Cgf is higher: closer together.
100Hz 16pF
1k 15.2pF
10k 14.7pF
100k 14.32pF
I'm not sure, that static measurements more meaningful, but shows, that brutally large surfaces results relative high capacitances.
Nonetheless EML 20A/B tubes are very well behaved.
Thanks 🙂
Yes You right surfaces are huge, grid is also more frequent for higher mju...
but Cgf decreasing values with rise of fo, when Cga increasing...
Probably Cgf will be smaller with voltage aplied?
Yes You right surfaces are huge, grid is also more frequent for higher mju...
but Cgf decreasing values with rise of fo, when Cga increasing...
Probably Cgf will be smaller with voltage aplied?
Agreed with euro21 that 600V supply for the rs282 is way too low with around 2W useful power
and the input stage has to deliver just 50Vp-p for that job since the -25V, 25mA, 600V is workiong point.
With 9.6K load.
not wort even to try...
.
Better, with -45V, 900V, 64mA point. About 6.9W
But You dont have PS for this...
.
These are static datas only...
.
and the input stage has to deliver just 50Vp-p for that job since the -25V, 25mA, 600V is workiong point.
With 9.6K load.
not wort even to try...
.
Better, with -45V, 900V, 64mA point. About 6.9W
But You dont have PS for this...
.
These are static datas only...
.
Anopther option to have RS282 in aplifier is to use this tube as input stage.
good aplification, relatively low distortion and in "lower" Va range. Pa=2 x Pheat cca.
Ua=450V, Ia=55mA, Ug=-10V
for (4Vrms) 5.66Vp-p Input => 133Vp-p output
can output even more...
.
RS282 will last forever if nos used before...
And to find proper output tube for given power supply?
.
Static datas for the 2Vrma input and 4V input.
And L load or transformer load
.
good aplification, relatively low distortion and in "lower" Va range. Pa=2 x Pheat cca.
Ua=450V, Ia=55mA, Ug=-10V
for (4Vrms) 5.66Vp-p Input => 133Vp-p output
can output even more...
.
RS282 will last forever if nos used before...
And to find proper output tube for given power supply?
.
Static datas for the 2Vrma input and 4V input.
And L load or transformer load
.
Zoran, thanks again for all the help. I do have a power transformer that will produce 900V. My only challenge was the chassis needs to be modified. I do want to use the RS282 as the output tube, so I will modify the chassis. So, here is where we are, I think 🤔
driver tube EML 20B: 412V, 40ma -7V
output tube RS 282: 900V, 63mA -45V, Pout=6.9W
And, no input transformer.
Sound correct?
driver tube EML 20B: 412V, 40ma -7V
output tube RS 282: 900V, 63mA -45V, Pout=6.9W
And, no input transformer.
Sound correct?
Pat,
Are you sure, that 9k6 OPT has 45H?
It's not so high....
Do you know other parameters (Cp, Lsp, DCR of secondary)?
With this inductance, the lower -3dB point goes too high (simulation shows 17Hz).
With such operating point as Zoran suggested in #64, the simulated power 6.02W at 4.74% THD.
I would prefer higher B++.
p.s. EML20A hasn't enough gain to drive this solution to A1 limit at 2V RMS. About 2.2V requiring.
Are you sure, that 9k6 OPT has 45H?
It's not so high....
Do you know other parameters (Cp, Lsp, DCR of secondary)?
With this inductance, the lower -3dB point goes too high (simulation shows 17Hz).
With such operating point as Zoran suggested in #64, the simulated power 6.02W at 4.74% THD.
I would prefer higher B++.
p.s. EML20A hasn't enough gain to drive this solution to A1 limit at 2V RMS. About 2.2V requiring.
If we're speaking of RS282 with a quoted datasheet Ra of 3.3k, the -3dB roll-off goes to 9.2Hz under loaded OPT conditions. If I'm not mistaken on the tube's internal resistance value
However the OPT was made for optimal conditions with a GM70 output tube.
Pat,
You wrote systematicly 9k6 ... and the OPT is 9k1:9. 😵
Wrong initial parameters= wrong result. 😱
You wrote systematicly 9k6 ... and the OPT is 9k1:9. 😵
Wrong initial parameters= wrong result. 😱
Alexander,
Are you measured Cp, Lsp?
I assumed 1200pF, 6mH, so simulation working with these parameters.
Are you measured Cp, Lsp?
I assumed 1200pF, 6mH, so simulation working with these parameters.
Bela - I should have adjusted the 20B operating point, as the IT can handle 25-30mA. Alexander always builds in some headroom. He is going to get me the headroom number soon.
Hint. The power transformer is oversized as well, made for cool operation at the rating. However I'm not at my workplace at the moment to dig through the specs, but by rough say I'm pretty sure it can sustain +33% of AC current through the secondary with no ill effect.
