Classic Dynaco and Heathkit Amplifiers: The Budget Audiophiler

Written By: 
Jeremy Sikora
Tags: 
Share:
  •  
Photo by Eric Pye (Audio Love YYC)

Looking for a classic vintage power amplifier? The Dynaco ST-70 needs to be on your radar if you crave that classic EL34 tube sound.

Not all vintage buys are wins. I hate to burst that bubble with this week’s installment, but it needs to be said. Now that I’ve had a few years to try a lot of vintage equipment, restore it, and experiment with a lot of amplifiers, turntables, CD players, and loudspeakers – I’ve discovered more than a few dogs along the way. None of that diminishes the excitement I get from the equipment that has taken up permanent residence in my systems at home, but reality bites sometimes. 

Two companies that have recently struck my interest are Dynaco and Heathkit; specifically their homebuilt kits which to some degree you can still buy. DIY amps, receivers, and audio scopes were not uncommon in the 1960s and 1970s. There is certainly a cult of people in the vintage audio community who love both brands; I’ve noticed that a number of high-end audio dealers have a constant flow of Dynaco ST-70 power amplifiers available for sale at really high prices so there must be some demand for it. 

Heathkit and Dynaco sold products that featured quality components, detailed instructions and could be completed over the course of a few days with decent soldering skills and patience.

The products were available factory-assembled, but what made all of these specific pieces unique was that they were mostly assembled by hobbyists. Some of these people were quite skilled and knew what they were doing. The finished product could be excellent, or really terrible if the person made serious mistakes. 

This week, I’m going to dig a little deeper into my own personal experience with two Dynaco and two Heathkit models that I purchased. The results varied from excellent to horrific nightmare worse than the 4 consecutive Super Bowl losses by my beloved Buffalo Bills in the 1990s. 

Damn you Scotty Norwood.

Dynakit Stereo 70

The Dynaco Story  

Dynaco was formed in 1955 by Ed Laurent and David Hafler in Philadelphia, and the brand quickly became popular for its affordable and wide range of audio components. The ST-70 stereo tube amplifier was its most popular component; Dynaco sold more than 350,000 units before the brand was liquidated in 1980. 

David Hafler had become popular in the Hi-Fi world in the 1950s with his brand, Acrosound. The company had developed high-quality output transformers for use with DIY home electronics and when Hafler moved on and formed the new company with Laurent, they realized that there was a big market for build-it-yourself kits. 

The Stereo 70 (ST-70) was Introduced in 1959 and was available as a kit (Dynakit) intended for assembly by the purchaser or as a complete factory-wired unit. The ST-70 used four EL34 output tubes, one GZ34/5AR4 rectifier tube, two 7199 input (driver) tubes, two output transformers, one power transformer, and a preassembled printed circuit board (PCB) containing the driver circuit. The power output was 35 watts/channel.

My journey with the ST-70 started off without a lot of drama; my wife located one that was for sale at a record store in Vermont and we made the trip for New York to take a look. What gave me confidence was that it was the personal unit of the shop owner and he knew everything about it and it’s always reassuring to have the history of a piece of vintage audio equipment before you open up the wallet. 

After we agreed on a price, he packed it up really well for our journey back to Buffalo, where it now resides at the home of our neighbor. He has helped me with a number of vintage audio projects, and it seemed like the best way for both of us to enjoy the product. The vintage audio community really has a different attitude in regard to trying products out. 

Since the purchase, the RCA plugs have be updated and the small hum it developed was remedied by placing it on a book or some vibration isolators. DIY indeed. 

The 35 watts/channel power rating gives one some latitude with loudspeakers; I’ve mated it successfully with every bookshelf loudspeaker I’ve tried with it and it’s a workhorse of an amplifier.

The overall tonal balance is quite warm, and I love the powerful presentation that it can deliver with the right pair of loudspeakers. The EL34 is one of my favorite output tubes; for both its tone and the availability of tubes (both new and NOS) from dealers online. 

