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Old 16th December 2013, 12:01 PM   #11
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Join Date: Sep 2007
Quote:
Originally Posted by Alfi1966 View Post
thank you very much for the information
i have looked for the orange drops in 716p 0.33uf, but that does not exist, as far as i can see.
do i use a different value, or use several in paralell, to reach 0.33uf?

alf david
They are available in 400v I found a few on ebay....

Bob
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Old 16th December 2013, 10:49 PM   #12
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0.1 to 0.47 uf will works. the voltage should be at least 200V
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Old 17th December 2013, 12:18 PM   #13
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Quote:
Originally Posted by bobrown14 View Post
Take a look at these OPTs:

EDCOR - GXSE15-8-3.5K
or
EDCOR - GXSE10-8-5K

Check the size compared to what you have they should be pretty close.

I like a 3.5 to 5K load for 6L6 so there's one of each. Although if you want the best for YOU we would need to know what speakers you will be using with this amp.

As Ray mentioned that .33uF coupling capacitor can be upgraded to a better quality cap, all the signal goes directly thru that cap so the best you can afford will work. There are several, and you could spend a lifetime trying to figure out which is best there.

Russian k40y-9 should be good there and easy to get where you are.
They have a significant break in period tho and will sound a little harsh at first.
Another good capacitor is a Sprague Orange Drop 716P (has to be the 716 NOT the 715). These are cheap and good for this amp will go along with the rest of the parts here.

The .33uF cap will need to have a voltage rating no lower than 400vdc.

For a bleeder resistor ~40k Ohm 5 watt resistor across the + and - pins on cap2 (c2) 330Ohm 450V cap the largest capacitor in the amp. If you want to get clever you can add a LED diode long with the resistor, the LED will stay lit as long as there's voltage indicating no touchy. Even then you should ALWAYS use a DMM and meter the caps to be sure there's no voltage. Safety first it's the only way. 450v is going to hurt if your hand discharges it.

Cheers,
Bob
hi, im slow with my answer on this.
i use a set of system audio mantra 50, rated at 4ohm for the fronts.

alf david
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Old 13th January 2014, 06:16 PM   #14
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Join Date: Aug 2013
Hello again
I have changed the sockets in the amp now, and put in the new tubes.
Im going to change the two condensators next.
What im wondering is how do i bias the amp with the new tubes?
Is it selfbiasing? Or are there a fixed bias?

Alf david
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Old 13th January 2014, 07:09 PM   #15
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Join Date: Sep 2007
Quote:
Originally Posted by Alfi1966 View Post
Hello again
I have changed the sockets in the amp now, and put in the new tubes.
Im going to change the two condensators next.
What im wondering is how do i bias the amp with the new tubes?
Is it selfbiasing? Or are there a fixed bias?

Alf david
This amp is CATHODE BIASED or self biasing. If say you wanted to up the current thru an output tube you would typically change the cathode resistor to a different (lower) value. That's assuming your power transformer has enough current available (it should). If you are just changing to another 6L6 family tube you will not need to change anything, just the tubes and enjoy.

So Cathode bias = self bias (no adjustment)

fixed bias = adjustable with usually a trim pot and needs adjusted from time to time and when changing tubes. Not the case here.

Cheers,
Bob
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Old 14th January 2014, 01:13 PM   #16
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hi
thank you for the answer. i have changed the tubes to sylvania 5y3gt, rca nos/nib 6sl7gt black plate, and a platinum matched pair of sovtek 5881wxt/6l6wgc, and would like to get them performing as good as possible, so im wondering if i can change the bias resistor to get a little more power from them. what bias voltage do they need, and what is the safe range of resistors i have to play with?

alf david
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Old 14th January 2014, 03:19 PM   #17
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Quote:
Originally Posted by Alfi1966 View Post
hi
thank you for the answer. i have changed the tubes to sylvania 5y3gt, rca nos/nib 6sl7gt black plate, and a platinum matched pair of sovtek 5881wxt/6l6wgc, and would like to get them performing as good as possible, so im wondering if i can change the bias resistor to get a little more power from them. what bias voltage do they need, and what is the safe range of resistors i have to play with?

alf david
Why 6SL7? 6N1 I think is closer to the 6SN7/6N8S tube. The 6SL7 is closer to the 6N2 not the 6N1. You will have to recalculate your tube curves for that swap to be sure you're driver tube is where it should be. That and of course the pins are different but you should know that already??

6SL7 - gain (Mu) = 70
6SN7 - gain (Mu) = 20

6N1 - gain (Mu) = 35

There are other differences but this is a starting point and looking at the gain on the 6SL7 you will need to re-design the driver stage, you'll be over driving the output tubes causing distortion. The 6N1 tube is a VERY good driver tube. You are not gaining anything IMHO going to a 6SL7, I'd probably opt for the 6SN7 if you want an octal triode (since I've got a bunch of good old stock ones) but that's me.
Going old school triodes in place of the newer 9 pin 6N1, I'm not real clear on any advantages there?

Cheers,
Bob
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Old 27th January 2014, 07:01 PM   #18
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Hi

I think you have looked at the wrong pre tube, it is a 9n6p, and that has the same mu as a 6sl7gt.
Im looking at optimising the voltages and bias for the new tubes, and there are a 40v difference between the two output tubes, so i would like to get that as similar as possible.
When im looking at the pre-tube, on the cathode resistors, do i add the 1k resistor to the 100 resistor, or calculate only the first one from the pin?

Alfi
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Old 28th January 2014, 09:03 PM   #19
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Join Date: Sep 2007
Quote:
Originally Posted by Alfi1966 View Post
Hi

I think you have looked at the wrong pre tube, it is a 9n6p, and that has the same mu as a 6sl7gt.
Im looking at optimising the voltages and bias for the new tubes, and there are a 40v difference between the two output tubes, so i would like to get that as similar as possible.
When im looking at the pre-tube, on the cathode resistors, do i add the 1k resistor to the 100 resistor, or calculate only the first one from the pin?

Alfi
40V difference at the output tube? Which pin are you measuring?
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Old 30th June 2014, 11:07 AM   #20
deanznz is offline deanznz  New Zealand
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The feel the Bass is weak on mine, is that normal or can I tweak it somehow ?

Dean.
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