I can restore your Dynaco ST-70 for $200.00
details at Dynaco-ST70.com
I was always interested in tube audio and used a Lafayette LA-250
integrated tube amplifier for years. There was something about a Dynaco ST-70
that appealed to me. Maybe it was the chrome chassis, the brown steel cage
covering the tubes or just the way it looks. I finally went on a hunt to purchase
a Dynaco ST-70 amplifier, PAS-3 tube preamp an a FM-3 Stereo FM tuner.
The first item I found was the Dynaco ST-70. It was located in Albuquerque, NM.
I checked ebay and missed out on a few ST-70's and then I checked Craigslist.org
After negotiating a price with the seller the ST-70 was mine. I eagerly waited for
it to show up via UPS. The day finally came and I opened up the box. The seller
removed and wrapped each tube individually and numbered them so I would put
them in the same socket. After carefully unwrapping and installing the tubes, I
connected my CD player directly to the input, connected vintage Lafayette speakers
and turned on the power. The amp sounded great. There was a very slight hum which
was only heard when the music was not playing. That will get taken care of after I
replace the filter capacitor can. I checked and corrected the bias which
was set to high. A slight turn of the bias pots took care of that.
Here are a few photos of the unit. The transformers are the desired cloth covered
wires. The chrome on the chassis is suprisingly in good condition. The nice thing
about this amplifier is that its all original except for the 4 coupling capacitors
that were replaced. Even the printed circuit board is original.
The tubes used in this amp are 4 6CA7's, 2 7199's and 1 5AR4
Who ever built this amp 40 years ago didn't really follow the wiring
practices as shown in the Dynaco assembly manual. A little sloppy
with the wiring but it works just fine.
When time permits I will take photos of my PAS-3 preamp and
FM-3 tuner. I replaced the voltage doubler circuit in the preamp which
consisted of a selenium rectifier and 2 2000uf electrolytic capacitors that powers
the filaments on the 12AX7's. The filaments are fed DC to eliminated hum.
The FM-3 tuner is on my bench getting overhauled.
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