I can recommend the ST-70 with the one caveat that you really need to understand the owner/builder and learn as much history as you can about the specific sample that you find. None of the tubes are very expensive to replace, but you don’t want to get into the business of buying new output transformers when you’re spending a decent amount of money on this kind of amplifier. 

Parts are readily available from a number of online dealers so you’re never going to be left out in the woods with the ST-70. The amplifier is a really a great looking piece of equipment and an iconic piece of audio equipment. 

The Mistake

Another Dynaco amplifier that I purchased was the STA-120. It has a similar case like the ST-70, but that’s where the similarities end. The STA-120 is a 60 watts/channel solid state amplifier, which was rather powerful for the period. I had read numerous very positive reviews of this amplifier, so I made the decision to purchase one without any hesitation. 

Dynaco STA-120 Stereo Preamplifier

When I got home and connected the amplifier to the rest of my system, I was somewhat shocked by the differences between the two amplifiers. I was very puzzled by its sonic presentation; cold and distant and nothing changed when I increased the volume level. 

I wondered if I had created a mismatch between the power amplifier and the pre-amp, so I began trying other preamplifiers and loudspeakers. Nothing improved. In some cases, the changes made the amplifier sound even worse, and I could barely get through a few songs before turning everything off.

I conducted a more thorough examination of the amplifier and did some more research online. What I discovered made me feel that I had wasted money on an amplifier that could be restored and modified with some rather expensive parts but that I was not really listening to a Dynaco STA-120 at that point. This was definitely a huge miss. Not an amplifier that I could recommend. 

Heathkit

Heathkit have been around since the 1920s and are still making kits available for sale. 

They sold just about every type of electric/electronic kit that you can think of for you to build; their radio kits being the most popular. In the 1960s, they sold tube amplifier kits like the AA-100 which looked and sounded great – but only if the hobbyist knew what they were doing. 

Heathkit Transistor Stereo Amplifier

I found a model AA-21D transistor amplifier and purchased it just because of the industrial design. It reminded me of a ‘60s car dashboard and it was a very clean example.

When it arrived in the mail, I was impressed by the level of packaging. The previous owner clearly wanted it to arrive in perfect working condition and without any dents or new scratches.

The power button (hidden behind the logo) was quite clever, and I became very excited to use the amplifier.

All the “dashboard lights” came on but that was it. No sound, not even white noise. I opened up the case and checked the usual suspects. I discovered the issue rather quickly. This unit was designed with a handful of self-resetting glass breakers. 

They were advanced technology a few decades ago (apparently), but every single one was broken inside the unit. I also discovered that replacements were not that easy to locate. The Heathkit has in the repair shop for 6 months. This product earns a “miss” at this point. 

I was a little depressed after misstep. You want a vintage component to work out but it’s never a good scenario when it’s DOA. 

But did I swear off Heathkit for life after this disappointing experience? 

Nope. I’m a curious type of person and there was another Heathkit product that I really wanted to find. 

Heathkit Audio Scope Front with instructions

After seeing an audio scope for the first time, I was hooked. I needed one. The “Holy Grail” of audio scopes is the Pioneer SD-1100; a rare component that is prized for its beautiful silver front faceplate, audio oscilloscope, and VU meters. A non-functioning sample of this product fetches more than my audio budget allows. 

Much to my delight, I discovered the Heathkit Model AD-1013. In a moment of pure madness, I purchased two samples that came with the original build manuals. The price was right, and I hedged my bets that at least one model would work properly with some restoration.

Karma is a thing. Sharing with others in the community must have earned me some luck because the first unit worked perfectly, and the second unit only required a replacement CRT tube that I was able to source on eBay for a reasonable price. 

These audio scopes allow you to troubleshoot L/R channels which is extremely helpful when testing vintage equipment. What I use the most is the “stereo” setting which allows you to see (not just hear) the channel separation. It’s neat to see a well-engineered and produced track on the scope — and easy to see one that isn’t. If you already own or want an audio scope, you need to check out the rather interesting “Audioscope” music being created by Jerobeam Fenderson

Both of these brands offer some great value in the vintage audio category, but you really need to do your homework and ask the right questions. The Dynaco ST 70 is a very special audio component that can work in a lot of new systems; not just the vintage variety. Partner this amplifier up with a good pre-amplifier and it delivers so much presence and gestalt with music. If you can find one in perfect shape and you have the right loudspeakers – a very smart purchase. 



