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Ampex AG-600s?
Old 3 weeks ago
  #1
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Ampex AG-600s?

This rack came out of an old radio station. I bought it on a whim with no knowledge of reel to reel recorders from a seller who didn’t know what he had. Having some tape sound for vintage productions sounded fun It also came with Tascam cassette and CD writers. Anyways, looking though the history of Ampex these look like AG-600s but the rear components do not completely match. There is also some other components installed inside the rack case that makes me think this was a custom job. Any knowledge y’all can drop of me based on the photos I’ve attached? Many thanks!
Attached Thumbnails
Ampex AG-600s?-4fde214e-af01-4b48-b4f9-77ba253f1964.jpg   Ampex AG-600s?-1306f9eb-19ff-45ce-aa31-2b70503ed8a6.jpg   Ampex AG-600s?-eeec29fe-c7a0-4865-be41-c41282a88b91.jpg   Ampex AG-600s?-98159c65-49ab-49dd-b592-59d5adeb3e95.jpg   Ampex AG-600s?-b8a00362-f238-4319-aab9-6f45d5d4fbab.jpg  

Ampex AG-600s?-6bd91d05-fe02-45b8-87dc-f52c825cbd66.jpg   Ampex AG-600s?-d3cbccb6-e88f-44a5-bae8-ccc840924044.jpg   Ampex AG-600s?-434f882b-a052-4618-a7a2-13af080c2526.jpg   Ampex AG-600s?-c29b56f4-5bf3-4003-a934-30b5b16411c2.jpg   Ampex AG-600s?-a5233080-a474-4240-b570-428c2a6eaa7b.jpg  

Ampex AG-600s?-0aeda4b5-2ab2-4f3a-ac3b-74c8ad7249d1.jpg  
Old 3 weeks ago
  #2
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Ampex AG-600

upper unit is an AG-600, earlier version with mechanical speed change.
input A: unbalanced via the dummy plug
input B: appears to be the plug-in microphone preamplifier

lower unit is an AG-600b, electronic speed change
inputs A and B: unbalanced via dummy plugs
Old 3 weeks ago
  #3
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Thank you cathode! My naive self was hoping they were somehow wired to work in stereo. What model would be recommended to restore or are they pretty much the same for reliability and sound?
Old 3 weeks ago
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600s were a good portable machine, but not up to the normal standards of Ampex excellence. A good project for retoration if you like doing that, but don't expect the supreme analog goodness that is possible with an AG 440 or ATR 100.

Think of them as the cassette deck of the 1950s. When I was in high school in the mid-60s, when the radio station came to record the youth orchestra, they brought a much larger and heavier AG-440 which took two men to carry each half of the recorder. A 600 could be carried with one hand but was not considered good enough to record music...
Old 3 weeks ago
  #5
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Quote:
Originally Posted by loujudson View Post
600s were a good portable machine, but not up to the normal standards of Ampex excellence. A good project for retoration if you like doing that, but don't expect the supreme analog goodness that is possible with an AG 440 or ATR 100.

Think of them as the cassette deck of the 1950s. When I was in high school in the mid-60s, when the radio station came to record the youth orchestra, they brought a much larger and heavier AG-440 which took two men to carry each half of the recorder. A 600 could be carried with one hand but was not considered good enough to record music...
Those were the initial stage of the gadgets. Now, every gadget is optimized and as small as possible in size. Amazing to learn about these things.
Old 3 weeks ago
  #6
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Quote:
Originally Posted by loujudson View Post
600s were a good portable machine, but not up to the normal standards of Ampex excellence. A good project for retoration if you like doing that, but don't expect the supreme analog goodness that is possible with an AG 440 or ATR 100.
Lou is being generous. They were kind of horrible, but they were cheaper than a 440 or even a used 350 and so a lot of stations got them.

The thing is... today, tape machines are worth what the heads are. You pay for the heads, you get everything else free in the bargain. These machines likely have full track mono heads, and you could take the two of them and a set of half-track heads and convert them into a stereo machine.... but the cost of those heads is likely about what a stereo recorder would cost. Ask JRF and see... he might have some bargain heads in a closet somewhere and you might get lucky.

