Bias
Hi
I've had Yaqin before and was no problem at all with bias.
I know another person in Poland who has exacly same problem.Maybe just a faulty batch.
I left amp with technician to fix the problem.
I was upset with that.
Thanks for help.
Regards
Hi
I've had Yaqin before and was no problem at all with bias.
I know another person in Poland who has exacly same problem.Maybe just a faulty batch.
I left amp with technician to fix the problem.
I was upset with that.
Thanks for help.
Regards
Audioromy FU13
Hi guys
My FU13 has arrived and is sounding quite good albeit it seems to distort at relatively medium volume. I also tried to set the bias to 0.55V DC on the 10 Ohm resistors but the highest it seems to go is 0.15V. Adjusting the resistor pot on 1 channel effects the bias current on both channels! Weird! Any clues anyone?
Hi guys
My FU13 has arrived and is sounding quite good albeit it seems to distort at relatively medium volume. I also tried to set the bias to 0.55V DC on the 10 Ohm resistors but the highest it seems to go is 0.15V. Adjusting the resistor pot on 1 channel effects the bias current on both channels! Weird! Any clues anyone?
If these are the real value's, you have probely a problem with your power supply. Check the rectifier tube and the anode voltage on the FU13 tubes, must be around 900Volts.
Ronny
Ronny I am measuring 568V DC from the FU13 cap socket to earth (chassis) for each of the two sockets. Should this be around 900V?
I also get the exact same measurements even if I take the rectifier tube out and I can see no glow from the rectifier tube. That must mean that the rectifier tube is faulty?
Sorted now and thanks for the pointers. it was simply the pins of the recyfier tube needing cleaning. Now measuring something like 870V at the FU13 anode. Biasing left for another day. Thanks again!
Themystical, great now you can enjoy.
Cobra2, just one pot for left and one pot for right channel for the biasadjustment. Please check also anodevoltage of the FU13 tubes. A defect rectifiertube can also effect biasadjustment.
Ronny
Cobra2, just one pot for left and one pot for right channel for the biasadjustment. Please check also anodevoltage of the FU13 tubes. A defect rectifiertube can also effect biasadjustment.
Ronny
I know,...it was just a suggestion, having had Audioromy El34 and FU29 amps, and seen many variations.
Arne K
Arne K
I just bought my second Audioromy 838 with 845 tubes. I am looking to convert it for use with 813. I have the sockets and am almost ready to go.
My big question is whether the power transformer can supply sufficient current for the 10 volt filaments. The 845 needs 3.25 amps and the 813 needs 5 amps.
From what I can guess, the 838 amp was originally designed for 838 tubes and then adapted to 845. I wonder if their Fu13 version is the same but adapted to 813 tubes. If anyone knows I would greatly appreciate it. Sourcing a cheap 10vac transformer and finding physical space for it in the chassis is not easy.
Thanks
My big question is whether the power transformer can supply sufficient current for the 10 volt filaments. The 845 needs 3.25 amps and the 813 needs 5 amps.
From what I can guess, the 838 amp was originally designed for 838 tubes and then adapted to 845. I wonder if their Fu13 version is the same but adapted to 813 tubes. If anyone knows I would greatly appreciate it. Sourcing a cheap 10vac transformer and finding physical space for it in the chassis is not easy.
Thanks
Hi guys
With all the problems I have been having having with my rectifier valve, It looks like the 4 No resistors which bypass the rectifier valve have burnt and failed open circuit so I cant measure their values. It has charred the board too. The schematic posted by Koi shows this to be a 10k 10w resistor? Does that mean that the four resistors are 40k 2.5W each? Alternatively, these could be 4 no 10K, 2.5W resistors giving a 2.5k, 10W rating? If somebody is able to measure and clarify, that would be fantastic.
With all the problems I have been having having with my rectifier valve, It looks like the 4 No resistors which bypass the rectifier valve have burnt and failed open circuit so I cant measure their values. It has charred the board too. The schematic posted by Koi shows this to be a 10k 10w resistor? Does that mean that the four resistors are 40k 2.5W each? Alternatively, these could be 4 no 10K, 2.5W resistors giving a 2.5k, 10W rating? If somebody is able to measure and clarify, that would be fantastic.
