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Ming-Da MC34-B

Ming Da El34-A Triode Mod

HI,I am the proud owner of a Ming-Da EL34-A ,'it is an excellent amp' I have already replaced the valves with the russian Mullards and replaced the 400v 0.10uf caps with black gates they have improved detail and made the sound more immersive and thats before they have berned in, I am also waiting for some Auricaps to be deliverd from the US.
I have bypassed the selector switch and removed the pre amp circuit so it is virtuley a power amp now and it sounds great.But I would like to add a triode mode
do you no where I could get some info and diagrams to help, ming da dont give them out understandabley and they dont give info on biasing with the amp,please could anyone help...
 
If you look above you'll see a picture and a description on how to bias the "B" model, which I'm assuming isn't much different from your "A" model. As far as triode mode goes I simply soldered a 100 ohm 1/2 watt resistor across pins 3 and 4. Removing or reducing the amount of feedback will also improve dynamics. Make sure you remove the UL connections before you wire it in triode, or if your ambitious you could add a switch for UL/Triode. I can't remember which preamp/driver tubes the "A" used, but I wired the heaters for 12**7 tubes. I had good success with both the ECC99 and 12BH7 for driver. I'm curious though, you said you removed the preamp circuit? How did you wire it afterwards?
 
I would like to add a triode mode to my Ming-Da mcm34-A but I whant to use the
pre amp switch as Ive removed the preamp cuircuit so the switch is now redundant,it would be very usefull if I could make use of this but I dont know where to start could anyone help.Ive whanted to do this mod for ages..
Alan
 
You'll have to wire the #4 pin to both ultralinear and to a 100ohm resistor to pin #3. You maybe able to do that through the stereo/headphone switch, but I'm not 100% sure. The circuit for UL will just be the #4 pin, but triode will be both #4 and #3 pins.
 
THANKS!! IM GETTING THE IDEA BUT IM NOT SURE WHAT MAKES UP THE UL CONNECTON'S,DO THEY GO FROM PIN 4 TO THE NEXT VALVE AND IS IT JUST ON THE EL34'S.DO I NEED TO TOUCH THE ECC82'S/ECC83'S?. :thmbsp:
 
The ultralinear connections go from the output transformers to the output tubes on pin #4. Triode connects pins #3 and #4 with a 100ohm resistor, removing the ultralinear connection on pin #4.
 
A few months back I did a circuit change that transformed this amp into a different category, I replaced the typical cathode bias setup, resistor and bypass capacitor, with a single AA 1.5v NIhM battery. I put one on each side per preamp tubes. The noise floor dropped, the clarity improved, and even frequency response seems to be better. Bass seems to go very deep now. This was almost like putting in a new amp it made it sound that much better.
 
Ping Thor, about the Ming-Da

I just ran across this thread... Thor I'm surprized you sold the Ming. Was that the same one that Rob "custom built" for you? The pictures are gone [now] but from what I remember it sure looked like a keeper to me. I thought you were very happy with it. What happened? You said you may "get another one" but will you be able to get one exactly like Rob put together for you? Did the amp just not provide long term enjoyment or did a change in components make it no longer compatible? Or did your listener priorities shift? Just curious.

MikE
 
No Rob didn't custom build it he imported it for me via his US distributor and gave me a deal on the price.

I was very happy with the look and sound of it, it was in need of a bias adjustment after using it for a year and I was also strapped for cash with my Miata restore. Since I had 5 very good Luxman SS amps I figured I could offload the Ming Da to subsidize my car project and not have to deal with a bias adjustment ;)

Someday I would like another tube amp, on top of the sound they are great conversation pieces when folks see them. They don't see tube gear at the local Best Buy and Circuit City.
 
