Just checked the pot/switch bodies, and they are all connected to ground via the ground cable I added to the front plate. But your comment led me to another issue that I think may be causing the right channel noise. Will update when I make the changes and if it addresses the issue
When I grounded the top plate, I ran it through the ground connection on the front plate. It was attached via a wire to a washer to the right channel gain pot. I removed it and ran it straight from the top plate to the earth ground. Should have done that first 🙂 I also ran a wire from the shield of the input cable from the volume pot. Ran it to the ground bus for the RCAs on the rear panel. It’s quieter, but there is still a slight hum.
Was going to swap out C39 and put a 1.0 in its place, but the cap I have is a bit big to put in there. May need to go buy an appropriate replacement so I can try that.
Was going to swap out C39 and put a 1.0 in its place, but the cap I have is a bit big to put in there. May need to go buy an appropriate replacement so I can try that.
Antek PT doesn't like metal. No matter you place left, right, or behind 4" away the PCB, you still get hum. So I replaced the top with aluminum.
I have tested the GND from PCB to chassis, it doesn't hum to connect or not to chassis.
C39: 0.1uF is fine
C6: 10uF (I think 1uf is fine)
R10: 82.5K
100K pot: no hum at max with 96dB speakers
B+ : 280vDC
Connect to tube amp : no hum
Connect to SS amp: hum (use audio transformer to convert from RCA to XRL to remove the hum)
C3: 1uF, each 1uF will lose 3dB (Doesn't matter what value you have with C3, the frequency response is the same. I have tested up to 10uF_
For example: 1uF at 20Khz = 18.35dB where 2uF will be around 15.xxdB
I have tested the GND from PCB to chassis, it doesn't hum to connect or not to chassis.
C39: 0.1uF is fine
C6: 10uF (I think 1uf is fine)
R10: 82.5K
100K pot: no hum at max with 96dB speakers
B+ : 280vDC
Connect to tube amp : no hum
Connect to SS amp: hum (use audio transformer to convert from RCA to XRL to remove the hum)
C3: 1uF, each 1uF will lose 3dB (Doesn't matter what value you have with C3, the frequency response is the same. I have tested up to 10uF_
For example: 1uF at 20Khz = 18.35dB where 2uF will be around 15.xxdB
Interesting observation.
The front and rear panels are aluminium, top panel is steel.
Wonder if I should try to place some kind of copper/aluminium shield around the transformers.
The hum is quite loud with the Hiraga connected as everything warms up, but it subsides as both units warm up after about 10 min.
Going to swap out the Hiraga with my GFA-545 which I know is quiet.
The front and rear panels are aluminium, top panel is steel.
Wonder if I should try to place some kind of copper/aluminium shield around the transformers.
The hum is quite loud with the Hiraga connected as everything warms up, but it subsides as both units warm up after about 10 min.
Going to swap out the Hiraga with my GFA-545 which I know is quiet.
Put the Adcom in, and I’m seeing the exact same hum. Leads me to believe the issue remains the SP14.
What exactly does C39 do in the circuit?
I may have an opportunity to pu a 1.0uf tomorrow…
Very frustrating 🙂
What exactly does C39 do in the circuit?
I may have an opportunity to pu a 1.0uf tomorrow…
Very frustrating 🙂
Mine heater is running 1 circuit for 4 tubes while yours is 2 for each side so check and adjust R25 if need to get under 75v
My R24: 300K, R25:47K, and C39: 0.1 uF (C39 is for voltage divider). Check the voltage pin 7 and 8 to the GND to make sure it's under 70-75vDC.
Do not use steel for top, That's where the hum comes from. I did shield around and had to place PT 6 inches away. But with top aluminum, you can place PT anywhere.
I only have top is aluminum, the rest are wood.
Mine can turn the volume max while turn on without hum/noise.
Here is 10K:10K audio transformer if you are using with SS amp. If not, you will hear hum. I believed I talked to someone, he said using 10K:10K but 600r:600r may be fine too.
I am not sure about left or right gain that you have but the loudness with volume pot would give you a lot of treble. This is what look like with loudness which I have to disable. It may happen if you add tone control as well.
My R24: 300K, R25:47K, and C39: 0.1 uF (C39 is for voltage divider). Check the voltage pin 7 and 8 to the GND to make sure it's under 70-75vDC.
Do not use steel for top, That's where the hum comes from. I did shield around and had to place PT 6 inches away. But with top aluminum, you can place PT anywhere.
I only have top is aluminum, the rest are wood.
Mine can turn the volume max while turn on without hum/noise.
Here is 10K:10K audio transformer if you are using with SS amp. If not, you will hear hum. I believed I talked to someone, he said using 10K:10K but 600r:600r may be fine too.
I am not sure about left or right gain that you have but the loudness with volume pot would give you a lot of treble. This is what look like with loudness which I have to disable. It may happen if you add tone control as well.
