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
2020
33rpm
45rpm
4AD
5 Selects
7"
99 Records
A&M
Abbey Lincoln
Aboriginal
Abstract
Ace Tone
Acid
Acid Archives
Acid Folk
Acid House
Acid Punk
Acoustic
Adrian Sherwood
Africa
African
Afro
Afro-Cuban
Afrobeat
Alan Ginsberg
Alan Greenberg
Alan Thicke
Albert Ayler
Alice Coltrane
All Genre
Altec
Amazon Music
Ambient
Amoeba Music
Amplifier
Analog
Anatolian Rock
Andy Warhol
Animation
AOR
Aquarium Drunkard
Archie Shepp
Archival
Art
Art & Design
Art Dudley
Art Film
Art Pop
Art Rock
Artform Radio
Arthur Russell
Article
Ash Ra Temple
Audiogon
Audiophile
Audiovisual
avant
Avant-Garde
Avant-pop
Avant-Rock
Avent-Garde
Balearic
Bali
Ballad
Bargain Bin
Baroque
Baroque Pop
Basquiat
Bass
Bauhaus
Bayou Funk
BBC
BBC Radiophonic
Beats
Beats in Space
Bebop
Belgium
Bennie Maupin
Berlin-school
Best of 2020
Beverly Glenn​-​Copeland
Bhutan Stamps
Big Band
Bill Laswell
Black Ark Studios
Black Jazz
Blaxsploitation
Blue Note
Blues
Blues Rock
Bob Marley
Bola Sete
Bollywood
Boogie
books
Boredoms
Bossa
Bossa Nova
Brazil
Brazilian Folk
Breakbeat
Breezy
Brian Eno
Bruce Weber
Bruton Music
Buddhism
Budget Audiophiler
Cabaret
Calypso
CAN
Canterbury
Cape Verde
Caribbean
Cartridges
Casio
Cassette
Cats
CD
Chamber Music
Channel One Studios
Chanson
Charles Lloyd
Charles Mingus
Chee Shimizu
Chet Baker
Chicago
Chillout
Choral
Christmas
City Pop
Classic Album Sundays
Classical
Classics
Clothing
Coctueau Twins
Coffee
Commercial
Community
Compass Point
Compilation
Concept Album
Condesa Electronics
Conny Plank
Contemporary Jazz
Cornelius
Cosmic
Cosmic Disco
Cosmic Folk
Country
Country-Rock
Covers
Cult Classic
Cumbia
Daft Punk
Dance
Dancehall
Dark
Dark Entries
David Bowie
David Byrne
Davida
Deep Dive
Deep House
Deep Listening
Delia Derbyshire
Demo
Dennis Bovell
Denon
Detroit
Devotional
Diasporic Disco
Dick Verdult
Diggin in the Mags
Disco
Discogs
DIY
DIY / Amateur
DJ
Documentary
Don Buchla
Don Cherry
Donald Byrd
Doom Metal
Downtempo
Dowtempo
Dr. John
Dream House
Dream Pop
Dreamy
Drone
Drum Break
Drum Machine
Drum n Bass
Drums
Dual
Dub
Dub Poetry
dublab
Dubwise
Durutti Column
Düsseldorf School
Eames
Earl King
Early Electronic
East African
Easy Listening
EBM
ECM
ecoustic
ecoustics
Electric Lady
Electro
Electronic
Electronica
Elegant Pop
Emahoy Tsegué-Maryam
Enossified
Environmental Music
EOY
Eric Dolphy
ESG
Esoteric
ESP Institute
Essential Listen
Essential Listening
Essential Listenning
Ethereal
Ethiopian Jazz
Ethnic
Event
Events
Exotica
Experimental
Factory Records
Fela Kuti
Festival
Field recording
Films
Fingertracks
Fingetracks
Fishing with John
Fleetwood Sound Company
Floating
Floating Points
Folk
Folk-Rock
Fonts
Fourth World
France
Free Improvisation
Free Jazz
Friends of ISC
Frippertronics
Fundraiser
Funk
Fusion
G.S. Schray
Gal Costa
Gamelan
Garage Rock
Garrard
Gems from the Dollar Bin
George Martin
Gifts
Gilberto Gil
Glam Rock
Gogo
Gospel
Grado
Graphic Novel
Grateful Dead
Group Sounds
Guide
Guitar
Hard Bop
Harold Budd
Harp
Harry Nilsson
Haruomi Hosono
Heavy Metal
Henry Lewy
Herbie Hancock
hi-fi
hi-NRG
Hidden Gem
Highlife
Hip Hop
Hiroshi Yoshimura
history
Holger Czukay
Holiday
Hollywood
Holy Grail
Home Listening
House
Hypnotic
Iasos
Ibiza
IDM
Illustration
Improvisation
Impulse!
