Bud OEL-20, 20 Meter 50 Watt Oscillator and Buffer Coil Used #1

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OEL-20

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Used

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Description

Description

Bud OEL-20, 20 Meter 50 Watt Oscillator and Buffer Coil Used #1

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The Bud OEL Series is a vintage line of plug-in oscillator and buffer coils manufactured by Bud Radio Inc. (Cleveland, Ohio) during the 1940s–1950s (documented as early as Bud's 1939 Parts Catalog No. 140). These were part of Bud's popular O-series inductors for amateur radio (ham) transmitters, specifically optimized for oscillator (crystal-controlled or VFO stages) and buffer (isolation/amplification/doubler) circuits in low-power HF setups.

The "OEL" designation stands for Oscillator End-Linked (fixed link at one end of the main coil, with no center tap on the main winding). This configuration suited triode or certain pentode oscillator/buffer stages where center-tapping wasn't required (contrast with OCL = center-linked/center-tapped, or OLS = adjustable/swinging center link). They were compact, high-Q designs for efficient RF performance and band-switching in homebrew or kit transmitters.Key Specifications

Power Handling: Rated for 50 watts input (conservative for oscillator/buffer use; suitable for CW or low-duty modulated operation—derate for phone/AM to avoid overheating or excessive dissipation).
Construction: Air-wound tinned copper wire on a glazed ceramic base/form with banana plugs (fits standard 5-prong tube sockets). Fixed end link (coupling coil at one end) for inductive coupling to antenna/grid circuits; windings cemented on acetate locking strips for stability; base elevates coil from chassis to reduce stray capacitance/losses.
Purpose: Band-changing in multi-band low-power transmitters (e.g., exciter stages before finals). High efficiency, low losses; plug-in socket mounting for quick swaps.
Tuning Data (from 1939 Bud catalog; capacity is total required to resonate at low end of band with typical variable capacitor):
- Lower bands need higher capacitance due to larger inductance.

Known Models in the OEL SeriesFrom Bud catalogs (e.g., 1939 No. 140), Walter Ashe 1955 listings, Radiomuseum.org, eBay/surplus sales, and ham archives:

OEL-160 (or OEL-160-A) — 160-meter band (1.8–2.0 MHz); ~90 mmfd capacity.
OEL-80 — 80-meter band (3.5–4.0 MHz); ~75 mmfd capacity.
OEL-40 — 40-meter band (7.0–7.3 MHz); ~50 mmfd capacity (most common survivor).
OEL-20 (or OEL-20-A) — 20-meter band (14 MHz); ~33 mmfd capacity.
OEL-10 — 10-meter band (28–29.7 MHz); ~28 mmfd capacity.
OEL-5 — 5-meter band (VHF, ~50–54 MHz era); ~18 mmfd capacity (rarer).

Higher bands (e.g., 15m) may exist as variants but are less documented.Related Bud O-Series for Comparison

OCL — Center-linked, center-tapped main winding (~50W).
OLS — Adjustable/swinging center link (~50W).
OCP — Pentode-specific, fixed link (~75W).
OES — Adjustable/swinging end link (~75W).
Some later variants (e.g., OEL-xx-A) rated up to 75W with minor design tweaks.