Luxman MB-3045/A-3000 amplifiers

Blue Shadow

Waiting for Vintage Gear from this century
There are those here that own these amps and I'm wondering what condition they are in as far as tube compliment and modifications done to the amps. For those that don't own these amps but want to participate, let's discuss the other mid-powered tube amps with a good following. A question about these at the end of this post.

For the modifications, there are those needed to make the amp operate in UL or Triode mode based on the documentation. They are different mods. Additionally, these amps can be improved with some other mods and I'm wondering what folks have done in this arena, too.

I'll start.
Backstory, swapped a Hafler DH-200 kit I built for these back in the day. Used them until I couldn't bias and balance the 8045G tubes in them. Unfortunately, I didn't buy a bunch of tubes, $15 back then to keep them running. So I put them in the double box and stored them for decades.

After finding the web and time to deal with the amps, I contacted folks that own the amps and got a copy of the Luxman modification manual to allow these amps to be converted to use the 6550/KT88. I did the mod and no joy. Gadget47 dropped by and found the problem straight away. The manual does not say to connect the choke to the tube resistor installed to the terminal block. Joy. Sound great.


I have stock MB3045 mono amplifiers converted to operate in the UL mode. One has gotten hot on the board and I did some board repairs, replaced the resistors, mounting them above the board (below as the component side is down) and installed replacement caps for that location. I have also installed a ICL, in-rush current limiter.

I have not installed a new RCA or modded the AC inlet or bypassed the input level control. These can be improved. Since the GE tube is too expensive for some and the Winged C is no longer in production, I have a set of Tung Sol KT88s in these that perform well. In an amp listening session, these walked all over the competition, Crown PSA-2, Hafler DH-200, Citation 22, McCormack DNA-1.

Post about your Luxman tube amps.

One other thing is which midpowered tube amp would you want? You get your pick, but since this is just a hypothetical question there is no value in the amp chosen. So picking the one with the highest resale will net you a big fat zero so pick it by experience, looks, sound quality or whatever reason you want, even name brand since a few have strong name recognition. Sound quality would be the choice for selection but many haven't heard these amps. Let's keep this to the 30-60 watt range.

Marantz 8b
McIntosh MC30
McIntosh 225
Luxman MB3045
Dynaco ST70
Citation II
and others, I guess.
 
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My A3000s were re-converted from Ultralinear to Triode, and have new Gold Lion KT-88s installed. I am running them on a Variac. They were bought used, and I really don't know their condition otherwise. Probably closer to original than to restored.

I also have a pair of unconverted MB3045s. One started making a mechanical (not through the speakers) hum. I turned it off and took it to Shelley's Stereo in Woodland Hills. Their tech ruined it (burned out the output transformer) on his bench, actually during a phone call when the store called him to check on status, as in "Wait a minute - he said something just happened. Let me talk with him and get back to you." They did not make good on it, even though it still played music when I brought it to them. It's mate is exhibiting some warning sign, I forget what, but wrote it down on a yellow sticky before I boxed it back up.

I also have a pair of MB3045s that have been converted (triode). One is working fine, the other makes odd noises for maybe 40 seconds after turn-on, plays fine afterwards, and then makes odd noises when shut off, so it's out of service now, too.

I should know more about tube amps than I do, to be running these. They are not reliable enough to be practical for me at present. I also think that just any ol' technician is not necessarily good enough to work on these; ideally one would have experience with this model. One tidbit that was relayed to me from the guy who fixed and re-converted the A3000s, and the MB3045 that is still working fine, is that there is a 10 ohm (I think) resistor that is designed to burn out to protect the output transformer when a tube starts failing. I believe the previous owner of the unconverted ones had replaced those with wire-wounds, which may have contributed to the burn-out at Shelley's.

All of them have worn-out original, or crappy replacement speaker terminals. They probably all need a thorough check-up. I would consider offers on the four MB3045s, PM if interested.

For a long-term replacement, I'm a bit leery of vintage now. I read Art Dudley's review of the Prima Luna Dialogue Premium amplifier, and wish he had tried it on his Quads. http://www.stereophile.com/content/primaluna-dialogue-premium-power-amplifier#piHQfxy54BJcDgCL.97

The SS amp I've been using seems impossible to damage in normal use; it's so well protected. I'm thinking that kind of engineering applied to the tube world might be more suited to me.
 
Blue Shadow, can you be more specific on the problem found with your amp, with the choke wire? I have had a pair of mb3045 amps since 96, did the mod to kt88 tubes, have not had any problems.
 
The Modification Manual did not show a connection from the resistor on Mold Terminal a pin 2 to the choke or from Mold Terminal b pin 2 to the choke. It simply stopped after step 7 and went to step 8, adjust the bias. This resistor is a 220Ω from Pin 5 of V5 and V6 going to respective mold terminals. Without that connection to the choke the resistor to the tube was not connected on that mold terminal end and the position of the bias or balance pot made no difference.

