I guess my PSU for the filment is to weak for filament bias. I only get 0,6v at the filament maximum.
And the input to the regulator is 4,6v so I guess its back to katod bias again then.
Please increase the input voltage to about 8V, if you want to try filament bias (2,5V bias).
Boomer! I had the variac not at full.
Now I have 1,4v at both tubes.
And its playing now.
But now I have a little hum in one channel.
Ill Hunt the hum Downey..
Now I have 1,4v at both tubes.
And its playing now.
But now I have a little hum in one channel.
Ill Hunt the hum Downey..
Well I dont know if it is funny...
If I ground the side where the hum is,the negative side of the filaments Elyts the hum stops.
But then the filament rises to 1900mv and it can´t be lowered.
So I guess it has to do with the filament.
Suggestions.....
If I ground the side where the hum is,the negative side of the filaments Elyts the hum stops.
But then the filament rises to 1900mv and it can´t be lowered.
So I guess it has to do with the filament.
Suggestions.....
The filament supplies need to be floating all the way to the socket/filament resistor. So make sure that there is no place where it is grounded earlier in the supply. What did you use for the raw supply to the regulator?
As an example - I tried to use a lm317 supply as the raw supply for Rod Coleman regulators - and I got hum. Used a regular CRC and no hum.....
As an example - I tried to use a lm317 supply as the raw supply for Rod Coleman regulators - and I got hum. Used a regular CRC and no hum.....
Yes I use CRC.11000uF 0,47 ohm and 11000uF.Goes to the regulator and after that to the tubes and groundet at the tube.
And same for the other channel.
And same for the other channel.
What transformer are you using for the filaments? Is it a transformer with multiple secondaries? heater supplies, and B+?
Its a R-core with 2x6v for filament and 2x15v wich is a connected back to back to the B+ transformer.
Would you have a separate transformer you could just connect up to try? I had an issue with 2 builds here where there were multiple secondaries that caused hum. If you had 2 single 12V transformer etc you could hook both up just to try.
So you have hum in only one channel acording to your post #64.
Have you tried swapping the 3a5s to see if the hum switches channel?
Have you tried swapping the 3a5s to see if the hum switches channel?
I use standard 5V SMPS. I removed Y capacitors and replaced all electrolytics caps with Panasonic. Then, from 5V to 1.4V you can calculate a few RC filters.
Simple as that and works like a charm. No problem with SMPS.
Regards
I'm not well versed in the technical aspects of SMPS so I didn't realize there was such a thing as a "standard" SMPS. What brand / model do you use?
I'm not sure if I'm comfortable modding one of them, though. What's a Y capacitor and why does it need to be removed?
I can figure out the voltage drop, I was more interested in learning what inductor (specifically, brand and model, specs if possible) you use. I assume it would need to have very low DCR.
I've used some Meanwell SMPS (3.3v 10w) to supply heater voltage to some 26s when I was breadborading an amp, but I think their current rating needs to be de-rated by a much larger factor because, over time (several months) their output voltage dropped a bit. They sounded fine (with some additional filtering) but I was concerned about the voltage drop so, when I built the amp, I ended up going with a more traditional DC supply.
I'd like to try the SMPS again, though.
Things Ive tried today,switched the secondary side ac leds with each other.
Switched the tubes L/R.
And used my bench supply to drive the filament of the humming tube.
None of this worked lowered the hum,the bench supply only varied the hum frekvensy.
It aint a loud hum if I play normaly volume I cant hear it its betwen the songs its irritating.
Switched the tubes L/R.
And used my bench supply to drive the filament of the humming tube.
None of this worked lowered the hum,the bench supply only varied the hum frekvensy.
It aint a loud hum if I play normaly volume I cant hear it its betwen the songs its irritating.
So when you switched the tubes L/R does the hum follow the tube or stay in the same channel?
Obviously, if it follows the tube, you need to try a different tube.