# Can't identify old part from 1976 DC motor controller

#### Stevereno

Joined Jan 12, 2015
3
I'm attaching two photos of an unknown part from the speed controller of a 1 hp DC motor on a potter's wheel built in 1976. I have had no luck finding it via Google, although to be fair I'm not a search expert. I'd really like to fix the wheel but since I don't know what this part is/does, I don't know if it's malfunctioning or what I would replace it with.

Here's a brief description, in case it's not clear from the pictures. The part is stamped on the top with the number "30" in a circle. The case is black plastic (possibly bakelite?). It has six round wire legs (not flat pins like an IC chip). The legs protrude upward from two plastic "shelves" on either side of the part (three per shelf), then bend around 180° to stick down into the circuit board. On the bottom of the part is stamped
NPI
PA-2392
7435

Also stamped on the bottom are the numbers 1 through 6, corresponding to the round wire legs.

Does anyone know what this is?

Thanks!

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#### tcmtech

Joined Nov 4, 2013
2,867
Most likely a old style pulse transformer for triggering an SCR.

#### Stevereno

Joined Jan 12, 2015
3
Very cool! I looked up "pulse transformer" and found the attached pdf from 1999 for a Rhombus P/N T-1214. This looks very much like the unknown part, and, on my circuit board legs 6 and 4 are connected to the gates of two thyristors. Thyristors and the like are all brand new to me, so if you don't mind would you confirm that this is consistent with it being a pulse transformer?

Thanks again!

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#### GopherT

Joined Nov 23, 2012
8,012
You might be better off saving the motor and buying a new DC speed controller. 1976 is getting pretty old for something like this.

Might be able to find something on eBay for $100 to$150. On the other hand, if you are able to safely make it work and have the time & interest, then go for it.

Joined Jul 18, 2013
23,612
I am guessing it is a 1:1:1 pulse transformer, these were common for that vintage, I used to get mine from Hammond, they should be still available.
If you were to reverse engineer it you could also use the later method of a couple of Triac output Opto's.
KB make modern SCR drive boards for DC motors.
Max.

#### Stevereno

Joined Jan 12, 2015
3
One more question ... in the schematic of the Rhombus pulse transformer above, what does the black dot mean on pins 1, 3 and 5?