Please anyone can help me with My Conrad Johnson MV100

[dhunte21]

I am somewhat in a somber state! I turned on my Beloved Conrad Johnson MV 100 today and I must have jumped 50 feet. To my behold a ton of sparks flew out the power button and all my tubes Bias are fully lit. But looking at the back of the amp and the Large buss fuses Nothing appears to be blown.

This one really has me, the only thing I did different is replaced the 5751 tubes with some low noise 12ax7. I really don't think that this would have taken out that amp. You can smell the electrical burnt smell. I have not had the chance to go inside to really see what has happened.

I am wondering if there is anyone out there who has had any experience with this unit. Also is there anyone who can help me out with a Service Manual.

 

[tube-a-lou]

Hi,
Conrad Johnson Design they have it all, you can call them to and talk to people
not recordings. what kind of 12AX7's were they JJ's.

Tube

 

[dhunte21]

They were telefunken tubes, but I really dont see that causing the problem

 

[century tek]

Open it up and have a look-see!

 

[tube-a-lou]

Yep! open her up!

Tube

 

[petehall347]

are the pinouts the same wondering about the heaters they are centre tapped on 12ax7 ? and they are higher gain by about 30 percent

 

[dhunte21]

Gentlemen Thanks for all your input, she is on her way back, I will open her up and put her on my workbench and see what the hell is going on!! Will keep you posted with my findings.

Thanks

 

[dhunte21]

Update on the cj mv100

Well I got a round to taking the Beast apart and going over it with a fine tooth. Conrad Johnson was kind enough to have supplied me with a Schematic for the amp. Thanks to the Technical Team at CJ. FINDINGS: Well on further inspection I notice that one of the traces had lifted off the board, well it was broken altogether. I dont know if this was a result of the spark or was this the cause of the spark.

Well whatever happened it took out a 300ohm 1/2 watt resistor, Which I replaced as well as a Motorola MPSU60 Transistor, I found Some NOS on ebay, actually got 3 for 12.00 plus shipping.

Conrad Johnson was more than happy to accept the amp for reapir, at a rate of 96.00 per hour. Humm, Maybe if I was not an Engineer!! LOL. Anyways I'll keep you posted as soon as they come.

Pics:

 

[LinuxGuru]

Is that original CJ PCB board pictured on the post above?
Unbelievably crude, cheap and poor build for that amount of money.

 

[GordonW]

Remember, these amps were designed and built in the 1970s. Unless you were NASA or the military, you weren't getting computer-layout PCB design back then. The HK, ARC and other high-end amps of this era weren't any better in circuit board construction...

One point for staying with point-to-point wiring, IMHO... but that's another subject too...

Regards,
Gordon.

 

[Stereo_type]

Linux:

Is that original CJ PCB board pictured on the post above?
Unbelievably crude, cheap and poor build for that amount of money.

That comment sounds unnecessarily offensive, especially when it has little to no basis in reality. Those who are familiar, know better.

I'm not sure what "Linux" thinks is so radical here. "Linux" seems rather unfamiliar with all of the audio products during that era.

As an aside, I probably won't sit here and defend CJ too much either, since I'd call a lot of their early-production products that I've repaired/upgraded about average overall, but not really 'worse' or even any different from much of anything else. They did what they did in order to market the products within the scope of cost vs. performance vs. profit. Sound familiar? It certainly should, as it's the defacto model for most any business.

As another, related aside, it sounds to me like the OP is receiving excellent support which is an option, not a requirement of any manufacturer, once their products reach a given age...

The build is also well within the context of the state of the industry for that time; as that was what was routinely used and it really amounted to what was available within reason. That comment of Linux's is not only out of touch with this context's reality, but also, serves as its own
definition, being "Unbelievably crude".

 

[LinuxGuru]

Remember, these amps were designed and built in the 1970s. Unless you were NASA or the military, you weren't getting computer-layout PCB design back then. The HK, ARC and other high-end amps of this era weren't any better in circuit board construction...

