Dynaco Dynakit Stereo 70 Tube Amplifier
Archived listing from the original vintage-amplifier.com. Prices, seller details and purchase links have been removed; this page is a reference record, and nothing here is for sale. About this archive.
1960 Dynaco Stereo 70 tube amp. 1 owner since new. All original with the exception of the bias capacitors, rectifier diode & output tubes. The original 7199 tubes (dated 1960) and GZ34 test very strong on my Hickok 539C. The EL34 tubes are new Electro-Harmonix. The circuit & transformers are all original. I replaced all the high voltage caps in the bias section and it is working excellent right now, all voltages are correct and stable. The selenium rectifier was also replaced and the bias voltage is now very responsive and stable. The amp sounds very nice, no hum or unwanted noises.
The cosmetics are very good with only light tarnish on the chrome chassis. The original owner engraved his ID # on the back and bottom (see photo). Both channels sound very nice through any speakers you pair it up with. The bias is perfect and the amp runs very cool and quiet.
About this model
A one-owner Stereo 70 dated 1960, close to the start of a production run that began in 1959. What makes the listing useful is its detail. The original 7199 driver tubes, also dated 1960, and the GZ34 rectifier tested strong on a Hickok 539C; the EL34 output tubes were new Electro-Harmonix replacements; the circuit and transformers were original; and the seller replaced the high-voltage capacitors in the bias section and the selenium rectifier that supplies the bias voltage.
That last repair matters. The Stereo 70 runs its four EL34s on fixed bias, and an ageing bias supply is the classic way these amplifiers kill output tubes. A Stereo 70 with a rebuilt bias section and correct, stable bias voltages is in much better shape than one with merely "good tubes".
A complete FM-3, PAS-3 and Stereo 70 system, built from kits by one owner in the 1960s, is also on file.
| Maker | Dynaco, Philadelphia, USA |
|---|---|
| Model | Stereo 70 (introduced 1959) |
| This unit | 1960, one owner (listing) |
| Output tubes | 4 × EL34, ultra-linear |
| Driver tubes | 2 × 7199 |
| Rectifier | GZ34 / 5AR4 |
| Rated output | 35 W per channel |
Questions collectors ask
What tubes does a Dynaco Stereo 70 use?
Four EL34 output tubes, two 7199 driver tubes (one per channel, handling voltage gain and phase splitting) and a GZ34/5AR4 rectifier.
Why is the bias supply so important on a Stereo 70?
The output tubes run on fixed bias. If the bias supply's capacitors or rectifier fail, the output tubes can draw excessive current and be damaged. Rebuilding the bias section is a standard part of a Stereo 70 restoration.
Was the Stereo 70 sold as a kit?
Yes. It was available as a Dynakit for the buyer to assemble, or factory-wired.
Sources: Wikipedia: Dynaco; Wikipedia: EL34.
