Just got my RM50 and it didn't work...

[chpsktplyr]

javascript:emoticon(':evil:')
Evil or Very Mad I pulled the chassis and after a thorough inspection found a bad connection on the impedance switch. So I thought, cool, that's it. Well, no. The amp also makes a crackling, popping sound. It is not that loud but is very noticeable. I could never record with it.
Has anyone had a similar problem? It is definitely not a module. I'm going to try tapping on all the tube couplers and resistors to see if I can find a bad component, if not, it's off to the tech$$$.
I should be jamming, but instead I'm stuck with a snap crackle pop POS. Not too happy with the guy who sold it to me, or Randall for that matter.

 

[kc2eeb]

Sounds like you bought it used. Is that correct? Pat L.

 

[chpsktplyr]

Sounds like you bought it used. Is that correct? Pat L.

Yup, it's used, from a seller who suckers people to get what he wants. There is no way he wasn't aware of this problem. You would have to be deaf to not hear it. Funny thing is I emailed him to thank him before I really tried the head-- Trust? He must be laughing it up counting my money. Buyer beware, right 'chasing shadows'. Well, I'm off to the amp$$ tech$$

 

[chpsktplyr]

Baaad transactions with chasing shadows.

 

[kc2eeb]

A bad connection to the impedance switch and crackling and popping noise.... I hope it's not your output tranny. A plate resistor failure is a lot cheaper. I hope for the best! Pat L.

 

[curtg]

Just a thought, but have you tried different tubes?

 

[lhrocker]

That sounds like my problem when I first got my RM50. I changed all of the preamp tubes with GT Gold 12AX7 and rebiased the 6L6. All the pops went away. Give it a try.

 

[chpsktplyr]

A bad connection to the impedance switch and crackling and popping noise.... I hope it's not your output tranny. A plate resistor failure is a lot cheaper. I hope for the best! Pat L.

Your close... real close. The impedance selector connection was just a bad solder joint that went possibly during shipping. The popping sound I suspect is either a plate resistor or a coupler cap. I was tapping on these with a pencil eraser to see if I could find the culprit, and one of the plate resistors (the 100k in paralell with an 82k on the phase inverter) was hot enough to melt the rubber on the resistor! So i replaced it and the two .002 uf caps and now, nothing no sound. I do have a tech nearby but he can't take a look at it untill late October and even then I don't have a schematic. Any ideas on what to do next? And yes, I tried swapping tubes, modules, cables, fuses,and speakers. I'm pissed. I can't do anything else and my money is gone. I need need help badly.

 

[kc2eeb]

Got to go to work right now but will check my schematics this evening. One thing I would check though, if you had sound before you changed the parts, and now no sound, back track everything you did, and recheck the H.V. fuses. All the best! Pat L.

 

[kc2eeb]

O.K. I'm looking at a schematic from my RT2/50. I'm assuming the PA is the same basic circuit. First, there's lots of high voltage in here so, if you are not sure of what you are doing, it's better to let a tech do it. Having said that, here's things to check. These tests are done with the power off and the amp unplugged. I have not been in my amps but from the schematic, many connections are via block pin connectors. If you can disconnect the output tranny from the power supply board, one side will go to the impedance switch. Black is ground, Orange is the 4ohm tap, Green is the 8ohm tap and yellow is the 16ohm tap. If you put your vom in its low range you should get progressively higher readings as you go between black and org. grn. and yel. If you get no reading, the secondary is open or 0 ohms it is shorted. On the high voltage side, you should have red, blue, and brown. Usually, blue and brown are the ends of the winding and red is the center. A reading between blue and brown should give a reading somewhere in a few kohm range and between red and blue and red and brown some fraction near 1/2 of that. It won't be exactly half because the winding is divided by turns, not lenght of wire. If you get no resistance, 0 ohms, the tranny is shorted, if you get High or infinite ohms, the primary is open. Give that a try and let me know. Pat L.

 

[chpsktplyr]

O.K. I'm looking at a schematic from my RT2/50. I'm assuming the PA is the same basic circuit. First, there's lots of high voltage in here so, if you are not sure of what you are doing, it's better to let a tech do it. Having said that, here's things to check. These tests are done with the power off and the amp unplugged. I have not been in my amps but from the schematic, many connections are via block pin connectors. If you can disconnect the output tranny from the power supply board, one side will go to the impedance switch. Black is ground, Orange is the 4ohm tap, Green is the 8ohm tap and yellow is the 16ohm tap. If you put your vom in its low range you should get progressively higher readings as you go between black and org. grn. and yel. If you get no reading, the secondary is open or 0 ohms it is shorted. On the high voltage side, you should have red, blue, and brown. Usually, blue and brown are the ends of the winding and red is the center. A reading between blue and brown should give a reading somewhere in a few kohm range and between red and blue and red and brown some fraction near 1/2 of that. It won't be exactly half because the winding is divided by turns, not lenght of wire. If you get no resistance, 0 ohms, the tranny is shorted, if you get High or infinite ohms, the primary is open. Give that a try and let me know. Pat L.

It's kind of funny, you have the schematic and never opened the amp and I have spent the better part of a week trying to trace the circuit, blind.
Well I have some good news, I did retrace what you just said. I checked every connection, even took the boards out again. I knew it was right, but it defied logic.
After going over it w/my meter, checking IR drops, continuity and stuff, I just plugged it in.Guts all hanging all out and I'll be damned if it didn't work!! All the undulating crackling was gone, as well as a few other things that where not working like the depth cont..
I'm going solder all those **** slip on connections , take out the 20ga wire on the output and change it to a 14ga, and change the AC input fuses to 10 A slo blo.
I'm going to make the amp as rugged as I can so I don't ever have to mess with it again. Another thing you said shocked me, you said, per schematic, that orange is the 4ohm tap? That means someone was messing with it and reinstalled the switch upside down!! Leaving the yellow with the 4 ohm designation! That should make a big difference, and for sure will keep me from blowing the tranny. Thank's for the heads up bro-- seriously. I'll let you know how it turns out.