HT studio 20 noise problem

[craigtsai]

Hi all,

I just get an around 2~3 years old HT studio 20
yesterday, i found some noise like hiss and a little hum
when i plug cable even standby the amp, the noise appear
but if i take out cable, the noise disappear
also, more master volume and get more noise
i already checked to use different cable and just connect guitar without any pedals, but the problem still exist
so, is the problem due to preamp tube??should i replace a new preamp tube??
or any suggests for help

thanks so much!!!

[thephantum]

The HT20's standby switch is integrated with the input jack. So when you unplug the cable, the amp goes into standby. That's why the noise stops.

It sounds like you either have a bad power tube or a mismatched/unbiased set of power tubes. So first thing would be to completely re-tube the amp (pre and power). You said yourself that it's 2 to 3 years old and you got it used. If the amp was gigged even moderately, it's at least time for new power tubes.

Whenever buying a used tube amp, it's always a good practice to take it to a tech to have it retubed and rebiased as well as checked out. That way you can fix any issues while they are still minor (and cheap to fix)...versus after they cause lots of other damage (and become expensive to fix).

[craigtsai]

thanks for response,

i record a video to check problem, https://www.youtube.com/watch?v=AEQ2PKz ... e=youtu.be
just remember to turn on volume louder
at 0:15 when i plug cable then noise appear
at 0:27 when i take out cable then noise disappear
also, more master volume and OD channel is obvious to noise
would anyone tell me what happened to my HT20
do i still need to replace a new preamp tube?or power amp tube?or both??
and..is it dangerous to replace power tube and rebias??(high voltage?)
thanks so much!!!

[thephantum]

The level of noise on the clean channel in that video is normal...as a matter of fact, it's as quiet as mine. The fact is, plugging the guitar cable in made more noise than the clean channel did...even at volume. I had to crank the volume on my PC to even hear it.

There is an audible buzz on the OD channel, but it's not that bad. Tube amps make noise...especially when used at higher levels of gain/volume.

To be fair, I will say that yours does have a little more hum in OD than my HT-20H. It's possible that replacing the preamp tubes will reduce the hum, but there are a lot of external factors that can cause hum as well (ground loops, noisy AC power, etc).

Again, I will repeat what I said earlier: Whenever buying a used tube amp, it's always a good idea to have it retubed, rebiased and checked out. As stated above, tube amps will always have some level of noise, but a new, quality tube set and a proper bias can reduce that noise to a minimum.

Replacing the tubes is not dangerous, but to set bias the amp needs to be powered on while you measure high voltages with lethal current levels. So yes, it's dangerous and should not be attempted unless you know what you are doing.

[craigtsai]

Hi thephantum,
very very appreciated for your response!
in your opinion, is my HT20 clean channel normal when i plug cable into front amp?
but it still make a low and sustained noise
i am a little bit confused

thanks so much!!!

[thephantum]

I would actually call what you are hearing on both channels normal. However you can most likely get the OD channel a little quieter with a retube and bias. The other thing that might help would be to use a power filter so that the amp gets "cleaner" AC power.

A low level of hiss, hum and/or buzz is normal with any tube amp. Tubes are not solid state components. With the exception of a thin piece of glass, there is no shielding and they are thus completely exposed to any EM interference.