• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

eico st70 irons!what to do?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
hi fellas,

i have a pair of eico st70 opts, and its pt along with a quad of 7591. i was thinking of building an integrated amplifier out of them ala "el cheapo" by eli. or the pp music machine by poinz. i have built the new version of poinz's 6gk5 6v6 machine and it sounds very good so was contemplating on going that proven route.

ive read that the 7591 is just as easy to drive as the 6v6 so im assuming that poinz's circuit will be able to the the job.

ill just be using the eico st70 power supply schematic for the 7591.

1. how do i make the changes to accomodate the 7591?

pls help. thanks

ivan
 

Attachments

  • eico st70 scheme.gif
    eico st70 scheme.gif
    35.4 KB · Views: 525
  • audiotropic el34 musical machine (tube rectified).gif
    audiotropic el34 musical machine (tube rectified).gif
    25.3 KB · Views: 518
Ivan,

Yes, the 7591 is as easy to drive as "12" W. multi-grid types. Therefore, either of the EC or MM splitter/driver circuits will work.

I suggest you use EC style circuitry, given those O/P trafos, which are designed to be used inside a NFB loop.

Both MM and EC require a B- supply. If you SS rectify the B+ rail, the 5 V. winding on the power trafo can be voltage multiplied to yield both the B- for the LTP and the C- for the 7591s. The extra Volts yielded by SS rectification of the B+ can be put to good use by combination biasing the "finals". Combination bias allows you to safely keep the 7591 grid leak resistance in the 300 KOhm area. Current production 7591s, unlike NOS, are intolerant of out of spec. grid leak resistors.
 
Administrator
Joined 2004
Paid Member
Hi Eli,
Might want to tell us what the abbreviation EC and MM stand for. I can't think of a single phase splitter or amp topology with those abbreviations.. Guess I am clueless.

Off the top of my head I can think of split load/cathodyne, differential/LTP, transformer or choke coupled, but these two have left me hanging, and I expect others are too..

How about electron coupled, European Community, moving magnet or motor mount? :boggled: :D
 
From reading what's been discussed, I would assume it's:
EC is El-Cheapo
MM is Music Machine


HollowState is correct. A high gain/high gm differential splitter/driver kicks serious butt in combination with these EASY to drive types. Whether or not GNFB is used is a matter of personal preference and the nature of the O/P "iron" available. Please notice that a separate preamp is needed only for a phono source, as a 2 VRMS I/P signal is more than enough to drive these designs into clipping.

I know the 12AT7 is very good in PP amps. You get an ear pleasing "waterfall" for the net distortion spectrum. Perhaps Poinz will see this thread and give us the "skinny" on the 6GK5 setup's distortion behavior.
 
hi eli, folks

ill measure the secondary voltages of the power transformer when i get home.im guessing there will be more than 400volts on the secondary. i also do have a 10h 200mA CHOKE for the ps. i want to use the tube rectifier as i do have a couple laying around gathering dust.

ive been wanting to build the el cheapo for a long time now but just can't stop tweaking my 6v6 music machine as it sounds very good to my ears.

i don't have the parts to build the el cheapo but i have all the parts needed to build poinz's 6gk5 driver circuit so i was thinking of taking that route. im still a beginner and know nothing about designing an amplifier so everybody's input are greatly appreciated.

ive seen the new thread about the fisher 500 irons being used but will shy away from that as ive read that it will be complicated.

ill download the psud designer when i get the chance.

thanks everybody

ivan
 
hi tony,

it all started when my pop brought home a nad integrated amp and a pair of martin logans 6 years ago. i thought they sounded fine. i was thinking of buying used equipment for use in my bedroom then i stumbled upon fullrangerdriver website and built the ratshack buschorn speakers and was hooked ever since.that was the beginning of my diy experience.i was a broke nursing student so i need to make do of what i have.

with regards to tubes i've read that tube amplifiers are better than transistors with letting the music out, so i decided since i built my speakers why not build my amplifier. since i have no experience whatsoever with electronics i asked a friend to teach me how to read schematics and went from there. the first amp i built was an se el84 amp which trashed the nad driving the buschorn.

my current system is poinz's 6v6 mm. lightspeed ldr. behringer src 2496 upsampler w tube output stage as dac, pioneer dv300 modded as transport. walmart ic and speaker cable the white stuff. and vintage telefunken 8", saba greencone tweets and vintage 15"organ speakers on open baffle.

magnavox pp 6v6, magnavox se el84 and se 2a3 (loaned to a friend but will not return it).

im still a newbie when it comes to electronics.


thanks,

ivan
 
hey folks,

i just measured the secondary of the power trafo and this is what i got!

