Amp/Preamp Asylum: REVIEW: Ming Da MC67-HA Preamplifier (Tube) by ironradio

Model:	MC67-HA
Category:	Preamplifier (Tube)
Suggested Retail Price:	$595.00
Description:	Tube pre-amp with MM/MC phono input
Manufacturer URL:	Ming Da
Model Picture:	View

Review by ironradio on August 30, 2008 at 08:53:31
IP Address: 75.164.206.131 Add Your Review
for the MC67-HA

In way of adding to and improving my review, I offer the following information:

Construction
============

The MC67-HA's polished stainless steel case holds high quality components installed in a very tidy fashion. See the photo:

http://i40.photobucket.com/albums/e234/tubeviper/P8100116.jpg

Metal oxide resistors and Solen caps are used throughout. Better caps that Solens could have been used and in fact that would make a good tweak.

And the signal path filaments are not only DC supplied, the DC is regulated and adjustable.

I thought the tube types chosen for the signal path were excellent. The two on the far left are for the MC/MM and are type 5670/2C51/396A. I ended up using Western Electric 396As. The five i the center are type 6DJ8/6922/7308. I ended up using JAN Sylvania 7308s.

But I don't think the tube types in the power supply were a good choice. First of all, they are the Chinese 6N6 which can be substituted with the Russian 6H6. But still, there is a better choice in my opinion.

The MC67-HA has four 6N6 triodes. The pair toward the rear are the rectifiers. The elements of the two triodes in each tube are tied together so that together, the two tubes function together as one rectifier. The two 6N6s in the front are part of the adjustable B+ voltage regulator.

The two rectifiers are also connected to a relay which activates when the voltage across the signal path filament supply filter cap charges sufficiently. The relay controls the grids of the rectifiers and permits the tubes to conduct.

Recently, the relay in my MC67-HA failed which took the power transformer and choke with it. After replacing the transformer and choke with superior Hammond units, I turned my attention to the tube type issue. Seeing as how the relay was gone, I removed it. I also removed the 6.8K resistors and then moved the wires from pin 6 to pin 7 on each socket. After inserting 6CA4 rectifiers, I had my MC67-HA back in it's full glory.

The only disadvantage of my mod is that there is no time delay relay control on the B+. But that's pretty minor in my book. The circuit is now simpler, it used real rectifier tubes and there is no more startup relay noise.

Product Weakness:	Power Supply rectifier and relay
Product Strengths:	Features, Design, Component quality, Construction quality

Associated Equipment for this Review:

Amplifier: Hand Built
Preamplifier (or None if Integrated): Ming-Da MC67-HA
Sources (CDP/Turntable): MHZS CD
Speakers: B&G RD50s
Cables/Interconnects: Zu
Music Used (Genre/Selections): New Age
Type of Audition/Review: Product Owner

Amplifier:	Hand Built
Preamplifier (or None if Integrated):	Ming-Da MC67-HA
Sources (CDP/Turntable):	MHZS CD
Speakers:	B&G RD50s
Cables/Interconnects:	Zu
Music Used (Genre/Selections):	New Age
Type of Audition/Review:	Product Owner