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What Speakers for Ampex 6556 CinemaScope Amplifiers

P

Potato_Head

Infected by Vintage Audio Bug
I have a set of Ampex 6556 Cinemascope amplifiers. From what I can tell on the web, they are close to 200 wpc. I currently have the amps connected to a pair of Infinity RS 1.5 speakers.

The amps are being fed with an APT Holman preamp. I cannot go past the 9 o'clock position on the volume control. (Zero volume is at the 7 o'clock position)

Two things happen if I do. One the volume level is LOUD. Second when a deep bass note hits, the OD3 tubes start to lose their purple glow in time with the bass notes. If I go further with the volume, all 4 OD3 tube dim and I hear distortion.

The amps have been modified by a previous owner and there is only one output. I am thinking that maybe this is a 16 ohm amp and the Infinities are 4 ohm with dips much lower with heavy bass.

I understand this is opening a can of worms but what type of speaker(s) would pair best with these amps.

Not necessarily looking for specific models but more generic info - Impedance, Power handling, type (electrostatic panel, horn, etc)

Thank you
 
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On a couple of items in your post:

- OD3 flickering under load: This would be normal since you're drawing more current to make power at higher volumes.

- Using relative levels in terms of o'clock: This just tells me that the amps are quite sensitive and take very little drive to get them going. This also means that your preamp is able to easily drive them. None of this is a bad thing.

- Mods by prior owners: All bets are off until you understand what was done and how this affects the behavior you're reported. It just means that the arm chair bench techs here at AK cannot just look at the schematic and be helpful to you.

I'm sure they're excellent amps and, from your reports, they must sound great!

Cheers,

David
 
dshoaf said:
On a couple of items in your post:

- OD3 flickering under load: This would be normal since you're drawing more current to make power at higher volumes.

- Using relative levels in terms of o'clock: This just tells me that the amps are quite sensitive and take very little drive to get them going. This also means that your preamp is able to easily drive them. None of this is a bad thing.

- Mods by prior owners: All bets are off until you understand what was done and how this affects the behavior you're reported. It just means that the arm chair bench techs here at AK cannot just look at the schematic and be helpful to you.

I'm sure they're excellent amps and, from your reports, they must sound great!

Cheers,

David
Click to expand...
Hello David,

Thank you for the response.

The Preamp ia an APT1 Holman preamp. I think that I read somewhere in the manual that I can add a resister(s) and possible cut a jumper to decrease the output of the preamp. I am not sure if I will stay with the APT1 to drive the Ampex amps.

From what I can find so far the only speakers that are in the range of 16 ohm and 200 watt are going to be VOTT type speakers. Out of my price range and way too big for my room.

For now I will use my Harmon Kardan A500 with a pair of LEAK Sandwich 15 ohm speakers for late night low level listening.

So far the worst thing with these new amps is that while good recordings sound better than they ever had - bad recordings sound much worse!

Michael
 
When were those amplifiers made? Can you post some pictures please? I'm having trouble locating them on the 'net.'
 
Newer eqpt may have a higher output voltage than vintage tube preamps did. Just a thought. Did you look for the SAMS folder on these?

Edit: SAMs site does not list the 6446.
 
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When they were modified did the 4 ohm and 8 ohm taps get removed? Just curious as to why you say you are limited to 16 ohm speakers.
 
toxcrusadr said:
Newer eqpt may have a higher output voltage than vintage tube preamps did. Just a thought. Did you look for the SAMS folder on these?

Edit: SAMs site does not list the 6446.
Click to expand...
64604d1148419741-do-you-know-these-ampex-mono-amps-a7_1.jpg


IN case you were not signed up for the DIY forum. These are the same model as mine.
 
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