Amp whistles with nothing plugged in but is perfectly fine once a cable is inserted.

[greengriff]

As above. I have one of these: https://www.reussenzehn.de/de/musike...-urversion.php . Mine has tiger fur covering, and a tiger's face on the baffle, with eyes that light up when you turn the amp on. It could not be any more 80s and is probably beyond parody, but it sounds really great.

If you switch the amp on with no guitar cable plugged into the input, and turn up the volume, it squeals uncontrollably. However as soon as you plug a guitar in, the problem goes away and the amp operates perfectly. Does anyone have any idea what this issue is?

[Helmholtz]

If you switch the amp on with no guitar cable plugged into the input, and turn up the volume, it squeals uncontrollably. However as soon as you plug a guitar in, the problem goes away and the amp operates perfectly. Does anyone have any idea what this issue is?

Do input jacks short with nothing plugged in?

[greengriff]

I don't know. I'll have to check it tomorrow.

[greengriff]

No, the jack is not shorted with nothing connected.

[Helmholtz]

No, the jack is not shorted with nothing connected.

So the input is open with nothing connected. No wonder it produces strange noises when you turn the volume up.
Make sure to use shorting jacks.

[greengriff]

I thought I'd post some gut shots out of interest.

[greengriff]

So the input is open with nothing connected. No wonder it produces strange noises when you turn the volume up.
Make sure to use shorting jacks.

I wonder why the original builder did not? He's quite famous in Germany as a builder and modder of valve hi-fi and guitar gear, so you'd think he would know.

[Helmholtz]

I wonder why the original builder did not? He's quite famous in Germany as a builder and modder of valve hi-fi and guitar gear, so you'd think he would know.

The jacks I can see from your pictures are actually shorting type. So you might have success cleaning and maybe re-bending shorting contacts.

[greengriff]

Ok thanks. Much appreciated.

[Helmholtz]

To make sure, dismantle input jack(s) from chassis and post a picture of the contact side.

[Jazz P Bass]

Nice job sucking up T Boy's drive with those pic's.

[greengriff]

I'm happy to shrink them in future. Is there an optimum size that still gives people sufficient detail?

[Jon Snell]

Make sure the input jack shorts to ground when empty.
I suspect the switched contact is bent.

When you upload photos, try and select Thumbnail, they stay small until selected. I expect you selected actual size.
No worries.

[pdf64]

Only the 4th pic has any value to the thread, as it's that one showing the input jack. As its wiring for the shorting contact is pretty obvious, in this case, only low res pic may be necessary.

[greengriff]

I just thought the pics would be of interest because of the layout that the builder chose - with the power valves nudged up to each other from front to back. They are cooled by an always on fan and there is a large resistor acting as attenuator that is also cooled by the fan. Any thoughts on why he might have chosen to arrange the valves that way? Shorter wiring and less noise? Something else?