Ampex 351-2 restoration project

mhardy6647

1) your definition 'ancient scope' and mine are somewhat misaligned.

DSC_1559 by Mark Hardy, on Flickr

(although I did get rid of my father's truly ancient Precision scope -- with a bandwidth of a couple hundred kHz, if memory serves)


2) nice lookin' iron!
I just got a custom PT for a little vacuum tube phono preamp project that's pending here. Now just need to source... most of the rest of the parts. May be gettin' the tubes tomorrow, actually. Another story for another day.

[Deleted User]

I like that 'scope, compact and does the job. Plus it's cool that it belonged to your dad, I use lots of tools that were my pop's. That h/p 'scope was purchased from Peter Aczel who you might remember wrote the Audio Critic magazine. I think it was advertised in The Stereophile magazine's classified.
If you need any parts for your project let me know, I've lots of odds and ends available.

[Deleted User]

I've decided to make a change in the manufacturer of the output transformer used in the 351's playback electronics. Instead of the Sowter transformers which use copper wire for all of the windings I would go with ones made by the Electra-Print company which offer stranded silver wire for either the primary or secondary or both. Silver wire audio transformers have been considered, for many years, to make an improvement in audio reproduction. Due to silver's higher sensitivity to flux change it is able to reproduce lower level information and hopefully more detail. I have a friend who makes spectacular recordings and he has used the same transformer maker for all of his recording and playback. I wanted to paint the transformer's frames so I first masked off the non-painted areas and then painted them with Model Master spray paint.
Before I take out the original transformers and replace with the newer versions I'm going to try and see if I can measure the differences between the copper and silver designs. Low level flux sensitivity measurements? I think current flow in the secondary relates to flux density, but I'll need to do some reading on this.

[Deleted User]

I've been able to return to the 351 project and have replaced both of the original output transformers with the Electra-Print made silver wire replacements. I had to remove the original transformers and find a new spot in the chassis as far away from the AC transformer s possible. Then rewire the primary, secondary and feedback connection to the rest of the circuit.

Once I finished the left channel electronics I connected it back with the transport just to hear what differences I could detect. That channel was certainly quieter, there was a faint very low level humming from the right channel but the left was completely quiet. The repositioning of the output transformer and using shielded Cardas cable for the secondary connections must have been the cause. Now to hook both to the transport and listen.

JayCee

KennethSwauger wrote: »

Before I take out the original transformers and replace with the newer versions I'm going to try and see if I can measure the differences between the copper and silver designs. Low level flux sensitivity measurements? I think current flow in the secondary relates to flux density, but I'll need to do some reading on this.

Were you able to measure a difference?

tonyp063

Thank you Ken.
This is lovely stuff.

The photos. The restoration information. The knowledge.
I very much appreciate what you have shared.

[Deleted User]

"Were you able to measure a difference?"
I'm afraid I missed that opportunity, I got preoccupied with the Advent 100A project and then forgot about trying to figure out how to measure differences. I just started in on pulling the old transformers and getting the switch done.
I started doing some listening this afternoon and have noticed some changes. I'll elaborate when observations are firmer in my mind.
Thank you @tonyp063 for your comments, I know this method of enjoying music and audio gear isn't very common and I'm glad it's at all interesting.

audioluvr

tonyp063 wrote: »

Thank you Ken.
This is lovely stuff.

The photos. The restoration information. The knowledge.
I very much appreciate what you have shared.

Agreed. I have no idea what you are talking about but it makes me want to buy a R2R to restore as a winter project.

[Deleted User]

After the new output transformers were installed I found that I had to recalibrate the playback EQ. It had changed by a few dB with the different transformers. I removed the permanent resistors and returned the variable trim potentiometers and adjusted the circuit to the NAB and IEC standards for both electronic assemblies. Then when I measured what the new resistor values should be ordered fixed resistors from Digikey. Then after installing them I remeasured the frequency response curves for NAB and IEC playback. Now after considerable listening and appreciation for the changes the silver transformers did I could install the transport and electronics units into the rack style cabinet.

[Deleted User]

[Deleted User]

This is the rear of the cabinet with the Tentrol constant tape tension controller mounted to the inside.

[Deleted User]

[Deleted User]

SIHAB

Holy sheep!
Wow!

p.s.
I have a not working Teac coming my way via a dumpster diver...

mhardy6647

re: @KennethSwauger 's most recent set of p R -o-n I mean eye candy photos -- oooooh.