In Conversation
India
Indian
Indian Classical
Indie
Indie Rock
Industrial
Ingmar Bergman
Installation
Instrumental
International
Interview
ISC Classic
ISC Collection
isc guide
ISC Record Store
ISC Selects
Island Records
Isolation
Italo Disco
Italy
Jackie McLean
Jamaica
James Baldwin
Japan
Japananese
Japanese
Jazz
jazz kissa
Jazz-funk
Jazz-rock
JBL
John Fahey
John Martyn
Jon Hassell
Joni Mitchell
Judee Sill
Jungle
K. Leimer
Kankyo Ongaku
Keith Haring
Keith Jarrett
Kid-Friendly
Kitty Records
Klaus Schulze
Klipsch
Kompakt
Kosmiche
Kosmische
KPM
Kraftwerk
Krautrock
L.Shankar
La Monte Young
Labels We Love
Lafawndah
Lagniappe Sessions
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
Liquid Liquid
Listening bar
Live Performance
Live Recording
Los Angeles
Lost & Sound
lost and sound
Louisiana Blues
Lounge
Lounge Lizards
Love Songs
Lovefingers
Lovely Music Ltd.
Lovers Rock
Luaka Bop
Mad Professor
Marantz
Marcel Duchamp
Marcos Valle
mbaqanga
McIntosh
Meditation
Meditative
Melancholic
Mellow
Melody As Truth
Meredith Monk
Metal
Michael Franks
Mid-Century
Miles Davis
Milford Graves
Mills College
Minako Yoshida
Minimal
Minneapolis Sound
Mixes
Mixtape
Mizell Brothers
Mobile Fidelity Sound Labs
Modal
Modern Classical
Modern Soul
Modular Synthesis
Moki Cherry
Mono
Mort Garson
Motown
MPB
MTV
Munich
Music Blog
Music from Memory
Music Interior
Music Therapy
Music Video
Mwandishi
Narrative
Neptunes
New Age
New Music
New Wave
New York
News
Nico
Nina Simone
No Wave
Noise
Non-Profit
Northern Soul
Now Sound
NTS
Nubian Pop
Nubian Soul
Numero Group
NYC
OBI
Obscure
Obscure Sound
On Screen
On-U Sound
online radio
Opera
Organic
Organic Music
Ornette Coleman
Ortofon
Oswalds Mill Audio
Outsider Pop
Overtone Singing
Painting
Painting with John
Pandit Pran Nath
Paradise Garage
Pastoral
Patrick Cowley
Paul Horn
Paul McCartney
Pauline Oliveros
PBS
Penguin Cafe Orchestra
Pensive
Percussion
Pharoah Sanders
Phillip Glass
Piano
Pioneer
Plantasia
Plants
playlist
Playlists
Plinth
Podcast
Political
Pop
Pop not Slop
Pop Rock
Popul Vuh
Post Bop
Post Rock
Post-Punk
Post-Rock
Power Pop
Premiere
Prince
Private Press
Producer
Productions
Professor Longhair
Prog Rock
Progressive
Progressive Rock
Prophet-5
Proto-techno
Psychedelic
Psychedelic Rock
Psyhedelic
Punk
Qobuz
Quadraphonic
QUARK
Quiet Storm
R&B
Radio
Raga
Rare Groove
rca victor
Receivers
Record Fair
Record Label
Record Stores
Record Stories
Reggae
Reggaeton
Reissue
Reissues
Releases
Religious
Remix
Retrospective
Rock
Rocksteady
Roland
Roland Kirk
Roller Skate
Room Recordings
Room Treatment
Roots Reggae
Rotary Mixers
Rough Trade
Rudy Van Gelder
Ryuichi Sakamoto
Ryuichi Sakmoto
Sacred
Sade
Sam Gendel
Samba
Samples
Sci-fi
Séance Centre
Seefeel
Sensual
Shamisen
share
Shibuya-kei
Shoegaze
Singer-Songwriter
Sisters with Transistors
Sly & Robbie
Smooth Jazz
Soft Rock
Solid State
Songwriting
Sonny Sharrock
Soul
Soul-jazz
Sound Collage
Sound Installation
Soundsystems
Soundtrack
South Africa
South African
South America
Space Rock
Speaker
speakers
Spiritual
Spiritual Jazz
Spoken Word
Staff Picks
Steely Dan
Stereolab
Stereophile
Steven Halpern
Stevie Wonder
Stoner Rock
stores we love
Stories
Streaming
Street Soul
Studio One
Sun Ra
Sunn O)))
Surround Sound
Susumu Yokota
Suzanne Cianni
Suzanne Kraft
Swamp Rock
SYNG
Synth
Synth Pop
Synth-pop
Synthesizer
Synthwave
Taarab
Takoma Records
Tangerine Dream
Tape
Tapes
TD-160
Techno
Techno Pop
Television
Terry Callier
Terry Riley
The Beatles
The Broad
The Loft
The Meters
The Mizell Brothers
The Music Center
The World Stage
Theater
Thelonious Monk
Third Side Music
Third Stream
This Mortal Coil
Thorens
Tim Sweeney
Too Pure Records
Total Luxury Spa
Traditional
Tribal
Trip-hop
Tropical
Tropicalia
Tuareg
Tube
Turntable
TV
UK
Underrated
Val Wilmer
Vandersteen
Vanity Fair
Velvet Underground
Vice
Video
Vince Guaraldi
Vintage
Vintage Gear
vinyl
Virginia Astley
Visible Cloaks
Visual Art
Vocal
Vocoder
Walearic
Wally Badarou
Water
Website
Werner Herzog
West Africa
West African
Windham Hill
World
Wrecking Crew
Yacht Rock
Yamaha
Yasuaki Shimizu
Yellow Magic Orchestra
Yma Sumac
YouTube
Zamrock
Zither
ISCHiFi ((ROOM RECORDING))
0:00 / 0:00
0:00
0:00