eico st70 irons!what to do?

[alexg]

Originally Posted by tubo

hi alex,

i was from bacolod city. visayas. but im in US now for almost ten years. migrated here when i was 15. where are you located in the phils?

thanks,

ivan

Hi Ivan,

I am in Sta Rosa, Laguna.

I still maintain a house in LA, CA, I immigrated to the US in the early 80's and lived in CA. Now I work in Laguna and visit the US almost yearly.

Anyway, good luck with your project. This hobby is so addicting, I have built more than a dozen amps already! (I started building tubed equipment 4 years ago)

[tubo]

Originally Posted by crispycircuit

I have a similiar project. I have the pwr and output trannys from a Scott receiver that used 7591s and have them mounted on a new chassis with switches and sockets. I'm gonna use 6L6s but have't decided which circuit to hard wire in ?? Or if I should use diodes or tube rectification? Let me know what interests you? Cheers!

i think ill just build what eli is suggesting. already have most of the parts needed. good luck on your build.

[vaughn]

I'm interested in the outcome of this project as I also have an Eico ST70 that I am thinking would be better built into a stand-alone amp...

Any progress?

[Captn Dave]

I was given an EICO ST70 without the tube compliment. He's not a very attractive guy and he needs new can caps and coupling caps. I already have a Fisher X-101C and a Scott LK72 (and thy are among my favorites) but I'm not too excited about another 7591A. So I'm looking for help vetting some ideas. Eli and others have already provided some thoughtful content so I thought I'd tack onto this thread.

I'm thinking of using 6L6G or GC in triode. The 6L6 heater voltage is just one tenth higher than the 7591 and I'll be eliminating some small signal tubes and the rectifier so I should be covered in that respect. The OTs are probably okay as load resistance appears to be similar. Bias voltage is similar.

What do you think of the 6L6 as applied here?

Would the El Cheapo or Musical Machine topology make sense here?

Note: See post #18 for the PT specs

[Cobra2]

Maybe you can use some of this?
diytube.com :: View Forum - eiclone

Arne K

[Captn Dave]

Originally Posted by Cobra2

Maybe you can use some of this?
diytube.com :: View Forum - eiclone

Arne K

Thanks. That's interesting, I didn't know about the eiclone. Pretty sure I don't want do go with EL34s because I don't have enough heater current from the power transformer. But that does look like a good circuit and I do like the 6SN7.

[rmyauck]

Looks like you could use Kt-88's too, with re-biasing.

Randy

[Eli Duttman]

Originally Posted by Captn Dave

I was given an EICO ST70 without the tube compliment. He's not a very attractive guy and he needs new can caps and coupling caps. I already have a Fisher X-101C and a Scott LK72 (and thy are among my favorites) but I'm not too excited about another 7591A. So I'm looking for help vetting some ideas. Eli and others have already provided some thoughtful content so I thought I'd tack onto this thread.

I'm thinking of using 6L6G or GC in triode. The 6L6 heater voltage is just one tenth higher than the 7591 and I'll be eliminating some small signal tubes and the rectifier so I should be covered in that respect. The OTs are probably okay as load resistance appears to be similar. Bias voltage is similar.

What do you think of the 6L6 as applied here?

Would the El Cheapo or Musical Machine topology make sense here?

Note: See post #18 for the PT specs

The 6L6 is anything but easy to drive, which is unlike the 7591. However, both types take 6.6 KOhm primary O/P "iron". If you are going to use 6L6s of some kind, a Mullard style circuit of some kind seems best. A superior implementation of Mullard style topology that uses 6L6 family "finals" is the H/K Cit. 5. You can't go full pentode, as the Eico O/P "iron" lacks the requisite power handling capability. However, Class "AB2" triode wired "finals" have promise. The best deal out there right now in 6L6 family tubes is the Russian 6П3С-Е (6p3s-e), from a reliable seller.

Oh yeah, you don't have to use the 12BY7, which is getting scarce, as the voltage amplifier. A 6922 cascode will give you similar gm and the gain that goes with it. Of course, use a CCS in the LTP's tail.

[Captn Dave]

Eli,

Yes, the Citation V circuit is a very good suggestion. I like the use of the CCS on the 6CG7 LTP.

I'm aware of the Russian tubes, but I have plenty of good vintage 6L6GCs on hand together with an embarrassment of 6CG7s. I'm going to switch to solid state rectification to gain a few volts and use a Maida regulator on one of SpreadSpectrum boards.

When you recommend the 6922, are you doing so in preference to the similar 6DJ8? I have not that much experience of the 6922 and I have a boat load of 6DJ8s.

Also, what do you think of THIS 6158 medium mu dual triode in place of the 6922?

[Eli Duttman]

6DJ8s in cascode will be fine, as the voltage amplifier. Regulating cascode B+ is necessary, as PSRR is very poor. Regulating O/P tube g2 B+ is a good idea, as an open loop linearity improvement is realized. FWIW, McShane puts a small choke in Cit. 5s to tighten "final" g2 B+ up. Space is limited in the 5's chassis.