1966 Univox U-305R Combo Amplifier

I picked up this 1966 (or 1967) Univox U-305R amp. It seems to work fine, but I feel it should have a lot more volume. The speaker is a vintage Jensen C15PS. When talking about a mid-60s Supro Thunderbolt amplifier, "Vintage Guitar" used the phrase "thunderous Jensen C15PS," so I'm guessing the speaker isn't the volume issue here. I mean, I have a 5-watt amp that blows this away volume-wise. Does anyone know what might be wrong? #univox #vintageamp #jensen