I should be receiving my 845 version soon. These resistors should be similar to the 813 model. I will go through it when it arrives and let you know unless someone does this first.
In my 845 version, there are 4 x 10k resistors. Each pair is connected in parallel and then series connected. I can't tell the watt rating but they look like 2 watters to me.
You should do well by replacing them with 3 to 5 watt rated resistors. There's enough room on the board I have.
You should be able to determine if they are series parallel with a multimeter.
I don't have my digital camera handy but may get it back next week so can send pictures if you need.
You should do well by replacing them with 3 to 5 watt rated resistors. There's enough room on the board I have.
You should be able to determine if they are series parallel with a multimeter.
I don't have my digital camera handy but may get it back next week so can send pictures if you need.
Bypass resistor on the rectifier
Why have they used a bypass resistor on the rectifier tube ? Just as a bleeder resistor on power down ?
Why have they used a bypass resistor on the rectifier tube ? Just as a bleeder resistor on power down ?
Thanks for that Mush. I wonder why he didn't use 2 20k resistors in parallel instead of the 4 10k parallel series arrangement? Presumably he only stocks 10k resistors?
I will probably get a 10W, 10k wirewound and stick it to the chassis and cable it to the appropriate connection points as the board is charred where the resistors connect.
Yes I would be interested in the function of this resistor too but suspect it is to do with a gentler power up until the recifier valve conducts rather then power down?
I think it's a form of soft start. Nailing the circuit with an instantaneous 900v isn't a great way to stress and underbuilt amp. (the cap stack is 2 x 450vdc caps for the power supply on either side of the choke.) I would go for at least 15 watts for the 10K resistor.
I am looking in the chassis of my 845 based Audioromy for space for extra filament transformers. I might be able to pull of the conversion to 813. The amp is poor/fair shape. One of the 845 sockets is cracked. I am looking at rewiring the entire front end simply to get some more clearance for a volume ladder switch. The signal caps are Wima MKS 0.47 @ 400vdc. Switching to nice inexpensive caps like Obbligato would be an improvement.
A weird thing about the Audioromy, almost all the wires are pink. It's a real headache to figure what goes where. The pictures of the Fu13 model look better.
Does anyone know how much better are the finned Fu13 to the smooth plate Shuguangs sonically?
I am looking in the chassis of my 845 based Audioromy for space for extra filament transformers. I might be able to pull of the conversion to 813. The amp is poor/fair shape. One of the 845 sockets is cracked. I am looking at rewiring the entire front end simply to get some more clearance for a volume ladder switch. The signal caps are Wima MKS 0.47 @ 400vdc. Switching to nice inexpensive caps like Obbligato would be an improvement.
A weird thing about the Audioromy, almost all the wires are pink. It's a real headache to figure what goes where. The pictures of the Fu13 model look better.
Does anyone know how much better are the finned Fu13 to the smooth plate Shuguangs sonically?
Helo Koifarm,
My Audioromy FU13 has exactly the same problem, as you described. Fuse was blown and after attemp of shortcircuit it the relay clicked with 50 or 100 Hz. What is the problem with 47uF capacitor. Is its rated voltage to low or is it temperature issue? I will replace it with higher voltage one with at least 125 C rate.
I also noticed problem with the proper bias. Min. current, I could adjust was 72 mA. Reason for that was too low value of negative voltage applied for the first grid of FU13. While diagram taken from german collegaues says, that this negative voltage should be -120V, in my unit I measured only -100V. I could help a little to increase resistor 22k to let say 100k to get more negative voltage from its rectifier.
Do you have a similar experience?
Thanks, Savim
My Audioromy FU13 has exactly the same problem, as you described. Fuse was blown and after attemp of shortcircuit it the relay clicked with 50 or 100 Hz. What is the problem with 47uF capacitor. Is its rated voltage to low or is it temperature issue? I will replace it with higher voltage one with at least 125 C rate.
I also noticed problem with the proper bias. Min. current, I could adjust was 72 mA. Reason for that was too low value of negative voltage applied for the first grid of FU13. While diagram taken from german collegaues says, that this negative voltage should be -120V, in my unit I measured only -100V. I could help a little to increase resistor 22k to let say 100k to get more negative voltage from its rectifier.
Do you have a similar experience?
Thanks, Savim