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Old 23rd May 2006, 10:31 PM   #1
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Default Do you know these Ampex mono Amps

I have never seen these and was thinking of a purchase, but cant even fid a schematic.

Here is the scoop on the ampex according to the seller...

no #'s on chassis as they were repainted but, according to the owner, they are Ampex catalog #6446 amps

120w each

each amp weights around 60lbs

tube complement: 807x4 6sn7x1 6bl7x1 5879x2 od3x4 oa3x1 5u4g x2

taps are 16,8,4ohms.

If you have a clue on 'em I'd appreciate your 2 cents.
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Old 24th May 2006, 12:22 PM   #2
EC8010 is offline EC8010  United Kingdom
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These look like public address amplifiers. The 807 are your output valves, probably running in Class B to get that power. They're probably being driven by the 6BL7, with the 6SN7 as the phase splitter. The 5879 pentode is probably the input stage. (And its data sheet describes it as a low-noise pentode for PA amplifiers.) The 0A3 (please use the "shift" key and capitalise when necessary) is a 75V regulator and the 0D3 are 150V regulators. That rather suggests some form of DC coupling/bias arrangement to the output stage, which adds further weight to the Class B supposition. The 5U4 are rectifiers.
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Old 24th May 2006, 03:23 PM   #3
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Great ! Thanks for the break down on what each tube is doing...

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Old 24th May 2006, 05:02 PM   #4
kevinkr is offline kevinkr  United States
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While I'm not familiar with this particular amplifier, Ampex never made "public address" amplifiers to my knowledge. Most of their stuff was pretty premium and fetches a good price even today. Far more likely these were monitor amplifiers intended to drive recording studio monitor speakers. I would guess they will be quite good sounding. Ampex made a lot of really high end studio equipment and I imagine these fit that category.

Tuners sold under the Ampex label for domestic use were made by HH Scott, and are rare and considered very collectable.
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Old 24th May 2006, 10:07 PM   #5
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Well if the price does not get too nuts, like under 500 I love to buy 'em as I plan to use 'em in my class room. I'm a shop teacher and we always have tunes on.

Plus it would be a great way to get my students into some old technology.

I wonder if they would make nice audio amps?
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Old 24th May 2006, 10:23 PM   #6
EC8010 is offline EC8010  United Kingdom
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It all depend on whether kevinkr is right or I'm right. You'll be hoping that kevinkr is right, and it's certainly true that Ampex made some highly regarded studio equipment, so the odds are in your favour. A useful clue would be dimensions of the output transformer. If the output transformer is is bigger than the mains transformer then you're onto a winner. Do bear in mind, though, that they will almost certainly require some serious refurbishment before applying power. Leaky coupling capacitors can be lethal to output valves, and the earth bond to the chassis is likely to be poor.
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Old 24th May 2006, 10:25 PM   #7
kevinkr is offline kevinkr  United States
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I am quite sure they are nice amplifiers, I would expect a pair like these to go for kilo dollars, however you never know. Perhaps you can scoop them.

I'd try them in a good home system, they certainly have enough power to run most modern speaker systems without problems.

The other Ampex stuff I have heard was very good, I'd expect the same here. Same ilk as a lot of the Altec theater amplifiers of comparable vintage. (A lot of them used 807's as well.)

I certainly wouldn't use these in a shop environment, the dust and vibration wouldn't be a good thing.
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Old 24th May 2006, 10:46 PM   #8
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EC's rule of thumb is a good one, but I have some Altec studio amps that would fail that test. Not because the OPTs are small (they're not), but because the power transformer is so huge.
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Old 24th May 2006, 10:59 PM   #9
kevinkr is offline kevinkr  United States
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Based on the photographs I would assume the output transformer is pretty large and comparable in size to the power transformer.

I'm not sure what Altec models SY has, but I have worked on 1570A/B IIRC and these have huge power transformers and puny (by comparison) output transformers. They needed some modification to remove the input transformers, and improve the low end extension as these were originally intended for PA work, unfortunately I don't remember the details any longer.

IMHO they sound pretty good, and the price they fetch sort of reflects that in addition to the Altec label on the front panel..
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Old 24th May 2006, 11:12 PM   #10
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Mine are some kind of weird number I haven't seen before I can find it if there are any Ampex experts who can identify them). Stereo, 6550 outputs in pentode, rackmount, 100W. Heavy suckers. One of them already gave up its iron for another project, the other is still intact. Nice thing is that all the transformer and choke ratings are screened onto their cases.
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