). From the middle position of the SPDT switch run a wire to the TIP connection of your speaker.

When the rotary is in position 1, and the SPDT switch is in Position 1 (yellow side open), you get 4 ohms (G/Y wire is in circuit). If the SPDT is flipped to position 2 it will be 8 ohms (Yellow in, G/Y out). If you switch the Rotary to 16 ohm position (Position 2), you should have the SPDT on Position 1 (4 ohm) but having it on pos 2 shouldn't be THAT bad - maybe a little bad but not fatal. Just be careful if you are concerned about it, you could ask Hammond what the impedance would be if it was wired that way.

So, in summary: Rotary switch position 1 + SPDT pos 1 = 4 ohms. Rotary pos 1 + SPDT Pos 2 = 8 ohms, Rotary Pos 2 + SPDT pos 1 = 16 ohms, Rotary pos 2 + spdt pos 2 = Unknown.

Another option is to use a 4PDT switch (with NO center off) instead of the rotary. Same deal, common (middle row) and 2 switch positions (top and bottom row). Keep in mind that when the bat is up, the bottom contacts are engaged and vice-versa. You will still need a SPDT with the 4PDT.

[sluckey]

You may be interested in this...

https://www.tubesandmore.com/products/s ... 600-series

I have a 1650 that uses that same awkward secondary wiring. If you look closely you will notice the jumpers for 8Ω and 4Ω are the same. I chose to just use the 4 and 8Ω taps wired to two separate jacks and just taped off the 16Ω tap.

[studiodunn]

Awesome! Thank you for the help.

I thought about omitting the 16ohm tap for the reasons you mentioned Sluckey, but every cab I have is 16ohm and it just seems like a negative to not have it.

That pre wired switch is the ticket!

I'll just wire my already drilled 3 jacks up for 2x8ohm and 2x16ohm

[pompeiisneaks]

I also noted wires coming through the metal chassis w/ no rubber gasket or protection, I'd fix that asap, as the wires, over time, can rub against the metal, get worn through and hit chassis, causing a very dangerous situation.

~Phil

[studiodunn]

I also noted wires coming through the metal chassis w/ no rubber gasket or protection, I'd fix that asap, as the wires, over time, can rub against the metal, get worn through and hit chassis, causing a very dangerous situation.

~Phil

Thanks Phil. I have grommets that just weren't installed yet.

[studiodunn]

Quick question.

Do the Blu/Yel and Brn/Yel UL taps just get individually sealed off and coiled up?

[Stevem]

Yes, if your not using those UL taps then just heat shrink them off and dog bone them , then cable tie them up to the OT.
But if you want the best way to go you should cut them off just long enough that should you ever want to use them you have enough lenght to splice new wire back to them.
This will make for the least possible unstable issues cropping up from being long yet coiled up!