I don't know about HK and ARC made in 1970, but I have seen and disassembled many other equipment made at the same time (including Soviet made boxes), most of which was considered just an ordinary commodity.

But it is the first time I encountered so crude design for something considered as exclusive high-end.

And no, my post is not *offensive*. I'm just got really surprised. PCB mentioned above is really fine for home or draft build. Just consider someone seeing Lexus or Infinity and finding parts inside from cheapest KIA.

 

[jwalker]

I don't know about HK and ARC made in 1970, but I have seen and disassembled many other equipment made at the same time (including Soviet made boxes), most of which was considered just an ordinary commodity.

But it is the first time I encountered so crude design for something considered as exclusive high-end.

And no, my post is not *offensive*. I'm just got really surprised. PCB mentioned above is really fine for home or draft build. Just consider someone seeing Lexus or Infinity and finding parts inside from cheapest KIA.

I'm very familiar with PCB design and I would agree with the others that the design itself is par for the course in that era. The only thing that could be considered crude is that the assembler did not clean up the flux after soldering and even that is not a problem at audio frequencies. And this isn't even a design problem.

Maybe you were expecting something else? Let us know specifically which parts of the design offends your sensibilities so we can discuss them.

 

[mech986]

Take a look at the APT Holman Preamp manual from 1979 here and check out the PC board overlays:

http://homepage.mac.com/planet10/TLS/downloads/AptHolmanPreManual.pdf

Although the component side is well laid out, the board side, aside from a large ground plane, still has a lot of hand drawn and laid out elements. If you did not hire a PC draftsman, you pretty much drew or used hand laid Printed circuit transfers to create the board side, then used photoresist boards, or had them etched in-house or in small batches (for relatively small boutique manufactures like APT and CJ). Even Dynaco using PC boards for everything in the 70's and making a ton of boards, used hand produced layouts and traces. Even Marantz and Pioneer boards of the era had a hand fabricated appearance to them.

And all three of the above makers, AFAIK, used hand labor to stuff and troubleshoot boards, What you saw from the large Japanese makers who had some economy of scale and larger facilities to draw from was maybe a bit tidier and packed tighter, but look at the rats nest of wiring and connectors and boards in many receivers and amps, even the best ones.

That was pretty much the state of the industry then in the 70's and early 80's, you didn't have the PC board houses that sprang up in the mid to late 80's when all of a sudden IC's, minaturized components, and digital computer related designs (motherboards) started to push the PC board makers. Couple that with DesignCAD type programs and CNC controlled board stuffing for really big projects that eventually moved board making into the next level, CAD based design.

There was no "High End" defined industry then, but a lot of enthusiastic and slowly growing group of makers who were trying all sorts of things. Most everything was still hand built as most did not have $$$$ to create mass production of their products on an automated assembly line. And not very many had the interest, $$$, or experience to lay out wiring and components in an "aesthetic" way or with Mil-spec lead and wire dress (pretty tough for trouble shooting).

 

[shelly_d]

I too was underwhelmed at the build quality of that circuit board. Even though the substrate of the circuit board of my Dynaco Stereo 70 is a much cheaper product, I consider the time spent in the layout and construction of it much superior to that shown in the photos. And that product was certainly earlier or contemporary with the CV.

In fact I clearly remember the insides of an RCA TV my parents purchased in the mid to late 50's that we kept until the year we moved to CA, 1981. It used a circuit board with traces of solder, not just copper. That was a low line model of the time as well.

For the time, that was at best a mediocre build in my opinion.

Just my take on the mater.

Shell_D

 

[Shadowdog]

Aside from the flux those boards look like to be very high quality thick glass ones with nice heavy traces. Much like the proprietary US military boards I've seen from back in the day. Being SS the parts were of course smaller, but the board material looked the same!

 

[LinuxGuru]

I'm not sure what "Linux" thinks is so radical here. "Linux" seems rather unfamiliar with all of the audio products during that era.

