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EICO ST-40 Question


CANT
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I recently picked one of these up without tubes (for cheap) and was planning on running through it this weekend if I have time...

 

My question is related to the 7247/12DW7's... I don't have any... but I do have AX's, AT's and AU's... what is my best choice for a sub for testing purposes? I've looked around online for help but many/most of the info I can find tends to lead to privately hosted links that are long dead. 

 

Side notes: My love of old switches and pots lives on (sarcasm) so expect most of them to be removed. I did located a gentleman who removed the tone control function (see ST40-mod-A4) though he left the Hi and Lo filter switches that I have no desire to use. This this amp is definitely no show pony so I am unconcerned with keeping it original. 

 

Thanks again for any help you can provide

EICO ST40.JPG

ST40-mod-A4.png

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22 hours ago, CANT said:

I recently picked one of these up without tubes (for cheap) and was planning on running through it this weekend if I have time...

 

My question is related to the 7247/12DW7's... I don't have any... but I do have AX's, AT's and AU's... what is my best choice for a sub for testing purposes? I've looked around online for help but many/most of the info I can find tends to lead to privately hosted links that are long dead.

 

It probably depends what you mean by "for testing purposes."  The pinout is the same as 12AX7 or 12AU7, but the 12DW7 is a funny hybrid, with two unequal triode sections; one has a lot more gain than the other.  You won't get fireworks if you try 12AX7 or 12AU7, but it may only give a rough idea of how it's working. 

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  • 2 months later...

Ok, so what are the advantages or disadvantages to leaving V3 & V4 in circuit if the the tone controls have been removed? The entire front end of this amp was corroded beyond deoxit-ing so if it is going to survive in any capacity, it will be as a power amp...

 

I did buy a pair of 7247 for the V5 and V6 positions to get a rough ideal of its sound but I am not trying to go nuts on parts in case this thing is really only worth its iron. I’ve seen a mod on another site that would mod V3/V4 for 12ax7 duty but it doesn’t make a ton of sense to me because it mostly modifies the already ax side of the 7247? I’ve also been looking over some of the over EICO schem that don’t use this tube like the ST84, HF85 and 81 just to get an idea of their thought process. 
 

I guess I was thinking worst/best case it could run similar to a Dynaco ST35 just off the single 7247 but maybe I am misguided.

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