Thank you, but my issue was with adding a second quote to a post and losing the attribution and first quote. I'm not smart enough to get a fix to stick back into the body of my post. It's OK; there's lots of things I don't know how to work. I can live with it - we live in a broken world.
All good fortune,
Chris
All good fortune,
Chris
the "quote" button at the top ( " ), you click on it and you will search for what you want to quote as many times as you need
The only way I can make nested quotes work is to quote both posts to get the opening tags and then use the "Toggle BB Code" button to nest them manually like this (take out the spaces after each [ in the tags shown below).
[ QUOTE="Chris Hornbeck, post: 7574372, member: 177867"]
I can live with it - we live in a broken world.
[ QUOTE="huggygood, post: 7574383, member: 172664"]
we live in a broken world.
[ /QUOTE]
[ /QUOTE]
Yes we are. Tomorrow I'll get back to load line experiments with the 6SL7 now that I know how. 🙂
I have come too far to quit now.
I guess it's going to be a while before I can get proper output transformers from China because Chinese New Year is almost here. Every year I shop the massive discounts for the Chinese New Year sale, but last year it took a month just for my items to leave China. All of the orders really add up from the sale, and the shipments just sit at the warehouses or at the airport in China for a month as almost everyone is on vacation for 1-2 weeks, and when they reopen there is such a massive backup that it takes a while to clear the backup. Oh well. Maybe I can get bigger ones due to the savings.
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Would someone check my work please? I think this will be just enough voltage swing to drive the EL34 (~335V B+, ~80-90% dissipation) that follows, correct? Or have I underestimated the swing required for that? All math shown below.
Also, do I have that 330R grid stopper correct? The original schematic does not use one and neither does my other Chinese amp.
1) DC plate load line (red)
end points:
a) Mark the bottom point of the line using B+ for the tube.
b) Calculate the left end of the load line using Ohm's law. Add the resistance of the
cathode and plate resistors because all the current that flows through the tube has
to flow through those two resistors.
c) Connect the two points
100k plate load resistor, 1.5k cathode resistor+150R NFB resistor, 320V B+
320/(100000+1650) * 1000 = 3.14mA
2) Cathode Load Line (purple)
Plot two points on the curved grid lines on opposite sides of the DC plate load line.
The size of the cathode resistor sets the operating point, which is the intersection of the
plate and cathode load lines (green).
-1.5 grid line = 1.5/1650 = 0.909mA
-2.5 grid line = 2.5/1650 = 1.515mA
3) AC load line (yellow)
draw the line from B+ at the bottom to the current on the left, then shift the line left until it crosses the operating point
100k plate resistor
330k grid leak follows
1/((1/100000) + (1/330000)) = 76744 Ohm impedence
320/76744 *1000 = 4.17mA
6SL7 bypass capacitor
-------------------------------
gm of 6SL7 is 1.6mA/V
C=(gm + 1/R)/(2πfc)
C=(.0016A/V + (1/1500))/(2*3.14*5Hz))
C=(.0016 + 0.000666)/(31.4)
C=0.000072186 = 72uF
try 100uF
Also, do I have that 330R grid stopper correct? The original schematic does not use one and neither does my other Chinese amp.
1) DC plate load line (red)
end points:
a) Mark the bottom point of the line using B+ for the tube.
b) Calculate the left end of the load line using Ohm's law. Add the resistance of the
cathode and plate resistors because all the current that flows through the tube has
to flow through those two resistors.
c) Connect the two points
100k plate load resistor, 1.5k cathode resistor+150R NFB resistor, 320V B+
320/(100000+1650) * 1000 = 3.14mA
2) Cathode Load Line (purple)
Plot two points on the curved grid lines on opposite sides of the DC plate load line.
The size of the cathode resistor sets the operating point, which is the intersection of the
plate and cathode load lines (green).
-1.5 grid line = 1.5/1650 = 0.909mA
-2.5 grid line = 2.5/1650 = 1.515mA
3) AC load line (yellow)
draw the line from B+ at the bottom to the current on the left, then shift the line left until it crosses the operating point
100k plate resistor
330k grid leak follows
1/((1/100000) + (1/330000)) = 76744 Ohm impedence
320/76744 *1000 = 4.17mA
6SL7 bypass capacitor
-------------------------------
gm of 6SL7 is 1.6mA/V
C=(gm + 1/R)/(2πfc)
C=(.0016A/V + (1/1500))/(2*3.14*5Hz))
C=(.0016 + 0.000666)/(31.4)
C=0.000072186 = 72uF
try 100uF
Driver stage done then. Hope it works.
I put all the calculations here, so maybe they will help someone in the future see how to do it.
