[UK-CONTEST] Ameritrom Amp.

[Christopher Plummer]

Guys,
 
Has anyone experience with the following fault on my amp?
 
It is a grounded grid tube amp with standard Pi tank type output tuning, and selects different bandpass filters for the input drive.
The amp works perfectly well on all bands until recently, but now won't amplify on 15m (all other bands it works perfectly well)
The input circuit seems to tune OK with my GDO (power off of course) as does the output circuits.
I have looked around the switch elements and there seems to be no damage or burning and the circuits are zero ohms at DC through the switch elements.
The input is selected by a wafer of the band switch and consists of a fixed SM cap to ground, a slug tuned coil and a second SM cap to ground, ( a classic Pi Tank type tuned circuit to match the input to the cathode of the tube.
 
Rather than rip the circuits apart has anyone got any experience or ideas?
 
Chris