---
product_id: 8370037
title: "MFJ Enterprises Original MFJ-557 Deluxe Morse Code Practice Oscillator Straight Key w/Volume Control"
brand: "mfj"
price: "593641₫"
currency: VND
in_stock: false
reviews_count: 8
url: https://www.desertcart.vn/products/8370037-mfj-enterprises-original-mfj-557-deluxe-morse-code-practice-oscillator
store_origin: VN
region: Vietnam
---

# 110 VAC compatible Compact size 9V battery powered MFJ Enterprises Original MFJ-557 Deluxe Morse Code Practice Oscillator Straight Key w/Volume Control

**Brand:** mfj
**Price:** 593641₫
**Availability:** ❌ Out of Stock

## Summary

> 🔊 Unlock the Code to Communication Mastery!

## Quick Answers

- **What is this?** MFJ Enterprises Original MFJ-557 Deluxe Morse Code Practice Oscillator Straight Key w/Volume Control by mfj
- **How much does it cost?** 593641₫ with free shipping
- **Is it available?** Currently out of stock
- **Where can I buy it?** [www.desertcart.vn](https://www.desertcart.vn/products/8370037-mfj-enterprises-original-mfj-557-deluxe-morse-code-practice-oscillator)

## 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

- • **Compact Design:** Perfectly sized for any workspace or travel.
- • **Master Morse Code:** Elevate your communication skills with precision practice.
- • **Unmatched Warranty:** Enjoy peace of mind with our No Matter What guarantee.
- • **Versatile Power Options:** Choose between battery or AC for ultimate flexibility.
- • **User-Friendly Volume Control:** Tailor your practice experience to your preference.

## Overview

The MFJ-557 Deluxe Morse Code Practice Oscillator is a versatile training tool designed for both beginners and seasoned operators. It operates on a 9V battery or 110 VAC, making it ideal for home or on-the-go practice. With a compact size of 8 1/2 x 2 1/4 x 3 3/4 inches, it fits seamlessly into any environment. Plus, it comes with MFJ's renowned one-year No Matter What warranty, ensuring your investment is protected.

## Description

Deluxe Morse Code Practice Oscillator, Has Volume Control, Tone Control and a Built In Speaker. Built In Straight Key Can be Removed for Use On A Transmitter. Requires 1 Optional 9V Battery, also can be used with an Optional AC adapter too! ( 9v Battery or AC adapter not included).

## 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.

## Product Details

- **Brand:** MFJ
- **Color:** Black
- **Power Source:** Battery Powered, Corded Electric
- **Style:** Modern
- **Product Dimensions:** 3.75"D x 8.5"W x 2.25"H
- **Finish Type:** Metallic
- **Voltage:** 9 Volts
- **Item Weight:** 1.3 Pounds
- **Indoor/Outdoor Usage:** Indoor
- **Model Name:** MFJ-557

## Images

![MFJ 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)
![MFJ 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)
![MFJ 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)
![MFJ 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)
![MFJ 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 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!

### ⭐⭐⭐⭐ I love it, not I can practice CW.
*by K***. on April 27, 2024*

It’s a great product. Easy to instal the 9v battery and to make adjustments to the straight key, volume and tone knobs. The sound when keyed is great. The only reason I gave it a 4* is because the packaging was damaged. The MFJ-557 was not damaged. Not sure if it was packaged like this from the store or if it gotten damaged en route. But, I was worried when I took it out of the box and took pictures right away.I haven’t tested the ear jack yet, need to buy a set of headphones. I’ve just started learning CW so i’m not going to post a video. I think many would cringe. Yes, I would recommend this product.

### ⭐⭐⭐⭐⭐ Exactly What do You expect from a Training Tool?
*by R***T on September 18, 2017*

I've seen some of the other reviews for this product, and I frankly wonder if some of the negative reviewers suffer from OCD.This is a training tool, and not designed as a "true" straight key.Yes, it doesn't have adjustments for left-to-right alignment, but if the contacts are making contact, then who cares? If they are reallyfar off you could bend the ears holding the paddle to make them align better. (Whatever happened to HAM's modifying their equipment?)As far as the two adjustments that are critical, gap and pressure, you can tune this key to whatever you like. (Think light and light!!!)My initial irk with the unit was that even under battery power, the frequency would shift, which was kinda annoying to a former audioengineer. Then, listening to the radio and trying to decode CW, I found that what you heard would also shift, so now I count that as abonus, a sort of "this is what you could expect to hear" kinda thing.Once I learn the code, I plan on using this product in real-time until I can find a vintage straight key73's!

## 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 Vietnam*
*Store origin: VN*
*Last updated: 2026-02-26*