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Ampex 600 input transformer question (also for sale)
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Rylan
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#1
7th December 2010
Old 7th December 2010
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Ampex 600 input transformer question (also for sale)

Hey all, long time reader, first time poster.. Here goes:

Does anyone know what kind of input transformers come stock in the Ampex 600? I had a look inside 2 of these just now and didn't see any markings on the input transformers.

When plugging into the unit from either the xlr mic input on the front or the rca line input on the side and running the output straight into my daw I notice the 600's I have seem to have a distinctively bright yet lovingly warm sound. Not really critical that I find this answer but I am quite curious. I have read around a little and am thinking they are Altec/Lansing maybe?

Thanks!

edit: oh yea I also have 2 of these for sale, and 2 Ampex 620's (the matching all tube self powered speaker)
#2
7th December 2010
Old 7th December 2010
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From my readings they used a variety but weren't always stock. Could be any number of things. With no manufacturer logo or part # it will be difficult to tell though exact physical dimension might suggest one thing or the other.

You looking to sell the whole machine or just the input transformer(s)?
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7th December 2010
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If I recall correctly, Ampex often used Beyer input transformers on the 600. Those small silver cans smaller than the tip of your little finger. There may have been some with plug in cans as well and I remember the UTC A-11 being mentioned as an upgrade.

Mike
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7th December 2010
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I believe the Beyers didn't come along until the 602 stereo machines - at least the small ones like you find on the MX mixers. Not sure if they made an octal plug in type
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8th December 2010
Old 8th December 2010
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The 600 had a high impedance unbalanced input (pin 3 hot, 1 and 2 ground) and a cover plate bolted onto the chassis over where an octal socket would be mounted. That octal socket is installed in the 601 model which had a transformer-balanced 600 ohm input.

I have a 601 amp chassis in storage....I can get at it early tomorrow and will post the info on it here, including Ampex part number, pin out, etc.
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8th December 2010
Old 8th December 2010
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Quote:
Originally Posted by lassoharp View Post
I believe the Beyers didn't come along until the 602 stereo machines - at least the small ones like you find on the MX mixers. Not sure if they made an octal plug in type
You are probably correct about this, the last Ampex I owned *was* a 602. But I do have a pretty clear memory of a service manual that mentioned the UTC A-10 or A-11 as a possible upgrade...of course that manual was sold years ago.
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7th January 2011
Old 7th January 2011
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ah thanks for the replies, and yea I am selling the entire unit as well as the matching 620
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8th January 2011
Old 8th January 2011
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Quote:
Originally Posted by lassoharp View Post
I believe the Beyers didn't come along until the 602 stereo machines - at least the small ones like you find on the MX mixers. Not sure if they made an octal plug in type

If there is a plug-in unit and it looks like this:

then it may be a nuvistor preamp. I have two, and they have Beyer transformers inside, which I will soon be publishing in-house performance tests on my transformer test page:

R&D Publications
#9
8th January 2011
Old 8th January 2011
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Quote:
Originally Posted by jlaber View Post
If there is a plug-in unit and it looks like this:

then it may be a nuvistor preamp. I have two, and they have Beyer transformers inside, which I will soon be publishing in-house performance tests on my transformer test page:

R&D Publications

Nice. Look forward to checking those out. Be interested to see what info could be gleaned on the saturation characteristics. The small Beyers as found on the Ampex mixers seem to overload easily and produce a bigger sounding bottom than you might expect from such a small core.
#10
9th January 2011
Old 9th January 2011
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Quote:
Originally Posted by lassoharp View Post
Nice. Look forward to checking those out. Be interested to see what info could be gleaned on the saturation characteristics. The small Beyers as found on the Ampex mixers seem to overload easily and produce a bigger sounding bottom than you might expect from such a small core.

Well I did another Beyer tranny of the same size, a 1:15 model that's probably for 200 ohm input and 50K load, and the max level at 20 Hz is -8 dBu. It will probably do 0 dBu around 30 Hz though. While input pads aren't the most popular way to accomodate moderate input levels, this is probably how they were used back in those days, considering most preamps had an otherwise fixed gain.

I'll probably get to testing them next weekend and post on the web site.
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10th January 2011
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I did a quick test on the transformer for the Ampex plugin preamp shown in the photos below. The preamp has what appears to be a Beyer input transformer, and uses two RCA 7586 nuvistors for amplification.

Compared to another Beyer I tested, a TR/BV 351 015 006, this tranny has a higher HF peak frequency, lower DC resistance, about the same voltage gain, but handles -6.7 dBu at 30 Hz where the other Beyer tops out at the same level around 20 Hz.

