Gates 5879 Pre's ID

[rackmonkey]

Was just posting the other day about doing a project using 5879s, which I have dozens of. Lucky me, got hold of a couple of 5879-based Gates pres over the weekend for cheap and I'm not quite sure what they are. Maybe Doug W or one of the other vintage broadcast gear gurus knows.

The guy told me they came out of the "low and wide" Yard console, but they don't really match up to what's in any of the catalogs (checked the '55, '57, '59, '60 and '63 catalogs). I thought they might be the M-5215s, but based on the schematic I have for that I'm starting to doubt it. I know the 5215 came in a 5879 early version and an EF86 later version. I have the 5879 schematic, and it appears I'm a resistor short and the primary winding on the input doesn't match the JAF-1s that are on these (JAF-1 is a single winding w/center tap, schematic shows two windings in series). The nominal frequency response doesn't seem to match up either. The JAF-1 spec says 60 - 15k. The low/wide Yard has 30 - 15k response. Printed board layout is different, too, from the 5215s I've seen with the multi-cap can under the board rather than on top. I checked the Dualux, Studioette, etc and most seem to use the M-5204s, which definitely doesn't appear to be what I've got here.

These are apparently speech input pres and like many of those Gates consoles from the era fed into the program amp, which is what's speced for mic input in the catalogs. I've got the opportunity to pick up the program amp too, but won't be able to get in touch with the guy for another week or so, so I'm hoping to find out what I can before then.

Any insight appreciated.

Sorry I can't figure out how to successfully embed a photo shared on Google Drive. Is anyone able to do that or should I just find another public location to store photos for embedding? Links below instead.

EDIT: Google discontinued support for hosting web images on Google Drive last year, according to their developer blog. Added images below via Imgur.

Thanks,
BT

https://drive.google.com/file/d/0B__Vr0ik2Gcgb09td29OaUdGNjQ/view?usp=sharing
https://drive.google.com/file/d/0B__Vr0ik2GcgcEp2UWw4bG5WSXM/view?usp=sharing

 

[emrr]

They say Gates on them somewhere?  Those are totally unknown to me, and not like anything I've ever seen in a Yard. 

 

[rackmonkey]

They don't, actually.  I'll take a few more pictures from other angles, but sounds like I might have to dig a little deeper to figure out what I've got here.

Thanks for the reply.

BT

 

[emrr]

They may be from cart machine electronics, or some other device.  They do look Gates, but not the standard Yard type. 

 

[Gene Pink]

... or some other device.

A long shot, but possibly a long distance telephone repeater?

Gene

 

[rackmonkey]

I started to think they might be out of some kind of cart unit after your initial reply, Doug. I've been combing the catalogs, but they don't tend to break out the internals of the cart machines like they do the consoles. Given the input transformer nominal frequency response (60 - 15k) it kinda makes sense that they might be tape recorder pres or something like that. Nothing that looks like an RIAA network on the board, so probably not phono pres?

I was going to just power them up with 300v B+ to test them, but now I'm thinking if they're tape pres they might take quite a bit less than that by design. Might start at 200v at move up based on what's on the scope/VM?

Those little ADC output transformers are tiny.  About the size of a UTC ouncer. Can't imagine they could handle more than about +8 dBm.

Anyway, thanks for looking! Whatever I manage to figure out on these I'll post back for anyone interested.

BT

 

[rackmonkey]

Traced this thing out tonight. Drawing below. Turns out, other than the transformers, there's only one difference between this circuit and the M-5215 circuit as represented on the Gates schematic for that pre (see dotted line on drawing). I don't know what effect connecting the V1 screen grid to V2's cathode vs connecting it to ground would have. Maybe someone could educate me.

Also took some shots from different angles.

I guess we can assume it's probably some kind of Gates preamp. If it's from a cart unit or something like that, it appears they reused the 5215 circuit and changed it to suit the purpose. Maybe it was the other way around, who knows. Anyway, this is what I've got.

 

 

 

 

[emrr]

Your dotted line can't be right, that would short out V2 R6 cathode.  V1 cathode R2  is also not right, it would be to ground.  The rest of V1 cathode is the standard feedback path. 

Definitely Gates.  Unusual to see a stock labeled transformer versus a custom #.  They did swap parts around at times if short on stock, I've seen SA-39's with Triad input transformers on adapter plates which suggests a lack of UTC on the shelf that day. 

 

[rackmonkey]

I goofed on R2. Correct that it should go to ground.  The dotted line doesn't indicate that the ground connection for C2 gets removed in the M-5215 Schematic when that connection is made. Meaning that on the 5215 Schematic I have, C2 doesn't go to ground, but rather is connected to V2 Cathode as shown. Schematic I compared to is attached. Would be interested to know what that difference does.

Mjrippe sold me a pair of real 5215s following this post (thanks again, Mike!).  It'll be fun to compare the two, although I don't expect these to sound as good as the 5215s with their wider bandwidth, bigger transformers.

Thanks for lending the knowledgeable eye, Doug.

Gates M-5215 Schematic:

 

[mjrippe]

Thank You, Nathan Bryan!  Glad they will be put to use.  Did they arrive safely?  Transformers are really not much bigger, but should be full range.

*sorry about the name change - had another GDIY transaction going on at the same time 

 

[rackmonkey]

Got 'em, Mike! Thanks again! The transformers are noticeably bigger and heavier than the ones on these, but we'll see if/how that affects the output.

Bryan

 

[marcuswilson007]

I've just started working on 12 of the M5215 preamps, hoping to rack them in pairs. Powering up the first one today.