Thanks

Someday I would like another tube amp, on top of the sound they are great conversation pieces when folks see them. They don't see tube gear at the local Best Buy and Circuit City.
Click to expand...
Pearching to the choir on that one brother! :D I sometimes haul my amp / crate to work just to hear "what's THAT?" hehe MikE
 
Last weekend I was able to get one of the MV34-A amps. At the time, I knew nothing about it (I only have SS) other than it sounded pretty good with a cheap CD player and a pair of bookshelf Wharfdales. I listened to several tube systems at the Atlanta AK meet we had in March and was quite impressed. Have been thinking about how to get started with a tube amp.

The guy that had it works for a company that sells them. I am an antique dealer and I was able to trade him an old fan for it! I didn't think it too much of a risk, got a great deal without having to layout any cash.

I was very pleased and not surprised to search AK and find this thread. Looks like I didn't buy a pig in a poke. I am going to get it hooked up in the next few days and give it a good test run. I like the idea of the mods DanTana has suggested so I'll make a run at some of those. Currently they are beyond my skills but I need to learn.

A new audio experience, should be fun!

Terry
 
First thing your going to want to do is check the bias, this will have to be done with the power on at operating temperature. I think 35mv is the correct setting. You need a DMM with clips and a small screwdriver to adjust the pots. You must be VERY careful when doing this only because there is high voltage inside. Use the one hand rule and keep the other hand away to avoid lethal shock. It really isn't too dangerous, but one slip and it could be. The bias points are very well diagrammed in this thread. Get a good baseline listening to this stock before you consider any mods. The mods are not that difficult either, those will be done with the power off. Still you must be careful, one bare wire can cause a short and poof. Radio Shack sells plastic alignment tools which will make adjusting the bias a much safer affair. It will include a small plastic flat screwdriver. I put 8ohm resistors across the outputs lean it back for easy access, take off the bottom cover, turn it on and let it warm up awhile. Then adjust.
 
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Thanks Dan, I'll follow your advice closely. This electrical work is new to me so I am going to take my time. As it is now I'm going to be out of town for the next week and a half so it will be later on in May before I can get started.

If you don't mind I will be looking for your help from time to time.

I'm looking forward to this project.

Terry
 
I first came across the MC34B on ebay, and was intrigued by Dan's review and experience of modding. I bought one about a month ago when I found a local distributor. So far I've switched to JJ EL34s (wired for triode a couple of days ago) and ECC83s and Winged C 61NPs - I have some Sovtek 6H30pi from an unfinished Hagerman kit, and will try those before I decide on the ECC99. I 've seen some negative responses to Dan's questions elsewhere on using the 6H30, but from what I can see the higher heater curent may be the only problem. I tried them in the amp as the first change with the other original chinese tubes, and it seemed fine - I'll let you know how I find them when I've had longer to listen to the triodes and done a few more of the mods you suggested - battery bias, NFB. Mine came with Solen MKP coupling caps which are decent, but will eventually be replaced. Have to say this is probably the best audio buy I've ever made.

From what I've read on the MC34A, it seems to come with 12AU7/12AX7/EL34 (and maybe triode/UL switching?) so TW is probably part of the way there already.

Thanks
David
 
The 6H30pi is probably an excellent choice, just a little pricey is all, changing to 12v opened up a plethora of options. Good luck.
 
Dan,
I can't convince myself that I'm sure about the exact location of the resistor to duplicate in series to reduce NFB. Could you confirm which part of the circuit to look at? What is the R in your amp?
 
The negative feedback circuit will begin at the speaker output, if I remember right it will be soldered to the 8 ohm positive post. You can just add another resistor right there if you wish. Trace the wire back and you will see a 100K resistor, a good starting point might be to double the value, you can remove the old reisistor increase the value you want. I don't use any negative feedback. A little feedback didn't sound bad, but the music detail seemed to increase as I decreased feedback.
 
Dan,
I wondered how far you'd gone in reducing NFB. I've just removed it completely, and the improvement in detail is not subtle - I'm listening now and I can hear something which was totally masked before - when the vocal channel is unmuted on the mixing desk just before the voice comes in, the ambient soundstage changes as the vocal mic images the studio. Amazing.
Battery bias is next.
 
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