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i have a pair of Atmasphere MA1 MK 2s the long ones with 14 tubes in 2 rows and 4 6SN7s. In any case I cannot get them to sound the same, one is quite a bit louder. I tried to replace all the tubes, swap the tubes, you name it. I have about 3 extra sets of 6AS7Gs swapped a number of them in and out...still no luck. I think it is time to open things up and start measuring. I really do not want to pack them up and ship them, i am pretty certain that i am qualified to muck around with them even though my BSEE certificate has been misplaced and have not designed a circuit in more than 30 years. So to fix anything i need a circuit diagram for the amp i have. can anybody help?
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
Follow Ups:
while you're waiting, may I ask if you know the previous history of the amplifiers, assuming you are not the original owner? All the gain comes from the input voltage amplifier stage, although a few dead output tubes on one side will be noticeable partly as a seeming loss of gain, because it compromises the ability to drive a low-Z load. But back to the input stage; it's a dual-differential cascode. There is an option to disable the cascoded triode (one of the 6SN7s) so as to reduce gain in order to drive a very efficient speaker. Maybe someone did that to one of your two monoblocks??? Just a shot in the dark. When you do go inside, I bet the solution will be obvious from your voltage measurements. Check also the RC coupling between the cascode and the driver stage.
Thanks Lew,
Yes, they are used I bought them form a guy a few years back and used it a little bit but not much. They did not like my unmodified Soundlabs, I pulled them out to try with the Vandersteens, and could not get the balance right :)....i have about 3 sets of output tubes and 3 sets of input tubes that came with it, some are still new :)...
Even without a full circuit diagram a few points of voltage measurements would be helpful :). Much easier than shooting in the dark. BTW, the offer to make the counterweight is open indefinitely :).
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
Mine might not be relevant, because my amplifiers use the MA2 power supply, essentially, which mainly means that my input and driver stages run on ~+/-400VDC. Plus I have heavily modified my driver stage. But I don't think you meant that anyway. You've gotta measure your own amps to find out what's up, I am sure you know.
BTW, if you still own the Sound Lab, the marriage to Atma-sphere can be rescued. It's too detailed to describe here, but send me a private email and we can discuss. There are actually two solutions, one available from SL and the better one (IMO) available from another source (maybe). The latter allows you to eliminate the high pass filter in the SL crossover, i.e., to go no crossover. The crossover is the culprit that lowers the input Z across the midrange and sucks up amplifier power and generally makes life difficult for tube amplifiers.
a circuit diagram is the most definitive source for that. I really do not have the time nor the energy to trace it through, If push comes to shove the solution is to take it to a reputable repair shop...like Bill Thalman, let him futz with it. if i had a circuit then i could figure it out :). Or just give up and take it to Bill. If Ralph was driving distance this would not be a dilemma.
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
You will find a schematic that is quite similar to your amp at the link below. The driver voltages will be nearly the same:
Cathodes of V1 about 0.3V
Plates of V2: about 175V
Cathodes of V4: about -65V
Plate of V4: about 275V
B+ and B- are about 300V
To get an idea of your power tubes take a look at this link
If your power tubes are good it may be that some of the resistors in the output section have failed. In your amp the larger resistors on the power tube sockets are 1 ohm 5 watts. Some earlier versions have 3 watt resistors.
You are great :)...
Thank you again.
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
Have you had time to evaluate the amplifier using the schematic? Have you identified the issue?
Thanks.
gardens took priority :(....Honeydo list expansion....
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
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