This article originally appeared at ecoustics.com and has been published here with permission.

Related Articles

Sort By
12th Isle
2 Tone
2020
2022
2023
33rpm
45rpm
4AD
5 Selects
5 Seletcs
7"
99 Records
A&M
Abbey Lincoln
Aboriginal
Abstract
Ace Tone
Acid
Acid Archives
Acid Folk
Acid House
Acid Mt. Fuji
Acid Punk
Acid rock
Acid Techno
Acoustic
Adrian Sherwood
ADS
Advent
Africa
African
Afro
Afro House
Afro-Cuban
Afrobeat
Alan Braufman
Alan Ginsberg
Alan Greenberg
Alan Thicke
Albert Ayler
Album Cover
Alejandro Cohen
Alex Patterson
Alice Coltrane
All Genre
Altec
Alternative Rock
Amaro Freitas
Amazon Music
Ambient
Ambient Jazz
ambient techno
American Primitive
Amoeba Music
Amplifier
Analog
Anatolian Rock
Andrew Weatherall
Andy Warhol
Anenon
Animal
Animation
Anna Butterss
Antonio Zepeda
AOR
Aphex Twin
Aquarium Drunkard
Archie Shepp
Archival
Armenia
Art
Art & Design
Art Dudley
Art Film
Art Pop
Art Rock
Artform Radio
Arthur Russell
Article
Arvo Part
Ash Ra Temple
Asian Underground
Audio Note
Audiogon
Audiophile
Audiovisual
Austin Peralta
Australia
Autechre
avant
Avant-Garde
Avant-pop
Avant-Rock
Avent-Garde
Balearic
Bali
Ballad
Bargain Bin
Bark Psychosis
Baroque
Baroque Pop
Basquiat
Bass
Bauhaus
Bayou Funk
BBC
BBC Radiophonic
Be With Records
Beat Scene
Beats
Beats in Space
Beaumont Hannant
Bebop
Belgium
Ben UFO
Bennie Maupin
Berlin-school
Best of 2020
Beverly Glenn​-​Copeland
Bhutan Stamps
Big Band
Bill Laswell
Black Ark Studios
Black Jazz
Blaxsploitation
Blood & Fire
Blue Note
Blues
Blues Rock
Bob Marley
Bola Sete
Bollywood
Boogie
Book
books
Boom Bap
Boredoms
Bossa
Bossa Nova
Boymerang
Brainfeeder
Brazil
Brazilian Folk
Breakbeat
Breezy
Brian Eno
Broadcast
Bruce Weber
Bruton Music
Buddhism
Budget Audiophiler
Cabaret
Calypso
Cambridge Audio
CAN
Candombe
Cannanes
Canterbury
Cape Jazz
Cape Verde
Caribbean
Carla Bley
Cartridges
Casio
Cassette
Cats
CD
Celluloid
Celtic
Chamber Jazz
Chamber Music
Chamber Pop
Chan Marshall
Channel One Studios
Chanson
Charles Lloyd
Charles Mingus
Chee Shimizu
Chet Baker
Chicago
Chicha
Chillout
China
Chinese
Chiptune
Choral
Christmas
City Pop
Classic Album Sundays
Classical
Classics
Clicks & Cuts
Clothing
Club
Cocteau Twins
Coctueau Twins
Coffee
Coldwave
Colorfield
Comedy
Commercial
Community
Compass
Compass Point
Compilation
Concept Album
Condesa Electronics
Conlon Nancarrow
Conny Plank
Contemporary Jazz
Cool Jazz
Cornelius
Cosmic
Cosmic Disco
Cosmic Folk
cosmic jazz
Country
Country Pop
Country-Rock
Covers
Cult Classic
Cumbia
DAC
Dacne
Daedalus
Daft Punk
Dan Greene
Dance
Dance Music
Dancehall
Daniel Aged
Dark
Dark Ambient
Dark Entries
David Behrman
David Bowie
David Byrne
David Sylvian
Davida
Dedicated listening session
Deep Dive
