Does this amp have a problem or is it OK to buy?


I'm considering a Jolida 302B. Having seen reports of humming trannies, I asked the seller about it. His response is below. I don't know if this is a problem or normal. Even if slightly wrong, I'd rather not buy. What do you think?
"With the speakers connected to the 302B, I can hear a very faint hum from the speakers, but you have to put your ear right against the speaker grill to hear the hum. Turning the volume knob on the 302B has no effect on the amount of hum - the sound level remains constant regardless of the volume setting. Again, I must stress that the volume of hum is so slight, I doubt if anyone in a silent room will notice it, even when standing close to it. You really have to put your ear against the speaker to hear the very faint hum. I believe this kind of hum is generated by all amplifiers - try listening to your current amp. When listening to music, I doubt if one can hear the effects of it even in quiet passages.

Now, with a CD player hooked up to the Jolida, the hum level increases as you increase the volume on 302B. When the volume dial is turned down to minimum, the level of hum is very faint (same level as if cd player was not connected). When the volume is turned to MAXIMUM, the hum becomes noticeable as you approach the speaker (about 3 feet away). In addition, when the CD player is on, and the input selector on the 302B is set to other than CD (such as AUX), turning the volume knob has no bearing on the hum level - it stays constant at the barely audible level. I believe what this indicates is that by itself, the 302B is very quiet (just a barely audible hum), and when you hook up a CD player or phono stage, the inherent noise (hum) from those external sources are magnified as you increase the volume. "

Thanks....
river251
Remember hum through the speakers can be caused by cable tv issues, interconnects etc. or other external issues that have nothing to do with the amp itself. Also, if there is a bit of hum through the speakers, and it is amp related, the loudness of the hum will also be a function of the sensitivity of the speaker. If your speakers are more efficient than the owners the hum could be louder. How old is this amplifier?
Humming to the speakers is because the AC filament supply to the 12AU7 is making it into a buzzy microphone.

Spent MONTHS on my previously modded 302B to fix the problem by taking out the center tap for the filament which had become intermittent, and building a 100Ohm--100Ohm center tap, and elevating the filament center to about 70V.

Most modders who know about filament elevation for SRPP gain stages would know how to do this.
Johnsonwu is telling you stay clear unless you know what you are doing with solder gun and circuit. If you want to fix the issue and look at it as a challenge, then have at it! Simply pay far less then the asking price .
In addition, when the CD player is on, and the input selector on the 302B is set to other than CD (such as AUX), turning the volume knob has no bearing on the hum level - it stays constant at the barely audible level.
River251
04-24-12
Of course, cos the hum is not from the input jack or internal wire, its from the filament supply.

Most modern power amps or integrated amps with reasonably high gain have DC filaments (read: no hum)

Regardless of AC or DC filament, the textbook treatment if you have a totem pole (SRPP or stacked triodes the call) configured first stage the filament MUST be raised to preserve tube life.

Those who throw NOS tubes at these Chinese amps you are flushing money down the toilet.

properly modded this amp is wonderful. tranny is overbuilt, lots of space to put in oversized components.

However, most modders simply put in new caps and new diodes and completely ignore this serious flaw of filament supply.