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Eico ST-70 Supermods
Eico ST-70 Supermods
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Old 21st September 2011, 07:40 AM   #11
pchw is offline pchw  United States
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Eico ST-70 Supermods
Quote:
Originally Posted by andresfont View Post
Hi Fred
I do not know how they(Sam) obtained the data from PT, I just want you to see the picture with the value of B +.Do you think that this value of B + can be had with 80 % about the specs?
Andres
Sams provides many the specs and the schematics of many equipments especially in the era. Those specs are usually published by the manufacturer. They are the best thing next to the original manufacturer manual of the vintage gear!!

There seems to be some disconnection here. I said 80% above the specs, not about the specs. I did assume each 7591 was drawing 38ma per Eico instructions. 38ma x 8 = 304ma total when idling. The PT specs is 170ma. Therefore, you are drawing 134ma (304 - 170) above the PT's specs which is approximately 80% of 170ma. This may present potential hazard as the magnetic wire might not be spec for such level of current either.

If you read the Sams from my attachment (you can download all 6 pages via the Eico group files section) on the specs of the OT, you will see the primary impedance is 6500 which is somewhat high for PPP of 4x7591 as well.
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Old 21st September 2011, 12:40 PM   #12
andresfont is offline andresfont  Venezuela
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Hi Fred
Sorry my english is bad, i want say "above" not "about". well I checked the amp for several days using it for several hours and so far has not had any problems. I am clear that the PT is over the limit, however now I have a bigger PT, I have not put because until now has not failed the original. On the other hand before of the mod I calculate the ratio of OPT, please if you see the attached schematic you will notice the taps of impedance values ​​in the secondary of the OPT is different.........
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Old 21st September 2011, 01:01 PM   #13
andresfont is offline andresfont  Venezuela
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File Type: pdf SuperMods_b.pdf (164.1 KB, 95 views)
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Old 21st September 2011, 04:21 PM   #14
pchw is offline pchw  United States
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Eico ST-70 Supermods
Andres,

No worry, English is not my native language either, and there are plenty of members like us here.

It is indeed good to see that you have fun and good result. I just wanted to do the
due diligent of a fellow hobbyist to warn the risk of pushing the (vintage) irons way beyond what they were designed for. As long as you are aware of that, I am happy for you. Safety is always first, and fun is only secondary :-)
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Old 21st September 2011, 06:05 PM   #15
andresfont is offline andresfont  Venezuela
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don't worry I love controversy! always is good to hear opinions
Thanks
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Old 8th October 2011, 11:56 PM   #16
rmyauck is offline rmyauck  Canada
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More info. Hotrodding the Eico ST-70

If you look at the Lundahl LL1679 you sure can get a lot more power using lower primary taps if possible in a amp design. Lundahl Transformers - Tube amplifier transformers

Last edited by rmyauck; 8th October 2011 at 11:58 PM.
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