Ampex Ultra Linear 6L6 Mono Block Amplifiers => Major Up-Grade & Rebuild - 16 Ohm Lowther-Quad.

A very special Holiday offering
  • Please read my full auction, it should answer most questions.

  • Golden Rule:
    This Ampex Mono Block Pair is in nice shape.  The sound is simply buttery awesome.  They sport a very compact space saving design - each Mono Block with the Wood Base is Only 13 3/4" Long x 6.5" Wide.  The Power and Output Transformers are Huge - amazing Iron given the compact chassis.  
  • I rebuilt the entire Power Supply which includes new upgraded Voltage Doubler Caps, Diodes, and all new Main Filter Cap sections.  
  • New Long-Life (12,000 Hour) 105C Degree Nichicon filter Caps that are approximately double in capacitance for superior Ripple Reduction.  
  • New Long-Life (10,000 Hour) 105C Degree Voltage Doubler Caps.  
  • New Signal Path coupling Caps - Nichicon Metallized Polypropylene.  
  • New Power Cords utilizing heater Cord - Rubber Based, much more Flexible and durable.
  • Power Supply voltages have been adjusted so the amp can be run on Modern Household voltage of approx. 122VAC
  • Original Telefunken EF86 and Amperex Bugle Boy 12AU7 Tubes included.  
  • The Sovtek 5881's were closely matched on my tube tester.
  • I suggest that you use a power strip to turn the Amps On/Off.
  • This Pair of Mono Blocks is way beyond most Ampex Amps sold on eBay.
  • I do the best I can to take great photos and describe the item accurately.  If you will note, I go way beyond the norm to Describe, Photograph, and Video Demonstrate my items.  
  • Local Pickup Welcomed.  
  • Unit is sold as-is.  I have done everything I can to update and make it work its best.  This is vintage and one must realize that there may be future maintenance required someday.

  • I might need to ship these Amps in  separate packages - particularly if it is an international shipment due to international size restrictions.  I might need to ship the tubes in a separate package.  There might be a separate shipping charge - the point is I need to get these to you safely - stay tuned...

  • Stay tuned to the VERY bottom of this Auction.  Once bids are placed any revisions will be at the very bottom in green print.  I may put additional information for you so please check back for any updates, especially in the remaining hours of the auction.

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  Here are the Mono Blocks in action: 


Using just the Level Controls on the front of the amp works great with a Phone!: 


Here I demonstrate the Precisely Matched Voltages between the two Amps.  These measurements are taken without tubes installed to avoid any variances they will create [NO 2 tubes are equal let alone 8 tubes!]  Remember, the following voltages are not Schematic/Operation Voltages with tubes.  The actual Operating voltages with tubes are also very accurately matched and within correct operating voltages.  I will identify the measurements with my finger (One Finger for Measurement 1 etc.).  Then I will take a measurement of Amp A and the same Measurement in Amp B to compare the two amps.  Try to follow along and hit Pause if you need to.  Please do not do this work unless you really know what you are doing - there are very dangerous voltages present.  Here we go:

Measurement 1 - The first Filter Cap Section: Amp A = 391.9VDC  Amp B = 391.4VDC
Measurement 2 - The Second Filter Cap Section: Amp A = 339.5VDC  Amp B = 340.0VDC
Measurement 3 - The Plate Voltage Left Socket: Amp A = 456VDC  Amp B = 458VDC
Measurement 4 - The Plate Voltage Rt Socket: Amp A = 455VDC  Amp B = 455VDC
Measurement 5 - The Screen Voltage Left Socket: Amp A = 458VDC  Amp B =459VDC
Measurement 6 - The Screen Voltage Rt Socket: Amp A = 457VDC  Amp B = 458VDC


