---
product_id: 8370037
title: "Enterprises Original MFJ-557 Deluxe Morse Code Practice Oscillator Straight Key w/Volume Control"
brand: "mfj"
price: "€ 189.93"
currency: EUR
in_stock: true
reviews_count: 13
category: "Mfj"
url: https://www.desertcart.at/products/8370037-enterprises-original-mfj-557-deluxe-morse-code-practice-oscillator-straight
store_origin: AT
region: Austria
---

# Dual power: 9V battery or 110VAC Heavy steel non-skid base Adjustable volume & tone control Enterprises Original MFJ-557 Deluxe Morse Code Practice Oscillator Straight Key w/Volume Control

**Brand:** mfj
**Price:** € 189.93
**Availability:** ✅ In Stock

## Summary

> 📡 Master Morse Code Like a Pro — Wherever You Are!

## Quick Answers

- **What is this?** Enterprises Original MFJ-557 Deluxe Morse Code Practice Oscillator Straight Key w/Volume Control by mfj
- **How much does it cost?** € 189.93 with free shipping
- **Is it available?** Yes, in stock and ready to ship
- **Where can I buy it?** [www.desertcart.at](https://www.desertcart.at/products/8370037-enterprises-original-mfj-557-deluxe-morse-code-practice-oscillator-straight)

## Best For

- mfj enthusiasts

## Why This Product

- Trusted mfj brand quality
- Free international shipping included
- Worldwide delivery with tracking
- 15-day hassle-free returns

## Key Features

- • **Precision Control:** Fine-tune volume and tone for discreet or classroom-level practice
- • **Trusted Durability:** Backed by MFJ’s famous 1-year No Matter What warranty
- • **Rock-Solid Stability:** Heavy steel base keeps your key steady for flawless sending
- • **Private or Public Use:** Earphone jack for silent practice, external speaker for group sessions
- • **Practice Anywhere, Anytime:** Compact & portable design fits your on-the-go lifestyle

## Overview

The MFJ-557 Deluxe Morse Code Practice Oscillator is a portable, versatile training tool featuring a heavy steel non-skid base, adjustable volume and tone controls, and dual power options (9V battery or 110VAC). Designed for both private and group practice, it includes an earphone jack and external speaker capability. Compact and durable, it comes with MFJ’s industry-leading 1-year No Matter What warranty, making it the go-to choice for serious CW enthusiasts and professionals sharpening their skills.

## Description

The MFJ-557 Deluxe Morse Code Practice Oscillator features a Morse Code straight key on a non-skid heavy steel base -- it stays put on table and doesnt move around while you're sending! The MFJ-557 lets you practice sending code at home, work, riding in your car -- practically anywhere -- because its so easy to take it wherever you go. Volume control adjusts from barely audible to blaring full sound. You can practice without bothering anyone. Tone control gives you a wide adjustment from high "squeaky" to low "booming" tones. You even get an earphone jack for private listening. You can plug in an external speaker for super high volume in the classroom. When you're finished cleaning up your sloppy fist with the MFJ-557, hook up the straight key to your transmitter and go on-the-air sounding like you were born working QSOs. Don't pass up this super CW buy! The MFJ-557 also has a built-in speaker and adjustable contacts. The MFJ-557 Deluxe Morse Code Practice Oscillator runs on a 9 volt battery (not included) or 110 VAC. It measures 8 1/2 x 2 1/4 x 3 3/4 inches. It comes with MFJs famous one year No Matter What warranty.