Deep House
Deep Listen
Deep Listening
Delia Derbyshire
Dembow
Demo
Dennis Bovell
Denon
Detroit
Devotional
DFA
Diabate
Diasporic Disco
Dick Verdult
Diggin in the Mags
Digi-Reggae
Disco
Discogs
DIY
DIY / Amateur
DJ
DJ Shadow
Documentary
Dogs
Don Buchla
Don Cherry
Donald Byrd
Doom Metal
Dou Wei
Downtempo
Dowtempo
Dr. John
Dream House
Dream Pop
Dreamy
Drone
Drum & Bass
Drum Break
Drum Machine
Drum n Bass
Drums
Dual
Dub
Dub Poetry
Dub Techno
dublab
Dubstep
Dubwise
Durutti Column
Düsseldorf School
Dust and Grooves
Dynaco
Eames
Earl King
Early Electronic
East African
Easy Listening
Eblen Macari
EBM
ECM
ecoustic
ecoustics
Eiko Ishibashi
Electric Lady
Electro
Electronic
Electronic Jazz
Electronica
Elegant Pop
Elvin Jones
Emahoy Tsegué-Maryam
Enossified
Environmental Music
EOY
Eric Dolphy
ESG
Esoteric
ESP Institute
Essential Listen
Essential Listening
Essential Listenning
Ethereal
Ethiopian Jazz
Ethnic
Ethno-Jazz
Event
Events
Exit to Vintage Street
Exotica
Experimental
Factory Records
Faye Wong
Feel Good All Over
Fela Kuti
Fennesz
Festival
Field recording
Films
Fingertracks
Fingetracks
Fishing with John
Fleetwood Sound Company
Floating
Floating Points
Folk
Folk Funk
Folk-Rock
Fonts
Footwork
Force Inc.
Four Tet
Fourth World
France
Frankie Knuckles
Free Improvisation
Free Jazz
Friends of ISC
Frippertronics
Frozen Section Radio
Fundraiser
Funk
Fusion
G-Funk
G.S. Schray
Gal Costa
Gamelan
Garage Rock
Garrard
Gems from the Dollar Bin
Geographic North
George Duke
George Martin
George Oban
German techno
Gifts
Gilberto Gil
Giorgio Moroder
Glam Rock
Glitch
Gogo
Gospel
Grado
Graham Sutton
Graphic Novel
Grateful Dead
Group Sounds
Growing Bin
Guide
Guitar
Gwo Ka
Gypsy
Habitat Ensemble
Haçienda Club
halloween
Hard Bop
Hard Rock
Harold Budd
Harp
Harry Nilsson
Haruomi Hosono
Hawaii
headphones
Heavy Metal
Henry Lewy
Herbie Hancock
hi-fi
hi-NRG
Hidden Gem
Highlife
Hip Hop
Hip-Hop
Hiroshi Yoshimura
history
Holger Czukay
Holiday
Hollywood
Holy Grail
Home Listening
Home Theater
House
Human Head
Hypnotic
Iasos
Ibiza
IDM
Illbient
Illustration
Improvisation
Impulse!
In Conversation
In Stock
India
Indian
Indian Classical
Indian Raga
Indie
Indie Rock
Indigenous music
Industrial
Ingmar Bergman
Installation
instock
Instrumental
International
International Anthem
Interview
Irish folk
ISC Classic
ISC Collection
isc guide
ISC NYC
ISC Record Store
ISC Selects
Island Records
Isolation
Italo Disco
Italo House
Italy
Jackie McLean
Jah Shaka
Jamaica
James Baldwin
Jangle Pop
Japan
Japananese
Japanese
Jazz
jazz funk
Jazz is Dead
jazz kissa
Jazz-funk
Jazz-rock
JBL
Jeff Parker
Jessica Pratt
John Coltrane
John Fahey
John Martyn
John Peel
Jon Hassell
Joni Mitchell
Judee Sill
Jungle
K-pop
