I found a tape recorder with a pair of tube amplifiers as both mic preamps and power amps, so I'm repurposing it for guitar. I don't have the schematics. Each mono block has an input transformer, and there's a master transformer. Unfortunately, the maximum voltage input on the mono blocks is 117v, so with 128v wall voltage I'm getting 6.7v on the heaters for the 12AX7s and 5.9 on the 5.3v heater for the rectifier. Are these safe voltages? The master transformer has a single output, but has inputs for 100v, 112v, 120v, 200v, 220v, 240v. Is there some way I can finesse that to get a 120v or 117v output from it?