If anyone wants photos of the distortion waveforms, just post a reply and I'll put it on the todo list. At some point I'll be racking these with line drivers, and I'll publish tests for the Ampex module as a whole.

Transformer Test results:

Voltage Ratio (at 2 KHz): 1 : 14.4 (roughly 23 dB voltage gain)
Estimated impedance spec: 200 ohm : 47K ohm

Frequency response (unloaded secondary, input tube removed):

-0.66 dB at 20 Hz relative to 2 KHz
+1.4 dB up at 20 KHz relative to 2 KHz
HF peak @ 51.2 KHz

Maximum operating level (at 1% THD, unloaded):

20 Hz: -12 dBu
30 Hz: -6.7 dBu
2K Hz: -1.9 dBu

Primary DC resistance: 57.5 ohms
Secondary DC resistance: 4.87K ohms

Note that there is no loading network on the transformer secondary in this preamp. The only loading is the tube grid, mainly capacitive.






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11th January 2011
Old 11th January 2011
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Those preamps were used with later machines like the 354. There was also a version of that preamp with 40 dB gain which used a single 7586 (or 6CW4).

The transformer used with the 601 is Ampex part number B-17331-1.
Attached Thumbnails
Ampex 600 input transformer question (also for sale)-dsci2495.jpg   Ampex 600 input transformer question (also for sale)-dsci2497.jpg  
#13
11th January 2011
Old 11th January 2011
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Quote:
Originally Posted by Ampex 354 View Post
Those preamps were used with later machines like the 354. There was also a version of that preamp with 40 dB gain which used a single 7586 (or 6CW4).

The transformer used with the 601 is Ampex part number B-17331-1.
Thanks for clarifying. I saw a haphazard mention that these preamps would plug into a 600-series, so I posted it here.
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30th January 2011
Old 30th January 2011
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[QUOTE=Ampex 354;6089646]The 600 had a high impedance unbalanced input (pin 3 hot, 1 and 2 ground) and a cover plate bolted onto the chassis over where an octal socket would be mounted. QUOTE]

That's exactly how I got mine and yes, also my research tells me the 600 didn't come factory equipped with an input xfrmr. There was an upgrade available and I too read it was a UTC A-11. Mine is dated 1954.

The 601 sported a factory installed rounded Ampex transformer (the one pictured in a previous post) and it's the same part # installed in the Ampex 350/351 models.

To Ampex 354: the input impedance on that transformer is either between 150-250 Ohms or 30-50 Ohms, depending on how you wire it. Definitely not 600 Ohms.

I purchased a transformer from Sowter, UK: they make an exact replacement part for the 350/351 so I thought it could work also for my 600, basically turning it into a 601 (just for the input section: I kept the output section stock with no transformer, just the Cathode Follower stage).

It's a wild crazy beast, with something like 4 times the gain you actually need, and it's beautiful in its 50s look.
#15
24th March 2011
Old 24th March 2011
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Quote:
Originally Posted by mjrippe View Post
You are probably correct about this, the last Ampex I owned *was* a 602. But I do have a pretty clear memory of a service manual that mentioned the UTC A-10 or A-11 as a possible upgrade...of course that manual was sold years ago.
Give that man a cupi doll. UTC A-11 or a cinemag 600 ohm input trafo is the correct part you could have upgraded a 600 for. Making it a 601 essentially. I just bought a 600 s that was used by the USAF as a flight data recorder. And UTC A11 are installed in both ( thank you ) do you still have the deck and speakers for sale? Pm me.
Rylan
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23rd July 2011
Old 23rd July 2011
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Ah yes you are correct, I found out through additional research the UTC-A11 could be used in the circuit but is not included with the 600, and yes I still have a pair, the 600 motorboats and I have not recapped it yet. I will pm you this as well.
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23rd July 2011
Old 23rd July 2011
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. . do make note that the 600 preamp circuit will not catch on fire or make poor audio sounds if a UTC A-10 or any one of the numerous other mic to grid transformers that can be found out there is used. The limitations will be left to the physical space available.
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24th July 2011
Old 24th July 2011
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Quote:
Originally Posted by lassoharp View Post
. . do make note that the 600 preamp circuit will not catch on fire or make poor audio sounds if a UTC A-10 or any one of the numerous other mic to grid transformers that can be found out there is used. The limitations will be left to the physical space available.

Of course! The highly overpriced Peerless 4722 will work fine, as will the UTC O-2, DuKane 3A55, etc.
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