It might be jargon, it might be a shift in expression. I am not sure that a transformer has "impedance" so much. It may be that it has become more common to specify primary inductance than impedance. But if the Sowter and Lundahl listings had been like the Allied listing none of us would have learned a thing.
With the Lundahl datasheets you should look at the recommended upper limit of source impedance. This is roughly equal to the plate impedance of the driver tube when connected through the transformer to the grid of the output tube. According to the Lundahl datasheet for the LL1660/10mA, the Alt S 4:4,5 stepup connection has a recommended source impedance limit of !4 KOhm. In this connection the LL1660 should certainly be suitable for the 76 valve. Another option is the LL1692A. For the LL1692A/18mA version Alt. S, 4:3:5 stepdown the recommended upper source impedance limit is 10KOhm. This is good enough, but if you order the LL1692A with a 10 mA gap the primary inductance will be considerably higher than the 125H for the 18 mA version and hopefully give better performance.
Choices and consequences, I see. The only job for this amp is to drive the horns of an active Altec 2-way. It will never see anything much below 500Hz. Does this promote one ahead of the other?
One thing Ive learned about Interstage Transformers is--
You gotta spend a Lot of dosh for only OK performance.
I do wonder why IT's seem to have this kudos, seeing a simple MOSFET will give better performance and at a huge money saving--That could then be spent where it'll do the most good--The Output Transformer!
You gotta spend a Lot of dosh for only OK performance.
I do wonder why IT's seem to have this kudos, seeing a simple MOSFET will give better performance and at a huge money saving--That could then be spent where it'll do the most good--The Output Transformer!
Agree.
To get good results an IT needs a lot of design effort, and construction is not easy (that's an understatement) .
In the Thirties there was not much else, but now we have options which are, at least Technically, much better and to boot cost way less.
There must be some reason, after all, that interstage transformers all but disappeared, except for a few fans.
Won't talk about "flavour" because taste is personal,to each his own.
To get good results an IT needs a lot of design effort, and construction is not easy (that's an understatement) .
In the Thirties there was not much else, but now we have options which are, at least Technically, much better and to boot cost way less.
There must be some reason, after all, that interstage transformers all but disappeared, except for a few fans.
Won't talk about "flavour" because taste is personal,to each his own.
I use IT transformers in almost all of my current amplifier designs, and there really is no substitute for quality, that said the Lundahl discussed previously should do a pretty good job and is a reasonably economical choice.
To my surprise a good one brings something different to the table sonically than the frequently superior measuring RC coupling. (If you need A2 then transformers or tube or SS followers are the only choices.) I'll spare you the details, I just subjectively like it better. (I use bi-radial horn mids, tweets, and Onken bass bins so I am off on another planet)
You could consider choke loading with coupling capacitor, also provides good results at somewhat less cost. Again Lundahl or Magnequest can fix you up with the right chokes.
To my surprise a good one brings something different to the table sonically than the frequently superior measuring RC coupling. (If you need A2 then transformers or tube or SS followers are the only choices.) I'll spare you the details, I just subjectively like it better. (I use bi-radial horn mids, tweets, and Onken bass bins so I am off on another planet)
You could consider choke loading with coupling capacitor, also provides good results at somewhat less cost. Again Lundahl or Magnequest can fix you up with the right chokes.
Without question output transformers sound different and to my limited knowledge this is not modeled well with equations or test instruments.
I have no creedal allegiance to any electrical component in particular so long as it does the job well. In your experience why does a this MOSFET coupling do as good or potentially a better job in this function as an interstage transformer. It is not a Million Dollar question but it is a $350 question.
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