In the '80s a hospital in Den Helder, built in the '60s, was renovated and one of the guys working at that renovation found, removed and took home this amplifier that I bought after almost 40 years. The amplifier was used for announcements on the microphone to be sent to all the speakers in the hospital.

So, I found this beast and I bought it and I'm gonna clean it up and fix where needed (mainly capacitors I guess).

Some pictures

The Geloso G3227-a is a single-ended tube amplifier from the early 1960s. It's a mono block — originally intended for public address use in hospitals, schools, and factories. But don't let the "PA amp" label fool you: underneath that utilitarian exterior is a beautiful point-to-point wired amplifier with massive transformers and quality components.

First look: the chassis

The amp arrived dirty but physically intact. All tubes are present (two EL34 output tubes, two ECC83/12AX7 preamp tubes, and a GZ34 rectifier). The power transformer and output transformer are both original Geloso units and feel solid — no hum or buzzing when I first applied power through a variac.

Here's what I found on initial inspection:

  • All electrolytic capacitors are original (from the 1960s) — definitely need replacement
  • One coupling capacitor has a visible crack
  • Potentiometers are scratchy and need cleaning
  • Tubes test strong on my tube tester — happy surprise
  • Transformers test within spec
  • Chassis is rust-free, just dusty

The recap plan

This is going to be a full capacitor replacement (recap) project. I'll replace:

  • All electrolytic power supply capacitors with modern low-ESR replacements
  • Paper coupling capacitors with polypropylene film caps
  • Cathode bypass capacitors
  • All resistors that have drifted more than 10% from their rated value

I'll also add a proper three-prong power cord (the original has a two-prong) and a fuse holder for safety.

Part 1: cleaning and teardown

I started by removing all the tubes and giving the chassis a thorough cleaning with isopropyl alcohol and a soft brush. 40 years of hospital dust comes off surprisingly easily.

Then I pulled the chassis from the wooden case and documented every wire connection before removing anything. With vintage gear, taking photos at every step of disassembly will save you hours of head-scratching later.

Next steps

In the next post I'll document the capacitor replacement, resistor checking, and first power-up after the recap. Stay tuned.

Giuseppe