MV45 Resistor Identification Help

[gtrplr2]

This is my first post here, and my first Conrad Johnson amp to repair. I received this amp with a blown up, and it is really blown up beyond recognition, just a pile of carbon! I am hoping that someone here will be able to help me with identifying the resistor in question, what value and wattage rating. Thanks in advance for any help with this issue.

[admin]

First, welcome to CJO. Nice to have you.

Wow, when you say "blown up", you really mean it. Check out our troubleshooting section as we have the schematic for this unit. You should be able to find the components. It looks like you may want to replace a couple of items on that board as they may have been damaged.

[gtrplr2]

Thanks for the reply! Yes I had planned on doing a complete cap job as well as one of the electrolytic caps on the other side of the board is showing the common bubble. I hope after the parts replacements it will come back to life, slowly of course!

[ronaldw441]

You're missing R13 which is shown as a 63.4 ohm resistor on the parts list. Of course this is an unusual value so the way CJ came up with this value is to solder a 90.9 ohm resistor on the component side of the board and a 220 ohm resistor in parallel on the trace side of the board.

You should be able to save this board but it's obvious that someone has already messed with this amp. Those capacitors are not original.

PM your email address and I'll send a photo or two of my board.

Ron

[highfigh]

Which caps aren't original? I have an MV45 and it has the same ones.

[gtrplr2]

Well the owner of the amp has decided to just sell the amp, instead of repair it. So I will get some pics of the chassis and exterior soon and will be listing it for sale. Other that the repairs that are needed on the board, it is in excellent overall shape.

[highfigh]

Where is it located and how much are they asking?

[gtrplr2]

Hello highfigh,

It is located in Montana, and he will be accepting offers. I hope that it is OK to discuss this topic here and not in the classifieds section. I will be listing it there sometime within the next day or so.

[highfigh]

Cool- it's always good to find something that could be repaired or the basis for a new design.

[highfigh]

I have an MV45 and haven't used it in a long time. I had an output tube turn into a light bulb while I was standing next to it (fortunately) and I shut it off immediately. The tube lost its seal, but biasing the next tubes was a problem because they were a set of JJ that were part of the recall because the pins were under-sized. I decided to replace the two electrolytics on the bottom of the board, mainly because they weren't changed with the PS filter caps. Well, that ended up on the back burner because we had a huge rain that caused water to enter my basement and I needed to deal with the cleanup and I just didn't get back to it until last week. I decided to bring the line voltage up slowly and watched the plate voltage over time and last night, I shut it off so I could insert the output tubes and bias it. I was going to clean the bias pots before doing this and when I opened it, I smelled something 'fishy' literally. I had installed F&T caps with higher voltage rating and the shrink-on labeling had split. The top of the chassis on that side had felt a bit warmer than the other, but it wasn't major, so I didn't open it. It leaked a bit of oil but it didn't go as badly as some that I have seen, fortunately.

Does anyone know if CJ sent service manuals to their dealers, or did they require shipping them back? Has anyone seen a circuit layout that's accurate, or has anyone created anything like this? It seems that CJ documentation is sorely lacking. If anyone has a diagram with voltage test points, I would appreciate seeing it.

Does anyone have a detailed list of what was changed in the MV-45a1? Has anyone come up with improvements that made a worthwhile difference?

I was surprised when I initially opened it- I would have thought the PS filter caps would be on a circuit board- what is recommended for replacements and what is the best way to mount them? Is there any consensus to the better brands of tubes for these? I have a set of JJ E34L Sky Blue that I never used (they were the replacements for the ones with the under-sized pins)- any opinions?

Thanks in advance.

[venu7777]

Sir,
Could you help me with mv45 schematic,there are diodes,transistor and resistor burnt.without schematic unable to replace the parts.pcb partly burn at biasing section.
Thanks.

[admin]

Sir,
Could you help me with mv45 schematic,there are diodes,transistor and resistor burnt.without schematic unable to replace the parts.pcb partly burn at biasing section.
Thanks.

First, welcome to CJO. Nice to have you with us.

You can download all our schematics (including the MV45) here: https://www.conradjohnsonowners.com/vie ... f=17&t=128