Eico ST40 find....

[Theron D]

(Cross-posted over at the Steve Hoffman site)

Yesterday's purchase in the neighborhood. Have not turned on yet. I believe this unit was factory wired since the work looks very good (IMO but I'm a novice in this area). Also the GZ34 rectifier tube is smoky grey at the top (see pic) so Im assuming it's bad? Those are Westinghouse 7951 Power Tubes (been looking for some for my Pilot 248B amp which is another recent adventure in itself.) Below are some pics, any feedback greatly appreciated, anyone have and can describe the sound? The small signal tubes are Mullard (Made in Great Britain), except the 12Ax7s which are Teles.

Description
The Eico ST40 amplifier was available as a kit or fully wired.

Specifications
Power output: 20 watts per channel into 8Ω (stereo)

Frequency response: 40Hz to 20kHz

Total harmonic distortion: 1%

Damping factor: 11

Input sensitivity: 3mV (MM), 360mV (line)

Speaker load impedance: 4Ω to 16Ω

Valve complement: 2 x 12AX7, 4 x 12DW7, 4 x 7591, 1 x GZ34

Dimensions: 403 x 130 x 333mm

Weight: 32lbs

Year: 1960

 

[Theron D]

 

[Fairlane]

Wow, nice time capsule. And that rectifier tube is toast as you know.
Become a subscriber and check out Barter Town and you will find some great vintage ones with a little patience. New ones are readily available as well but that beauty deserves a vintage one.

Read up on some of the great literature here about starting out in tubes and what not to do etc.

 

[Theron D]

Wow, nice time capsule. And that rectifier tube is toast as you know.
Become a subscriber and check out Barter Town and you will find some great vintage ones with a little patience. New ones are readily available as well but that beauty deserves a vintage one.

Read up on some of the great literature here about starting out in tubes and what not to do etc.

thank you ! I just signed up and became a Subscriber!

 

[radioactive]

Just a sort comment but do a search for eoco St 40 mods

 

[Fairlane]

 

[gadget73]

Hard to say if thats factory wired or not. Fairly neat job either way. I've seen factory built stuff that is sloppier.

 

[Big Harry]

I don't know that the amp is factory wired as everything is assembled with screws and the factory would usually use rivets. It does appear to be assembled by someone experienced in electronics as the work looks good. I owns your amp's big brother, the ST70 which after I recapped it sounds really good. I know that there are several circuit mods that you can do that are supposed to improve the sound, just look around the internet and you can find the info.

 

[Dandy]

Mine came with a similar toasted rectifier and missing fuse. It came alive when both were replaced, but it needs the usual recapping and cleaning of tube sockets and pots. The loudness switch has a well-known mod/correction. It's good that you have all the knobs, as some of those split tone controls are hard to find.

Yours is a very clean example. I agree with others who say it was a built by a competent home builder, not the factory. Download the assy manual for parts and voltage references.

 

[primosounds]

I don't know that the amp is factory wired as everything is assembled with screws and the factory would usually use rivets. It does appear to be assembled by someone experienced in electronics as the work looks good. I owns your amp's big brother, the ST70 which after I recapped it sounds really good. I know that there are several circuit mods that you can do that are supposed to improve the sound, just look around the internet and you can find the info.

For EICO units this is not necessarily true. And neither is the converse, where if the components are riveted that the unit is factory made. In later eico kits, most of the sockets, solder lugs were pre riveted on the chassis to make assembly easier for the builder.
Factory wired amps and preamps will have a stamp on the underside of the chassis marked "INSPECTED BY Suzey Katoochie" or whoever.

 

[s-petersen]

Something o keep in mind, someone may have tried to turn the amp on without using a dim bulb tester, or variac, and toasted that tube,It also could have just lost vacuum. check the fuse to see if it is the proper size, and intact. When you try to power it up, use a dim bulb tester, and or a variac. recapping is recommended for reliable use.
I have some ST-70's the bigger brother of this amp, and they sounded good, I also have a ST-40, which I haven't tried.My first ST-70 had some issues with the tube sockets making noise, they needed retensioning.

 

[primosounds]

thank you ! I just signed up and became a Subscriber!

I have owned and passed on several ST40 and it is a killer sounding amp even in stock form. The eico st70 is a more powerful version of the amp with those large OPT but it is also more problematic because of the amount of gain and feedback (which can also multiply the amount of spurious noise) needed to achieve that lofty number. Anyway, to get to the point you might also want to join the Yahoo eico group which is full of schematics and knowledgeable members, some of whom got their first wiff of melted solder on that very site.

 

[gadget73]

There are some revisions to correct for all the gain on the ST-70 though. I remember reading through it once and it seemed like the results were good, but never having owned one I never bothered to really study it too deeply. I think that one is on the Tronola site somewhere. Don't know if they apply to the ST-40 too.

 

[Dandy]

Re Scott's point about tube sockets, yes I also had some noise from the B9A sockets. I replaced mine, but retensioning may work just as well.

 

[primosounds]

There are some revisions to correct for all the gain on the ST-70 though. I remember reading through it once and it seemed like the results were good, but never having owned one I never bothered to really study it too deeply. I think that one is on the Tronola site somewhere. Don't know if they apply to the ST-40 too.

Right Steve Lafferty of the Tronola site along with Dave Gillespie are the main contributors. They worked on trying to make the ST70 a better amp but the mods i haven't tried.
I did do a mod on the ST70 where i completely bypassed the tone control section which made the amp quieter and to me better sounding. One could probably apply that to the ST40, but maybe you would lose some gain.

 

[Theron D]

I have owned and passed on several ST40 and it is a killer sounding amp even in stock form. The eico st70 is a more powerful version of the amp with those large OPT but it is also more problematic because of the amount of gain and feedback (which can also multiply the amount of spurious noise) needed to achieve that lofty number. Anyway, to get to the point you might also want to join the Yahoo eico group which is full of schematics and knowledgeable members, some of whom got their first wiff of melted solder on that very site.

muchas gracias! ill look into it and join!

 

[primosounds]

Te nada!

 

[Theron D]

(4) 12DW7 / 7247 tubes and (2) 12AX7 / ECC83 tubes that were in the Eico ST40 when purchased. Mullards made in Gt. Britain

 

[gadget73]

They're nice tubes. I have a pair with Hammond labels on them in my Fisher.