I have worked at Russian radio factory in the mids of 1980 (CJ MV100 was introduced in *1988*, and not in 197x). Soviet electronic industry was at least 10 - 15 years behind compared to Japanese or USA, and I did remember curiosities like 30% DOA rate for newly arrived electrolytic caps.
But *THAT* kind of design and build quality would never go beyond test lab even in Soviet factory which, simply put, didn't care at all about consumer's opinion.
I don't praise Soviet electronic products because I hated them, but man, they were really cheap, and one can't expect wonders. I mean 50 - 120 rubles in average (divide by 0.8 ... 0.9 to get approximate equivalent in USA currency).

The first electronic gear I repaired (back in 80) was tube TV. Now I own Russian tube tester which is an industrial equipment (nobody cared about aesthetics of PCB), and a bunch of vintage gears some 20 years older then MV100, so I have something to compare with.

CJ is considered a top level brand, so expectation of every aspect of the products is well above average. Correct me if I'm wrong here.

I'm sorry if my comments were offending to the original poster who probably love the product he owns, and was seeking for help.

PS. IMHO the most probable cause of fireworks was lifted track causing corona mentioned by OP. Otherwise he should have exploded electrolytic capacitors.

Maybe you were expecting something else? Let us know specifically which parts of the design offends your sensibilities so we can discuss them.

Tracks on that PCB looks like being drawn by someone who was drunk or don't know how to use a drawing board. Finished board left *dirty* with flux.
Again, its OK for draft build or home-made equipment, but for "state of the art" (as advertised by CJ), it leaves much to be desired, especially taking into account 1988 (!!!) release time.

 

[jwalker]

Tracks on that PCB looks like being drawn by someone who was drunk or don't know how to use a drawing board. Finished board left *dirty* with flux.
Again, its OK for draft build or home-made equipment, but for "state of the art" (as advertised by CJ), it leaves much to be desired, especially taking into account 1988 (!!!) release time.

I already addressed the issue with the flux. The flux itself doesn't affect anything electrical in an audio amplifier. And it isn't even a design or a reliability issue and will not affect the performance of the amplifier. If it's a problem, go in there with a q-tip and some alcohol and clean it up.

The traces could have been hand drawn, or they could have used tape and photo-resist applied by hand. Even in the 80's that was an acceptable approach in the electronics industry. I was seeing hand taped boards even in the mid 90's.

The things you've pointed out are basically cosmetic and really have no bearing on whether the amplifier works or is reliable. I would say you're a bit hung up on the perceived quality versus the actual quality.

In the end I'd rather have a design that was "ugly" and worked than something that was "pretty" and was broken from the start. And based on Conrad-Johnson's longevity in the business I would say that they've done that part right.

 

[tube-a-lou]

Hi,
As a once owner of CJ equipment, sometimes the mixed of solid state and tube
didn't mix. I had a PV-3, PV-7 preamps which had the same type circuit board in it.
My PV-3 held up wonderfully for 15 years with no problems and was used to boot,
PV-6 with that same type of circuit board looked like it went thru the ringer, by the
power supply area all burnt up. I was told by a repair person who repaired a lot of
CJ equipment that sometimes the stuff didn't hold up from the heat from the tubes
and all. I not saying that all that stuff will do that, but care must be taken
more with the circuit board stuff than the point to point stuff, which I now have
(Fisher) it is easier to fix, the circuit board stuff is a little trickier but can be done,
my PV-3 proved that it was 30 yrs old and still going strong when I sold it to a happy
customer. A final thought $96.00 labor wow that's the big boys price, when I had my
PV-6 they said they can restore it with the new Teflon Caps for $900.00 ouch! the
price to be in the big leagues.

Tube

 

[dhunte21]

Exactly true, I have started to change out all the old state components in that stage that blew. I have found a burnt resistor, a zener diode and a transistor as well as some to the traces are kind of flakey. I will take my time and change out as much as I see fit, and then take it from there. I have found one member who underwent the same process and has given me a wealth of info.

Thanks for all the support, if you think there is something else I might do feel free to share the knowledge.