The preamp cans with what I feel is about 99% surety, use a Beyer peanut, either the stud mount style such as found in the MX-10, or the pcb style, such as used in the AG440 reproduce preamp. Note that the small metal can transformers do not say Beyer on them, but given that Beyer was marketing these parts in the United States at the time, most of us are pretty confident that they are actually made by Beyer.
I found that I had images of the insides of one of the AG440 type units, part number 4010066B. I also have images of the 40dB nuvistor preamp, part number 96440-01. See the links, below
|4580100-10||AM-10||peanut||visual by RChinn. Marked Ampex, W. Germany.|
|4580100-10F||MX-10||peanut||visual by RChinn. Same yellow band as confirmed by LCross. No other markings.|
|96908-01||MX-35||peanut||manual, type confirmed by LCross.|
|4580100-10||MR-70 accessory preamp||peanut||manual, parts list, type confirmed by LCross|
|4580197-01||4010066B preamp||PCB mount||manual, type confirmed by photo|
|4580199-01||AG440 Reproduce Amplifier||PCB mount||
|Ampex P/N||Description||Used on||Source|
|01-96440-01||Preamp, plugin, 40dB, tube (nuvistor)||
354, PR10, MR70, SA-10
SA-10 uses -03 variant.
|Sales lit, MR70 manual. Confirmed that it uses a peanut transformer.|
|01-96440-04||Preamp, plugin, 60dB, tube (dual nuvistors)||354, PR10, MR70, SA-10||
Sales Lit and MR70 manual
LCross has two of these, with different peanut transformers within. One is p/n 4580100-10F, the other is p/n 96908-01.
|4010066B||Preamp, plugin, 40dB, transistorized||AG440, AG500, AG600, AA80, AM10||
manual, sales lit, 1968 price list
The line input transformers couldn't use a Beyer peanut transformer. First, they're too heavy. You could ascribe that to extra shielding, but this is a line level transformer, and the extra weight is undoubtedly due to core size rather than shielding. At line levels, although shielding is needed, it is not nearly the degree that a microphone input transformer needs. Goran already mentioned that the Beyers will not handle line levels, not even on a bet, so I'll just reiterate that.
I have a couple (96134-01 bridging) where the octal base rotates freely, and I'm betting that all of the wires are broken inside. I think I'll sacrifice one of them to have a look.
I turned out that just the octal base was loose, so a bit of judicious prying revealed a transformer roughly the size of a Jensen JT-115K sealed into the top half of the can. No Beyer Peanut transformer was found.
I bought some transformers a long time ago from Modular Audio Devices (aka Melcor) that looked like Beyer peanuts, but didn't say Beyer on them. I don't know who made them, and my recall is that they were not marked, but they were very similar in appearance. I never measured them. I think they were made by Microtran (could have just as easily been made by Beyer). The Melcor p/n was 400-16.
Ampex Plug-in Mic Pre 1971 (p/n 4010066B, has pictures), 1.57mb
Ampex Plug-in Mic Preamp, description of 4010066B, 230kb
Ampex Plug-in Input Transformers - describes line input transformers, 12.54kb
Transformer pages from 1968 Ampex Parts List. 340kb
MR70 Preamp, 40dB, 01-96440-01
MR70 Preamp, 60dB, 246kb, 01-96440-04
MX-35 parts list, page 5, 67kb
Microtran Peanut Transformers, from 1974 catalog, 163kb
Beyer Peanut Transformers, from 1969 Beyer catalog, 362kb
Beyer Transformer blurb from Gotham Audio, 363kb
Last modified 08/17/2009.
Goran Finnberg's mod for the 39V regulator
Last modified 08/17/2009.