Review: A Cool Tool - It's a great learning tool. You can use it as a keyer-only if you disconnect the wires. There are adjustment screws for pressure and gap. Battery use is adequate but it seems to wear down fast; sound is more robust if you use the adaptor. There is a somewhat annoying "pucker" sound when releasing the key each time, probably related to the speaker quality. Using an external one seems to eliminate that. I keep this on the end table next to the chair and tap out any words I see on the TV screen, almost obsessively. I heartily recommend this!
Review: A good product made by good people. - I miss the days when someone could walk in to any Radio Shack and buy a solid brass key for $6.95, BUT those days are gone :-( and I have to get used to it. This is a nice little straight key on a solid, heavy base, and I like having the oscillator to practice CW in the car (yes, I'm that nuts) when I'm not making actual contacts. About that, it's quite easy to modify this unit to quickly switch between practice and sending, mine has a 1/4" jack in the side for the transmitter, the kind that breaks tip connection when you plug in but if you've read this far you know what to do :-) Sorry MFJ, guess my warranty is void. And about MFJ, they are one of the best known and highest quality manufacturers in the business, well known and loved by many in the amateur radio world. Check out their guarantee. Before I sign off, one important warning: And I ain't pointing fingers, I'm just sayin. If you're planning to buy radio equipment, or ANY equipment for that matter, through desertcart or eBay or craigslist or a classified ad in the newspaper, do yourself a favor and view or download a catalog from the manufacturer (you can download the entire MFJ catalog from their website) or a reliable reseller (GigaParts, Ham City, etc.) to ensure that the price is in the right ballpark and the warranties etc are intact. Cause somebody might, hypothetically, buy this unit for $50 and try to sell it to you for $150. I'm just sayin. Cheers!

## Features

- The MFJ-557 Deluxe Morse Code Practice Oscillator runs on a 9 volt battery (not included) or 110 VAC. It measures 8 1/2 x 2 1/4 x 3 3/4 inches. It comes with MFJs famous one year No Matter What warranty.

## Technical Specifications

| Specification | Value |
|---------------|-------|
| ASIN | B00OAHNA10 |
| Best Sellers Rank | #291,706 in Industrial & Scientific ( See Top 100 in Industrial & Scientific ) #35 in Industrial Electrical Oscillators |
| Blade Material | Plastic |
| Brand | MFJ |
| Brand Name | MFJ |
| Color | Black |
| Connector Type | Standard AC Power Plug |
| Control Method | Touch |
| Controller Type | Button Control |
| Customer Reviews | 4.2 out of 5 stars 376 Reviews |
| Electric Fan Design | Blower |
| Electric fan design | Blower |
| Finish Type | Metallic |
| Indoor Outdoor Usage | Indoor |
| Item Dimensions D x W x H | 3.75"D x 8.5"W x 2.25"H |
| Item Weight | 1.3 pounds |
| Manufacturer | MFJ |
| Material | Alloy Steel |
| Model Name | MFJ-557 |
| Model Number | MFJ-557 |
| Mounting Type | Floor Mount |
| Number of Blades | 3 |
| Number of Speeds | 3 |
| Part Number | MFJ-557 |
| Power Source | DC or Battery |
| Product Dimensions | 3.75"D x 8.5"W x 2.25"H |
| Room Type | Classroom |
| Size | Medium |
| Special Features | Portable |
| Style | Modern |
| UPC | 744288052305 796793893676 702646177954 757183018185 |
| Unit Count | 1 Count |
| Voltage | 9 volts |

## Product Details

- **Brand:** MFJ
- **Color:** Black
- **Controller Type:** Button Control
- **Electric fan design:** Blower
- **Mounting Type:** Floor Mount
- **Power Source:** DC or Battery
- **Product Dimensions:** 3.75"D x 8.5"W x 2.25"H
- **Room Type:** Classroom
- **Special Feature:** Portable
- **Style:** Modern

## Images

![Enterprises Original MFJ-557 Deluxe Morse Code Practice Oscillator Straight Key w/Volume Control - Image 1](https://m.media-amazon.com/images/I/71CSErlhoRL.jpg)
![Enterprises Original MFJ-557 Deluxe Morse Code Practice Oscillator Straight Key w/Volume Control - Image 2](https://m.media-amazon.com/images/I/71AR8HeZlyL.jpg)
![Enterprises Original MFJ-557 Deluxe Morse Code Practice Oscillator Straight Key w/Volume Control - Image 3](https://m.media-amazon.com/images/I/81qnbfVlryL.jpg)
![Enterprises Original MFJ-557 Deluxe Morse Code Practice Oscillator Straight Key w/Volume Control - Image 4](https://m.media-amazon.com/images/I/819mwLtjgTL.jpg)
![Enterprises Original MFJ-557 Deluxe Morse Code Practice Oscillator Straight Key w/Volume Control - Image 5](https://m.media-amazon.com/images/I/71GbGfy53KL.jpg)

## Questions & Answers

**Q: It says practice machine; can it be used in real life applications? If not would you recommend a unit that would?**
A: The key can be removed from the practice oscillator base, and hooked up to most CW transceiver / transmitters for real world applications after you are done using it for audible practice .

