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Received my new M-60s today.

70.162.169.147
Posted on April 12, 2016 at 19:58:52
jeffreybehr
Audiophile

Posts: 5707
Location: Phoenix, Arizona
Joined: December 10, 2004
Contributor
  Since: December 13, 2004
 photo 2016Apr12_LCh cooking_1800w_zpsos0o4yji.jpg

This version is configured and assembled more neatly than the Mk. 2s I had a half-dozen years ago.
photo 2016Apr12_bottom off from rear_1800w_zpssymxdpin.jpg

Took me a minute to determine the front-end tube numbers. Viewed from the front of the amp and NOT upside down, V4, the cathode follower, is the single in front. V1, the input tube, is the left-rear, and that's easy to deduce--it's the 'N7 closest to the signal-input jacks. V2, the upper part of the CCS* is the center tube. V3 is in the right-rear. The eagle-eyes among us can probably determine that from the pic.

Both amps are in process of their minimum-24-hour new-amp-and-new-tubes conditioning. More pics of the circuitry are at the link.

* and pls correct me if this is the wrong terminology.

 

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Got the new couplings caps and load resistors installed..., posted on April 17, 2016 at 01:24:01
jeffreybehr
Audiophile

Posts: 5707
Location: Phoenix, Arizona
Joined: December 10, 2004
Contributor
  Since: December 13, 2004
 ...Wednesday evening and got the amps in the system and the system rebalanced (for their higher gain) last nite. Tonite, even after enjoying a fabulous concert of REAL music played by the excellent Phoenix Symphony Orchestra and with only about 30 hours on the amps and with too-long, lower-quality speaker and IC cables in the left channel, the system sounds GREAT! I'll be running these about 15 hours/day weekdays and 24-per on weekends until they get at least 500 hours on them.

The new coupling caps are very small (0.01uF) SoniCap Platinums driving new PRP load resistors of 390K for a high-pass filter of 42Hz. This will protect the otherwise-filterless MR drivers in my Serenity Super-7s.
photo 2016Apr17_room w M60s_1800w_zpsvksl29bn.jpg
I'm THRILLED!

BTW I'm using Tung-Sol 'N7 roundplates in what I believe are Vs 1 and 3. I plan to use A-S's gain-reduction plugs in the V2 positions, and probably I'll select some low-testing TSRPs to use in the cathode-follower (V4) positions. Right now, the four TSRPs were selected for moderate transconductance and low microfonics.

 

RE: Received my new M-60s today., posted on April 13, 2016 at 15:37:20
pathologymd
Audiophile

Posts: 22
Joined: August 9, 2003
 Definitely a thing of beauty. Hmmm. What is the purpose of the bridge with the 2200uF caps behind the fuses? I don't recall seeing that little circuit board either!

 

some Mk3.3 changes, posted on April 19, 2016 at 09:35:51
Ralph
Manufacturer

Posts: 4769
Location: Minnesota
Joined: April 24, 2002
 The little circuit board is a 2-stage CCS circuit, replacing the 6SN7 2-stage circuit of older amps. It has better performance (although the older CCS performance was excellent); because the MOSFETs have so much more gain, they really can perform better in a CCS circuit. The circuit has the added benefit of really preventing any chance of filament/cathode arc-over in the voltage amplifier circuit although that really wasn't a serious problem with 6SN7s in general.

This freed up a tube socket, which is in this case paralleled with the original 'V1' tube sections, to allow the bottom portion of the differential cascode to better drive the top portion. This yields lower distortion and slightly more headroom out of the voltage amplifier.

The other device, the bridge with the caps on it, is for blocking any DC component that may occur on the AC power line due to electric heaters and the like.

 

RE: some Mk3.3 changes, posted on April 20, 2016 at 15:34:25
pathologymd
Audiophile

Posts: 22
Joined: August 9, 2003
 Thanks so much for the information, Ralph.
William

 

Ralph, TYVM. 'Twas a pleasure talking with you today. More on tube positions., posted on April 19, 2016 at 16:52:14
jeffreybehr
Audiophile

Posts: 5707
Location: Phoenix, Arizona
Joined: December 10, 2004
Contributor
  Since: December 13, 2004
 Straight from the Ralph's mouth, about the M-60 Mk.3.3:
1. The old 'input tube', V1, is now two input tubes in parallel, labeled V1a and V1b. V1a is in the right-rear position (see picture) while V1b is at the left-rear. These two input tubes are physically separated by the...
2. Old and new V2 which I can never remember what to call this function--it's the Voltage-gain 'top' tube in the Mk.3.1 schematic I have. This is the rear-center tube and is the one that would be replaced with the gain-reduction plugs that A-S sells.
3. The good-old V4 cathode follower is in the front of the amp.