There is documentation out there that shows this connection on a schematic. I don't know if I had that or didn't read the schematic to compare to the procedure. I have the docs now with the schematic together for my next pair needing a modification.
 
Just to clarify about the missing connection, there was no supply to the screens on the output tubes. These do not actually operate in ultralinear either, despite what the modification manuals say. There are no UL taps on the output transformers.
 
Thanks Gadget73. Update... my 3045 amps were previously modified with sweep tubes installed when I purchased them. The tops of the cages hit the power tube "top hats", so I just did the modifications to use kt88 tubes, wired in triode mode following the Luxman instructions, and did not look at much else on the boards for changes previous owner may have done.Recently I checked and found the feedback capacitor value had been changed, so without the use of a good oscilloscope to check distortion, I replaced it with the stock value. Also added volume control pots. I could never get the original volume control pots to match, between the two amps, and had removed them. I found a much better volume control recently, high quality, and have those installed. The amps can be used without a preamp again, eliminating various wires, resistors, and capacitors the audio signal doesn't have to travel through. I had replaced the capacitors on the CB-A3000M board with all Mundorf Supreme Silver/Oil and Silver/ Gold, all 6. That may have been too much of a good thing. Recently I replaced 4 of those caps on these boards with a "pulse" rated type, that made a huge difference. I am enjoying my 3045 amps now, and I still have not played around with "tube rolling" or power tube bias adjustment.
 
Hooked mine up yesterday for the season. Kinda just getting cold here and I need to listen to these for a while to get spoiled with their sound. The input level controls on mine are mostly used wide open with the preamps I have and I need a preamp. Too much gear to hook up need something to switch and 3 phono inputs. This will be my first long term use of these amps in a number of years. Last few years I had much more demanding speakers, Magneplanar and Dahlquist, both of which will work just fine with the Luxmans but the ADS are more efficient, 3 or 4-dB not a lot but...
 
I would rate these as follows...
in original form
Marantz 8B
Luxman 3045
McIntosh 225
McIntosh MC30
HK Citation II
Dynaco ST70

If all are hot rodded, the 8B and 3045 still retain the top slots, the Citation improves the most(joining the top tier), and the ST70 becomes quite good.
 
I have to disagree with the statement that a tube amp needs a tube rectifier. My Mac MC40 amps use diodes for rectification and they sound awesome, not sterile like a lot of SS amps do.

BillWojo
 
Also on the board, I replaced the orange Yamato 0.22 capacitor with a Sprague 716p poly film and foil.
 
The stepped volume control pot was purchased off Ebay, DACT Type 21 Stepped Attenuator 100k 2A3D. Sounds and works good, gold plated contacts.
 
The Audyn caps are almost too large, but I wanted to try them. Lead wires have to be insulated of course to avoid touching other components, and caps were turned a bit. Got these as it was recommended "pulse rated" caps work best in this position. Very happy with results. The bottom plate does fit.
 
Vampire input connector. Solid copper speaker terminals, of a minimalist design. I dont like the expensive large chunks of metal speaker terminals, they look pretty but the music signal has to pass through all that metal. I made custom Plexiglass boards for the terminals.
 
Excellent. Individual posts for each upgrade, helping with the post count.

elektron on another board said bypassing the volume control and going straight to the first tube is a nice improvement. Keeping the volume control but using a really nice one is getting a step closer. Thanks for the list so far.
 
Excellent. Individual posts for each upgrade, helping with the post count.

elektron on another board said bypassing the volume control and going straight to the first tube is a nice improvement. Keeping the volume control but using a really nice one is getting a step closer. Thanks for the list so far.
Thanks for the positive comment, Blue Shadow.
 
I had a mentor on the Luxman forum years ago, he didn't post what he told me, but instead sent me emails. I lost all those emails after Yahoo thought I was someone else, and locked me out. But I wrote down everything he told me, mostly about what he was using for tubes. He said he had rebuilt several pairs of the MB3045, so I was inclined to believe him. But until this year, I had not taken the time to try the tubes he said to use. For power tubes, a closely matched pair of Electro-Harmonix KT88. I am running each tube at .55V, a little higher than the generic .50V the modification manual shows. The original tubes were run at .75V, apparently could not take the heat but sounded great (have only read about them).
 
The 6240g tubes get replaced with Sylvania 6GU7 tubes. He said "no long plate 6GU7, only short box plates like what the 6240G has, the Sylvania 6GU7 for valve 4 is magical". I am using a pair on mine. Just bought another pair off the bay.
 
Was told the original Matsushita ECC82/12AU7 tube was second best, compared to the recommended RFT brand ECC82.
 
For the ECC83/12AX7, I had to do my own research. I am using Mullard "black plate" tubes. They are expensive it seems, I had a pair pulled from who knows what in my used tube bin.
 
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