EICO ST-40 Stereo 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.
EICO stereo tube amplifier model ST-40. This amp is a 1 owner amplifier, was used up until 4 months ago and has the original build instruction manual. I brought the amplifier up on my variac to 120 volts where i was getting nice clear output. All function work correctly except the loudness switch, when i click it on the volume cuts down, but works fine when off.
The tube complement is 4-7591’s, 2-12AX7’s, 4-12DW7’s and 1-5AR4. The 7591’s are original and still test good, the amperex 12AX7’s are also original and test good. One of the 4 12DW7’s is missing, i used a personal tube to test the amp. The 5AR4 rectifier is a vintage american. Cosmetic wise this amplifier is in great condition, the chassis is clean and has only a few minor scratches that are not to noticeable from a distance, see pictures.
About this model
The ST-40 is one of the stereo integrated amplifiers Wikipedia names among EICO's hi-fi products. This one-owner example came with its original build manual. The listing gives the full tube line-up: four 7591 output tubes, two 12AX7s, four 12DW7s and a 5AR4 rectifier.
The 7591 was an American octal output tube popular in late-1950s and early-1960s stereo amplifiers; McIntosh used four of them in its MA230. The 12DW7 is an unusual dual triode with two dissimilar halves, so a missing one, as here, needs a correct replacement rather than a 12AX7 substitute. The seller reported everything working except the loudness switch.
| Maker | EICO (Electronic Instrument Company), USA |
|---|---|
| Type | Stereo integrated amplifier |
| Output tubes | 4 × 7591 (listing) |
| Small tubes | 2 × 12AX7, 4 × 12DW7 (listing) |
| Rectifier | 5AR4 (listing) |
| Documents | Original build manual (listing) |
Questions collectors ask
What tubes does the EICO ST-40 use?
Per the archived listing: four 7591 output tubes, two 12AX7s, four 12DW7s and a 5AR4 rectifier.
Can a 12AX7 replace a 12DW7?
Not as a like-for-like swap. The 12DW7 has two different triode sections, one similar to a 12AX7 and one to a 12AU7, so the circuit expects both.
Sources: Wikipedia: Eico; McIntosh legacy integrated amplifiers.