1. 390-0-390volts
2. 88volt tap
3. 5volts for rectifier
6. 6.3volts for filaments

from what i can see i can build poinz's el34 version and make my life a lot easier.
now the question is

1. will the 7k opts be ok driven by el34? they are a little high which will lower the power a bit but will have lower distortion.
2. should i just stick with 7591?
3. is there a tutorial on how to use psud? any tips?


here is the scheme for the el34 amp.


good day,

ivan
 

Attachments

  • audiotropic el34 musical machine (tube rectified).gif
    audiotropic el34 musical machine (tube rectified).gif
    25.3 KB · Views: 290
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!
 
hey folks,

i just measured the secondary of the power trafo and this is what i got!

1. 390-0-390volts
2. 88volt tap
3. 5volts for rectifier
6. 6.3volts for filaments

from what i can see i can build poinz's el34 version and make my life a lot easier.
now the question is

1. will the 7k opts be ok driven by el34? they are a little high which will lower the power a bit but will have lower distortion.
2. should i just stick with 7591?
3. is there a tutorial on how to use psud? any tips?


here is the scheme for the el34 amp.


good day,

ivan
Is this the PT from the ST-70? If so, it probably doesn't have enough juice to drive the EL34's.
 
Is this the PT from the ST-70? If so, it probably doesn't have enough juice to drive the EL34's.

yes it is the PT from the eico st-70 which uses 7591. how do i measure the current supplied by the secondary? when i measured it i got 250ma from each 390v tap. will recheck again.

do you have any tips on how to measure the PT?
why will it not be suitable for a pp el34?i apologize for the ignorant questions.:)

thnks
 
yes it is the PT from the eico st-70 which uses 7591. how do i measure the current supplied by the secondary? when i measured it i got 250ma from each 390v tap. will recheck again.

do you have any tips on how to measure the PT?
why will it not be suitable for a pp el34?i apologize for the ignorant questions.:)

thnks
Here are the PT's specs:
Primary
117V @ 1.4A
Secondaries
720VCT @ 0.17A (B+)
Tap 80V @ 0.001A (bias)
5V@1.9A (GZ34)
6.3V@3.6A
6.3V@3.2A

Notice that this PT 's B+ is only rated at 170ma, you will have to bias the EL34 probably @40ma each max which is a little low. The filament supply is also a little short, each EL34 draws 1.5A, that will leave you 0.2A and 0.6A from each filament taps which won't be enough for the driver and the input tubes. You can either overload the filament sections, which is not recommended, or buy another filament transformer for the driver tubes and the input tube.
 
hi fred,

so ill just stick with the 7591 as suggested by eli and save my self a lot of trouble. i won't be using the 80v tap as ill derive all bias voltage from an amveco 62035 toriod.

what bias voltage does a pair of 7591 need and what is an optimum bias resistor for them?

ill still be using the el34 circuit but with the 7591 instead.

thanks

ivan
 

Attachments

  • audiotropic el34 musical machine (tube rectified).gif
    audiotropic el34 musical machine (tube rectified).gif
    25.3 KB · Views: 244
Ivan,

One of the nice things about the 7591 is that its drive requirements are the "same" as the EL84 and 6V6. Approx. 25 V. of bias will cut the tube off. Therefore, you use Poinz's 6V6 driver circuitry. ;)

Eico's power trafo, with a little ingenuity, can provide ALL the necessary voltages.

SS rectify the B+ into a CLC filter whose 1st cap. is made just large enough to keep the rail voltage up. You can follow the CLC setup with paired (1/channel) RC sections that provide the take of points for the 7591 pairs. With all that, the B+ rail voltage will be higher than that obtained with vacuum rectification. Take advantage of the extra Volts by employing combination bias. Each pair of 7591s "stands" on a 100 Ω/470 μF. network. That resistance value makes setting the "idle" current easy.

The negative voltages needed for C- (7591 bias) and B- (LTP tail) are obtained by voltage multiplying the 5 VAC winding, according the layout shown here. Use Schottky diodes in the multiplier to hold both forward drop losses and switching noise down.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.