They were talking about a 100R on the cathodes of the 6CA7's to create a mixed biasing scheme.
20-20
Quote:
I'm not getting how a diode on the secondary limits the inrush current when a diode is not a current limiting device. About all it it can do is drop the forward voltage the usual @.7v which is not the problem with inrush current. The reverse peaks are not the problem through the GZ34, which is what a diode would supplement.
A good old GZ34 doesn't need any help. However the new crop of reissues if they are truly subpar could benefit from a power resistor on the CT to bring the DCR up a bit, to make them happy.
Who said anything about putting diodes on the secondary?😱
Why don't you try the two diodes on the 5Ar4 and see what you think. I've used them in my problematic Quicksilver mono blocks and went from replacing the (2) 5ar4's roughly every 4-5 months to more than 4 years and still counting. I'm not an engineer by any means but the explanation to me was that the diodes in the primary took the strain off the 5Ar4 and the 5Ar4 basically was there as a slow start device. Take a look at the schematic of the Quicksilver mono block amp and you will see that the cap size is very large and exceeds the design goal of the 5Ar4 tube. But hey don't take my word for anything 🙄 I've just used it and it works. No need to re-invent the wheel just drop the two diodes in on the primary and you will find out that any run of the mill 5Ar4 will last.
Quote:
I'm not getting how a diode on the secondary limits the inrush current when a diode is not a current limiting device. About all it it can do is drop the forward voltage the usual @.7v which is not the problem with inrush current. The reverse peaks are not the problem through the GZ34, which is what a diode would supplement.
A good old GZ34 doesn't need any help. However the new crop of reissues if they are truly subpar could benefit from a power resistor on the CT to bring the DCR up a bit, to make them happy.
Who said anything about putting diodes on the secondary?😱
Why don't you try the two diodes on the 5Ar4 and see what you think. I've used them in my problematic Quicksilver mono blocks and went from replacing the (2) 5ar4's roughly every 4-5 months to more than 4 years and still counting. I'm not an engineer by any means but the explanation to me was that the diodes in the primary took the strain off the 5Ar4 and the 5Ar4 basically was there as a slow start device. Take a look at the schematic of the Quicksilver mono block amp and you will see that the cap size is very large and exceeds the design goal of the 5Ar4 tube. But hey don't take my word for anything 🙄 I've just used it and it works. No need to re-invent the wheel just drop the two diodes in on the primary and you will find out that any run of the mill 5Ar4 will last.
Your placement still isn't clear to me. You say try them ON the 5AR4 and then you say they should be in the PRIMARY.
Do you put the diodes on the DC rectified side of the 5AR4 or the tranny side (secondary)? Or are you putting them in the primary?
When you say you were told the diodes "took the strain off" why not use some real electronics lingo that actually describes the function of the diodes by the change in current flow? No need for math, just some ballpark estimate of the reduction in current rate or direction. And how that takes the inrush down to keep a 5AR4 from arcing.
The secondary.
So I'll stick to electronics theory here that a diode ahead of the 5AR4 only supports a higher PIV. Not current limiting for the purpose of creating a minimum series resistance required for inrush current limiting. The ST-70 power supply doesn't create a PIV concern, the voltages are too low. If they were high enough to blow back through the 5AR4 then they would be overvolting the input capacitor and it would go off like dynamite.
20-20
Imagine putting two diodes in series withe the transformers secondary going to pin 4 and six I believe (the plates of the rectifier tube. The diodes rectify the AC prior and the tube conducts (the slow warm up) and there is no more arch over problem thus a cheap run of the mill 5AR4 will survive and there won't be a need in put a $125.00 Mullard in. I don't need any electronics lingo to explain it...I have your for that.😉🙄
To make a long story short it works🙂
Imagine putting two diodes in series withe the transformers secondary going to pin 4 and six I believe (the plates of the rectifier tube. The diodes rectify the AC prior and the tube conducts (the slow warm up) and there is no more arch over problem thus a cheap run of the mill 5AR4 will survive and there won't be a need in put a $125.00 Mullard in. I don't need any electronics lingo to explain it...I have your for that.😉🙄
To make a long story short it works🙂
That's my reason as well. I use < $20 5AR4 and so far so good. I even bought a spare just in case (easy to do since it's cheap).
Hey I've been doing a lot of research on the ST-70 and came across this driver board and wanted to see some feed back on it
http://www.kta-hifi.net/projects/amp_page/st70amp/ST70R.pdf
The only thing I see right now that throws me off from other is why there is 2 bias points per channel where other circuits there connected together for each channel or I'm I seeing something wrong
Thanks
http://www.kta-hifi.net/projects/amp_page/st70amp/ST70R.pdf
The only thing I see right now that throws me off from other is why there is 2 bias points per channel where other circuits there connected together for each channel or I'm I seeing something wrong
Thanks
Allows you to make sure that the tubes are well matched, and there are also implications in terms of distortion spectra. (IIRC and I may not, I recall there was slightly more 3rd harmonic with the common cathode connection.) I preferred it this way when I designed it 20+ yrs ago..
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