I'd put these machines up on eBay or reverb for collectors... there are a lot of people who collect Ampex machines and don't actually care about usability but just want to have them because they are a link to our collective recording history.
--scott
Old 3 weeks ago
  #7
You also might pose this question on the Ampex list serve Ampex Mailing List <[email protected]>

FWIW
Old 3 weeks ago
  #8
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Ampex AG-600

Quote:
Originally Posted by Thrillium3000 View Post
What model would be recommended to restore or are they pretty much the same for reliability and sound?
The AG-600b transport lacks the wanky speed change mechanism, thus a better machine to restore. Belts are available on ebay.
With a set of stereo heads, you could use the electronics from the earlier machine to make a stereo unit. The older machine becomes your replacement parts source.
Highest speed is 7 1/2 ips, decent enough.
Sending you encouragement, a fun project.
Old 3 weeks ago
  #9
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I appreciate everyones responses. Very informative. It is a bit of a bummer that I bought some duds in the way of fidelity but that’s ok. I’ll just use it for “character”. Dirty loops and trashed vocals. The Ampex mailing list contact, knowing the 600b is superior, and that stereo operation is possible is encouraging. If I can learn a few things and get the 600b running nice I’ll be able to justify the investment in a better model.
Old 3 weeks ago
  #10
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Quote:
Originally Posted by Thrillium3000 View Post
I appreciate everyones responses. Very informative. It is a bit of a bummer that I bought some duds in the way of fidelity but that’s ok. I’ll just use it for “character”. Dirty loops and trashed vocals. The Ampex mailing list contact, knowing the 600b is superior, and that stereo operation is possible is encouraging. If I can learn a few things and get the 600b running nice I’ll be able to justify the investment in a better model.
It is a good machine to learn on. It's the first machine I ever rebuilt myself, because my boss was too cheap to spend $200 for a used 350 from Harris-Allied.

And it's a machine that is very salable to collectors.
--scott
Old 3 weeks ago
  #11
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Fired up both units and the tapes they came mounted with. The plackback, reverse, and fast forward functions all worked. The 600b audio sounded pretty great out of the headphone jack, the 600 was a lot more noisy. Input knobs A/B were hissy in both units when turned above 0. All and all it was exciting enough for me to order some belts, pinch roller rejuvenator, bearing oil, and empty tapes. I’ll need a lot more investment to come and calibration will test my know how but it’s a start. I really dig the tape sound, from a guy who grew up in the digital world its really something special. On a side note, it’s crazy what some of these that are modded into preamps only go for.
Old 3 weeks ago
  #12
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Ampex AG-600

the electronics are a fine design and well made.

it may be prudent to invest in a pair of the -01 bridging input transformers,
and perhaps a pair of -02 matching units (if you can find them).
the -02 provide 14 dB of "free" gain provided your gear can drive 600 ohm loads.

take a moment, pull off the bottom panels, locate the "death" capacitors across the AC line and remove them. C31 and C32 in the attached schematic.
Attached Thumbnails
Ampex AG-600s?-ag600b.jpg  
Old 3 weeks ago
  #13
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Quote:
Originally Posted by Thrillium3000 View Post
Fired up both units and the tapes they came mounted with. The plackback, reverse, and fast forward functions all worked. The 600b audio sounded pretty great out of the headphone jack, the 600 was a lot more noisy. Input knobs A/B were hissy in both units when turned above 0. All and all it was exciting enough for me to order some belts, pinch roller rejuvenator, bearing oil, and empty tapes. I’ll need a lot more investment to come and calibration will test my know how but it’s a start. I really dig the tape sound, from a guy who grew up in the digital world its really something special. On a side note, it’s crazy what some of these that are modded into preamps only go for.
You will also need an alignment tape and I would suggest shotgunning paper capacitors throughout.

I don't think that this machine will bias up modern tape formulations, but PEM468 and the new Capture tape will work on it. Most of these spent their life pulling Ampex 641 tape or similar red oxide stuff, and there is likely a lot of 641 on the surplus market today.
--scott
Old 3 weeks ago
  #14
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Needed to hip myself on some terminology before I could reply. Bear with me

- When I remove the death capacitor should I replace it with a safety capacitor or is there really no reason to? Was it designed to be an RFI noise filter like with old guitar amps?

