Hello everyone. I am very disappointed.
I completed the amplifier, but something is wrong and I don't know what.
I checked all the components, all the tracks, except the tubes that I bought from Tub Amp Doctor.
So what happens; all the voltages are within the parameters but without tubes.
I connected a speaker (8 ohm 20w) to the output, and a signal source to the input. First I connected the filaments of all the tubes and after 10 minutes I connected the transformer that powers the amplifier.
For a second, the signal is heard in the loudspeaker, after which the small neon tube lights up and the voltage +150 v drops to @25v, and the negative voltage of 150v increases to @350v.When connecting the supply voltages, the Ammeter indicates over 3 A, after which it drops to 400 milliamps.
Can someone explain what is happening?
Sincerely, Mario
I have the honor to greet you Sir Victor, I just built an amp and it doesn't work, I would like if possible to communicate by phone. here is my number 0745842641 Mario
I bought supposedly EF86 Tubes from ebay, and when they arrived, I couldn't see any part markings on them just an OTK logo. They visually compared internally to pictures online. So as any self respecting engineer would do, I did no more research than "Well they look similar" Plugged them in, let them warm up a bit, but like you i could not see them glow. I just presumed they were so low powered fillaments, hidden behind all the screening that i could not see them. So on with the HT. They seem to work just fine ???
I can't check that right now; recently there was a problem with the amplifier and I've not had a chance to locate the fault yet. I think one of the 6C33C tubes must have failed.
I think my distortion meter only registers harmonics up to 20kHz, but still that should allow me to get a reasonable measure of distortion up to a few kHz, I suppose.
It may be a while now before I have time to get the amplifier back in operation. After that, I'll try to report on the distortion at higher frequencies.
Do you have any speaker protection ??? Are the offset and bias correctly adjusted, With input shorted to ground adjust offset untill you have 0v on speaker output (before the protection, no speaker connected) any dc on output will trip the protector.
Hello everyone. I am very disappointed.
I completed the amplifier, but something is wrong and I don't know what.
I checked all the components, all the tracks, except the tubes that I bought from Tub Amp Doctor.
So what happens; all the voltages are within the parameters but without tubes.
I connected a speaker (8 ohm 20w) to the output, and a signal source to the input. First I connected the filaments of all the tubes and after 10 minutes I connected the transformer that powers the amplifier.
For a second, the signal is heard in the loudspeaker, after which the small neon tube lights up and the voltage +150 v drops to @25v, and the negative voltage of 150v increases to @350v.When connecting the supply voltages, the Ammeter indicates over 3 A, after which it drops to 400 milliamps.
Can someone explain what is happening?
Sincerely, Mario
Hallo Mario
Ich bin neu hier!
Hast Du den OTL erfolgreich gebaut?
Ich suche ein fertig aufgebautes Gerät.
Eine Mono-Version würde genügen.
Gruss
Richard
@RICHARD877 You must post in English on this forum. Check your posts. I have provided a translation below.
I'm new here!
Did you successfully build the OTL?
I am looking for a fully assembled device.
A mono version would suffice.
Greeting
Ich bin neu hier!
Hast Du den OTL erfolgreich gebaut?
Ich suche ein fertig aufgebautes Gerät.
Eine Mono-Version würde genügen.
Gruss
Richard
@RICHARD877 You must post in English on this forum. Check your posts. I have provided a translation below.I'm new here!
Did you successfully build the OTL?
I am looking for a fully assembled device.
A mono version would suffice.
Greeting
Last edited by a moderator:
Hi , Captain First of all, thank you for the advice that was very useful.
Here's how things are now: negative voltage = 145V, positive voltage =192V,
The voltage of 146V measures 186V, and the negative of 430V measures 465V, the voltage for V1, pin 1 = 105V, and at pin 6 = 152V
I also managed to adjust the bias current to 200mA, but the offset cannot be adjusted to have 0 V on the output terminals without speakers and the input connected to ground (when I adjust RV2, I get these voltages 1.8V...0.79V)
Regards.
Mario.
