Ampex electronics for the best possible sound

[hvbias]

Tom-I currently have an Otari MX-55 that I use with a pair of Ampex 350s. I love the sound of the Ampex 350s and they are the only tubes that remain in my system. I would love to hear a properly functioning Ampex 350 tape deck into my pair of Ampex 350 repros.

Do you use the stock output heads on the MX-55? What would be an average output one should be looking for with 350 tape pre's?

 

[mep]

Yes, I'm using the stock heads on my MX-55. The Ampex 350 tape deck had a playback head with high output and if you wanted to go into the Ampex 350s repros straight from the head on your deck you would need high output in order for it to work. This would most probably require a new head to be installed. The output from my MX-55 even using balanced cables is on the low side. I run the output from the MX-55 into the line input of the Ampex 35o repros using balanced cables and the volume is just right. This also allows me to use the IEC position on the MX-55 (the MX-55 has a switch to change between NAB and IEC) for all IEC tapes and the NAB position for NAB tapes.

 

[hvbias]

Thanks mep.

 

[RogerD]

I have got the electronics mounted and cables in place. I have a few more things to do and then I'm going to see how the Jack Mullin Special sounds. I have a Clarity Records CD that Robert Porter recorded using this MR70. It has some Bay Area artists such as Maria Muldaur and Dan Hicks. The Cd sounds great....plenty of presence and a rich weighty sound....just like a MR70....I am excited.

 

[RogerD]

I'll say that this is a beast at 200+lbs,but the roll a round is really nice. Maybe some day this deck will be on location again.....that would be nice indeed.

 

[RogerD]

Came up without a hitch....god I do love that. Sounds great,at least the record side. I'm going to run it for a few hours and then put one of my 1/2 inch masters on and see how the Paravicini heads sound. Until you hear those Bell Telephone relays click in...nothing like it.

 

[DonH50]

Wow Roger, that's impressive! I'm a bit jealous...

 

[c1ferrari]

Dear Roger, I am happy to respond to a fellow admirer of the Duesenberg of audio, the Ampex MR 70!
I have owned three MR 70s. A 1/4 inch, a 1/2 and the most rare of them all, a one inch three trac!. From what I have found there were maybe THREE TOTAL of the one inch decks.
I used the 1/4 stock This came from Arnie Nudel of Infinity fame. The manual had "Electra" stamped on the inside in red. I once asked Bruce Botnic if he had used an MR 70 to record the Doors? He said that he was not sure...
The half inch was a four track unit and came from Neil Sinclair of Theta fame. It had two track heads that Tim had made for me in the UK.

The half inch deck was also stock, except for the UK made heads. There is NOTHING anyone can do to IMPROVE the Nuvistor based MR 70 electronics!
I moved away from them, in spite of their FORMIDABLE SOUND, because they are heavy maintenance decks and I was unable to do the maintenance work myself.
I did however change the input transformer from the stock Beyer units to US made Triad transformers on the half inch deck.
I had christened my MR 70 decks "The Jack Mullin Special" in honor of the audio legend and magnetic tape pioneer, who had worked on my 1/4 inch once and got it running for a session! "Jack Mullin Special" sounds like a very rare rye whiskey, but as you well know, an MR 70s is better than any booze, no matter the vintage!!!
Below I list the Water Lily recordings done on MR 70s.
1) "Mountains and the Sea". 1/4 inch.
2) "Electric Modes" LP Vol. 1. . Later a 2 CD set with Vol. 2 added. 1/4 inch.
3) Liszt solo piano. 1/4 inch.
4) Ricci/Brook Smith. 1/2 inch.
5) Organ/Trumpet. 1/2 inch.
6) Saudades. 1/2 inch.
7) Bach flute sonatas. 1/2 inch.
8) Lily of the Nile. 1/2 inch.
9) Maihar. Ali Akbar Khan. 1/2 inch.
10) Mysterio. 1/2 inch.
11) Ajmer. 1/2 inch.

And the two recordings I did for Stereophile. Solo piano and flute/piano.

I hope the above info helps...

All the very best...
KAVI.

