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Old 28th March 2008, 07:08 PM   #1
G is offline G  United States
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Default Will this work?

Will the Edcor interstage transformer work as I have it in this schematic? I have it reversed to get a 600:2.4K ohm configuration and I have it cap coupled on the primary to keep DC out of the winding. I'm attempting to use it as a step up interstage. The Edcor interstages can be found here:

http://www.edcorusa.com/products/tra...xsm/index.html
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File Type: gif se 396a - 6as7 interstage coupled.gif (8.5 KB, 304 views)
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Old 28th March 2008, 08:46 PM   #2
nafanja is offline nafanja  Ukraine
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It's not work if this "w"- FeSe core.

If You have 13 ma in input, may be you need 60-120 Henry in primary for 30-50Hz -0 Db, for 20Hz more.
And secondary from this transformer is the question.

it's 2:1 (2.1k,600 Ohm) and this little dimentions...?
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Old 28th March 2008, 09:13 PM   #3
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Quote:
Originally posted by nafanja
It's not work if this "w"- FeSe core.

If You have 13 ma in input, may be you need 60-120 Henry in primary for 30-50Hz -0 Db, for 20Hz more.
And secondary from this transformer is the question.

it's 2:1 (2.1k,600 Ohm) and this little dimentions...?

Since I cap coupled it I won't have any DC on the primary. As pictured I have it reversed with the 600 ohm winding as the primary and the 2400 ohm winding as the secondary.
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Old 28th March 2008, 10:17 PM   #4
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I might be inclined to use the 10K:15K (and a driver with more gain if you need the gain), or to use a power toroid, but otherwise it will work.

Also, especially if you are using some edcor iron, I might lose the plate choke and use a good CCS instead. Performance is arguably better, and it will be cheaper and it will make your power supply requirements a little simpler.
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Old 28th March 2008, 10:45 PM   #5
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Quote:
Originally posted by dsavitsk
I might be inclined to use the 10K:15K (and a driver with more gain if you need the gain), or to use a power toroid, but otherwise it will work.

Also, especially if you are using some edcor iron, I might lose the plate choke and use a good CCS instead. Performance is arguably better, and it will be cheaper and it will make your power supply requirements a little simpler.
Using a CCS will mean I need a little more voltage for gain stage? How will a CCS make my requirements simpler? I'm not following. Sorry to be dense. Also if I use the 10K:15K can I use half the winding on the primary and use it as a 5K:15K?
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Old 28th March 2008, 10:49 PM   #6
nafanja is offline nafanja  Ukraine
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I am understand that it's reverse.

But dimention is so small if You want bass frequency.
Original is calculated for 2.4K section where calculate Low Frequensy in primary.

In this variant You stay secondary like primary.
Low frequncy looses will be more.
If there (like exapmle) 3000 w (2.4K primary) in
secondary will be 3000/2 = 1500 w(are)
(n=2:1 ( get calcilativly))
How many Henry in 600(secondary section) will be?
If primary(2/4) calculate for 40 Herz in reverse (1500w) will be 100 Hz.

If You don't use special methods for 1:2 transformer - You will start to loose the High freqency.
You walk with input capasitanse of 6AS7 tube, and current (for work with this) stay smaller in 4 parts.

For example, For driving three 6s19p I use 40ma for high pulse rate,
in Your variant (in better variant), if Io = AC curent 13ma< your curent in primary
13/4=3ma.
If Ac(Iout of driving tube) = 5ma/4=1ma

If Your interest is Mid freqensy range - is/t that You need.
Many excluse schemes of this kind (some Japaneess costructors) have a smalll diapazon.
If You like no wide frquency diapason - Use this.
May be use resistive cascade and You will have what You need?

But if You want to sell more expencivly like exotyic tube amp...it's Yours.

Understand?
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Old 28th March 2008, 11:00 PM   #7
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Quote:
Originally posted by nafanja
I am understand that it's reverse.

But dimention is so small if You want bass frequency.
Original is calculated for 2.4K section where calculate Low Frequensy in primary.

