Near each other? -perhaps neighbours in the same solar system! one is a variable-mu element, the other is a FET. -If they can be considered very "similar" then it shoudl be possible to make a FET version of a Fairchild... (I think not!)
The 176 ...and 175, and -rarest of all the 177 are OPERATIONALLY similar to the 1176 et all, insofar as the threshold is fixed, and the input gain drives the compression. (Unlike other units which have a threshold control for example). (the 177 had no metering, and the 175 I think had no 'trim' controls (labeled "Vernier"); just the stepped input and output levels)
This is somewhat timely, because last week I dropped off a newly-completed 'Bloo' 1176 type unit to a local studio owner for his opinions. -I'd built it specifically to investigate why my OTHER bloo units sounded 'hairy'. -People LIKE the way they sound, and everyone told me that the units did NOT sound like Purples or UA's when you pushed them hard. -I wanted to find out why, but nobody wanted me to 'change' anything, in case it lost the 'mojo'!
-So I built a third, and -surpise surprise- NO MOJO!
I ended up with the lids off of all three, probing around and looking at all of the revisions, and I discovered where I'd used a 'wrong' value resistor in the output stage. -This was biasing the output to run MUCH hotter, and causing some power rail 'sag', which was fuzzing the output stage (and others, probably!) somewhat.
So I made the 'effect' switchable, and have dropped it off with a trustwirthy engineer, for evaluation. -Also last weekend, I dropped the original two off for Colin Richardson to use on a project... Again, I'll hear back on how they were perceived.
The first ones were Blue-Stripe and Revision A. Only about 25 were made.
There was a interim Revision 'AB' which had minor resistor and capacitor changes, I understand.
Revision B followed shortly, still blue-stripe. This used FETs ONLY for the gain reductionand metering bridge elements... Two FETs per unit. (Revisions A and AB had used FETs in the input stage as part of the signal amplification path).
Revision C was the first black-face, and the first to bear the 'LN' mod from the factory. -Earlier 'B' versions were able to be retrofitted with "the blob", which was an epoxified lump of circuitry designed by Brad Plunkett (later designer of the LA-3) to reduce noise and control distortion around the FET.
Revision D re-laid out the main board to include the blob components on the board, but apart from the layout, nothing changed.
Revsion E also nothing in the circuit changed... just a slide-switch added to the transformer primary winding to allow switchable AC voltages.
Revision F saw the output stage changed from a tertiary-wound transformer driven by a class-A all-discrete signal path, to an IC driving a simple primary/secondary output transformer. This was capable of driving higher loads with less distortion, but is less loved.
Revision G saw the INPUT transformer eliminated and replaced by a differential IC front end. (The input transformer had changed from a 'Peerless' in the earliest blue-stripe models to a UTC "ouncer" by the start of the black-face 'C' revisions). By now, the gain reduction meter-drive circuitry was also an op-amp, and units were cheaper to manufacture, though less loved. MOST of these last units were silver-face, but black-face versions exist. NEVER judge a unit by its front panel!
Note: Revisions C, D and E were all the same in terms of circuitry, -Any B units which have "the blob' inside were ALSO the same circuit. Revisions A, AB, F and G and B without 'the blob' inside are all different from one another, and from the "golden" period from C to E'.
On a related note: I was rummaging the other day, and delighted myself to discover TWO new-old-stock 0-12 "ouncer" transformers in a box I'd forgotten about. -Guess who's going to build a couple more 1176 replicas? -Maybe I'll have a crack at the version 'A' this time?