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In Reply to: My measurements posted by serus on September 29, 2004 at 21:47:59:
we're talking about 2 different things, you, the whole amp ( I think ) and I am only refering to the front end, loaded a little bit lighter than it would be in service. plus a 1M/40 pF probe circuit, alos balanced. They all turned square waves to something like a saw tooth by 10k, not to mention being imbalanced.Add a loop NFB and it can get fairly clean at the amp's output.
regards.
Douglas
!
Beware the man who behaves deceitfully towards others, for there is nothing else to save you from his deceiving you
Follow Ups:
I wouldn't get too stuck on square wave response, despite the popularity in the "free press". My amp has zero feedback, so the front-end response is just that - and it shows a tremendous rise fall time.
The front-end by itself extends to well over 500 KHz, while the whole amp from input to 8 ohm output (I measured at 10 watts) extends to 80 KHz - without any global feedback.
The front-end produces a near-perfect 10 KHz square wave. The amp as a whole shows some smoothing of rise and fall, as one might expect. But do you really care when it extends beyond the last RIAA mandated pole (that very few implement anyway...), not to mention the roloff of your super tweeters at 40 KHz (typical) and your average ear at 13 KHz (as I found in a group test!)...
quoted> > > The front-end produces a near-perfect 10 KHz square wave.into what load? try it through equal coupling caps and a grid resistor. Add to this a scope probe and it will probably look like a power valve grid, or at least enough to make some judgements.
Don't worry, not hung up on the square wave response, just a measurement ref. and test method. WIth loads other than the 'scope probe, response sucked on my test rig. B+ in the 420V range, plate V of the amplifier stage about a fourth...
Clearly we are doing something different, else our results should match more closely.
regards,
Douglas
!
Beware the man who behaves deceitfully towards others, for there is nothing else to save you from his deceiving you
> try it through equal coupling caps and a grid resistor.Load was 100K bias resistor and a standard probe.
The difference is a 12AT7 at 4 mA vs. a 12AX7...My friend built a second amp and measured 175 VDC on the voltage amp plate and 130 VDC plate-to-cathode on the splitter, just intended by design.
Start with a 500 volt supply, a 12BY7 for the voltage amp, and direct couple it to a 7233 running with 6k loads...I'll bet it will run to past a hundred kHz before it thinks about dropping a volt out of 40.
regards,
Douglas
!
Beware the man who behaves deceitfully towards others, for there is nothing else to save you from his deceiving you
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