Eico ST40.....

Where do i put the speaker wires on those terminals at the back ?

Well first you have unlearn most of what you ever learned. Then scratch your head. Here's how I did it, following the manual, and it works. Note the bare wire running from the top terminal to the one below it:

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I also did a re-cap, here are some shots. The JJ can caps are fairly low cost, as are the white Mallory couplers.

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I also did the infamous Loudness mod, as well as the phono section mod. Lots of resources here for these fine sounding (but occassionaly confusing) amps.

RWood
 
I need to do the loudness mod on my ST-70 as the stock setup if truly faulty.

I *have* been wondering about what we've discussed here as being maybe a "typo" in the screen-painted speaker hookup diagram on the back and in the book with regard to the positive/negative--I've found that the ST-70 *requires* me to flip that "Phase" switch to "Reverse" for both channels to sound correct with equal presence. What I'm wondering is if I hooked up that one speaker *exactly* as the book/screen diagram shows, with positive and negative opposite of general convention, if I could actually use the "Normal" position. Next time I'm out in the shop where the thing lives, I plan to give that a try.
 
Also, if it was advertised as working then it damn well should have come with that 5ar4, and those aren't exactly cheap tubes. Some compensation is due to your friend for the fact that it's missing.

Only other thing that comes to mind is if the PO did some mod to it to install a solid state rectifier in place of the 5ar4. If that was done then I guess it could work, though most folks would agree that's not the best way to go.

Why? Because he only got $175 worth of tubes, plus the iron and chassis for his $95 instead of $250 worth of tubes???

He got a sweet deal that could of been sweeter, but he's still way ahead and darn lucky.

I made that comment when it sounded like he was sold a 'working' amp that wasn't due to a missing , fairly expensive, rectifier tube. However I later surmised, the tube was missing because a solid state modification had been performed.

Not sure why you're getting all jacked out of shape. :scratch2:
 
I *have* been wondering about what we've discussed here as being maybe a "typo" in the screen-painted speaker hookup diagram on the back and in the book with regard to the positive/negative--

Yeah, you might be right. And mine might be wrong, lol.
Fwiw, here is the diagram from the manual:
 

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OK guys, new rectifier tube ordered and a new matched quad set of output tubes ( JJ's) and some caps.

Watch this space for when i need help re wiring the tube base after the knuckleheads work......
 
I made that comment when it sounded like he was sold a 'working' amp that wasn't due to a missing , fairly expensive, rectifier tube. However I later surmised, the tube was missing because a solid state modification had been performed.

Not sure why you're getting all jacked out of shape. :scratch2:

Because I think you were being petty. He got a helluva deal, The iron itself is worth more than what he paid, so everything else is a bonus, and worth a couple multiples of what he paid. To ask for an adjustment when you paid far less than an informed seller would ask I think is bogus.

When one buys stuff used from private parties, it's caveat emptor; you pay your money and take your chances. The OP and his friend admit that they were ignorant of these things as they should have noticed an oddball tube and an open socket, or even asked to power it up. But they didn't and wound up getting a killer deal on a good amp regardless.

I think my original post pretty much says it all...
 
Because I think you were being petty. He got a helluva deal, The iron itself is worth more than what he paid, so everything else is a bonus, and worth a couple multiples of what he paid. To ask for an adjustment when you paid far less than an informed seller would ask I think is bogus.

When one buys stuff used from private parties, it's caveat emptor; you pay your money and take your chances. The OP and his friend admit that they were ignorant of these things as they should have noticed an oddball tube and an open socket, or even asked to power it up. But they didn't and wound up getting a killer deal on a good amp regardless.

I think my original post pretty much says it all...

My friend would normally ask me before he bought something he wasn't sure of but he so wanted the amp that he rushed out and bought it without asking to see it with the top cover at least removed or see it working, the seller said he was inundated with emails, and at the price now we realize why.

Anyway, as i said above the parts are on order and i will report back when they arrive for more help from you tube guys.

Thanks in advance.

Neil.
 
Be really careful about those JJ's. I hear a lot of things questioning their reliability. The EH tubes are supposed to be better in this regard. I have no experience with any JJ or the EH7591's so take that bit of hearsay for what you will.

I'm not going to pretend to know anything specific about the Eico amps, but in some applications there are changes suggested to help make sure the tubes don't blow up. Fishers at least get the grid resistors and caps changed to different values. I don't know if that applies to the Eico but it might be worth looking in to.


I do have to admit that I'm baffled as to why someone would re-wire the socket to stick a 6L6 in there paired against a 7591. Thats just....no. At least it was rewired though instead of just having a random different tube jammed in there. If it had not been, that would have done some really interesting and probably very bad things to the amp.
 
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Be really careful about those JJ's. I hear a lot of things questioning their reliability. The EH tubes are supposed to be better in this regard. I have no experience with any JJ or the EH7591's so take that bit of hearsay for what you will.

