I have an Aphex 107 Tubessence Mic pre.
It works, but is a bit noisy. I wanted to try a new tube, read where it shipped originally with a 12AX7 but was spec'd for a 12AT7.
Opened it up, the existing tube has no markings on it at all, so I'm not sure if it's a 12AX7 or not.
At any rate, I ordered a 12AT7 to give it a try. When I install the 12AT7, I get nothing. No output at all. I thought I got a bad 12AT7, contacted the seller, he sent me another one. Same results.
I tried the new tubes in a guitar preamp I have, which has a 12AX7 in it. They work fine in that amp.
I put the original tube back in the Aphex 107, it works but still a bit noisy. I'm stumped as to why the new tubes don't work in the 107.
Any advice? Are there differences in 12AT7's?
Thanks, gabo
It works, but is a bit noisy. I wanted to try a new tube, read where it shipped originally with a 12AX7 but was spec'd for a 12AT7.
Opened it up, the existing tube has no markings on it at all, so I'm not sure if it's a 12AX7 or not.
At any rate, I ordered a 12AT7 to give it a try. When I install the 12AT7, I get nothing. No output at all. I thought I got a bad 12AT7, contacted the seller, he sent me another one. Same results.
I tried the new tubes in a guitar preamp I have, which has a 12AX7 in it. They work fine in that amp.
I put the original tube back in the Aphex 107, it works but still a bit noisy. I'm stumped as to why the new tubes don't work in the 107.
Any advice? Are there differences in 12AT7's?
Thanks, gabo
Perhaps the tube used in your unit is not even a 12AX7A, but something similar.. I'd check with the manufacturer to find out whether they used something like the 6N2P for example. (Similar to 12AX7A, but some differences including filament connections)
Do the 12AT7A filaments glow in the Aphex, if not that could be a clue that the original tube is not a 12A*7 series tube.
Do the 12AT7A filaments glow in the Aphex, if not that could be a clue that the original tube is not a 12A*7 series tube.
I wouldn't put the new 12AT7's back in it until you figure it out. If you have a multimeter and you are safe around the voltages I would recommend measuring for voltages at the pins to find out at least if the heater pins are the same. As Kevin pointed out, you probably have a Russian or Chinese tube that's not equivalent to the 12AT7.
Yes the filaments do glow with a new tube in place. I do have both a data sheet and a schematic for the unit, both of them list the tube as a 12AT7/ECC81 dual triode tube.
I am comfortable around the voltages and can measure the voltages at the pins.
I am comfortable around the voltages and can measure the voltages at the pins.
Next step is to compare voltages against the schematic.
If there are no voltages present on the schematic us members can pretty closesly approximate what they should be. If you don't feel comfortable posting the schematic you can PM it to me and I will have a look.
If there are no voltages present on the schematic us members can pretty closesly approximate what they should be. If you don't feel comfortable posting the schematic you can PM it to me and I will have a look.
I checked the voltages, the heater voltage (pin 5) is 12.09v, which is what the schematic says it should be.
Grid voltages (pin 2 and 7) are both 5 v and cathode voltages (pin 3 and 8) are both 6.2v.
Here's the schematic.
https://www.gearslutz.com/board/attachments/so-much-gear-so-little-time/316737d1352588096-aphex-107-schematics-aphex-107-schm.pdf
Grid voltages (pin 2 and 7) are both 5 v and cathode voltages (pin 3 and 8) are both 6.2v.
Here's the schematic.
https://www.gearslutz.com/board/attachments/so-much-gear-so-little-time/316737d1352588096-aphex-107-schematics-aphex-107-schm.pdf
It's strange that the original tube works, the new 12AT7 lights up but doesn't work.
Are the voltages you measure with the original tube in it or the 12AT7?
Maybe check C115, I don't think you should have 5v at the grids (pin 2 and 7).
Are the voltages you measure with the original tube in it or the 12AT7?
Maybe check C115, I don't think you should have 5v at the grids (pin 2 and 7).
Yes, that's my thoughts (that it's strange)! Those voltages are with the original tube in it.
C115 visually looks good, but I can take it out and check it. I don't have one of those on hand so I'll have to order some .1uf caps. I live in a rural area so I have to order everything as there is no store locally.
It does strike me odd that both C115's (actually C215) would be bad in the same way as there are two, one for pin 2 and one for pin 7 and they both read 5v.
C115 visually looks good, but I can take it out and check it. I don't have one of those on hand so I'll have to order some .1uf caps. I live in a rural area so I have to order everything as there is no store locally.
It does strike me odd that both C115's (actually C215) would be bad in the same way as there are two, one for pin 2 and one for pin 7 and they both read 5v.
Check for solder blobs between pins around the sockets maybe? But I would think that would effect both tubes, unless one that works isn't a 12AT7. Pull the tube and see if there is still 5v at the grid.
No solder problems or gunk around pins. Visual inspection is very clean, the entire board is very clean. In general no swollen caps or leaking, no brown/burned areas, all looks good. Grid voltage is 0v when the tube is out.
I'm hesitant to do much to it since it works with the old tube. I was just trying to improve it a bit, especially when it comes to noise and the fact that the tube is known to be 25 years old.
I'm hesitant to do much to it since it works with the old tube. I was just trying to improve it a bit, especially when it comes to noise and the fact that the tube is known to be 25 years old.
- Status
- Not open for further replies.