Well I might have to rewire a couple of sockets.
I've tried about 10 6N24P tubes so far, but they all sound like a spring reverb when you hit them. Even changing inputs makes a sound through the speakers.
ECC84 / 6N14P is an option but has more gain. Maybe I will just suck it up and rewire for 6DJ8 in that position.
I've tried about 10 6N24P tubes so far, but they all sound like a spring reverb when you hit them. Even changing inputs makes a sound through the speakers.
ECC84 / 6N14P is an option but has more gain. Maybe I will just suck it up and rewire for 6DJ8 in that position.
So I opened the PSU up to make a vent for the ATX supply inside.
It took 4 of those little Dremel cutting wheels to do it.
The LED dropping resistor is an example of running a Chinese 2W resistor at 2W in a hot chassis. it still works and measures ok though so j'men câlice.
It took 4 of those little Dremel cutting wheels to do it.
The LED dropping resistor is an example of running a Chinese 2W resistor at 2W in a hot chassis. it still works and measures ok though so j'men câlice.
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Nice work!
One Dremel wheel per side. How thick is the material? Aluminum?
Good luck with the “6N24P problem”.
It was 16 ga steel.
It's not such a problem per se, in normal operation it's never a problem, but if you tap or change the inputs without signal, you'll hear it. On the bench with the speakers coupled to the amp via the table etc, I can get it to feedback just from the microphonics though haha. The dominant frequency is around 5 kHz or so by the sound of it.
My "new" issue is that when the phono stage is on, and the power stage is on, I get 120Hz on the output of the phono even though it's being powered from the DC side of the system. If I turn off the power stage and use an external amp, no hum. If I switch back the internal amp no hum until the tubes are hot and conducting (on the phono output, not the power stage output). I can only figure this is either magnetic coupling in the PSU... Now that the cooling issue is solved, I may try the boost module instead of the linear supply. No 120Hz hum if no linear supply, right?
It's not such a problem per se, in normal operation it's never a problem, but if you tap or change the inputs without signal, you'll hear it. On the bench with the speakers coupled to the amp via the table etc, I can get it to feedback just from the microphonics though haha. The dominant frequency is around 5 kHz or so by the sound of it.
My "new" issue is that when the phono stage is on, and the power stage is on, I get 120Hz on the output of the phono even though it's being powered from the DC side of the system. If I turn off the power stage and use an external amp, no hum. If I switch back the internal amp no hum until the tubes are hot and conducting (on the phono output, not the power stage output). I can only figure this is either magnetic coupling in the PSU... Now that the cooling issue is solved, I may try the boost module instead of the linear supply. No 120Hz hum if no linear supply, right?
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I had the same problem with UCC85's in a guitar amp I built years ago. Every tube was microphonic, some worse than others. Even with the best tube in the input stage, you couldn't set the amp on top of the speaker. I wound up rewiring for 12AX7's and I put a 5751 in the first stage.
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Nice! Are those EL34s Svetlana? I bought an unneeded quad for a good price a while back...
In my case, the amp was upside down with no input connected and hitting the chassis would cause this spring reverb sounding ringing. So I cranked the volume and voilà!
It's a shame really, other than the fact the second triodes' grid is connected to the shield (was designed for cascode) it's basically a 6DJ8 for like 2 bucks.
I'm also happy to report that other than the hum in phono, the amp is completely silent. Unless I turn it up past 30%, then there is a massive oscillation on the right channel, but only when using the internal power amp. I need to reroute the signal feeds. Instead of going up the middle and over to the pot, they go around the right output stage and wiring... I think there's some kind of coupling going on.
In my case, the amp was upside down with no input connected and hitting the chassis would cause this spring reverb sounding ringing. So I cranked the volume and voilà!
It's a shame really, other than the fact the second triodes' grid is connected to the shield (was designed for cascode) it's basically a 6DJ8 for like 2 bucks.