All of these in my amps are currently Tung-Sol roundplate 6SN7GTs. Those in the CF positions are my least-good tubes, low in transconductance and relatively high in microfonics--that in these CF positions are free of microfonic noise when tapped lightly with a pencil.
photo 2016Apr19_R-ch w TSRPs amp Herbies dmprs_1800w_zpsnmltb43x.jpg

FWIW, even with only dozens of hours on new amps, new tubes, new Teflon-film coupling caps, etc., these amps have helped my system sound even better, particularly in transparency and spatial resolution. I'm very happy.

 

RE: Received my new M-60s today., posted on April 15, 2016 at 13:17:25
llwhtt
Audiophile

Posts: 192
Location: SOCAL
Joined: October 28, 2008
 Since Ralph is using toroid power xfmrs I'll bet those are hum busters to deal with DC on the AC line.

Craig

 

RE: Received my new M-60s today., posted on April 13, 2016 at 17:33:18
jeffreybehr
Audiophile

Posts: 5707
Location: Phoenix, Arizona
Joined: December 10, 2004
Contributor
  Since: December 13, 2004
 pathologymd:
"Definitely a thing of beauty." Yes, it's certainly neater and more attractive, top and bottom, than my earlier ones were.

"Hmmm. What is the purpose of the bridge with the 2200uF caps behind the fuses?" I have no idea right now; don't have a current schematic. Caps are only 16VDC.

"I don't recall seeing that little circuit board either!" Me too. I think it's some kind of regulator; the devices have 3 pins. One wire is labeled 'cathode'; another is labeled 'coil', but I don't see one of those.

Output-stage caps are Nichicon 2200/200s, 35mm OD; can't see the model designation. Total OS capacitance is (6 X 2200 =) 13200uF. The schematic for a Mk.II.3 shows (6 X 1500 =) 9000uF. My old Mk.3.1 with large-PS option had (12 X 1800 =) 21600uF. I'm fantasizing about substantially improving the quality of those caps. I have 24 BlackGate VK-series 470/160s for (12 X 470 =) 5640uF per amp; probably I'll use something larger in the 1st-two cap. stages of a CRCRC filter. I also have 16 BG VK 150/350s to replace those axial-lead caps in the front-end HV supply.

We'll see.

 

The small circuit board, posted on April 15, 2016 at 04:18:51
Cousin Billy
Manufacturer

Posts: 243
Location: Greater Toronto Area
Joined: September 10, 2004
 Unless I'm mistaken, Ralph is liking the idea of a solid state constant current source. There are a great many plus'. Though I can't remember what they are?.

The biggest advantage, and this is huge, it frees up a 6SN7. Your M60 now has two input tubes, like the MA-1, I think?.

If I'm not mistaken, this drops distortion to really low levels.

 

OK on the CCS. No it does not have two input tubes. , posted on April 15, 2016 at 11:54:48
jeffreybehr
Audiophile

Posts: 5707
Location: Phoenix, Arizona
Joined: December 10, 2004
Contributor
  Since: December 13, 2004
 It still has four front-end 6SN7s, and AFAIK, they're configured the same way as they were in the Mk.IIs.

 

I've been scratching my head Mr. Jeffrey Behr , posted on April 16, 2016 at 02:11:39
Cousin Billy
Manufacturer

Posts: 243
Location: Greater Toronto Area
Joined: September 10, 2004
 I've been trying to think?
If the CCS is now solid state, what would Ralph use that spare tube for?

I looked closely at your 'inards' picture.

If you look closely, the signal wire from the XLR connection goes to a tag strip.
From there the signal goes through two input resistors. These are attached to V2.
There are two wires which connect those two input points to V4, also input points.

If someone else could look at the picture, that would be much appreciated.

If someone else could look

 

RE: I've been scratching my head Mr. Jeffrey Behr , posted on April 16, 2016 at 12:45:54
llwhtt
Audiophile

Posts: 192
Location: SOCAL
Joined: October 28, 2008
 The MA2s that I repaired years ago had paralleled tubes for the bottom part of the cascode diff. So it looks like the two side tubes are the lower part of the cascode, the middle tube is the upper part of the cascode, and the front tube is the cathode follower/driver tube.

Craig

 

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