K. Leimer
Kankyo Ongaku
KEF
Keiji Haino
Keith Haring
Keith Jarrett
Kid-Friendly
Kim Yaffa
Kitty Records
Klaus Schulze
KLH
Klipsch
Kompakt
Kora
Kosmiche
Kosmische
KPM
Kraftwerk
Kranky
Krautrock
Kruatrock
Kuduro
kwaito
L.Shankar
La Monte Young
Labels We Love
Lafawndah
Laraaji
Larry Levan
Last Resort
Laswell
Latin
Latin Jazz
Laurel Canyon
Laurie Spiegel
Leaving Records
Lebanese
Lee Scratch Perry
Left-field
Leftfield
Lena Horne
Les Baxter
Lester Bowie
Library
Library Music
Lijadu Sisters
Liquid Liquid
Listening
Listening bar
Listening Party
listening room
Listening Session
Live Performance
Live Recording
Live Video
Lo-Fi
Loose Ends
Loren Mazzacane Connors
Los Angeles
Lost & Sound
lost and sound
Louisiana Blues
Lounge
Lounge Lizards
Love Songs
Lovefingers
Lovely Music Ltd.
Lovers Rock
Luaka Bop
Mad Professor
Magazine
Mali
Mandopop
Marantz
Marcel Duchamp
Marcella Cytrynowicz
Marcos Valle
Mark E. Smith
mbaqanga
McCoy Tyner
McIntosh
Media
Meditation
Meditational
Meditative
Melancholic
Mellow
Melody As Truth
Meredith Monk
Metal
Mexico
Miami
Michael Franks
Microhouse
Mid-Century
Miles Davis
Milford Graves
Mille Plateaux
Mills College
Minako Yoshida
Minimal
Minimal Synth
Minimal Techno
Minimal Wave
Minneapolis Sound
Mixes
Mixtape
Mizell Brothers
mo wax
Mobile Fidelity Sound Labs
Modal
Modern Classical
Modern Soul
Modular Synthesis
Moki Cherry
Mono
Mood Hut
Mort Garson
Motion Ward
Motown
MPB
MTV
Munich
Music Blog
Music from Memory
Music Interior
Music Therapy
Music Video
Musique Concrète
Mute
Mwandishi
NAD
Narrative
Neapolitan
Neneh Cherry
Neo Soul
Neo-Classical
Neptunes
New Age
New Islands
New Jack Swing
New Music
New Orleans
New Wave
New York
News
Nico
Nigeria
Nightmares on Wax
Nina Simone
No Wave
Noise
Non-Profit
Northern Soul
Now Sound
NTS
Nubian Pop
Nubian Soul
Numero Group
NYC
OBI
Obscure
Obscure Sound
Occult
On Screen
On-U Sound
online radio
Opal Records
Opera
Optimo
Organ
Organic
Organic Music
Ornette Coleman
Ortofon
OST
Oswalds Mill Audio
Outernational
Outsider Pop
Overtone Singing
Painting
Painting with John
Pan Sonic
Pandit Pran Nath
Paradise Garage
Pastoral
Pat Metheny
Patrick Cowley
Patrick Shiroishi
Paul Horn
Paul McCartney
Pauline Oliveros
PBS
Penguin Cafe Orchestra
Pensive
Percussion
Peru
Pharoah Sanders
Phillip Glass
Philly Soul
Piano
Pioneer
Pioneer Works
Plantasia
Plants
Player Piano
playlist
Playlists
Plinth
Podcast
Poetry
Political
Polygonia
Pop
Pop Art
Pop not Slop
Pop Rock
Popp
Popul Vuh
Post Bop
Post Rock
Post-Punk
Post-Rock
Power Pop
Premiere
Prince
Private Press
Pro-Ject
Producer
Productions
Professor Longhair
Prog Rock
Progressive
Progressive Rock
Prophet-5
Proto-techno
Psych-folk
Psychedelic
Psychedelic Rock
Psychic Hotline
Psyhedelic
