Ampex 350 Power Supply build?

[soulsystem]

I have an Ampex 350 preamp without a power supply. I've heard people say they can be built. The power supply unit that originally goes with it is 3731R2. Anyone out there able to point me in the right direction?

 

[Brian Roth]

I had the same thing come up years ago and actually had an original PSU to work with, I took various measurements and scrawled them <g> on a copy of the original Ampex schemo. I attached a scan of my doodles. I'm pretty sure I made up a "candidate" BOM to replicate the supply. Hopefully it's on my hard drive.....

Bri

 

[soulsystem]

I had the same thing come up years ago and actually had an original PSU to work with, I took various measurements and scrawled them <g> on a copy of the original Ampex schemo. I attached a scan of my doodles. I'm pretty sure I made up a "candidate" BOM to replicate the supply. Hopefully it's on my hard drive.....

Bri

If you do have the BOM, that would be vry helpful. Thanks!

 

[Brian Roth]

I found a very clean scan of the PSU schemo in my files and attached it. Just a few thoughts:

1. The B+ supply uses a 5Y3, which is a workhorse tube. In these times, solid state rectifiers would be a good alternative.

2. The DC filament supply used a selenium rectifier. Those are not only obsolete, but when they fail, they emit obnoxious (toxic?) fumes. Again, I suggest silicon rectifiers.

Duncan Amplifiers website has a cool program called something like PSU Designer which allow you to do "what if" designs for situations like this.

Bri

 

[Brian Roth]

Sorry....the BOM I recall was for a totally different tube power supply I was designing for a friend around that same time. So, all I did was document an original Ampex PSU as shown in the scan in my first reply. I'm certain we can figure out how to replicate that PSU with currently available parts.

Bri

 

[soulsystem]

Sorry....the BOM I recall was for a totally different tube power supply I was designing for a friend around that same time. So, all I did was document an original Ampex PSU as shown in the scan in my first reply. I'm certain we can figure out how to replicate that PSU with currently available parts.

Bri

Thanks, @Brian Roth - Are you interested in building one? What do you suppose it would cost? Feel free to send PM

 

[samplebias2]

How about some pics! I have a complete preamp that I no longer need since I finally got a complete machine.

 

[MidnightArrakis]

Thanks, @Brian Roth - Are you interested in building one? What do you suppose it would cost? Feel free to send PM

HEY THERE!!! Once both you and Brian Roth get a schematic designed and finalized, I can assist you with the mechanical design of the chassis and any PCB-designs, should they also be required. And, if needed, I can also have the sheet-metal work fabricated for you and shipped to your front-door!!! After taking a look at the photos that "SampleBias2" had included (THANKS!!!), it doesn't appear to anywhere near difficult to do at all!!! All I need are more accurate mechanical dimensions in his original hand-drawn sketch that Brian had shown.

And.....just as a means of gaining a certain amount of "trust" from somebody that you don't know, I have attached a PDF file containing several examples of rack-mount chassis that I have designed for various other companies. You will notice that these designs are largely audio and video-based equipment chassis.

If you need the help.....just let me know, OK??? If not.....then, that's fine as well.

/

 

[Brian Roth]

I've been migrating to a new computer after a recent hard drive crash (fortunately, my backups of data files were pretty recent) and just reinstalled Duncan Amplifiers' PSU Designer software.

I've been looking through Antek transformer choices and hope to start dropping candidates into PSU Designer and do "what ifs" soon.

Grids

www.antekinc.com

Bri

 

[Brian Roth]

Question to :

soulsystem​

I know some (many?) folks remove tubes from the 350 units that are not required to re-purpose the box as a mic preamp. That impacts the current draw for both the B+ and filament rails.

Bri

 

[MidnightArrakis]

WHELPP!!!.....IT'S A START!!!.....





NOTE: THANKS, BRIAN!!!

JBW

/

 

[Brian Roth]

Hiya JBW/Arrakis! My old reversing engineering notes were intended to assist some folks from the Ampex mailing list who were restoring old 350 machines and thus wanted a "drop in" PSU replacement. That project never got off the ground.

In these times, the electronic units (many folks call them "preamps" which is a wrong description of the original function) from the old Ampex machines ARE being gutted/modified/bastardized for usage as a mic preamp. I hate to see this happening....with the transports being sent to a landfill....but it's reality.

I see no need to faithfully recreate the 350 audio power supplies unless one wants to fully restore a 350. That is a complex project!

Instead, I'm thinking along the lines of a new PSU ***BASED ON*** the original schematic but in a package that doesn't have to fit the footprint of the OEM supply as required when doing a full restoration of the recorder.

The schematic is bare-bone simple from that 1950's era. One gotcha is the OEM power transformer. It had four secondary windings supplying:

1, High voltage for the B+ rail.

2. 5 VAC for the 5Y3 B+ rectifier.

3. "Whatever VAC" <grin> to feed the selenium rectifier which supplied DC to the filament of the input tube.

4. 6.3 VAC for the rest of the fire bottles.

If a change to the OEM design is made using modern silicon rectifiers for the B+, winding #2 (5 VAC) is no longer required.

I've been pondering the use of Antek toroidal transformers to provide at least two of the remaining windings, with a second "vanilla" transformer to provide the remaining filament winding. The Antek transformers are FAR less expensive compared to Hammond iron.

It's all just mental masturbation <g> for me at the moment.

I'm sure someone will step in and propose a complex solution using all sorts of modern solid state regulation circuitry.

I'm envisioning: a power transformer (probably a second for a filament rail), some silicon diodes, a pair of filter chokes, and some electrolytics to replicate the OEM supply's functionality for a "mic preamp" adaption of the original Ampex unit. That is the crux of the Ampex 351 PSU (with minor mods to the original design...silicon diodes) I am pondering.