The deck, electronics, and cabinet are beautiful and inspiring.

JayCee

Wow! Just, WOW!

tonyp063

That is just simply beautiful.
I can only imagine how it sounds.

Well, well done. Thank you for sharing.

[Deleted User]

Thanks for everyone's comments, I really appreciate them. I just noticed that I started this thread in November of 2015 and it's finished five years later.

msg

Wow, Ken, that looks like something that belongs in a magazine. Great photos, too. The warm lighting gives a sense of atmosphere, just like what I'd expect for listening sessions with a piece like that. I've never had the pleasure of hearing a proper tape.

audioluvr

KennethSwauger wrote: »

Thanks for everyone's comments, I really appreciate them. I just noticed that I started this thread in November of 2015 and it's finished five years later.

Anything done right takes time. Lots of time. I've never done electronics but I've restored several cars, a 1970 Starcraft Holiday (boat) and now almost done with my 1976 34' Holiday Rambler Presidential 5th wheel (made by Harley Davidson). So I know the dedication it takes.

Excellent work!

R

CH46E

I have Never had the pleasure of hearing a reel to reel. Frind of mine in Jr high, his mom had one. Should have asked to hear it.

How would tall describe the sound? As compared to maybe a LP?

pitdogg2

You ever listen to a cassette player? Not much different just a heck of a lot more tape.

SIHAB

There must be something to it as R2R tapes new go for $500.00

[Deleted User]

The best analogy I can come up with is to relate it to analogue photography, back when people used film negatives and made prints from them. The best, most convincing copy of a print was to start with the original negative, put it into a high quality enlarger, use the very best photo sensitive paper and having the original photographer make a print. The odds were good that the results would be as close as possible to what the very first image seen by the photographer would be. Maybe there would be very slight differences in shading due to the manipulations of the photographer during the print's exposure step. But by carefully controlling the variables, such as exposure time, any filters used, the condition of developing chemicals and other factors an almost ideal copy could be made. And yes depending upon who the photographer was it would be expensive.
This is broadly similar to listening to master quality open reel tapes and even early '60's two track prerecorded tapes. You are closer to the original, everything that we audio enthusiasts find important (wide dynamic range, extended frequency response, low distortion and minimal coloration) to believing something sounds real is possible.
Plus there's the satisfaction of seeing the mechanical process fully in front of you. No silver disc disappearing in a hidden drawer, but physically turning reels of thin tape moving from one hub to the other. A precision mechanical device that you have to operate and maintain and care for, designed and built in another era.

msg

Man.

mhardy6647

pitdogg2 wrote: »

You ever listen to a cassette player? Not much different just a heck of a lot more tape.

well, if we're talking consumer decks, true.

If we're talkin' Studer, Ampex, Scully, MCI (and even Stellavox and Nagra) kind of stuff -- not so much.

[Deleted User]

For additional information on this part of the hobby I can recommend: https://thereeltoreelrambler.com

mhardy6647

SIHAB wrote: »

There must be something to it as R2R tapes new go for $500.00

Don't forget that those are real time duplicated at 15 ips, half-track. That's quite a bit of tape and real time. I also reckon that the licensing costs for the content of these low production volume tapes is not insignificant.

The cost of brand new blank tape is still (borderline) reasonable -- assuming one is dabbling in quarter-track stereo at 7-1/2 ips (i.e., 1200 or 1800 foot, 1/4 inch tape).
https://www.atrtape.com/
https://www.splicit.com/
https://www.recordingthemasters.com/

Good quality used tape is a viable alternative, albeit not exactly inexpensive any more. Good used tape (e.g., Maxell UD) will last for a long time if properly stored -- and tape's reusable! It can be erased to "as new" noise levels with a bulk eraser.

Just take care to avoid (or at least to proceed with extreme caution with) tape formulations known to exhibit "SSS"
https://psap.library.illinois.edu/collection-id-guide/softbindersyn
https://www.npr.org/sections/npr-extra/2012/05/30/153917107/a-sticky-situation-baking-the-tapes

SIHAB

Thanks doc! I thought I was being hissed at
Returning now to KS's R2R thread.
It looks to me like something the best in the biz would own!

Jetmaker737

Ken, thanks for sharing the journey with this beautiful machine. Same with the Advent NR unit. As a RtR "hobbyist" I find your work inspiring and fascinating.