Traynor YGM4 hum. Need some expert advice/input

[geofo]

I have a Traynor YGM4 which originally had no output. Changed the output tubes and the Amp is back working. I have contacted the Traynor technical staff and although I do respect their feedback, afterall getting advice from the horses mouth should be taken without any doubt, but I just wnated to get a second opinion. The issue (if it is an issue) is that when you plug in a guitar, if the guitar's and Amp's volumes are down you hear nothing. If you keep the Amp volume down and the guitar volume up you hear nothing but as soon as you bring the Amp volume up it starts humming but it is not jus a low hum, it is very noticeable to the point that you wonder if this is normal. When playing the guitar, the hum is overshadowed by the guitar playing. So the question that I have is, is this normal? I plugged another instrument with a pickup which had no volume controls (it is not a guitar, it is a Greek instrument called bouzouki) and as soon as I increase the Amp's volume the hum is heard.
I thought that it may be a grounding issue but according to the Traynor's expertise that's not the case. Any other thoughts???
Thank you

[Alex R]

There are many grounding issues, which one did you think might be the cause? Given your description one doesn't spring to my mind.

It sounds a bit as though you were trying to get some hum out of the amp, which is always going to be possible. Does it hum with no guitar plugged in?

[geofo]

Not all. Without anything plugged in there is no hum, only when an instrument is plugged in and the instrument's volume is up.

[MWJB]

How does the amp bias up? Does turning the intensity control have any effect on the hum? What is the plate voltage on the power tubes?

[Alex R]

There's only one stage before the vc on that amp, not a lot there to cause hum. More likely it's normal hum picked up by the guitar. Have you tried turning the guitar volume down with the amp volume up? If that quiets it then it's the guitar not the amp, and if it's single coils it's normal.

[geofo]

There's only one stage before the vc on that amp, not a lot there to cause hum. More likely it's normal hum picked up by the guitar. Have you tried turning the guitar volume down with the amp volume up? If that quiets it then it's the guitar not the amp, and if it's single coils it's normal.

Yes when the guitar volume is off there is no hum even with the Amp volume turned up

[geofo]

If I remember correctly the intensity control was down but I wll double check that tonight. The plate voltage is around 400 to 450 volts. The Amp plays fine and you don't hear the hum when the guitar is playing. It is only when you just hold the instrument without playing and the instrument's volume is ip. If you turn the guitar's volume down the Amp is quiet

[MWJB]

If I remember correctly the intensity control was down but I wll double check that tonight. The plate voltage is around 400 to 450 volts. The Amp plays fine and you don't hear the hum when the guitar is playing. It is only when you just hold the instrument without playing and the instrument's volume is ip. If you turn the guitar's volume down the Amp is quiet

+1 What Alex R says above...

[52 Bill]

Have you tried replacing the preamp tube?