KISS!!! Let's not overthink this with all sorts of "I can make this better" ideas. It worked for Ampex back then and they made a ton of money selling 350 machines with "stone age" designs.

BTW, I did find a Triad candidate for the B+ filter chokes....

Bri

 

[MidnightArrakis]

Well.....whenever you get to a point of being beyond "mental masturbating" (imagine the vocal sounds of Robert Plant during the "space-out" period [2:10 - 2:20] of "Whole Lotta Love" !!!), 1) send me PDF files of all of your component datasheets, 2) Let me know of the size and shape of the enclosure you would like to have and I can easily enough whip something up for you!!! Unless, of course.....you are able to find some BUD or HAMMOND enclosure that fits your needs. Then you can "hack and whack" as is necessary to make everything fit and go together. YAY!!!

I was looking at the ANTEK toroidal transformers myself for a special "Power Distribution" project I was thinking about. These transformers were in the neighborhood of 1,800VA and 2,500VA and the ANTEK's became too pricey for me.

[Let's not overthink this with all sorts of "I can make this better" ideas] -- OK!!!.....I personally am not "thinking" or "overthinking" anything whatsoever!!! I just saw this thread about some guy needing to put together an AMPEX 350 power-supply and I simply offered him my expertise of performing 3D mechanical designs in order to help him out. I do, however, find it a bit unusual that the OP (SoulSystem) has not responded back to any of the comments left here in response to their original posting. That then makes me think that their wanting a "New/Old" AMPEX 350 power-supply isn't really - THAT - important to them after all. So.....because of that, I am guessing that this thread is actually a "dead issue" from here on out!!!

[I did find a Triad candidate for the B+ filter chokes] -- Well.....as I have stated previously, once you "git yer shit tahgezzer", send it all to me along with with however you envision the enclosure to be and I can whip you up something pretty nifty!!! And, as I have also mentioned previously, I (or, you) can e-mail my CAD-file to one of several specialized "prototype & low-volume" sheet-metal shops that I am aware of in order to have your enclosure fabricated and shipped to your front-door.

Whenever you're interested in tackling this project of yours, just let me know, OK??? Maybe send me a PM would be best.

By the way.....I have browsed through your website and I have seen what you have accomplished "long, long ago" and I am very highly impressed with all of your end results!!! I was actually thinking that it was too bad that you and I didn't know one another "way back then" and teamed up to be a "design team" together!!! THAT would have been a FUN THING to do together!!!

JBW

/

 

[rmburrow]

I found a very clean scan of the PSU schemo in my files and attached it. Just a few thoughts:

1. The B+ supply uses a 5Y3, which is a workhorse tube. In these times, solid state rectifiers would be a good alternative.

2. The DC filament supply used a selenium rectifier. Those are not only obsolete, but when they fail, they emit obnoxious (toxic?) fumes. Again, I suggest silicon rectifiers.

Duncan Amplifiers website has a cool program called something like PSU Designer which allow you to do "what if" designs for situations like this.

Bri

I like the 5V4 wherever I run into a 5Y3. No socket rewiring needed. The indirect heated cathode in the 5V4 brings up the B plus slowly, minimizing surge voltage. BTW a nice regulated power supply for audio work is the Tektronix 160A. The Tektronix supplies were used in TV stations to power waveform monitors and other gear. Well built unit.

 

[neowalla]

I have an Ampex 350 I'm looking to sell. Mono full track 1/4". I was planning on putting it up on Reverb. Maybe I should post it here in the marketplace?

 

[soulsystem]

I know some (many?) folks remove tubes from the 350 units that are not required to re-purpose the box as a mic preamp. That impacts the current draw for both the B+ and filament rails.

Bri

@Brian Roth If it would make it easier to build a power supply I would consider removing the tube. I thought the tube would be part of the character/coloration of the preamp. But if I can't power it up, then I can't use it at all!

How much do you think you would charge (ballpark) to build such a unit? Feel free to send a message

 

[soulsystem]

I just saw this thread about some guy needing to put together an AMPEX 350 power-supply and I simply offered him my expertise of performing 3D mechanical designs in order to help him out. I do, however, find it a bit unusual that the OP (SoulSystem) has not responded back to any of the comments left here in response to their original posting. That then makes me think that their wanting a "New/Old" AMPEX 350 power-supply isn't really - THAT - important to them after all. So.....because of that, I am guessing that this thread is actually a "dead issue" from here on out!!!

@MidnightArrakis thanks for your input here! I did see your design and I guess you are correct in saying it doesn't have to be exactly like the original Ampex unit. I'm just a bedroom producer who got a decent deal on the Ampex unit but wasn't thinking clearly about the power supply issue. I would just like to record some mics through this unit and if I like it, keep it in my studio. If not, I'll try to sell it. I see @Brian Roth website and considerable amount of knowledge in these old units. Appreciate you guys taking interest and for all your comments and suggestions.

 

[Brian Roth]

I have been distracted by a family member's health issues, so I haven't spent much time trying to create a version of the PSU built with modern parts, yet staying close to the original Ampex design.

Bri

 

[soulsystem]

I have been distracted by a family member's health issues, so I haven't spent much time trying to create a version of the PSU built with modern parts, yet staying close to the original Ampex design.

Bri

@Brian Roth very sorry to hear. Family first. If/when you want to chat about this send me a message

 

[Brian Roth]

One missing thing from the power transformer specs (Hammond and Antek) are the resistances for the secondary windings which come into play when trying to do a sim.

Bri