ok g2 as anode
where to tie the anode and g3?
anode resistance should be as low as possible the MOT has a ratio of 10:1
where to tie the anode and g3?
anode resistance should be as low as possible the MOT has a ratio of 10:1
There are no need to push voltage more than 700-800V in any way. Or try to obtaine "more" power. 40-45W is huge enough for SE A1 class. (The guy who measure the tube in triode mode wrote that the abs max for G2 is about 700-750V.)
The key point for the GU-81M tube in triode mode IS LOW Req to drive low Primary inductance Output transformer.
And it is about 300 ohms !!!
From the sims it is 15Hy of the primary inductance needed for very very low end - read truly low bass without distortion and phase shift. Still has to be big and from quality, because of the higher current, and more gap again because of the current... This OT will be with thick wire, very low Rdc, Secondary even more tick wire, less Rdc... This leading to significantly higher damping factor than ususal SE designs. Relatively small number of turns will produce lower capacitances of the transformer so the HF will be good as lF too.
But is still more friendly to make than for other higher Ri tubes with significantly less undistorted and clear output power.
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Bare in mind the capacitors voltages and rectifiers voltages and current, so it is the goal to make ALL tube power amp. So the "lower" voltages are better in this case.
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One thing is more important - to obtain high input signal in Vp-p for power tube?
In my example is abot 280Vp-p value. And should be capable to cope the dynamic capacitances of the power tube. Generally low Req impedance driver. How low could be calculated and simulated...
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If we want say 2Vrms (5Vp-p cca. ) as input to this power amp, than we need in this case, 280/5=56 X amplification gain pre-output tube... And with low distortion, less than power tube has for max power, otherwise there is no point... Maybe more input voltage because it is a power amp and should be used with Tube preamp?
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Also should be designed to use same power supply without much voltage drop... To keep the dissipation and heat low...
The key point for the GU-81M tube in triode mode IS LOW Req to drive low Primary inductance Output transformer.
And it is about 300 ohms !!!
From the sims it is 15Hy of the primary inductance needed for very very low end - read truly low bass without distortion and phase shift. Still has to be big and from quality, because of the higher current, and more gap again because of the current... This OT will be with thick wire, very low Rdc, Secondary even more tick wire, less Rdc... This leading to significantly higher damping factor than ususal SE designs. Relatively small number of turns will produce lower capacitances of the transformer so the HF will be good as lF too.
But is still more friendly to make than for other higher Ri tubes with significantly less undistorted and clear output power.
.
Bare in mind the capacitors voltages and rectifiers voltages and current, so it is the goal to make ALL tube power amp. So the "lower" voltages are better in this case.
.
One thing is more important - to obtain high input signal in Vp-p for power tube?
In my example is abot 280Vp-p value. And should be capable to cope the dynamic capacitances of the power tube. Generally low Req impedance driver. How low could be calculated and simulated...
.
If we want say 2Vrms (5Vp-p cca. ) as input to this power amp, than we need in this case, 280/5=56 X amplification gain pre-output tube... And with low distortion, less than power tube has for max power, otherwise there is no point... Maybe more input voltage because it is a power amp and should be used with Tube preamp?
.
Also should be designed to use same power supply without much voltage drop... To keep the dissipation and heat low...
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814 in triode mode can be good driver for GU-81M. And probably it is possible to find the obtainable tube from desired -A, higher Va, and with a Cap? To have all tubes with a caps... 🙂
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For rectifiers 3B28 is good. Or some similar.
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I think that 813 can be used as driver tube also?
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So bare in mind about DHTs. Active circuits for DH deserves more space and own bigger heatsink for pass transistors devices. This is a high current DHTs.
So the most rational way to heat the GU-81M is with DC (RC nets). There will be the less dissipation on the Rs...
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For rectifiers 3B28 is good. Or some similar.
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I think that 813 can be used as driver tube also?
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So bare in mind about DHTs. Active circuits for DH deserves more space and own bigger heatsink for pass transistors devices. This is a high current DHTs.
So the most rational way to heat the GU-81M is with DC (RC nets). There will be the less dissipation on the Rs...
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Better way without NFB is to try to design "Super Triode Connection" with that tube.
280v pp to drive the gu81 os quite a lot
triode mode leader to low gain?
is there a way to have higher gain so that an high voltage op amp could be used as driver? Let's say 40-60Vpp?
could use a 1:3 interstage transformator to gain some dB
triode mode leader to low gain?
is there a way to have higher gain so that an high voltage op amp could be used as driver? Let's say 40-60Vpp?
could use a 1:3 interstage transformator to gain some dB
this is for 45W output with given working point and load value...
IF You dont need 45W, input signal can be lower and settings can be different.
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No need to use other device than tube for this.
Step up will only increase Req with square of ratio... 🙁 and capacitances, and huge self distortion.
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IF You dont need 45W, input signal can be lower and settings can be different.
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No need to use other device than tube for this.
Step up will only increase Req with square of ratio... 🙁 and capacitances, and huge self distortion.
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The cathode looks appropriate to me. Probably best to attach it to the middle of the cathode( I think there is a pin for this; if not make a virtual one ). I do PP on AC and it is entirely quite.
Douglas
to do triode operation with low output resistance is:
G2 and G3 connected to anode vith 300 to 600v supply 100mA current
G1 some negative bias, or maybe 0v bias for class A2
ideal output transformer ratio 100:1?
since I will use this amp only for bass up to 400hz my plan is the following:
use a microwave oven transformer MOT (230 to 2000v) as output transformer,
connect the speaker to the filament winding and anode to the 2000v winding
or connect the speaker to the 230v primary directly or via a second toroidal transformer 230v to 24v
making an actual ratio of 2000/24= 83:1
G2 and G3 connected to anode vith 300 to 600v supply 100mA current
G1 some negative bias, or maybe 0v bias for class A2
ideal output transformer ratio 100:1?
since I will use this amp only for bass up to 400hz my plan is the following:
use a microwave oven transformer MOT (230 to 2000v) as output transformer,
connect the speaker to the filament winding and anode to the 2000v winding
or connect the speaker to the 230v primary directly or via a second toroidal transformer 230v to 24v
making an actual ratio of 2000/24= 83:1
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Here is how to deal with the GU-81m in SE:
https://www.diyaudio.com/community/...ntode-retaliation.373257/page-12#post-7229160
Douglas
https://www.diyaudio.com/community/...ntode-retaliation.373257/page-12#post-7229160
Douglas
Actually not 🙁
I dont see any point to "mix" OP amps, MOSFETS, Solid State rectifiers or so into the pure Vaccum tube design?
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I dont see any point to "mix" OP amps, MOSFETS, Solid State rectifiers or so into the pure Vaccum tube design?
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No it is not
base concept here
http://www.gem.hi-ho.ne.jp/katsu-san/audio/what_STC1_english.html
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one example
http://www.ne.jp/asahi/evo/amp/kt90/report.htm
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