I want to thank Stephe for sharing the Youtube video and her adventure with the amp that I am considering to build.
I want to clarify a few quesions
1) can I use solid state diode power supply for the B+ ?
2) What about using an ac to dc power smps from Meanwell for the heaters ?
3) I notice that most output transformer show usage of 2.5 or 3.5 K output transformer . Is there any issue with 5K output transformer ?
What is the wattage of the output transformer ?
Thank you
Kp93300
I want to clarify a few quesions
1) can I use solid state diode power supply for the B+ ?
2) What about using an ac to dc power smps from Meanwell for the heaters ?
3) I notice that most output transformer show usage of 2.5 or 3.5 K output transformer . Is there any issue with 5K output transformer ?
What is the wattage of the output transformer ?
Thank you
Kp93300
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Compare this to https://www.diyaudio.com/forums/tubes-valves/373171-advice-set-amp-build.html#post6679841 post 1 - which one is the original ?
5K is fine for the output transformer. Pout will be roughly 5-6 watts. You could squeeze a meaningless watt or two out of that transformer combo by going to solid state rectification and adjusting the bias resistor. I’ve never tried a smps for the filaments but the Coleman regulators are inexpensive and work well.
They are both 'no brainers', just a slightly different build with similar parts. There are close to an infinite way these can be put together with good results. And low mu triodes like the 300B are very tolerant to the OPT used, within reason.
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In the youtube, Stephe justifies why she change the value of the 27K from the B+.
The change result in more voltage swing for the 300B .
The change result in more voltage swing for the 300B .
I intend to buy a 3.5K output transformer.
What is the minimum current rating to specify ?
Is 100 ma maximum current capacity adequate ?
Thanks
kp93300
What is the minimum current rating to specify ?
Is 100 ma maximum current capacity adequate ?
Thanks
kp93300
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I asked why not just build with a pentode input ie. EL84.
Response was that it was harder to drive than the trioded cascode input.
I'd walk away.
Response was that it was harder to drive than the trioded cascode input.
I'd walk away.
1) can I use solid state diode power supply for the B+ ?
Yeah, I think 350-0-350 would be fine or whatever you need to get B+ 430v
3) I notice that most output transformer show usage of 2.5 or 3.5 K output transformer . Is there any issue with 5K output transformer ?
Someone was using CXSE25-8-3k Edcor OPTs with this schematic without problem
Is 100 ma maximum current capacity adequate ?
Need 200mA both channels or 90mA mono
Yeah, I think 350-0-350 would be fine or whatever you need to get B+ 430v
3) I notice that most output transformer show usage of 2.5 or 3.5 K output transformer . Is there any issue with 5K output transformer ?
Someone was using CXSE25-8-3k Edcor OPTs with this schematic without problem
Is 100 ma maximum current capacity adequate ?
Need 200mA both channels or 90mA mono
I prefer 5K with a 300b and so do others, though it depends on the OPT and operating point. Not a major worry.
You probably only need 70mA current for a typical 300b operating point, so 100mA per OPT would be fine.
Using a Meanwell for the heaters is fine. Their outputs are floating and they are very clean. Just make sure you rate the SMPS for about twice the nominal heater current so it can cope with inrush current.
Cheers
Ian
Cheers
Ian
What is your timetable for this project? When can we expect to see the performance result, 3 months, One year??🙂
I have used both 3.5k ohm and 5k ohm output transformers with my 300B amp and don't think the change is very significant: they both sound excellent. One point I would make is that I would abandon the Sun Audio topology with the 6SN7 entirely and use the Western Electric 91 amp as my inspiration and drive the 300B with a 6J7. There is actually a Sun Audio SV 2A3 (the same amp with the filament tap connected in series) on auction right now that was converted to the WE 91 amp schematic. You should be able to drive the 300B to full output with the 6J7 and you could also regulate the screen grid with zeners as Yamamoto does in his amps.
Think I'll pass on that one!! Reading the not so fine print-
All tube is good, install resistor for 120V operation don't need transformer
May not pass UL, CSA or anything else. Pls don't set that Christmas tree on fire! With that kind of gelt ($$$) I'd buy another garden tractor.🙂
'you could also regulate the screen grid with zeners as Yamamoto does in his amps'.
What kind of benefit results from Zenering the screens? Can it be measured? Or do we have to depend on our imaginations?😀
All tube is good, install resistor for 120V operation don't need transformer
May not pass UL, CSA or anything else. Pls don't set that Christmas tree on fire! With that kind of gelt ($$$) I'd buy another garden tractor.🙂
'you could also regulate the screen grid with zeners as Yamamoto does in his amps'.
What kind of benefit results from Zenering the screens? Can it be measured? Or do we have to depend on our imaginations?😀
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It should be obvious to the most dense casual observer that I was not advocating the purchase of the amp on epay: I was advocating for ditching the original Sun Audio topology for the Western Electric 91, as was done with the one on auction. It is simply a 6J7 pentode driving the 300B. The original Asano topology that has been roundly denigrated here (and I agree) is not worth building. Here is the circuit I am suggesting.
As for regulating the 6J7 screen grids with zeners: is it really so wrong to have a little fun?
As for regulating the 6J7 screen grids with zeners: is it really so wrong to have a little fun?
The circuit in post#1 is not using the "Sun Audio" topology, the circuit diagram has been edited to convert the original 6SN7 cascade to a cascode. Seems a perfectly valid choice.
l am gathering the parts now and expect to get it operating in about 6 to 9 months
Here is the circuit I am suggesting.
Yeh, I've got that article & the rest of Joe Roberts magazines. Did Paul Joppa ever build his proposed version of the WE amplifier?
Joe's magazines did have some interesting stuff. And some containing gross errors. I had some correspondence with Joe, he confided that some of the contributors had problems getting their stuff to perform. OTOH Alan Douglas & Norman Crowhurst also appeared in those pages.
Tying the screen of a voltage amplifier pentode to a zener hardly makes sense, the screen resister is there to stabilize the operating point of the tube as it ages. So the zener may be OK for a while, then what? The bypassed screen resister (not a voltage divider) provides about 10 db NFB at LF as OP stabilization, I had a look at this a few years ago on the bench. The results are here.
And something seldom seen, a plot of screen curves!😀
I didn't mean to imply you recommended that amp on eBay, that was MY opinion!🙂
Yeh, I've got that article & the rest of Joe Roberts magazines. Did Paul Joppa ever build his proposed version of the WE amplifier?
Joe's magazines did have some interesting stuff. And some containing gross errors. I had some correspondence with Joe, he confided that some of the contributors had problems getting their stuff to perform. OTOH Alan Douglas & Norman Crowhurst also appeared in those pages.
Tying the screen of a voltage amplifier pentode to a zener hardly makes sense, the screen resister is there to stabilize the operating point of the tube as it ages. So the zener may be OK for a while, then what? The bypassed screen resister (not a voltage divider) provides about 10 db NFB at LF as OP stabilization, I had a look at this a few years ago on the bench. The results are here.
And something seldom seen, a plot of screen curves!😀
I didn't mean to imply you recommended that amp on eBay, that was MY opinion!🙂
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Let's be clear, my reply was "That's an option, but a cascoded 6SN7 is very linear, is a great sounding tube and I have a pile of them to choose from 🙂 Plus not all pentodes are easy enough to drive off of line level on the grid."
I think it's pretty clear you're not going to get 140-160Vpp into a 300B grid from a 3Vpp signal using just any 'ol pentode tube. And you didn't mention any specific tube, just: why did you do this cascode instead of just using a pentode.
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