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Hi all, I don't know if I'm in the right section but I currently have this mesaboogie clone on the bench. Not exactly sure which model its based on but it has 3 separate switchable channels and mounts 4 6L6's and 5 12ax7s. It was a mess when they brought it in to me especially the filter...

Thanks again for all the help, and sorry about taking your time away.... I still have no idea where the hum is coming from but I'm starting to think of the pots themselves but that would be really strange, I just changed both gain pots with original mesa replacements and that took away the...

Well the only other thing I would like to know is if you get ground on the very left pin of the left LDR, the pin that is connected to the 1.5Mohm input resistor. thanks again for all your help

Nope it's not wrong, well if you look at the last page of the official schematic you'll find that the AC heater line gets rectified to DC for the heaters on V1 (to provide a quieter first stage). The rectifying diodes in the schematic are designed with errors but it shows exactly how the heaters...

I tried grounding the junction between the 3 components but that only took a little cable hum away, the mid-bass pot hum is still present. So whatever that hum problem is, it has nothing to do with tube voltages, wrong LV or HV voltages or grounding problems. I also tried the "bad jack test" but...

Yeah sorry if I didn't explain my question properly, there are 2 wires coming off the input jack, one goes to ground and the other goes to the circuit. Looking at the original schematic, one end of the 1.5Mohm resistor and also one leg on the LDR should test to ground when there's no cable...

Well I went through the grounding and the only doubts are right off the input jack: 1) Am I supposed to be getting ground off both input wires? 2) the mystery resistor before the 1.5mohm input resistor is probably blocking grounding to one of the LDR's.... could this be true? thanks

Hey thanks for that, great news, sounds like our readings are pretty much the same that's making me feel better. Just to sum things up: AC voltage on the resistor end of the LV supply diodes: Diode 1 to 3.3k resistor : around 10vAC Diode 2 to parallel resistors: around 16-18vAC There's really...

To answer Dougs questions: 1) yes the hum is only on the rhythm channel 2) I don't think the LV supply problems have anything to do with the hum I'm getting, here are some more tests that you can do for me if you have the time, measure the AC voltage on the resistor side of the LV supply...

Can any one do a simple dc resistance test on the power transformer connector for me? All you need to do is: 1) unplug the connector from the circuit board 2) measure the dc resistance across the LV voltage supply wire( blue wire which is 5th wire from the right on the plug - having the control...

Hi yes I do have the full official mesa boogie schematic for this model but the LV supply and many other sections of the amp are totaly different, that's why I ended up drawing up my own. http://www.flickr.com/photos/73835524@N00/3592697774/

I might have found where the problem may be, as you can see in the LV supply schematic above there are 2 x 1N4007's feeding the LV supply circuit. I tested the voltages across these diodes and I'm getting 52vAC from the power tranny though they are letting through 10-16vAC ito the circuit. any...

Hi just a few straightfoward questions: 1) Clean channel: background noise sounds like hum or bad jack noise but I just can't figure out where it's coming from. No instruments attached, turn up 1/4 output volume, 1/4 master volume and gain up 1/2. The hum comes up strongly after I turn the Bass...

Can anyone tell me whether the 1N4007 diode in parallel between the 2 relays on a DC-3, is supposed to be giving low dc resistance readings both ways? I changed it out but that didn't change anything, I'm getting around 330ohms both ways. thanks

Well that's why I thought of the MPSA transistors in the EQ/ output section.... it could also be a bad wire or just a dirty connection, I dowbt it's a problem with the tubes because the old ones were giving me the same problems. I've also replaced these plate load resistors: 220k off pin 6 V3...

Well I've changed just about all the 100k plate load resistors and that didn't change anything, on pin 6 of V1 there was a 62k resistor which I replaced with a 100k & 150K in parallel. The hiss is mainly present and louder in the rhythm channel and comes out when I turn the gain up, it is also...

After a long and time consuming repair I finally got rid of the hum problems in the amp and the short that was happening in the LV supply on my DC-3. The shielded rhythm channel gain pot wire was creating some sort of interference with the input jack wire and I changed out some of the resistors...

No I don't think it's a tranny problem, they're all original and haven't been giving me troubles. I will follow ur advice and start at the HV but I really think the problem is in the LV supply, and I suspect those 2 zener diodes too!

Ok I've done some testing and I'm posting up the results here. What I tried to do is find out where the negative voltage is coming from. I tested the bias supply and the low voltage supply and a components. here are the links to the charts and schematics: 1) bias supply voltages...

PM sent..... just one question, I'm wondering where that 330k resistor is in the schematic.... can't seem to find it anywhere.