Cool, Roger

Is Kavi in/about Santa Barbara, still?
I spoke with him some time ago about a tt.

 

[RogerD]

Wow Roger, that's impressive! I'm a bit jealous...

Don thanks.....they are impressive.....I guess that's why I have a house full. This one is about as quiet as I have experienced. It's the nuvistor sound that I like so much. A friends analogy fit's....like a redwood forest....lush with the sun filtering through and a wet misty luscious feel in the air.

 

[RogerD]

Cool, Roger

Is Kavi in/about Santa Barbara, still?
I spoke with him some time ago about a tt.

Yes Kavi is in Goleta,beautiful area......thanks...

 

[RogerD]

I talk a lot about the Bell Tell relays used in the MR70 transport,so I thought I would post a photo. They number 8 or 9 and have a real distinctive "clunk" sound on activation. I cleaned all of them today. Next it's oiling the capstan motor,cleaning the pinch roller arm and cleaning the contacts for the fast speed micro switch assembly. There is other things but one at a time.

I am surprised how quiet these preamps are,compared to my other set I use. These are totally stock.... these others have been gone through. I will have to pull the nuvistors from one channel and test and replace them. I have a boat load of these and at close to 40lbs each I will get a serious workout to bring them all up to spec. Oh well everyman needs a hobby.

The relay stack is on the right of the transport control board.

 

[RogerD]

I have been busy today as I removed two 1/2 reel motors from one of my spare parts transports and will have them rebuilt. I also dug through my many parts and found a master bias oscillator I need for my restoration on one of my other 1/4 inch decks. I was lucky enough to pick up 6 electronics and pulled two perfect face plates,so I can replace them on my first 1/4 inch deck. I will have 4 electronics sent for improved grounding scheme and some minor tweaking. That will take care of my 1/4 2T machine and a 1/2 2T also. But more needs to be done on the 1/2 4T and my other 1/4 2T.....3 head stacks go off to John French next week.

 

[RogerD]

I have ordered the ABEC 7 bearings for the reel motors and idler motor. The motors go to the shop next week. I shipped off 4 MR70 headstacks to John French this morning....probably a record,as he probably hasn't seen that many in one box before. The 2 pair of electronics ship off tomorrow. I'll start detailing the JMS deck today.....cosmetically it is in very fine shape......I hope to have it all restored in 60 days.

 

[RogerD]

These are the output amplifiers on the MR70,showing a stock and recapped version. Also the amplifier uses 2 7587 RCA Nuvistors and 2 7895's. A perfect candidate for teflon caps. I am hoping the already great clarity can be improved with the teflon. The cost will be less than $300 for both channels,a no brainer in my estimation for world class sound.

 

[DonH50]

Are the originals mica or ceramic? (Or something else?)

I observed in the past that a large part of the change in performance from changing caps appeared to be from getting the right values back in circuit comapred to some older caps that lose capacitance and/or have higher leakage with age.

I also replaced a lot of bias resistors as they tended to run hot and gradually increase in value, reducing bisaing and hurting performance. Especially the old carbon-comp. One caveat: carbon film actually exhibits lower noise in most cases than metal film. Annoying to replace all the resistors with expensive metal films, only to rip them out and use stock carbon film for a better result.

YMMV! - Don

 

[RogerD]

Are the originals mica or ceramic? (Or something else?)

I observed in the past that a large part of the change in performance from changing caps appeared to be from getting the right values back in circuit comapred to some older caps that lose capacitance and/or have higher leakage with age.

I also replaced a lot of bias resistors as they tended to run hot and gradually increase in value, reducing bisaing and hurting performance. Especially the old carbon-comp. One caveat: carbon film actually exhibits lower noise in most cases than metal film. Annoying to replace all the resistors with expensive metal films, only to rip them out and use stock carbon film for a better result.

