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Re: Why? [message #8759 is a reply to message #8758] Wed, 26 January 2005 11:56 Go to previous messageGo to next message
TubeCraft is currently offline  TubeCraft
Messages: 30
Registered: May 2009
Baron
Well, in theory, the resistor should load the tube more evenly across a wider frequecy range than a choke. And, there seems to me to be a lot of wierd interaction between a choke load and the coupling transformer, (and the all-important parafeed cap) - wierd in that it is very difficult to predict how it will sound - it can sound great. And, of course, the resistor is smaller and cheaper - but it needs more HT to deliver the same swing as a choke loaded circuit.

If you need the voltage - use a choke, but I think a resistor gives a smoother, more coherent response (in some set-ups). Or I may just be lazy.

Both my amps, SE and PP, are transformer driven in a parafeed connection with a resistor load instead of a choke. My preamp is resistance loaded parafeed.

All this being said - my parafeed SE amp is choke loaded on the output. I'm too lazy to build that big of an HT supply!

Let me say this, too. I'm not nearly smart enough to have figured out any this stuff on my own. Read Steve Bench's article on parafeed - he's someone who really knows his stuff.

TC


Re: Why? [message #8760 is a reply to message #8758] Wed, 26 January 2005 11:58 Go to previous messageGo to next message
TubeCraft is currently offline  TubeCraft
Messages: 30
Registered: May 2009
Baron
Well, in theory, the resistor should load the tube more evenly across a wider frequecy range than a choke. And, there seems to me to be a lot of wierd interaction between a choke load and the coupling transformer, (and the all-important parafeed cap) - wierd in that it is very difficult to predict how it will sound - it can sound great. And, of course, the resistor is smaller and cheaper - but it needs more HT to deliver the same swing as a choke loaded circuit.

If you need the voltage - use a choke, but I think a resistor gives a smoother, more coherent response (in some set-ups). Or I may just be lazy.

Both my amps, SE and PP, are transformer driven in a parafeed connection with a resistor load instead of a choke. My preamp is resistance loaded parafeed.

All this being said - my parafeed SE amp is choke loaded on the output. I'm too lazy to build that big of an HT supply!

Let me say this, too. I'm not nearly smart enough to have figured out any this stuff on my own. Read Steve Bench's article on parafeed - he's someone who really knows his stuff.

TC


Re: Why? [message #8761 is a reply to message #8759] Wed, 26 January 2005 11:59 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
Messages: 4973
Registered: May 2009
Illuminati (13th Degree)
Thanks; Will do. He is the real deal.

Re: Why? [message #8764 is a reply to message #8754] Wed, 26 January 2005 15:19 Go to previous messageGo to next message
akhilesh is currently offline  akhilesh
Messages: 1275
Registered: May 2009
Illuminati (3rd Degree)
"So in the parafeed you need to replace an expensive transformer with an expensive large choke"

Not quite. a transformer wwit ha small gap is MUCH harder to make than a large choke.
-akhilesh

Re: transformers [message #8766 is a reply to message #8746] Thu, 27 January 2005 22:13 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18675
Registered: January 2001
Illuminati (33rd Degree)
I think output and interstage transformers have more requirements than power transformers.

Power transformers need to be efficient at line frequency, and they need to be able to pass current without fatigue. It's nice if they are physically robust too, with sturdy construction and wiring and with laminations that don't vibrate and buzz. But basically, they work at a single frequency and they aren't required to do much but transform line voltage to the levels required.

Output and interstage transformers are required to pass a wide frequency range and may be in the presence of reactive components. They are asked to pass a bandwith of three decades and to be flat even if other reactive values in the circuit change. So in my way of thinking, these are really pretty critical components.

Just my 2ยข

Re: transformers [message #8767 is a reply to message #8766] Fri, 28 January 2005 07:23 Go to previous message
akhilesh is currently offline  akhilesh
Messages: 1275
Registered: May 2009
Illuminati (3rd Degree)
I agree totally, Wayne. ANd this is reflected in the prices, too!
-akhilesh

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