I would think some Thyratrons would work better for firing off fuel injectors (high current capable), provided they are fast enough.
Mercury/argon thyratrons are rated <150Hz
Hydrogen or Deuterium (multi kilovolts) does work in radars around 1000PPM
Not sure about PWM needed for injectors, how to turn them off variably 😀
Hydrogen or Deuterium (multi kilovolts) does work in radars around 1000PPM
Not sure about PWM needed for injectors, how to turn them off variably 😀
"Not sure about PWM needed for injectors, how to turn them off variably"
Ugh, that IS a problem. I guess there were some fancy thyratrons with a turn off gate. Try and find them now though... There is the technique of using another thyratron/scr with a bucking coil to make a series turn off pulse for the 1st thyratron. (I think that scheme likes to be overlapped/complementary however)
Is this going to be an injector per cylinder? An O2 Fdbk sensor? (visualizing a rack full of tube electronics now) Unless some PWM chip is being considered, I doubt drifting tube stuff is going to be very stable or compact or safe. Drive over a big bump and the smoke starts rolling. Engine damage tear downs coming soon...
Ugh, that IS a problem. I guess there were some fancy thyratrons with a turn off gate. Try and find them now though... There is the technique of using another thyratron/scr with a bucking coil to make a series turn off pulse for the 1st thyratron. (I think that scheme likes to be overlapped/complementary however)
Is this going to be an injector per cylinder? An O2 Fdbk sensor? (visualizing a rack full of tube electronics now) Unless some PWM chip is being considered, I doubt drifting tube stuff is going to be very stable or compact or safe. Drive over a big bump and the smoke starts rolling. Engine damage tear downs coming soon...
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How about if I tune the load with B+?
I could use a Varic for B+, and a halving transformer from B+ to screen so that they move in direct relation to each other?
"I could use a Varic for B+, and a halving transformer from B+ to screen so that they move in direct relation to each other?"
That will cause the tube dissipation to skyrocket when B+ and Vg2 are increased together. Max power output ability would increase though. Output impedance of the tube(s) varies with average tube current, not voltage. Which will change tube dissipation also, so some hefty reserve tube Pdiss needed. 2nd harmonic cancels out in P-P anyway, so only odd harmonics will be varied. Odds usually not wanted at all.
To vary 2nd harmonic, just unbalance the phase splitter resistors some. A relatively small effect on tube Pdiss then as well, if 2nd H is kept within reason. Class A operation works best for this, but class AB could likely get away with a limited amount of imbalance.
Or is this back to SE mode now?
26E6s will need to be "trioded" or some local N Fdbk used to get the output Z down some (SE or P-P).
Without careful design and goals, this could well end up becoming a fire breathing, tube eating "deviant" amplifier!
Good thing those tubes were cheap. Paralleled tubes will be more likely to have run-away problems too, unless individual bias current control pots are included. I suggest operating the tubes at 1/2 rated Pdiss for any "left field" type experiments.
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That will cause the tube dissipation to skyrocket when B+ and Vg2 are increased together. Max power output ability would increase though. Output impedance of the tube(s) varies with average tube current, not voltage. Which will change tube dissipation also, so some hefty reserve tube Pdiss needed. 2nd harmonic cancels out in P-P anyway, so only odd harmonics will be varied. Odds usually not wanted at all.
To vary 2nd harmonic, just unbalance the phase splitter resistors some. A relatively small effect on tube Pdiss then as well, if 2nd H is kept within reason. Class A operation works best for this, but class AB could likely get away with a limited amount of imbalance.
Or is this back to SE mode now?
26E6s will need to be "trioded" or some local N Fdbk used to get the output Z down some (SE or P-P).
Without careful design and goals, this could well end up becoming a fire breathing, tube eating "deviant" amplifier!
Good thing those tubes were cheap. Paralleled tubes will be more likely to have run-away problems too, unless individual bias current control pots are included. I suggest operating the tubes at 1/2 rated Pdiss for any "left field" type experiments.
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The current target is to test my brain, and see if I like even harmonics as much as I think I do. Therefore Class A SE with slightly low output load on the tubes (the curves show that odd harmonics drop while the even rise, with a slight increase in total distortion)
Therefore the current plan, working from the speakers back:
4 Ohm speakers, 104db @ 1W @ 1 meter (Klipschorns) (db level is sometimes challenged as optimistic)
Edcor GSXE15-1.7K wired for 8 ohm rather than 4 (explained below)
Class A SE, using three 6Y6 in parallel (actually the military version which is 26E6)
B+ controlled by a Variac, targeting 200-240V, but capable of 300
Ultra Linear, with a switch for triode
Cathode bias of 333 Ohm @ 240V and 2550 output load should provide .045 A each, with a published limit of .066A.
At 240V I am 40V over the limit, but other threads have reported success up to 300V
The published output load at 200V is 2600 Ohms (and 2000 Ohms at 135V). So my output load is per the spec. sheet at B+ of 200, and shifts as voltage is increased to 240V where I extrapolate 3555 Ohm as the normal load . This "under-load" should shift the odd component of total distortion from 75% of total distortion to 25%
https://frank.pocnet.net/sheets/127/6/6Y6G.pdf
With 3 tubes in parallel I wanted 850 Oms on the output transformer to simulate the 2550 load line. This does not exist so I picked the 1700 ohm input and 8 ohm output to provide 850 Ohms on the 4 Ohm speakers
One problem is that Edcor expected higher voltage tubes to be used, so even though I should be OK with the 15 W rating, the 14.6 winding ratio will provide 175 mA to a transformer rated for 130. How much headroom should I expect from the output transformer?
