I paralleled a 68mfd@400vdc across section A of C16 and the noise is gone. Can't hear anything no matter where the input control is. It measures about 0-1mV AC across the 8 ohm speaker terminals.
I would assume a cap transplant is in order. Got any suggestions for power supply caps C14, C15, C16 ? Actually any suggestions for all the caps? Budget caps that is.
I would assume a cap transplant is in order. Got any suggestions for power supply caps C14, C15, C16 ? Actually any suggestions for all the caps? Budget caps that is.
Nice. Yep. That cap is dead.
Often they do get slowly hot when they are on their way to Valhalla, so that's an indication.
Often they do get slowly hot when they are on their way to Valhalla, so that's an indication.
Thanks for the help. Ya forced me to look at the problem instead of thinking I couldn't find it. Still learning on tubes and I think its a never ending learning process.
Any suggestions for replacing the caps?
Any suggestions for replacing the caps?
I made a post on AK regarding the Mighty Allen Organ 75.
You'll find some info. I used a KTL41 Authenticaps but I removed the 12AT7 so didn't need the last supply rail.
The mighty Allen Organ 75 | Audiokarma Home Audio Stereo Discussion Forums
You'll find some info. I used a KTL41 Authenticaps but I removed the 12AT7 so didn't need the last supply rail.
The mighty Allen Organ 75 | Audiokarma Home Audio Stereo Discussion Forums
Nice thread. I did a screen shot of your modifications. I assume the 21A 1200 volt bridge will replace the (8) 1n1696 1A 600 volt diodes.
I'm going to have to budget my cap replacement a little cheaper and stick with a new set of 6550's instead of the KT120's.
I'm going to have to budget my cap replacement a little cheaper and stick with a new set of 6550's instead of the KT120's.
Posting a list of caps and resistors for those like myself that can't see the items on the schematic.
I will note that I was unable to find C10 and C11 in the amp or on the schematic.
Also I removed C17 from my amps
Feel free to correct if you find errors.
I will note that I was unable to find C10 and C11 in the amp or on the schematic.
Also I removed C17 from my amps
Feel free to correct if you find errors.
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I'm retired with too many hobbies. Too much money spent on other things unfortunately and not enough left for this hobby for probably another 6 months to a year. I'd love to try the KT120's. Is it stressing the transformer running them as they draw more current?
Nice. Thanks !
Yep C10/C11 are not in the amp.
C5 is ceramic 250 pf on the EF86 pin 6 and 8.
The PS changed a bit between the 2 versions with power resistors under chassis and above chassis.
And V4 has the heater powered like all the other tubes and not elevated on its own winding. Mine were unused and tucked in nicely.
Yep C10/C11 are not in the amp.
C5 is ceramic 250 pf on the EF86 pin 6 and 8.
The PS changed a bit between the 2 versions with power resistors under chassis and above chassis.
And V4 has the heater powered like all the other tubes and not elevated on its own winding. Mine were unused and tucked in nicely.
Cool.
On the heater side, not really. The PT can take it easily. And I removed the 12AX7 so the increase is nominal.
On the HV PS side, yes. I bias them at 80 mA which is nothing for the KT120, but higher than that and the choke starts to make noise.
But it sounds wonderful.
Enjoy your hobbies !
On the heater side, not really. The PT can take it easily. And I removed the 12AX7 so the increase is nominal.
On the HV PS side, yes. I bias them at 80 mA which is nothing for the KT120, but higher than that and the choke starts to make noise.
But it sounds wonderful.
Enjoy your hobbies !
Ok, located the ceramic that I had overlooked before. Measured it in circuit with the tube pulled at 350pf. So, is the 250pf a starting point or is my meter that far off or am I just getting a bad reading because it is in circuit? Mine is showing a white band followed by brn,green,red,and what looks like gray. Don't remember how to read these things. Should I replace it too?
finding the resistors is proving to be the most difficult part of building the AO75. "R35 3830 OHM 1/2W" has minimum orders on mouser of 1000 for either 4000+ dollars or 400+ dollars. thinking of just putting several 1/2 watt resistors together in series to make the odd or difficult to find ones.
Don't sweat it. If you install a 3.8K 1%, you'll be good. 30 R won't make much of a difference for the NBF network.