I built my amp using boards from Ares audio. I currently have the whole thing disassembled, as i am building a nice chassis for it. Work commitments have slowed progress a bit, but will hopefully be able to find some time in the next couple of weeks. It took me quite a while to get it working. I started simple, single channel with just two 6c33's on output, all built on a wooden test rig. I did try getting it going just spread out on bench, but then decided to build a test rig for safety reasons. There seems to be quite a bit of mis-infomation out there on different sites, the Ares audio has several "mistakes" (seen my earlier posts).
I used to often jump into these projects, throw the whole thing together, and expect it to work (ish), but that very really happened, you just end up with lots of smoke and loads more expense! Build it section at a time start with the power supply get that going with all the correct voltages. Then add the amplification section. In the beginning use a variac or some old incadesent lamps in series, will save you a fortune in fuses. Check and double check before applying power. You will get there in the end. remember If anybody could buy the parts assemble it and it just work out of the box then is wouldn't be anything so special !
As soon as i get it back together, i will take some pictures and voltage readings.
I built my amp using boards from Ares audio. I currently have the whole thing disassembled, as i am building a nice chassis for it. Work commitments have slowed progress a bit, but will hopefully be able to find some time in the next couple of weeks. It took me quite a while to get it working. I started simple, single channel with just two 6c33's on output, all built on a wooden test rig. I did try getting it going just spread out on bench, but then decided to build a test rig for safety reasons. There seems to be quite a bit of mis-infomation out there on different sites, the Ares audio has several "mistakes" (seen my earlier posts).
I used to often jump into these projects, throw the whole thing together, and expect it to work (ish), but that very really happened, you just end up with lots of smoke and loads more expense! Build it section at a time start with the power supply get that going with all the correct voltages. Then add the amplification section. In the beginning use a variac or some old incadesent lamps in series, will save you a fortune in fuses. Check and double check before applying power. You will get there in the end. remember If anybody could buy the parts assemble it and it just work out of the box then is wouldn't be anything so special !
As soon as i get it back together, i will take some pictures and voltage readings.
What Transformer are you using for the HT ? and what Power supply circuit are you using. I am using a 500w toroid that Ares Audio recomended and the Ares Audio PSU PCB. I couldn't find any schematic online for this PSU (it is slightly different from the original Tim Mellow) so i made my own. Ares just told me to populate it with what was marked on the silk screen of the PCB ?? So I did and it works great. all output voltages are pretty close to what they should be and the + / - 150v are perfectly balanced. Your 145v and 192v are way out ???
Hi Captain, so I used Tim Mellow's OTL diagram (https://audioxpress.com/article/your-can-diy-a-25w-otl-tube-amplifier) including the power supply diagram.
and I use a 600VA toroid for HT.
Another toroid for the 6C33C heaters.
I made two changes; I used 2 capacitors instead of 8 pieces. and I put a resistance of 0.15 ohm in parallel with the ammeter, otherwise I completely respected Tim's project.
I still don't know why I can't relate the offset voltage, I'm afraid to put the speakers on and do more tests until I find out what's wrong
and I use a 600VA toroid for HT.
Another toroid for the 6C33C heaters.
I made two changes; I used 2 capacitors instead of 8 pieces. and I put a resistance of 0.15 ohm in parallel with the ammeter, otherwise I completely respected Tim's project.
I still don't know why I can't relate the offset voltage, I'm afraid to put the speakers on and do more tests until I find out what's wrong
Don't connect any speaker of any value until you are confident the output has no DC on it. Use dummy loads or junk speakers while testing.
I have just tried to get the schematic that i made by reverse engineering the Ares Audio PSU PCB but it didn't save it properly (in Ki-cad, i'm a linux guy). so i only have partial of it. The + / - supplies on mine have 4 capacitors 2 x 1000uf + and 2 x 1000uf - .
the main difference i can see from Tim's design is The resistor on the centre tap of the transformer, Tim's is 1K on my Ares it is 100R (7watt).
I have just tried to get the schematic that i made by reverse engineering the Ares Audio PSU PCB but it didn't save it properly (in Ki-cad, i'm a linux guy). so i only have partial of it. The + / - supplies on mine have 4 capacitors 2 x 1000uf + and 2 x 1000uf - .
the main difference i can see from Tim's design is The resistor on the centre tap of the transformer, Tim's is 1K on my Ares it is 100R (7watt).