I will use a 24V power supply for the 26V heaters, and adjust the DC down a bit to pursue the life reported in this link
The Tube CAD Journal: Voltage regulators for the 2A3
Thoughts?
Therefore the current plan, working from the speakers back:
4 Ohm speakers, 104db @ 1W @ 1 meter (Klipschorns) (db level is sometimes challenged as optimistic)
Edcor GSXE15-1.7K wired for 8 ohm rather than 4 (explained below)
Class A SE, using three 6Y6 in parallel (actually the military version which is 26E6)
B+ controlled by a Variac, targeting 200-240V, but capable of 300
Ultra Linear, with a switch for triode
Cathode bias of 333 Ohm @ 240V and 2550 output load should provide .045 A each, with a published limit of .066A.
At 240V I am 40V over the limit, but other threads have reported success up to 300V
The published output load at 200V is 2600 Ohms (and 2000 Ohms at 135V). So my output load is per the spec. sheet at B+ of 200, and shifts as voltage is increased to 240V where I extrapolate 3555 Ohm as the normal load . This "under-load" should shift the odd component of total distortion from 75% of total distortion to 25%
https://frank.pocnet.net/sheets/127/6/6Y6G.pdf
With 3 tubes in parallel I wanted 850 Oms on the output transformer to simulate the 2550 load line. This does not exist so I picked the 1700 ohm input and 8 ohm output to provide 850 Ohms on the 4 Ohm speakers
One problem is that Edcor expected higher voltage tubes to be used, so even though I should be OK with the 15 W rating, the 14.6 winding ratio will provide 175 mA to a transformer rated for 130. How much headroom should I expect from the output transformer?
I will use a 24V power supply for the 26V heaters, and adjust the DC down a bit to pursue the life reported in this link
The Tube CAD Journal: Voltage regulators for the 2A3
Thoughts?
Probably less than 5%, in fact, you usually want to have some cushion, so the 130mA should be derated some.
That is what I feared.
The CXSE will handle the current, but nothing in the 800-900 Ohm primary is available (from Lundahl either).
I could move up to 4 tubes and use the CXSE25-1.25K for 8 Ohms, or down to 2 tubes and return to the GXSE line.
I am worried that 2 of these little tubes in triode mode (about 3.5 W total) just will not be enough, even with the Cornerhorns.
It depends on how loud you listen to the music, since the Cornerhorns are so efficient, you really do not need that much power, so 2x triode may do the trick.
I assume run-away is due to imperfectly matched tubes, bias resistors, etc.?
I noticed that some parallel circuits use a single resistor for cathode bias so every tube sees the same resistance. Does this help?
My tubes are from a single lot produced at the height of tube production (August of 1956). Does this help?
Or should I still use a pot on each cathode to tune them?
Note that I am targeting .045 mA on a plate rated for .066 which hopefully provides some headroom.
For PSE you want the ability to bias each end-stage tube/valve individually. This allows you to better adjust current for mis-matched or aging tubes/valves.
Imho the only reasonable way to do this is by using a negative grid reference, and an individual bias trimmer (+ decoupling cap) for each tube/valve.
It may seem a bit fastidious, but its fairly easy and you won't regret being able to tune each tube/valve.
Also, with negative grid bias, your B+ often doesn't need to be quite so high, and you don't need to concern yourself with hot cathode resistors and their associated by-pass capacitors. 😉
Ian
Imho the only reasonable way to do this is by using a negative grid reference, and an individual bias trimmer (+ decoupling cap) for each tube/valve.
It may seem a bit fastidious, but its fairly easy and you won't regret being able to tune each tube/valve.
Also, with negative grid bias, your B+ often doesn't need to be quite so high, and you don't need to concern yourself with hot cathode resistors and their associated by-pass capacitors. 😉
Ian
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Will I lose the self-biasing of the cathode resistor? If so I will need to change the neg. grid bias every time I change B+?
What should the new title be? Greg's Egregious Amp?
In any case, I need to continue working backwards through the amp into tone controls, pre-amp, etc., even further from the OPT
Probably. But if you change B+ then you should be considering your bias point anyway, and last time I checked, turning a screw was easier than soldering in a new cathode resistor.
Hey greg. Your speakers are 104db. How big is the room for this set-up?
I run 104db speakers on a 1 watt '45 SE amplifier and the sound is delightful.
Also, Look here:
Single-Ended 6Y6 Amplifier | Evil Science Audio
Ian
p.s. using your 1.7k:8k transformer as a 850Ohm:4Ohm has some problems. Yes, it will work, but if your primary inductance is not be enough, then your low frequency could suffer. I'm not an expert here, just warning you... Of course feedback can be applied to fix things too.....
I run 104db speakers on a 1 watt '45 SE amplifier and the sound is delightful.
Also, Look here:
Single-Ended 6Y6 Amplifier | Evil Science Audio
Ian
p.s. using your 1.7k:8k transformer as a 850Ohm:4Ohm has some problems. Yes, it will work, but if your primary inductance is not be enough, then your low frequency could suffer. I'm not an expert here, just warning you... Of course feedback can be applied to fix things too.....
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