**Q: can you hook  paddles up instead of the straight key ?**
A: You can not. Paddles need additional intelligence and an additional circuit that will send dots or dashes when you move the paddles right or left. This is essentially like the buzzer on a door...as long as you press it buzzes, when you stop it stops.

**Q: Can this transmit**
A: Yes, you could transmit with it, but straight keys are so cheap why not just buy another one.

**Q: can you wire this to a radio**
A: Dear Writer, 10x 4 msg. You can do if your radio has MORSE key wire's input (not morse key speaker input). Simply un-screw two wires which connects to morse key from inbuilt MFJ device then connect radio's morse key wires. Have a g8t day. 73. Mayank Gupta (VU3MFT)

## Customer Reviews

### ⭐⭐⭐⭐⭐ A Cool Tool
*by O***H on January 2, 2026*

It's a great learning tool. You can use it as a keyer-only if you disconnect the wires. There are adjustment screws for pressure and gap. Battery use is adequate but it seems to wear down fast; sound is more robust if you use the adaptor. There is a somewhat annoying "pucker" sound when releasing the key each time, probably related to the speaker quality. Using an external one seems to eliminate that. I keep this on the end table next to the chair and tap out any words I see on the TV screen, almost obsessively. I heartily recommend this!

### ⭐⭐⭐⭐⭐ A good product made by good people.
*by J***C on January 16, 2017*

I miss the days when someone could walk in to any Radio Shack and buy a solid brass key for $6.95, BUT those days are gone :-( and I have to get used to it. This is a nice little straight key on a solid, heavy base, and I like having the oscillator to practice CW in the car (yes, I'm that nuts) when I'm not making actual contacts. About that, it's quite easy to modify this unit to quickly switch between practice and sending, mine has a 1/4" jack in the side for the transmitter, the kind that breaks tip connection when you plug in but if you've read this far you know what to do :-) Sorry MFJ, guess my warranty is void. And about MFJ, they are one of the best known and highest quality manufacturers in the business, well known and loved by many in the amateur radio world. Check out their guarantee. Before I sign off, one important warning: And I ain't pointing fingers, I'm just sayin. If you're planning to buy radio equipment, or ANY equipment for that matter, through Amazon or eBay or craigslist or a classified ad in the newspaper, do yourself a favor and view or download a catalog from the manufacturer (you can download the entire MFJ catalog from their website) or a reliable reseller (GigaParts, Ham City, etc.) to ensure that the price is in the right ballpark and the warranties etc are intact. Cause somebody might, hypothetically, buy this unit for $50 and try to sell it to you for $150. I'm just sayin. Cheers!

### ⭐⭐⭐⭐ Great learning tool, internal build quality is pretty bad.
*by N***F on April 8, 2023*

I have learned a lot of CW in the short time that I've had the MFJ-557. I think being able to actually hear my morse as I pound it out on this has really helped me start taking off in my CW journey. That being said, I was pretty horified when I opened up the cover to put a 9 volt in it. Holy moly, it's an absolute mess of wires, hot glue, and tape. The speaker is held on by tape to the plastic housing... just so cheap lol. I mean, I paid 90 bucks for this, and to be honest I don't even think I would expect that kind of internal build quality from something even $50 bucks. Overall, I am enjoying it though.

## Frequently Bought Together

- MFJ Enterprises Original MFJ-557 Deluxe Morse Code Practice Oscillator Straight Key w/Volume Control
- Learn Morse Code - Easy Tutorial Workbook for Beginners: The Easiest Way to Study Morse - LISTEN to Morse Signals with QR Codes! Morse Practice Book for Kids Ages 8+ and Adults
- Morse Code Operating for Amateur Radio – Your Guide to Ham Radio’s First Language

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*Product available on Desertcart Austria*
*Store origin: AT*
*Last updated: 2026-08-22*