- I found pairs of used -01 & -02 bridging input transformers between $75-$150 depending on condition. Are there cheaper modern transformers I could use instead?

- What does shotgunning capacitors mean?

- I found this capacitor restoration kit on ebay. A solid buy for something already put together with detailed instructions? https://www.ebay.com/itm/Ampex-600-6...cAAOSwExtcmN50

- I bought some old 641 tape. I'll get some Capture 914 tape next. Great value compared to other new recording tape brands.

- I cant find alignment test tape anywhere. This bronx parody test is pretty hilarious https://www.youtube.com/watch?v=dUP3OrUXA6U

- Do I need a tape head demagnetizer? Any other tools/parts I should consider?

Many thanks for the help!
Old 3 weeks ago
  #15
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Ampex AG-600

Quote:
Originally Posted by Thrillium3000 View Post
- When I remove the death capacitor should I replace it with a safety capacitor or is there really no reason to?
simply remove them.
it is a RFI filter but rather poorly implemented. it was sadly an Ampex tradition dating back to the model 300.
if concerned about RFI, install one external to the machine with filters such as those made by Corcom. you may have to fabricate the assembly with power cords.
Quote:
Originally Posted by Thrillium3000 View Post
- I found pairs of used -01 & -02 bridging input transformers between $75-$150 depending on condition. Are there cheaper modern transformers I could use instead?
those bridging transformers are fine, they solve a litany of interfacing issues.
the gensen fan club will undoubtedly chime in with stories of how awful the Ampex parts are. most of those modern parts are expensive, difficult to wire in place, and frankly sound vanilla or worse.
Altec/Peerless plug-in transformers are sometimes fitted to Ampex machines, they are readily available, but keep your Ampex "Ampex".
Quote:
Originally Posted by Thrillium3000 View Post
- What does shotgunning capacitors mean?
it means changing out all the capacitors without a clue if any are actually defective. this is a modern theme, many a circuit board has been butchered by the process.
please read this, it will enlighten you about capacitors.
http://conradhoffman.com/capchecktut.htm
The large can capacitors on the rear of the AG-600 electronics might need replacing, but they are of high quality. Don't mess with them unless you KNOW they are defective.
The film capacitors on the circuit board are NOT paper; they are "modern"plastic film types, probably polyester. If this was a tube unit, I would advise to change them.
But 1970 vintage plastic caps, should be ok.
now I do recommend replacing the few axial lead electrolytics capacitors on the circuit board. research how to do the repair without board damage.
a reminder: if it isn't broken, DON'T fix it.
Quote:
Originally Posted by Thrillium3000 View Post
- I cant find alignment test tape anywhere.
http://www.mrltapes.com/
Quote:
Originally Posted by Thrillium3000 View Post
- Do I need a tape head demagnetizer?
https://www.rbannis.com/products/handmags/1.html
Old 3 weeks ago
  #16
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Quote:
Originally Posted by Thrillium3000 View Post
Needed to hip myself on some terminology before I could reply. Bear with me
- When I remove the death capacitor should I replace it with a safety capacitor or is there really no reason to? Was it designed to be an RFI noise filter like with old guitar amps?
That is a religious issue. Many people will tell you that if you aren't going to be running it at an AM transmitter site that you should just remove them. I figure RF protection is always a good idea, and I would put safety capacitors in. But then I am the guy that goes around retrofitting Corcom EMI filters to things just in case.

Quote:
Originally Posted by Thrillium3000 View Post
- I found pairs of used -01 & -02 bridging input transformers between $75-$150 depending on condition. Are there cheaper modern transformers I could use instead?
Sure, they are just 600:600 transformers I believe. You could take whatever you liked and put it on an octal plug (either a proper Vector one or one scavenged from a bad octal tube). Or you could just use a jumper and run unbalanced. My personal feeling is that the original Ampex transformers weren't all that great, and I ran all my 440s unbalanced when I could, or with better transformers when I could not.

Quote:
Originally Posted by Thrillium3000 View Post
- What does shotgunning capacitors mean?
Replacing without testing or diagnosis. Instead of specifically pinpointing caps that were likely to fail (and the paper caps fail into shorts and cause collateral damage when they do), just swap them all out and be done with it.