In this variant You stay secondary like primary.
Low frequncy looses will be more.
If there (like exapmle) 3000 w (2.4K primary) in
secondary will be 3000/2 = 1500 w(are)
(n=2:1 ( get calcilativly))
How many Henry in 600(secondary section) will be?
If primary(2/4) calculate for 40 Herz in reverse (1500w) will be 100 Hz.

If You don't use special methods for 1:2 transformer - You will start to loose the High freqency.
You walk with input capasitanse of 6AS7 tube, and current for wokr with tis stay smaller in 4 parts.

For example, For driving three 6s19p I use 40ma for high pulse rate,
in Your variant in better variant, if Io = AC curent 13ma< your curent in primary
13/4=3ma.
If Ac(Iout of driving tube) = 5ma/4=1ma

If Your interest is Mid freqensy range - is/t that You need.
Many excluse schemes of this kind (some Japaneess costructors) ,thay like exotic variant, and love mid FR.
If You like no wide frquency diapason - Use this.
If know - try to use resistive cascade and You will have what You need.

But if You want to sell more expenxivly like exoyic tube amp...it's Yours.

Understand?

I understand I think. The problem I am trying to overcome is that the gain tube of my choice is just a little shy of having the gain that I actually need to drive the power tube to full output. dsavitsk is correct in that I should probably use the 10K:15K interstage instead of trying to rig it with the wrong transformer. It sounds like you concur. The question I have is if I use only half of the primary of the 10K:15K transformer in order to get a impedance ration of 5K:15K will the frequency response still be 20Hz to 20KHz? Using a CCS on the plate of the 396A and using the interstage at its normal 10K:15K ratio would come within a hair of giving me full output from the power tube. Right at 100v I think. That might be as good as it gets with the tube I have chosen and using this interstage transformer.
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Old 28th March 2008, 11:28 PM   #8
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Quote:
Originally posted by G


Using a CCS will mean I need a little more voltage for gain stage? How will a CCS make my requirements simpler? I'm not following. Sorry to be dense. Also if I use the 10K:15K can I use half the winding on the primary and use it as a 5K:15K?

I see what you are saying (that the plate choke will allow the stage to swing above B+). If, however, you bias the input tube to 2V instead of 3V, then with your 6mA operating point, you will have ~130V on the plate. You already have a 200V supply for the output stage that can be shared, and assuming that the CCS will work within 20V of the rail or so, you have lots of swinging room (enough for ~4V p-p on the input).
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Old 28th March 2008, 11:40 PM   #9
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Quote:
Originally posted by dsavitsk



I see what you are saying (that the plate choke will allow the stage to swing above B+). If, however, you bias the input tube to 2V instead of 3V, then with your 6mA operating point, you will have ~130V on the plate. You already have a 200V supply for the output stage that can be shared, and assuming that the CCS will work within 20V of the rail or so, you have lots of swinging room (enough for ~4V p-p on the input).

Thanks for the reply. This is my first foray into interstage coupling(obviously) and I'm a little lost. On the secondary of the interstage I have almost a infinite impedance because the grid of the 6AS7 is only connected to ground through the interstage so the actual impedance being reflected to the primary is actually much higher than 10K correct? If this is so then I think I will be better served to use a CCS as it will give me more of a load on the plate of the 396A. If someone can cut in here and hold my hand for a few minutes I would appreciate it. I'm not sure that everything is as I think it is when it comes to parafeed interstaging.

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Old 29th March 2008, 01:08 AM   #10
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My understanding, and I am with you that this is not necessarily clear, is that the primary difference between a 10K:15K transformer and a 5K:7.5K is the inductance. So, even if you have a higher reflected load, it doesn't really translate like an infinite load. Moreover, you might have ringing problems with the infinite load. Whether this is a problem is up for debate, but putting a 15K resistor to act as a load might not be the worst idea. I think you just have to try both. Whether this influences the decision between CCS and choke, I don't know. But, you can always start with the CCS and switch to a choke with a simple change of Rk later on.

One other thing, the unbypassed capacitor on the driver will raise the rp significantly and it might be too high for the interstage transformer. You can counter this in a few ways, but the easiest might be a western electric connection -- connecting the transformer primary to the top of Rk rather than ground. Otherwise, you should bypass the resistor, or use an LED.
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