1，B+=420V, it is Ok, I am wrong, it is not necessary to add res to reduce it
2, I have added a 180ohm res and 50uf cap to the power circuit for a test, the hum voltage has not changed, the hum is not caused by ripple of B+
2, I have added a 180ohm res and 50uf cap to the power circuit for a test, the hum voltage has not changed, the hum is not caused by ripple of B+
1, 9mV of hum which I put the Potentiometer of input Attenuator to the position of normal listening
2, when I put the potentiometer to maximum position, the voltage of hum is about 136mV
3, I unpluged the first and second stage of 310A, voltage of hum reduced to 31mV
4, plugged second 310A back on, hum is still about 30mV
Maybe the hum mainly coming from first stage?
2, when I put the potentiometer to maximum position, the voltage of hum is about 136mV
3, I unpluged the first and second stage of 310A, voltage of hum reduced to 31mV
4, plugged second 310A back on, hum is still about 30mV
Maybe the hum mainly coming from first stage?
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Hi Troy, you are expert of WE91〈[emoji7]ノ
1, with AC(5V), how much the voltage of hum when put the Potentiometer to max?
2，what is tentlabs filament supply?
1. My volume pot is before the fist stage so it doesn't matter if it's min or max. On such measurements you should always terminate your input to ground (pull down).
I measure 12 mV hum on my AC filament version.
So your 9 mV is a good result. No need to change to DC...
2. Tentlabs filament supply:
Tube filament supply
Even better would be a DIY module from Rod Coleman:
Rod Coleman DHT Filament Regulator
But it will need even more AC input (>8V).
1, You mean I should put the pot like pic-A, Not pic-B?
2, some noise come from 1st, the heater wire connection is like pic-A, should I change it to Pic-B?
As for the DC heater, my power trans have only 5V(a little bit more), this circuit will work with only 5.1V AC input
1. If your RCA input is not connected use pic-A (tube input to gnd) for measurements.
2. I guess this won't make any difference but you can try if it's easy to patch.
I would stick to AC filament supply if possible (1:1 91A clone). Afterwards you can always try out some DC heater and decide if it's improving the sound/hum issue.
2. I guess this won't make any difference but you can try if it's easy to patch.
I would stick to AC filament supply if possible (1:1 91A clone). Afterwards you can always try out some DC heater and decide if it's improving the sound/hum issue.
HI. i have experience with hum .guitar amp and hifi . i think when start new project .....pcb is not good choice .grund shude change for reduce hum . musician order fender guitar amp .hum in speaker !!!!!disassembly and change....for 3 times !!!the last was quit .nothing in speaker .no Change parts not dc in filament just changing ground .
1-hi sensitivity speaker =hear very small signal from amp !!!it is very bad chans in tube amp .
2-dht out put =noise in output . dc filament with good filtering and 100 ohm balance pot .some times i use battery for filament to understand source of hum .if change ...should try on filtering of dc for filament .
3-disconnect the signal of tube driver to 300b and see the oscop .if have hum try to fix it .
4- reduce hum in out put dht tube is not difficult .but most of problem happen in gain stage and first tube .this kind of hum need spend time to detect source of hum .
2-dht out put =noise in output . dc filament with good filtering and 100 ohm balance pot .some times i use battery for filament to understand source of hum .if change ...should try on filtering of dc for filament .
3-disconnect the signal of tube driver to 300b and see the oscop .if have hum try to fix it .
4- reduce hum in out put dht tube is not difficult .but most of problem happen in gain stage and first tube .this kind of hum need spend time to detect source of hum .
Use battery to the heater, quite a good testing method, how to connected it to 300B filament?
2 YEARS before i send circuit and parts to my customer for 300 b amp project .pleas look at the power supply and amp .first i design circuit whit c3m...vt25...300b...
2 dht !!
before to assemble and make box by customer ...i test all of circuit and check sound with hi sensitivity speaker .
hum=0
musical sound 😉
no pcb .
Begin to rebuild the second one of this mono.
Two changes:
1, used shield twisted cable for heater
2, change connection point of two 310A, from 1st stage to 2nd stage
Two changes:
1, used shield twisted cable for heater
2, change connection point of two 310A, from 1st stage to 2nd stage
