Hey Everyone. I have a really neat red bear MKE60 that I won on ebay and re-tubed. before the re-tubing it had the ORIGINAL weird Russian tubes in it. I order the US replacements(12ax7's and 5881's). I got the tube swap info from a red bear fan site. NOW the output of the amp is whisper quiet. I can hear the sound of the amp but it is just super low. Before i replaced tubes the master volume and the pre-amp gain pots where very intermittent, and cutting in and out when you would turn them up and down. I am hoping that this may just be what the problem is. it is not blowing fuses or anything like that and no smoke(thank goodness) .I have found a schematic on the web for the amp and could probably switch out the pots.(the original pots all look like Dual ganged pots, crazy Russians) but I am sure standard linear gain and preamp pots will work JUST fine.
you might try cleaning the pots before you replace them. Go to Radio Shack and get some TUNER cleaner, not contact cleaner. I would open the amp up, and have the edge with the pots hanging over the edge of the bench with a garbage can below to catch all the drippings. Then I stick the little hose thing that comes with the tuner cleaner in the opening of the pot and soak it good while turning the pot back and forth. 9 times out of 10 this does the trick. It's really important to use Tuner cleaner, I can't emphasize that enough, contact cleaner destroys pots.
As for the whisper quiet, it sounds to me like something isn't right with the tube conversion. Clean the pots first and see what happens.
thanks I will try the tuner kleener. I did not do any rewiring as the red bear fan site said it should work fine going from the 6H2P-EB tube to 12ax7's in the preamps. and the power section already had 5881's loaded in it from russia anyhow.
if you still don't have any luck after the pots are lubricated...
Do you know the tubes you put in are good strong tubes?
Can you check the preamp tubes in another amp to confirm they are healthy? if the new tubes are good then you may find the original preamp tubes are still good aswell. if all the tubes test good and you have the schematic.. but no sound... and only if you are comfortable with electricity and know how to safely work on amplifiers. test the amp for voltages marked on the schematic and make sure it's running at within 20% or better of manufactor spec. If not trace back why. that should at least help pin point the problem zone. make sure you have the amp connected to a dummy load or proper ohm cabinet if you are powered on and apply signal. be safe best wishes i'm sure it's something easy!
well from what I am finding out about the amp I think I need to perform a wiring mod to the preamp sockets. BOTH filament leads for each socket are running to pins 4 and 5 with a ground wire coming off of pin 9 this is for the original 6N2P preamp tube that these are wired for. the mod says too remove the ground pin 9 wires for each socket and MOVE the filament leads to pin 9 and 5 with a jumper between pin 4 and 5. again I can hear the amp working but it is SUPER QUIET. and I have also discharged the caps and amp getting a millivolt reading from the caps of 1.5-2.0 and on the power tube sockets as well. so I am thinking that this is safe for me to start looking at working this mod. if anyone wants to tell me that this mod is DUMB please feel free to post asap. I Am gonna check the cleaning thing today after some drum edits in the studio
okay, I did the Mod and removed the 9 pin ground from each 12x7 socket, then I moves the 4 pin filament heater to bridge the 4 and 5 pin. moved the 5 pin filament heater too the 9 pin. NOW I get a very load hum from the amp. when I go to turn it off or to standby thought the amp starts to play sound through it. I will post some pix of the sockets the green and purple leads are the new filament wires. the purple are going too pins 4 and 5, and the green is going to the 9 pin filament
You do not have the required permissions to view the files attached to this post.
Did you reference the heater supply? It was referenced to ground before with the one leg tied to ground. What are you doing now? 100ohm resistors to ground?
I recently changed a Redbear60 over from 6n1p to 12Ax7 at a customers request.
The mod is pretty straight forward, but to be honest, I'd advise against it.
The 12AX7 has WAAAAYYYY more gain than the original russian tubes, and can cause some stability issues with the amp. The 6n1p's can still be had from several online suppliers.
If you decide to stay with the mod, I'd recomend that you try some 12AT7 tubes, which will get you back closer to the stock gain structure.
no, there is nothing going to ground off of the pin 9 sockets now. I took the 5 pin heater lead and moved it too the 9 pin. I jumped the 4 pin heater to the 5 pin as well. and the Jacks in the shots are the FX loop jacks and speaker jacks outs. and you can see that off of pin 2 there is a white wire with ground lead going too pin 9 on two of the dour sockets. should I move this ground lead to the little chassis ground lug off too the side of the socket? AND should all of the tube sockets be grounded? I would think so BUT what do I ground to these little lugs next too the sockets? as far as 12x7 conversion goes, I am not really concerned with Distortion but more with ease of tube replacement. I have bunch of lower gain 12at7 and 12au7's and well as some cool 5751 preamp tubes so after I get it running I am gonna play around with it.
what I am saying is that someplace in the circuit the 6.3vac has to be referenced to ground. It was done before with one leg of the heaters tied to ground. The most common way to do this is to tie a 100 ohm resistor from each leg of the 6.3v to ground.
so can I tie the 9 pin too ground with a 100ohm 1/2watt resistor then and not goof up the circuit? I have BOTH heaters in the correct pin configuration BUT do I need to ground EVERY tube socket with a 100ohm? sorry too be so high maintenance BUT I am very new at this adventure!!
Love Curran
P.S. thanks for the help you have been giving me on this!!!
okay so off of one side of the 6.3v heater run a 100ohm1/2watt then at another point from the OTHER 6.3v heater run another 100ohm 1/2 watt YES? then I should be good?
.I have found a schematic on the web for the amp and could probably switch out the pots.(the original pots all look like Dual ganged pots, crazy Russians) but I am sure standard linear gain and preamp pots will work JUST fine.