Quote:
Originally Posted by Thrillium3000 View Post
- I found this capacitor restoration kit on ebay. A solid buy for something already put together with detailed instructions? https://www.ebay.com/itm/Ampex-600-6...cAAOSwExtcmN50
I can't tell from that exactly what capacitors those are. Panasonic makes some very stable high temperature capacitors and they also make 85C caps with limited life. I would ask the man exactly what you are getting. But this is basically the idea, yes.

Quote:
Originally Posted by Thrillium3000 View Post
- I bought some old 641 tape. I'll get some Capture 914 tape next. Great value compared to other new recording tape brands.
The machine will line up very easily for 641. You will want to do the bias setting at 1kc exactly like it says in the service manual.

With the Capture tape, you may have trouble finding the bias peak. If so, use modern overbias method: find the peak at 10kc and then go past the peak until the meter drops 2dB or so.
[/QUOTE]


Quote:
Originally Posted by Thrillium3000 View Post
- I cant find alignment test tape anywhere. This bronx parody test is pretty hilarious
There is that Vanilla Fudge album with a sample of the old Ampex alignment tape on it too.

MRL at http://mrltapes.com is the last guy making them. They are not cheap. If at all possible, borrow one from a friend. If at all possible get the 21T204 tape, which has the full tone ladder at 7.5ips, NAB equalization, 250 nW/m level. You can use a 15ips test tape at 7.5 ips and you can use a higher or lower level test tape, but doing these things will involve fudge factors and be generally a pain. The 21T204 will be the easiest.

You can use the 7.5ips tape at 3 3/4 with some fudge factors but I would not even bother doing the 3 3/4 alignment, since it's not really useful.

Quote:
Originally Posted by Thrillium3000 View Post
- Do I need a tape head demagnetizer? Any other tools/parts I should consider?
This is another thing you should borrow if you can. I have seen more people screw things up with a demagnetizer rather than fix them. Heads and tape paths do not get magnetized easily or often, unless something weird happens. But sometimes weird things happen. In a studio environment normally you have an Annis Han-D-Mag kit with a magnetometer and you check the heads weekly and if you ever DID see remaining magnetic field you would get out the demagnetizer and wipe it. But I never actually did see any remaining field except once on a 440 where a capacitor got leaky and put DC on the head and we had to run the head through the tape degausser to get it down because the handheld degausser wouldn't do the trick.

Radio stations and similar folks that would be using the 600 would probably not do regular alignments, magnetometer checks, and sweep checks like a studio would do on their machines. A radio station would probably have an alignment tape in the vault and pull it out and do an alignment whenever someone noticed something wrong, and stuff would get WAY out of tolerances before those guys would notice anything.
--scott
Old 3 weeks ago
  #17
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Quote:
Originally Posted by cathode View Post

The film capacitors on the circuit board are NOT paper; they are "modern"plastic film types, probably polyester. If this was a tube unit, I would advise to change them.
But 1970 vintage plastic caps, should be ok.
If this is true, then I agree completely. I haven't actually opened up a 600 machine for forty years so I do not recall all details. When you pop the cover you'll see what they are.

My last experience with 600 machines was watching the program director and general manager tossing a stack of them into a dumpster while the whole station staff cheered.
--scott
Old 3 weeks ago
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Correct me if I'm wrong... the AG-600 did NOT have RW/FF tape lifters did they?
Old 3 weeks ago
  #19
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Quote:
Originally Posted by GYMusic View Post
Correct me if I'm wrong... the AG-600 did NOT have RW/FF tape lifters did they?
Yeah, there was an aftermarket manual lifter but the machine didn't come with proper lifters. Which is... not beneficial for head life.

I am also reminded that these are probably half track mono and not full track. But you'll know when you look at the heads.
--scott
Old 3 weeks ago
  #20
To the OP. I owned the original Ampex 601 and did a lot of recordings on it early in my audio career. A workhorse of a machine and always sounded GREAT. I used it with an Altec M-21 microphone and did a lot of classical recording with it while in college. I also used an AG-600 while working in a TV station and the unit was indestructible and always worked. It was left on 24/7 for some reason and the only thing I had to change out was the idler puck and clean the heads. You got some great machines. Congrats!
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