Vance & FixItFella
Vance Vance
FixItFella FixItFella
FixItFella FixItFella
Hey Vance, I found an old 1920s vacuum tube radio that won't power up. I have a pile of spare parts and a plan—want to help me crack the schematic and bring it back to life?
Vance Vance
Sure thing. Let’s start by listing what you’ve got: the power supply parts, the vacuum tubes, and any known resistors or capacitors. Once we have a clear inventory, we can sketch a quick schematic and pinpoint where it’s stuck. Give me the list and we’ll map it out.
FixItFella FixItFella
Sure thing, here’s the rundown of what I’ve scavenged from the junkyard: Power supply: - 1× 230 VAC‑to‑12 VDC transformer (old cast‑iron core) - 1× 1N4007 rectifier diode - 1× 47 µF, 25 V electrolytic (smoothing) - 1× 7805 5 V regulator - 3× 100 Ω and 3× 1 kΩ carbon film resistors (for bias) - 2× 0.1 µF ceramic caps (decoupling) - 1× 1 A fuse (safety) Vacuum tubes: - 2× 12AX7 (for the pre‑amp) - 1× 6SN7 (for the power amp) - 1× 6V6 (to give it some punch) Miscellaneous: - 1× 10 µF electrolytic (for the high‑voltage supply) - 2× 5 V DC power jack - A few extra screw terminals, a stray magnet, and some old brass clips that I’m not sure how to use yet That’s the core kit. If you spot a missing piece or think I’m overlooking something, let me know. I’ll sketch the quick schematic once we confirm the parts. By the way, if you need a wrench, just remember I’m holding onto the lucky one for the next project—won’t lend it out.
Vance Vance
Looks solid for the low‑voltage side, but you’re missing the high‑voltage transformer that turns the 12 V DC up to 300‑400 V for the tubes. Without that the 12AX7s and 6SN7 won’t get enough plate voltage. Also double‑check the rectifier orientation and that the 1N4007 is actually rated for 230 VAC. Once you have the HV transformer, we can wire the bias resistors and split the plate supply. Let me know when you’ve got that piece and we’ll finish the schematic.
FixItFella FixItFella
Yeah, you’re right—gotta get a proper 12‑V to 300‑400‑V transformer. I’ve got an old one in the basement that’s probably the right size, but it’s been sleeping since the 90s so I’ll need to check its winding and insulation first. I’ll also double‑check that the 1N4007 is 1 A 400 V; it’s a 1 A 400 V part so it should handle 230 VAC after rectification, but I’ll test it with a multimeter. I’ll grab it tonight, test the winding and the diode, then we can slot the bias resistors in. Hang tight—I’ll ping you once I’ve verified the high‑voltage section.
Vance Vance
Sounds good. Just remember to keep the HV side insulated and never touch it while the rectifier’s on. Hit me up when you’ve got the winding verified, and we’ll map the bias network. No rush—tactics first.
FixItFella FixItFella
Got it, I’ll check the winding and make sure the HV side stays sealed off. I’ll keep the rectifier out of reach while it’s live. I’ll ping you once the transformer’s verified and the insulation is solid. And of course I won’t touch the lucky wrench until the job’s done.
Vance Vance
All right, keep me posted. Once the HV transformer checks out, we’ll set the plate bias and get those tubes firing. Stay safe.
FixItFella FixItFella
Got the winding sorted, HV side’s sealed off and insulated. All good on the transformer side, so we’re ready to set the plate bias next. I’ll give you a heads‑up when I’m ready to wire it up. Stay safe, too.