Punk
Qobuz
Quadraphonic
QUARK
Quiet Storm
R&B
Radio
Raga
Ragas
Rap
Rare Groove
Ras G
Rave
rca victor
Receivers
Record Club
Record Fair
Record Store
Record Store Day
Record Stores
Record Stores We Love
Record Stories
Reggae
Reggaeton
Reissue
Reissues
Releases
Religious
Remix
Retrospective
Robert Wyatt
Roberto Musci
Robin Guthrie
Rock
Rocksteady
Roland
Roland Kirk
Rolando Chía
Roller Skate
Room Recordings
Room Treatment
Roots Reggae
Rotary Mixers
Rough Trade
Rudy Van Gelder
Russia
Ryuichi Sakamoto
Ryuichi Sakmoto
Sacred
Sade
Saint Etienne
Sam Gendel
Samba
Sample
Samples
San Francisco
Sawako
Saxophone
Sci-fi
Séance Centre
Seefeel
Sensual
Serbian Disco
Shackleton
Shamisen
share
Shibuya-kei
Shoegaze
Silver Apples
Simeon Coxe
Simon Reynolds
Singer-Songwriter
Sisters with Transistors
Ska
Sly & Robbie
Smooth Jazz
Soft Rock
Solid State
Songwriting
Sonia Pottinger
Sonny Sharrock
Soul
Soul-Funk
Soul-jazz
Sound & Vision
Sound Art
Sound Collage
Sound Installation
Soundsystems
Soundtrack
South Africa
South African
South America
Southern Soul
Space Rock
Spain
Speaker
speakers
Spiritual
Spiritual Jazz
Spoken Word
Squama Records
Staff Picks
Steely Dan
Stereolab
Stereophile
Steve Guttenberg
Steve Roach
Steven Halpern
Stevie Wonder
Stina Nordenstam
Stoner Rock
stores we love
Stories
Streaming
Street Soul
Strut Records
Studio One
Substack
Sugar Plant
Sun Ra
Sunn O)))
Supergroup
Surround Sound
Susumu Yokota
Suzanne Cianni
Suzanne Kraft
Suzanne Langille
Swamp Rock
Sweetback
SYNG
Synth
Synth Pop
Synth-pop
Synthesizer
Synthwave
Taarab
Tadanori Yokoo
Takoma Records
Tangerine Dream
Tannoy
Tape
Tapes
TD-160
Technics
Techno
Techno Pop
Tel Aviv
Television
Terry Callier
Terry Riley
The Armed
The Beatles
The Books
The Broad
The Fall
The Loft
The Meters
The Mizell Brothers
The Music Center
The Orb
The World Stage
Theater
Thelonious Monk
Third Side Music
Third Stream
This Mortal Coil
Thomas Fehlman
Thorens
Tim Sweeney
Time Capsule
Todd Rundgren
Tonto
Tony Wolski
Too Pure Records
Total Luxury Spa
Traditional
Tribal
Tribe
Trip-hop
Trish Keenan
Tropical
Tropicalia
Tuareg
Tube
Turntable
Turntable Lab
TV
UK
UK Jazz
Ultramarine
Underground Resistance
Underrated
Val Wilmer
Vandersteen
Vangelis
Vanity Fair
Varia Instruments
Velvet Underground
Vice
Video
Video Art
Vince Guaraldi
Vintage
Vintage Audio
Vintage Gear
vinyl
Virginia Astley
Visible Cloaks
Visual Art
Vocal
Vocal Jazz
Vocoder
Wackies
Wah Wah Watson
Walearic
Wally Badarou
Warp
Water
Website
Wendy Carlos
Werner Herzog
West Africa
West African
Western Acoustics
Windham Hill
wiring
World
Wrecking Crew
Yacht Rock
Yamaha
Yann Tomita
Yasuaki Shimizu
Yellow Magic Orchestra
Yma Sumac
YouTube
Yu Su
Yukihiro Takahashi
Zamrock
Zither