That is easy to test - just shut down all equipment in the room - if You hear something then and in the other areas in Your place then it might be line noise.
I hear it all the time, like mosquito's buzzing in the background - it was definitively line noise when the power was out two times in a row - both times there was real silence in the apartment and only then.
I do have a lot of noisy crap plugged in…
I put some isolation (electrical tape) between all the contact points for the spacers between the top metal plate and circuit board. Left channel is free of hum, all that remains is the slight hiss I hear with other gear.
Right channel dropped the higher frequency hum, and is now only 60hz. I didn’t use shielded wire between the selector/gain/volume. Going to replace that with shielded wire and ground that shield to the ground bus on the RCA’s. Seeing as how the hum is in the right channel, and the right gain is next to the transformers, I’m hoping that removes the 60hz issue.
Picked up some 1uf caps yesterday and will try putting those in place after I try tye preamp with the shielded wires in place.
I put some isolation (electrical tape) between all the contact points for the spacers between the top metal plate and circuit board. Left channel is free of hum, all that remains is the slight hiss I hear with other gear.
Right channel dropped the higher frequency hum, and is now only 60hz. I didn’t use shielded wire between the selector/gain/volume. Going to replace that with shielded wire and ground that shield to the ground bus on the RCA’s. Seeing as how the hum is in the right channel, and the right gain is next to the transformers, I’m hoping that removes the 60hz issue.
Picked up some 1uf caps yesterday and will try putting those in place after I try tye preamp with the shielded wires in place.
I recently built a totally scratch, p-to-p Aikido with a Neurochrome regulator board and a regulated filaments. It's dead quiet in my system. I sent it to a friend who has a pair of amps that I built for him, the same as mine(!) assuming there would be no issue. It hummed like the dickens. Some sort of ground loop. He's not at all technical and I could not diagnose the problem over Facetime, so he sent it back. I'm using it was great pleasure now. Which is all to say that preamps are tricky... :-( Hoe you get it working to your satisfaction!
Ugh…
What causes rectifier tubes to short/create a firework show?
The preamp has been running well, except for the hum. I rewired the pots with shielded wire, but when I did it, I neglected to snip the left incoming signal wire, so there was no sound from left channel.
I let the amp drain with the music playing, took it out of circuit and removed the tubes. They were certainly warm, as they gab been on for a couple of minutes, but certainly not so hot I couldn’t hold them.
Fixed the wire I had missed, put the tubes back in and hooked it back up. Powered it up, left channel was fine.
Took a moment to call a friend I had promised to check in with, and after a minute or so, happened to look at the amp, and the rectifier was making quite a show. Shut the amp off immediately. There was no noise or other odd sounds coming from the speakers because of this, it gradually faded as normal.
I’ve gone through the amp, and there is no indication of any short, transformers are not shorted, as best I can tell from measuring resistance.
Is this just a coincidence? I’ve read that 6X5GT tubes are prone to shorting. Did I jar something then I pulled the warm tube?
So frustrating….
I have another 6X5 here, an old radiotron, but it’s noisier than the Sylvania I was using. Had another Sylvania, but it went bad because of something else that happened - a short went through a rubber insulator. I have no idea how that is possible, other than a bit of solder flakes from the solder sucker found it’s way down there.
Thanks.
What causes rectifier tubes to short/create a firework show?
The preamp has been running well, except for the hum. I rewired the pots with shielded wire, but when I did it, I neglected to snip the left incoming signal wire, so there was no sound from left channel.
I let the amp drain with the music playing, took it out of circuit and removed the tubes. They were certainly warm, as they gab been on for a couple of minutes, but certainly not so hot I couldn’t hold them.
Fixed the wire I had missed, put the tubes back in and hooked it back up. Powered it up, left channel was fine.
Took a moment to call a friend I had promised to check in with, and after a minute or so, happened to look at the amp, and the rectifier was making quite a show. Shut the amp off immediately. There was no noise or other odd sounds coming from the speakers because of this, it gradually faded as normal.
I’ve gone through the amp, and there is no indication of any short, transformers are not shorted, as best I can tell from measuring resistance.
Is this just a coincidence? I’ve read that 6X5GT tubes are prone to shorting. Did I jar something then I pulled the warm tube?
So frustrating….
I have another 6X5 here, an old radiotron, but it’s noisier than the Sylvania I was using. Had another Sylvania, but it went bad because of something else that happened - a short went through a rubber insulator. I have no idea how that is possible, other than a bit of solder flakes from the solder sucker found it’s way down there.
Thanks.
Thanks.
Ghosts in the machine…. But maddening. I expected some challenges when I built this, there’s usually something, but I wasn’t prepared for all this silliness I’m dealing with…
Yes, unfortunately, 6X5's are notoriously fussy. This is probably why Don Sachs switched to the 6BY5. I use the Bendix 5852, but they are pretty pricey. What value input cap are you using? That can also mess them up. A cheap and more robust alternative is the 6AX5GT. This draws twice the filament current (1.2A) so you'll want to remove R-FIL and jump those connections. IIRC the power tranny filament tap is 2A and should be fine, but you may want to check that.
Thanks!
Wait, 6X5 and 6X5GT are not interchangeable?
I wasn’t aware of that?
I’ve been using the GT’s…
And I had read about Don changing to the other rectifier, but it’s not a drop in replacement and would require some changes?
And I’m going to look into the Bendix.
The first cap they see is a Solen 630V 22uf, which I would think is well within their operating specs?
Wait, 6X5 and 6X5GT are not interchangeable?
I wasn’t aware of that?
I’ve been using the GT’s…
And I had read about Don changing to the other rectifier, but it’s not a drop in replacement and would require some changes?
And I’m going to look into the Bendix.
The first cap they see is a Solen 630V 22uf, which I would think is well within their operating specs?
I told you! ;-) But it's pretty much indestructible and sounds really good. 6X5/GT, same thing, I was just using short hand. ;-)
You can mod the board for a 6BY5. You remove R-FIL and jump the eyelets, then add jumpers between pins 1 & 8 and 3 & 4. If you compare the pinouts of the two, you'll see that it's not difficult.
I don't know what 6X5GT you were using, but I've had better luck with the brown-base mil spec versions. They're not expensive at all. Like I said, the 6AX5GT is another option and a much more rubust tube, really more of a twin damper diode like the 6BY5.
You can mod the board for a 6BY5. You remove R-FIL and jump the eyelets, then add jumpers between pins 1 & 8 and 3 & 4. If you compare the pinouts of the two, you'll see that it's not difficult.
I don't know what 6X5GT you were using, but I've had better luck with the brown-base mil spec versions. They're not expensive at all. Like I said, the 6AX5GT is another option and a much more rubust tube, really more of a twin damper diode like the 6BY5.
Thanks for all that!
I was using some NOS Sylvania, the two tubes I received from the tube store were very different looking. One had a top getter, and the plate configurations were different inside the tubes.
Did a quick search on the 6BY5, and the jumpers seemed to be the only thing that needed to be done. Which seems simple enough… (famous last words…) It would seem that Don felt the added current capability was a big benefit to the sonic presentation of the amp.
Why does the resistor get replaced with a jumper? Wondering what it us about the current that necessitates that?
Is there a noticeable difference between the Bendix and 6X5 that you can hear? Curious why you have not tried the 6BY5 mid yourself? The tubes seem to be very inexpensive.
I’ve just had so many issues with this build, I’m a bit gun shy to try to do the mid st this point….
Looking at the doc sheet, would I have to drop the value of the input cap also?
Thanks again,
P
I was using some NOS Sylvania, the two tubes I received from the tube store were very different looking. One had a top getter, and the plate configurations were different inside the tubes.
Did a quick search on the 6BY5, and the jumpers seemed to be the only thing that needed to be done. Which seems simple enough… (famous last words…) It would seem that Don felt the added current capability was a big benefit to the sonic presentation of the amp.
Why does the resistor get replaced with a jumper? Wondering what it us about the current that necessitates that?
Is there a noticeable difference between the Bendix and 6X5 that you can hear? Curious why you have not tried the 6BY5 mid yourself? The tubes seem to be very inexpensive.
I’ve just had so many issues with this build, I’m a bit gun shy to try to do the mid st this point….
Looking at the doc sheet, would I have to drop the value of the input cap also?
Thanks again,
P
I assume that R-FIL resistors were to tame a surge to the 6X5 filaments. The 6BY5 mod is very easy. You should check the filament voltage is you do it, you can always ad a single R-FIL on one side, like .5 ohms or something, but it shouldn't be needed.
I have indeed tried the 6BY5. It's very open and smooth, a bit more realism to the instruments and voices, a different sound from the 6X5, which can sound a bit "thin." The Bendix is another matter altogether. A very dense, rich tone, very fleshy instruments and voices performing in a well-defined space.
I'll send you a PM.
I have indeed tried the 6BY5. It's very open and smooth, a bit more realism to the instruments and voices, a different sound from the 6X5, which can sound a bit "thin." The Bendix is another matter altogether. A very dense, rich tone, very fleshy instruments and voices performing in a well-defined space.
I'll send you a PM.
You're very welcome. I just love my p-to-p version, I stole the SP14 operating points, which seem to work very well. Having paid for an assembled board at one point, I don't feel guilty. ;-) But the board version should work, I hope you get it sorted out. I use homebrew Williamson amplifiers and they like a stout preamp with lots of gain, and the 6SN7s make for a consistent sonic match with the classic Williamsons. I was rather crushed when my friend couldn't get it to work, he needs a good preamp. :-( I may just go visit him (I'm in Oregon, he's in Florida) to generally work on his system and see if we can make it happen. ;-)