Trying to understand this

[throbscottle]

Image shows part of the Y input circuit for a Shumberger oscilloscope of some vintage. You are invited to look at U1a and U1b. I believe U1 is a LM3045/46/86 or similar.
I don't get anything about how U1a is connected. Two of the transistors in the package have their emitters connected together for you, but then one of them has it's base and emitter tied together, and it's collector connected to the collector of it's pair. My best guess is it's for thermal stability because I can't think of another reason.
And then there's the other part of U1a, wrapped around the CC half of Q1. My best guess is it's some kind of bootstrap.
So anyway, I find it really interesting - would anyone like to help me understand what's actually going on?

 

[Diver300]

U1 is five transistors in a 14 pin package. As each transistor has 3 connections, they are one connection short so two transistors share pin 3 as the emitters. This circuit can't use two transistors where the emitters are joined, so the design had to have something to stop one of those transistors doing anything, so the base was connected to the emitter.

I don't know why the collector was connected to the other collector. It could the that the diode formed by the base-collector junction is protecting the other transistor in some way, but I think that it's simply an unused part of the integrated circuit that is U1

 

[Tony Stewart]

I agree.
I've never seen this before, but it appears to be a unity gain buffer with null offset adjust.
- emitter follower with controlled current sink and FET follower front-end with feedback current mirror around 7mA.

 

[Nigel Goodwin]

At a wild guess, perhaps it's something to reduce thermal drift?

 

[throbscottle]

Tony, is it the transistor with pins 12, 13, 14 that is acting as the current mirror to the lower jfet? And R14 is setting the current?
Probable datasheet here.
I checked the model number - this is on a 100MHz oscilloscope. Could that strange connection be bandwidth related?