I'm also happy to report that other than the hum in phono, the amp is completely silent. Unless I turn it up past 30%, then there is a massive oscillation on the right channel, but only when using the internal power amp. I need to reroute the signal feeds. Instead of going up the middle and over to the pot, they go around the right output stage and wiring... I think there's some kind of coupling going on.
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Can anyone assist with this oscillation? There is no oscillation until about 30% volume, then 400 kHz.
If the power amp section isn't on, the oscillation stops. The entire power section runs from linear supplies. I'm connecting the scope at the input to the power stage / output of the line stage.
If the power amp section isn't on, the oscillation stops. The entire power section runs from linear supplies. I'm connecting the scope at the input to the power stage / output of the line stage.
They are older Electro Harmonix brand. Nearly 10 years ago a tube seller offered me a big box full of "pre auditioned" Russian tubes cheap, with a story about them only being used for a short time at an "audio show."
There were 6 or 8 of these EH EL34's, and all had "teeth marks" in the base from the hold down clamps used in guitar amps that hang the chassis upside down. All had Tubestore.com stickers on them, and I suspect that they were returns.
Regardless of the real story I got about 30 tubes for $200. All have been good tubes, and other than a EH KT88 that I blew up due to my own stupidity, the tubes that I still have are all still alive.
You might try moving the series resistor on the green wires over to the end nearest the output tube's grid. As it is the green wire acts like a long antenna connected to the grid. A ferrite beat on the lead of the stopper resistors might help too if you have any.
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Ok I'll try that... But I wonder why the output stage would cause the line stage to oscillate. The oscillation might be at the speaker, but it manifests on the output of the line stage but only when the power stage is on. If using an external amp there is no oscillation.
It's only happening on the right channel, too.
Changed from 6N24P to 6N14P then rewired for 6N1P, No change.
Changed from 1M input to 100k input. No change.
It's only happening on the right channel, too.
Changed from 6N24P to 6N14P then rewired for 6N1P, No change.
Changed from 1M input to 100k input. No change.
I doubt it. Got it to act correctly with the 50k pot after it was buttoned back up, but then the left channel effed off. Now I'm back to a 100k pot which seems only to oscillate when set to an input with nothing connected to it and crank the volume pot.
Admittedly the input wires to the pot are not shielded. The only wire I have that is close to shielded audio cable is RG174. I could try it when I replace the 100k pot with a 50k job.
Admittedly the input wires to the pot are not shielded. The only wire I have that is close to shielded audio cable is RG174. I could try it when I replace the 100k pot with a 50k job.
Oh, and the a couple of 600V caps hit 700V for ~10 seconds on start. Surge voltage can be rated voltage *1.1 so 660V.
Besides a zener string as a clamp, any ideas on capping the voltage?
BUT! The good news is the hum on the phono is gone.
I added two 10R/470uF filters in the 320V power supply and swapped the boost module that did 560V for a quadrupler. Now I have an extra 140V with no load though Hence the above problem. I also rerouted the wires a bit.
Besides a zener string as a clamp, any ideas on capping the voltage?
BUT! The good news is the hum on the phono is gone.
I added two 10R/470uF filters in the 320V power supply and swapped the boost module that did 560V for a quadrupler. Now I have an extra 140V with no load though
Hence the above problem. I also rerouted the wires a bit.
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The filters are actually 5R/470uF. My bad.
Ok. So upon reflection I'm pretty sure it was just a matter of using a 1M input to the power stage. I usually use 51k or 100k with the 6F12P.
It's not the first time I've "figured this out" either. I remember now that once upon a time, I was using a 1M input on a power amp and it would pick up radio if the RCA cable was disconnected (and oscillate ~ 1.5Mhz I later found out).
Ok. So upon reflection I'm pretty sure it was just a matter of using a 1M input to the power stage. I usually use 51k or 100k with the 6F12P.
It's not the first time I've "figured this out" either. I remember now that once upon a time, I was using a 1M input on a power amp and it would pick up radio if the RCA cable was disconnected (and oscillate ~ 1.5Mhz I later found out).
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