Here I Demonstrate the Ampex Mono Block Amplifiers with an Oscilloscope.  The top Sine Wave is the Left Mono Block Amp and the bottom Sine Wave is the Right Mono Block Amp.  What we are looking for is an identical Sine Wave in each Amplifier as I move up through the Audio Band.  (and even past the Audio Band)  I always stop at an even frequency so you can see the steps.  I start at 200 Hz (You will see .20 kHz.  1000 Hz = 1 kHz).  Then I move up the Audio Band.  At 800 Hz (.80 kHz) you will note I change the scope settings so you can see the Symmetry.  Then I continue up through 2000 Hz (2.00 kHz).  At 2000 Hz (you will see 2.00 kHz), I need to change the multiplier on my Audio Generator and you will quickly see the 2.00 kHz established again.  I then move on up to 8,000 Hz, the Midrange (you will see 8.00 kHz).  I change the scope settings so you can see the symmetry).  Then it is clear up to the top of the Audio Band at 20,000 Hz (You will see 20.00 kHz at the very end.)  Now I go above 20,000Hz to show how good the amp is.  I change the multiplier and you will quickly see 20,000Hz re-established (20.00kHz).  What we need to see is when the Amplitude will drop off.  I go to 30,000Hz, good.  I go to 40,000Hz, good.  I go to 50,000 and quickly after 50,000Hz (50kHz on the Counter) you will see the amplitude drop off.  These two Mono Blocks are equal in Amplitude and Symmetry all the way out to some odd 50,000Hz.  I go back and forth, below 50K and above 50K Hertz so you can see the Amplitude Drop-Off.  No distortion in the Sine Wave is present in either Mono Amp.  Each channel is working perfectly.  This is a very good Mono Block Amplifier Set:  The amplifiers have a perfect Sine Wave Match all the way out to 50,000 Hz as shown on the Oscilloscope.  These are Serious Stereo Amplifiers:

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This Ampex 6L6 Mono Block Amplifier Pair has been very, very serviced.  This is NOT a Potentiometer spray job with a “Serviced” tag tied to it.  The Voltage Doubler was completely rebuilt with 105 Degree, 10,000 Hour Capacitors and capacitance was Upped from 100uf to 150uf.  New Matched Motorola Diodes were used.  The Filter Cap sections were replaced with 12,000 Hour 105 Degree Nichicon caps and approximately doubled in capacitance.  The Power Supply was carefully analyzed and adjusted to operate at standard USA Voltage which seems to be 121VAC or Greater.  Nichicon Metallized Polypropylene coupling caps were used.  The Balance Potentiometer was adjusted so the Grid Voltage is balanced between the two tubes on each Amp.  The Transformer Bells were finely restored.  NEW Custom Built Output Transformers that were researched and analyzed by studying the original output transformer.  The New Output transformers are precisely matched with better Iron and wire.  The precise match of the Output Transformers is probably the dominant reason why the Soundstage of this set is excellent.  They were built by Heyborer - one of the most experienced Audio Amplifier Transformer Companies in the world.  After all, they did the Famous Eico HF-81.  I pumped clean the main solder joints and resoldered.  Ampex relied on the Preamp to Power-On and Off the amps – I suggest that you use a Power Strip to turn On & Off.  Many days were invested in making these amps the best that they can be.  

There is something very special about the Sound Stage of these amps.  In addition to being Two separate Amplifiers, I believe the following contribute to the excellent soundstage:
1)  Precise matched windings of the OPT Transformers.  
2)  Matched Voltages between the two Amps.  
3)  Matched Part Values between the two Amps.  
4)  The Sovtek 5881 Tubes have a very close Match.  
5)  The Circuit, The Circuit, The Circuit...

These are 16 Ohm Amplifiers.  I have been using them with an 8 Ohm Pair of speakers and the fidelity is great so the impedance is not that critical.  However, the Amps would run a pair of Lowther/Quad/Jensen/Zu Audio/etc. 16 Ohm Speakers wonderfully.

How do they sound and run?  The precise match of the Output Transformers and matched voltages is probably the dominant reason why the Soundstage of this set is excellent.  I have owned many tube amps and this pair is certainly the best I have heard.  I have played a lot of material through them, from old Vinyl to the latest digital and the amps can reproduce it all.  The Original Telefunken EF86 and Amperex Bugle Boy 12AU7 are original.  They are not the strongest - I tried other EF86 and 12AU7 and the original tubes were much better so chalk it up to the Teles and the Bugle Boys. The Power Transformer runs just warm to the touch with the Output Transformers running even cooler - nothing is being stressed on these amps.  I adjusted the Power Supply so that the plates are running at approx. 415VDC - a very optimal Plate voltage for a 6L6 or a 5881.  The Level control is very handy and as you can see one can use a Phone to run these amps.  The original design did not have a Power Switch on the amp and relied on the Preamp Switched AC Outlet to turn on the amp - I suggest that you use a power strip to turn the Amps On/Off.  

Realize that these are Vintage.  If you are concerned about a Dot, Scratch or other Imperfection I suggest that you buy a new amp.  Ampex did not intend these to be chrome plated living-room show case pieces.  First and foremost Ampex was an Electrical Engineering firm that produced many technological advances in the industry.  They were a Silicon Valley phenom in their day much like Apple is today.  They look great but they are vintage - these are serious Hi-Fi Amplifiers and you should view them for what they are.  

Service Steps: