Hi everyone,
New to forum and am undertaking this project. Building a set of ANK class AB EL-34 monoblock tube amps. I guess I should say that I have built them as they are complete but I'm now in the troubleshooting stage and need some help here. I've done the voltage checks and all looks well. Please take a quick listen here to the audio recording of the sound I'm getting upon power-up. -- Nice and silent for about 10 seconds, then a hum that gets louder, and louder until I shut power off... then a high pitched whistle-like sound as power dissipates.... same sound on both amps.
Ok, so apparently I have to learn how to use a computer before I can build a tube amp. audio recording won't load to site but hopefully some of you may have encountered my description above on a previous build???
Have been through the manual a complete 2nd time and can't see any errors or missed steps. This is my last ditch effort to fix this myself before I take these in to a pro.
Can anyone help shed some light here?
New to forum and am undertaking this project. Building a set of ANK class AB EL-34 monoblock tube amps. I guess I should say that I have built them as they are complete but I'm now in the troubleshooting stage and need some help here. I've done the voltage checks and all looks well. Please take a quick listen here to the audio recording of the sound I'm getting upon power-up. -- Nice and silent for about 10 seconds, then a hum that gets louder, and louder until I shut power off... then a high pitched whistle-like sound as power dissipates.... same sound on both amps.
Ok, so apparently I have to learn how to use a computer before I can build a tube amp. audio recording won't load to site but hopefully some of you may have encountered my description above on a previous build???
Have been through the manual a complete 2nd time and can't see any errors or missed steps. This is my last ditch effort to fix this myself before I take these in to a pro.
Can anyone help shed some light here?
Attachments
Have you try switching the primary wires on the output transformers? It sounds a lot like oscillation caused by the wrong output transformer Connection. I have had that problem before, when feedback is attached, and the phase is wrong, you end up with positive feedback, tons of hum, and lots of squealing until the capacitors discharge.
Is it hum after 10 seconds of powering up, or is it clean audio for 10 seconds and then the hum superimposes on that clean audio.
If the latter then I would begin by monitoring the cathode current of the EL34's and seeing if it is rising unexpectedly. Such a rise could increase the ripple on the supplies and introduce hum.
I don't dabble with valve gear
but my first thoughts and starting point would be the above.
Noises on power off may or may not be normal... it doesn't necessarily signify a fault.
(you can attach a large audio file by using something like Dropbox which is free to use and doesn't cause grief for those wanting to access the file)
If the latter then I would begin by monitoring the cathode current of the EL34's and seeing if it is rising unexpectedly. Such a rise could increase the ripple on the supplies and introduce hum.
I don't dabble with valve gear
but my first thoughts and starting point would be the above.Noises on power off may or may not be normal... it doesn't necessarily signify a fault.
(you can attach a large audio file by using something like Dropbox which is free to use and doesn't cause grief for those wanting to access the file)
Hi Mooly, Ok this is extremely weird/interesting. I hadn't actually tried running a music signal through it yet as I was wanting to get the hum to stop being an issue first.
So here's what happened. I was running an audio signal to it before I powered it up. When powered up, no audio signal coming through though amp was nice and silent... then after ~10-15seconds the hum comes in and gets louder and louder until I shut the power off. HERE'S WHERE IT GETS INTERESTING... when I shut the power off, I could then hear the music signal coming through (along with the high pitched whistle-like sound) until the caps disipated... weird. What would you make of that?
So here's what happened. I was running an audio signal to it before I powered it up. When powered up, no audio signal coming through though amp was nice and silent... then after ~10-15seconds the hum comes in and gets louder and louder until I shut the power off. HERE'S WHERE IT GETS INTERESTING... when I shut the power off, I could then hear the music signal coming through (along with the high pitched whistle-like sound) until the caps disipated... weird. What would you make of that?
The focus on the first photo is a little soft so pardon me if I've got it wrong but it looks like some some of the pads are open. If you haven't already done it, it might be a good idea to go through all the solder joints in a systematic way, touching up with a dot of fresh solder any that are open or are grey/dull in appearance .
2¢
2¢
Completely agree. First thing to try. Happened to me as well on a KT88 pp.
Can't figure out why as the connection was apparently correct, but it fixed the problem.
check here:
page 65(41)
https://www.americanradiohistory.co...ronics/50s/1953/Radio-Electronics-1953-05.pdf
page 55
https://www.americanradiohistory.com/Archive-Radio-News/50s/Radio-News-1950-11-R.pdf
The Power Transformer and the OT (?) (one on the left) should be 90 degree to each other not in line (like the PT & the choke (?) below it.) Turn it 90 degrees.
The red & black wires between the Power Transformer & OT (?) looks very close to it. You could put that red & black in a rubber hose to shield it.
Are the input wires shielded? You could use coax/shielded cable- the center copper wire.
page 65(41)
https://www.americanradiohistory.co...ronics/50s/1953/Radio-Electronics-1953-05.pdf
page 55
https://www.americanradiohistory.com/Archive-Radio-News/50s/Radio-News-1950-11-R.pdf
The Power Transformer and the OT (?) (one on the left) should be 90 degree to each other not in line (like the PT & the choke (?) below it.) Turn it 90 degrees.
The red & black wires between the Power Transformer & OT (?) looks very close to it. You could put that red & black in a rubber hose to shield it.
Are the input wires shielded? You could use coax/shielded cable- the center copper wire.
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The others who are far more experienced in the practicalities of valve stuff have given you much to go on
If the problem persists then I would then look at isolating one end of C4 and C5 to remove drive from the phase splitter and then see if the output stage is silent.
(Would that cause any issue running the output stage open loop?)
Hearing music come through while the caps are discharging might suggest a problem in the bias points somewhere with the rapidly falling rails taking an incorrectly biased stage briefly through a working point on its curve.
Try what the other guys suggest first though
Thank you all very much for your advice and input! Much appreciated.
I will be talking to Brian at ANK to discuss this shortly, but I'll try your suggestions first. Just so I'm clear about your recommendation.... from the wiring diagram I've attached here, which wires would you suggest switching 1st? (or 2nd or 3rd if required)?
I will be talking to Brian at ANK to discuss this shortly, but I'll try your suggestions first. Just so I'm clear about your recommendation.... from the wiring diagram I've attached here, which wires would you suggest switching 1st? (or 2nd or 3rd if required)?
Attachments
Hey Waltube, unfortunately, if you don't understand why R21 and R22 are where they are, I certainly won't either! (this is my first kit build) and if I had to rely on the schematic (which is all Greek to me) I wouldn't even bother trying! haha... I'm quite pictures-and-instructions dependant at present!
mctavish - if by 'center tap' you mean the yellow wire, then yes I'm sure. I'll try swapping the R1 and R2 wires and see what happens.
and if I had to rely on the schematic (which is all Greek to me) I wouldn't even bother trying! haha... I'm quite pictures-and-instructions dependant at present! mctavish - if by 'center tap' you mean the yellow wire, then yes I'm sure. I'll try swapping the R1 and R2 wires and see what happens.
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