YMMV! - Don

Don they are mylar. I have atleast 3 pair of these amplifiers that are spares,so I'm going to experiment a little. One pair will be teflon,another mundorf supreme & SGO's, and maybe the last I will use Mundorf silver oils by passed with teflon. Were only talking six .1 uf 400v here so not really expensive. I just want to see how far I can push these nuvistors to sound better. I'm not going to change the carbon film resistors,been there done that. Thanks

 

[RogerD]

I made the final trip to pick up the rest of the MR70 parts. I was pleasantly surprised that the haul included a boxed console with all the pieces and both a 2 rack and 4 rack equipment struts. Also a 1/4" full track new in wrapper plus 1/2 inch 3 track & a 1/2" 4 track head stack looks like NOS also ,motors,ect
All the head stacks look to be in good shape and I can now build a 1/2 inch 3 track deck....very rare.

I also met a new Ampex friend who sold me a SE-10 Ampex degausser that is like new and has the manual. This gentleman has a home recording studio and uses a Ampex AG-440-4 1/2,ATR 800-4 and a ATR 102....I found the ATR 800 very interesting as it uses 4 Teac electronics and probably similar to a Tascam. Several Crown DC300A's are used a long with a IC150 preamp. He uses KEF speakers for monitors. Very impressive.

Overall a great trip to my home town area.

 

[RogerD]

I am going through the head stacks I picked up yesterday and found this factory NOS 1/4 inch full track. The cables have never been fitted,the glass on the tape lifters are not broken and the 49 year old protective coating was still on the stainless cover.

I'm not sure which stack I'm more excited about,this full track or the 1/2 inch 3 track. I have listened to the Beach Boys for years and Brian Wilson loved full track,so I am just happy to have it. Gary wants to build a home recording studio on the lower floor....I say good idea.

I don't know how rare a MR70 1/4 full track is but I would think it is rare,given multi track was well on it's way in 1964.

 

[RogerD]

The MR70 1/2 inch 3 track,the protective coating was still on this one too.

I still think 3 track format was the best.

 

[RogerD]

Never saw this before.....Reprinted from the Harvey Radio Company of New York City Electronics catalog in 1966.The MR70-4 1/2" Recorder in console was $8950.00 back then.

The Ampex MR-70: (ca. 1968)

Without any argument the best tube Ampex ever made, probably the best analog tape deck ever made, period. This machine was an all-out effort to make a cost-is-no-object, state of the art recorder. According to a 1966 GSA price schedule in my collection, a two-track, quarter-inch MR-70 in console cost $5456.25 and an identically configured AG-300 cost $3496.00.

Transport is similar to the 300, but considerably beefed up. Nuvistor electronics. Custom-wound transformers, metal film resistors, film capacitors, etc., etc. Available in many track configurations, up to eight tracks on one-inch tape, and speed pairs of 7.5/15 ips or 15/30 ips. Some track configurations (e.g., two track on half inch tape) anticipate today's preferred analog formats; some configurations were available only on special order.

It and the much-despised Model 400 series were the only Ampexes before the ATR-100 to have constant tension. Completely mu-metal shielded. Motor drive to reel idler for faster starts. Allegedly fewer than 100 made. Parts not shared with the 300 are scarce to the point of being impossible to get.

According to Bill Vermillion, a Studer engineer once told him that Willi Studer's goal in life was to make a tape recorder better than the MR-70. He tried for two decades; then came to the conclusion that he could equal it but not surpass it. All-in-all, a fantastically elegant piece of industrial design. See Rein Narma and Mort Fujii, "Performance and Reliability Requirements for a Master Tape Recorder," Journal of the Audio Engineering Society, v. 12, no. 4 (Oct. 1964): 274-279 for a full discussion of the rationale behind the MR-70's design. Microphone preamps plugged in to octal tube sockets and usually are not present.
Andere sagen über die MR70 :
We felt that 1/2" 3-track was a special format that deserved special treatment. So, we've rebuilt the ultimate 1/2" 3-track machine - the legendary Ampex MR-70.
The Ampex MR-70 is the final and best sounding professional vacuum tube analog tape recorder ever built. There are many who feel that the sound of this machine has never been surpassed. It is believed that Ampex technicians hand-made only 50 of them and that every one was in some way custom-built.

http://www.tonbandmuseum.info/nach-den-ampex-3xx.html?&no_cache=1&sword_list