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Old 16th October 2009, 10:55 AM   #11
tubo is offline tubo  Philippines
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Location: Mundelein, Illinois
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
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Old 16th October 2009, 07:05 PM   #12
tubo is offline tubo  Philippines
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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
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Old 17th October 2009, 01:43 AM   #13
AJT is offline AJT  Philippines
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Quote:
i was a broke nursing student so i need to make do of what i have.
hi ivan,

so, have you finished you studies yet?

the tube gurus will help you out for sure, just be patient....
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Old 17th October 2009, 03:34 AM   #14
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Location: Near Buffalo NY USA
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!
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Old 17th October 2009, 04:21 AM   #15
pchw is offline pchw  United States
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Quote:
Originally Posted by tubo View Post
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.
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Old 17th October 2009, 05:29 AM   #16
tubo is offline tubo  Philippines
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Location: Mundelein, Illinois
Quote:
Originally Posted by Tony View Post
hi ivan,

so, have you finished you studies yet?

the tube gurus will help you out for sure, just be patient....
hi tony,

i finished school 3 years ago.

yup, im glad i joined the forum. evrybody is friendly and very helpful.
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Old 17th October 2009, 05:36 AM   #17
tubo is offline tubo  Philippines
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Quote:
Originally Posted by pchw View Post
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
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Old 17th October 2009, 07:27 AM   #18
pchw is offline pchw  United States
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Quote:
Originally Posted by tubo View Post
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.
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Old 18th October 2009, 11:51 AM   #19
tubo is offline tubo  Philippines
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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
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Old 18th October 2009, 02:14 PM   #20
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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.
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