[Heathkit] HO-10 low vertical

[Chuck Penson]

Hi, all. I've got an HO-10 with very low vertical response from the vertical input jack on the back panel. I've checked all the resistances (including the gain control), all the voltages and, of course, the 12AU7. Everything checks out. I also checked the cable that connects the rear panel jack to the amp. 

All other functions normal. 

It's such a simple circuit. There isn't much to go wrong. This has got me a little stumped. 

Any ideas would be appreciated. 

Best,

Chuck / WA7ZZE