I'm not going to pretend to know anything specific about the Eico amps, but in some applications there are changes suggested to help make sure the tubes don't blow up. Fishers at least get the grid resistors and caps changed to different values. I don't know if that applies to the Eico but it might be worth looking in to.


I do have to admit that I'm baffled as to why someone would re-wire the socket to stick a 6L6 in there paired against a 7591. Thats just....no. At least it was rewired though instead of just having a random different tube jammed in there. If it had not been, that would have done some really interesting and probably very bad things to the amp.

Hi there thanks for the reply.

I know little or nothing about tube amps as this is the first one i have tackled, the last time i used anything with a tubed amp section in was when i was a kid many years ago.

Well JJ tubes were bought by my friend ( the rectifier tube is a Sovtek, i bet that one is no good as well eh ? ) and they are a matched quad set that are said to have been tested and matched, if we picked some sort of rubbish tubes then i am a bit disappointed, what can you do.....sigh.

Anyway i have done my best and i will test her out for a few hours today and see how she gos, she sounded lovely last night, the amp was making my test bench Minimus 7's sing, and few amps can manage to drive those speakers that well.
 
That's a great amp....

They have excellent basic circuits that sound great. You'll have a hard time topping this amp. The coupling caps can make a big difference in sound so experiment with caps till you find what you like. Learn how to check the bias for each 7591 tube. Keep the 5AR4/GZ34 because it's a slow start tube and lets the filiment/heaters warm up before the high voltage/B+ is applied. Actually rewiring for 6L6s tube is fine and the Sovtek 7591s are 6L6s with a rewired base. The only problem would be the height of the tube and if you can get the cover to clear. Your amp is very clean and in great shape. The price was a DEAL! This amp will put older solid states to shame. You have a real gem and may not know it..... Cheers
 
They have excellent basic circuits that sound great. You'll have a hard time topping this amp. The coupling caps can make a big difference in sound so experiment with caps till you find what you like. Learn how to check the bias for each 7591 tube. Keep the 5AR4/GZ34 because it's a slow start tube and lets the filiment/heaters warm up before the high voltage/B+ is applied. Actually rewiring for 6L6s tube is fine and the Sovtek 7591s are 6L6s with a rewired base. The only problem would be the height of the tube and if you can get the cover to clear. Your amp is very clean and in great shape. The price was a DEAL! This amp will put older solid states to shame. You have a real gem and may not know it..... Cheers

The amp just went back to its owner.

I only had it here for repair, i had it on test for maybe 10 to 15 hours and it sounded great, my friend who owns it was very pleased with it.

No more mods will be done, it will be in use in his system from tomorrow.

I am just very pleased i could sort out the amp for him so it worked and sounded good.

I can't say i wish to have another tube amp to fix anytime soon tho.

I think i was lucky this time :)
 
Your a good friend. Tube amps take special repair knowledge like any hobby. Get to know a tube repair man that will share his experience with you. Or just start reading tube forums and it will make sense.... Anyway, your friend should be very happy.....
 
Your a good friend. Tube amps take special repair knowledge like any hobby. Get to know a tube repair man that will share his experience with you. Or just start reading tube forums and it will make sense.... Anyway, your friend should be very happy.....

No doubt about it, i learned a huge amount fixing up the Eico.

My friend just informed me he has an old Heathkit tube amp in his storage locker that needs attention, here we go again.........

:thmbsp:
 
This is an old topic, but I think it important to state that, prior to sending this amp back to the friend, the push-pull pairs should have been biased, each channel. Not setting the bias means that the matched quad of tubes probably isn't any more. I'd bet that one tube per pair is suffering for it.
 
How would you bias the push pull pairs as this amp doesn't have fixed bias? Each channel is cathode biased.
 
Near as I can tell you do not. The schematic indicates no adjustments of any sort. There are some cathode bias rigs with balance adjustments, but this doesn't appear to be one of them. Looks like all you'd have to do is check to see if its reasonable.
 
< Newest kid in class raises his hand.I have read that you can change resistors in a cathode bias amp to get closer to speck.?:dunno:
 
you can if it needs to be changed, but in stock form there isn't any adjustment on this amplifier. Usually unless the factory bias point is just not useful or things have changed a lot because of higher voltages its not something you typically need to do though.
 
Yup - someone made it into a solid-state rectified ST-40 (and should have taped off the two 5V taps...including the one that's being shared with the downstream end of the diodes as well as the power resistor and the HV B+ lead). If you have decent voltage on the 5V taps it would be good to revert it to the original tube rectification. However, before you do anything else you need to (1) get a matched set of 7591 tubes and (2) replace all those old capacitors, including the two multi-section can caps.

-D
I've had a solid state rectifier in my ST40 for years, works fine. There are a few tube amps that will take a SS rectifier and the ST40 is one of them.
 
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