For-Sale: Amplifier (Tube) Post an Ad
Flag Ad: Miscategorized  Spam or Suspicious


Atma-Sphere M-50 Mono Blocks + Z-Music Transformers + Spare Tubes - Price Drop

Price:  $2,100.00
Days/Views:  269 / 804 (Posted 2023-09-29)
Condition: 8/10 Very Good
Seller:  baileyler   (Contact Seller)
(Other Seller Items For Sale)
Feedback:  5.0/5.0


I never thought I would do this, but I have learned to “never say never”.

I am downsizing and have come to the point where I don’t feel I use these enough, so I am putting them up for sale.

Price is $2100 for the M-50 + Z-Music Transformers (OBO, especially for a local transaction).


This pair of M-50s is likely one of the few left in this condition. I am not the original owner and do not have their entire history, but they look to be completely original with 2 exceptions. At some point I believe someone replaced the power supply caps, and I upgraded the coupling caps to VCaps.

These even have the original power transformers. My understand is that most were replaced with toroidal transformers due to upgrades and other quality issues with the original transformers.

The gold face plates are in beautiful condition.

They are Serial #150 (stamped below the power cord). I was originally told by a previous owner that these were M60 Mk. 1, but Atma-Sphere has no record of these being upgraded, and the presence of the original power transformers seems to confirm that.

They are operationally great with only two issues that I am aware of.

First, the “Power Available” LED on one of the blocks is dim. Second, the bias and balance pots on the other block are functional, but need to be jiggled a bit to work and shut off.

I have always used these hooked up to a constant voltage power source.

The Atma-Sphere Z-Music Transformers are Serial #106 and #107.

Physically they are in good condition, except that the case screws on the bottom of unit #106 have stripped from the wood and are loose. This is how they were when I acquired them several years ago. These are extremely heavy pieces, and it is easy to see how this could happen. They do not move, so it has never been an issue for me, but I suspect it is a relatively easy fix.

These were designed to be impedance modifying autoformers, for example, for connection between Atma-Sphere OTL amps and lower impedance speakers so that the impedance could be adjusted to closer to the optimal operating point of the amps.

There is a detailed discussion of the operation of such units on the zeroimpedance website.

As I later came to find out, there was a defect in the Z-Music Transformers in that they were not wound properly and did not function as intended.

Paul Speltz (developer of the Zero Autoformers) discovered this and provided connection instructions so that the Z Music Transformers can function as intended. I have all that information and will provide it to the new owner. You can also find this information on audioasylum under the OTL thread.

Just as a general note, the guys at Atma-Sphere are great (as are their products), and have always been available to answer any questions I have with these amps.

The current tube set in each amp is 8 vintage 6H13C (Russian 6AS7G) tubes of various brands, 2 Mullard CV4024, a United Electronics branded ECC801S (believed to be a relabeled Tungsram or EI made 12AT7/ECC81), and an AMC branded 6680/12AU7 (believed to be a relabeled Tungsram or EI made 12AU7/ECC82).

In addition to the above, I have a few vintage 6H13C (Russian 6AS7G) tubes laying around, both NOS (“new” old stock) and used. I do not know the exact number, as they have been in storage for a while. All of these will go with the amps.

Also, I will include shorting plugs for the balanced inputs (needed for using the unbalanced inputs).

I also have a nice pair of Speltz Zero Box autoformers that I will sell with the M-50/Z Music Transformer set for an additional $500. THESE ARE NOT FOR SALE SEPARATELY.

I can provide additional pictures or info on request.


Please note that these units are being sold "AS IS, WHERE IS”.

I am more than happy to demo these prior to sale.

Preferred payment is cash, no fee Paypal, crypto or Venmo. Money order/cashiers check/personal check can be accepted, but all must clear my bank first.

A CONDITION OF ANY ELECTRONIC PAYMENT IS THAT YOU EXPRESSLY WAIVE THE RIGHT TO FILE A CLAIM OR CHARGE BACK with the payment vendor (but do retain the right to sue me in my local court should you so desire).

I don’t really have any needs, but I will consider trade value on a good-condition IPhone 12 or later, at least 128GB, unlocked, a decent Andriod tablet and/or possibly one or more Nvidia RTX 4000 series video cards. Other trade value might be of interest, so it doesn’t hurt to ask.

There is a strong preference for LOCAL SALE (Chadds Ford, PA 19317), or a meet up at a reasonable distance, but I might be willing to ship. Shipping will be complicated and expensive (probably four boxes for everything), and fully for the cost of the buyer (including insurance). Further, I will not be responsible for any shipping damage, but will assist with the processing of any legitimate insurance claim.

Please check my feedback on Ebay (ID=baileyler) and buy with confidence.

Payment and Shipping
Ship Weight: 100 lbs.
Ships From: 19317 (Chadds Ford, PA)
Ships To: USA Only
Shippers/Payer: UPS, FedEx / Paid by: Buyer
Shipping Notes: See listing.

More Seller Info
Seller:  baileyler   (Contact Seller)
(Other Seller Items For Sale)
Membership:  Audiophile
Asylum Feedback:  5.0/5.0
AudigoN Feedback: baileyler
eBay Feedback: baileyler
Location:  Chadds Ford, PA, United States
Registered on:  2007-01-17
Posts:  359

Contact Seller

[ Terms of Use ] [ How This Works ] [ Contact Us ] [ Support/Wish List ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]