Vintage Tube Amp

Vintage EICO HF-12 12-watt mono tube amplifier, previously modified from its original hi-fi configuration for apparent guitar/instrument amplifier use. This is an interesting restoration or further-conversion project for a tube guitar amplifier builder or vintage audio enthusiast. CURRENT CONFIGURATION – Original EICO HF-12 chassis, enclosure and transformers. Original four-position input selector removed and replaced with a front-mounted 1/4-inch input jack. Three remaining front controls: volume, bass and treble. Original rear audio inputs removed. Rear 1/4-inch speaker output jack added. Original speaker terminal strip remains, with altered connections. The 8-ohm terminal is presently unwired. Original decorative front faceplate is missing. Replacement Mallory electrolytic capacitors installed. Three-prong grounded-style power cord installed, but protective grounding has not been verified as satisfactory. Other previous wiring and component changes are visible. ELECTRICAL TESTING PERFORMED The amplifier has NOT been powered up or audio-tested. Resistance and continuity measurements were performed with a multimeter. Output transformer: – Primary end-to-end: approximately 341 ohms – Primary halves: approximately 187 and 154 ohms – Secondary G-4? : approximately 0.9 ohms – Secondary G-16? : approximately 1.3 ohms Power transformer: – Primary: approximately 40 ohms – Heater winding: approximately 0.4 ohms – High-voltage secondary: approximately 205 ohms total – High-voltage secondary halves: approximately 105 and 98 ohms No open windings were identified in the circuits measured. These are resistance/continuity measurements only and do not establish transformer performance under operating conditions. IMPORTANT ELECTRICAL CONDITION The three-prong power cord was checked for continuity between its grounding pin and the metal chassis. Meter lead resistance: approximately 0.2 ohms – Grounding pin to chassis: approximately 2.5-2.7 ohms The protective chassis-ground connection requires further inspection and verification. The power wiring, capacitors, previous modifications and overall electrical safety have not been fully evaluated. DO NOT CONNECT TO AC POWER UNTIL PROPERLY INSPECTED AND SERVICED BY A QUALIFIED TUBE-AMPLIFIER TECHNICIAN. RESTORATION POTENTIAL The EICO HF-12 originally used a push-pull EL84/6BQ5 output stage rated at 12 watts in its factory configuration. The existing instrument-style conversion offers an interesting starting point for a vintage guitar amplifier project. Actual instrument input characteristics, operating condition, output power and sound have not been verified. The amplifier could also be considered for restoration toward its original hi-fi configuration. This would require sourcing missing controls, connectors and faceplate components, tracing the wiring and making appropriate circuit repairs. Not represented as a working or electrically safe amplifier. Includes the amplifier and installed components as photographed. No additional accessories are represented as included. Please review the detailed photographs of the chassis, underside wiring, transformers, controls and connections.

The Stromberg-Carlson APH-1030 Tube Amplifier is a vintage piece with a classic design and powerful 30W output, perfect for guitarists looking to add a unique sound to their amp. This vintage amplifier allows for a guitar amp conversion, making it versatile for various musical styles. With the reputable Stromberg-Carlson brand name and tube technology, this amplifier delivers warm and rich tones that are highly sought after by musicians and collectors alike.

Vintage Grommes Precision 20PATube Amp – Converted for Guitar or Harmonica. This Precision 20PA amplifier has been professionally restored and converted to a Guitar/Harp amplifier by Mad Daddy Amps. This really cool vivid red vintage amp is unique amont these vintage PA Tube amps. The Precision 20PA model offers early break up with rich harmonics and is perfect for musicians looking for a vintage sound with modern reliability. This amplifier is ideal for professionals and enthusiasts seeking a classic audio experience with top-notch build quality. It sports 2-6BQ5 tubes providing 10-17 watts of power for that early British toned, perfect as a studio amp or performing in small venues. There is a clean and dirty input which allows for clean or dirty sound for use with harp or guitar at most volume levels. Features 4, 8, and 16 ohm speaker outputs. Mad Daddy is one guy, Carl, based in Medina, Ohio. He was an electrical engineer for 50 years and in the 60′s worked on torpedo guidance systems. He’s also a guitar guy that enjoys building and rebuilding amps. He has a few signature pieces such as his Pure Daddy Combo, a skillfully reconfigured EVJ chassis and cabinet with a hand wired point to point Champ circuit. He also is extremely skilled at rebuilding vintage PA amps like this one, voiced for guitar and/or harp. Carl will also take special orders to modify or repair your amp or revoice it for your individual needs. If any of the amps we modify come to us with death caps, they are replaced with a safer circuit and all amps are outfitted with safer 3-prong electrical plugs. The new badge and labels placed on the amps are there for your convenience but are readily changed or removed at your discretion. We have other vintage amps we are working on but this is the only one of these we have. It’s unlikely we’ll find another, especially in this condition.

Working condition, see photos to view condition.

Bell Model 3725B Tube Amp.