I have a power supply PCB and its parts that puts out 300V regulated for the EL34 screens. Regulation seems to be one factor in preventing "pentode" sound. It works in my other Chinese pentode amp. Waiting for Chinese New Year sale next week to get proper OPTs.
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I am rebuilding mine with an Akido front end / gain stage and depending on the results, might upgrade the HT transformer and OPTs so I can make a parallel SE version.
Lots of useful info, as well as pcbs and kits:
https://glass-ware.stores.turbify.net/listheam.html (just ordered his Unbalancer pcb for my dual dac - his 12AX7s are a great price ($13each)
Have you a link to your Aliexpress OPT?
Lots of useful info, as well as pcbs and kits:
https://glass-ware.stores.turbify.net/listheam.html (just ordered his Unbalancer pcb for my dual dac - his 12AX7s are a great price ($13each)
Have you a link to your Aliexpress OPT?
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I would argue that there are no special evil spirits involved in pentode valves, or in semi-cons with pentode curves, or even in semi-cons with pentode curves and diode-y inputs. Unless we're listening to Edison cylinders or shellacs through pre-War playback machines, we're likely listening through hundreds or thousands or more NotTriode amplifying stages. Such is life, and we soldier on.
One thing that we primates do hear well is broad changes in frequency response (sensitivity at the 1dB level, better than we hear most things) so an amplifier's contribution to frequency response is its dominant initial characteristic. Later we may hear its various distortions and modulations, but we immediately hear frequency response, just like we do with speakers.
And to have identical frequency responses into a complex impedance load like a real speaker, amplifiers must have the same source impedance into that load. The amplifier's source impedance and the speaker's load impedance are a simple voltage divider. No amplifier is a perfectly zero source impedance and no speaker is a perfectly resistive (meaning equal impedance independent of frequency) load. Modern (Not! valve) amplifiers and modern speakers are designed for the only possible repeatably common paradigm, a zero impedance source and a who-cares? load - the resulting frequency response will be predictable, and all modern amplifiers, at first blush, sound identical.
For DIY, especially for you with a deep history with a particular pair of speakers, in a known room, etc. some of the classic paradigm can be bent. But I would argue that the fundamental principle of the amplifier's source impedance's contribution to system frequency response is worth exploring.
"Cannot be rescinded. Not even questioned" - the letters of transit, Casablanca 1942
One thing that we primates do hear well is broad changes in frequency response (sensitivity at the 1dB level, better than we hear most things) so an amplifier's contribution to frequency response is its dominant initial characteristic. Later we may hear its various distortions and modulations, but we immediately hear frequency response, just like we do with speakers.
And to have identical frequency responses into a complex impedance load like a real speaker, amplifiers must have the same source impedance into that load. The amplifier's source impedance and the speaker's load impedance are a simple voltage divider. No amplifier is a perfectly zero source impedance and no speaker is a perfectly resistive (meaning equal impedance independent of frequency) load. Modern (Not! valve) amplifiers and modern speakers are designed for the only possible repeatably common paradigm, a zero impedance source and a who-cares? load - the resulting frequency response will be predictable, and all modern amplifiers, at first blush, sound identical.
For DIY, especially for you with a deep history with a particular pair of speakers, in a known room, etc. some of the classic paradigm can be bent. But I would argue that the fundamental principle of the amplifier's source impedance's contribution to system frequency response is worth exploring.
"Cannot be rescinded. Not even questioned" - the letters of transit, Casablanca 1942
Indeed, that drives me nuts, but there is nothing I can do about it. Since my music collection was built mostly in the 1980's, that meant CD. I remember when Sheffield Labs specifically went for tube gear, even designing their own, to make their recordings. Well, that was great for those who could listen to their direct-to-disc versions, but for me all I have is the CDs that were made from their 2-track live analog master tapes. Nevertheless, they are good. I use The Sheffield Track Record and Drum Record as one of my system test standards and have since the 1980's. At least CD is a stable recording medium that doesn't change with physical wear. Also, D-to-A processing has improved significantly over the decades. Still all transistor though.
A lot of people hate it when I say the last 9 words.
Agreed. Lots more info on damping factor, for anyone interested in one person's explanation, is here:
https://www.audioholics.com/audio-amplifier/damping-factor-effects-on-system-response
As a rule of thumb, I always have heard that a damping factor of 5 is as low as we would want to go, with 10 being a reasonable real-world number, and anything above 50 not necessary.
Damping factor of my ST-70 series ii is specified as 15 or greater. Works fine. It is ultra-linear. I have no idea what damping factor I can achieve with SE pentode EL34 and GNFB. I guess we will find out what it sounds like, but unless someone knows how to estimate the damping factor, I have no idea.
I put together a spreadsheet for the OPTs on AliExpress. It all comes down to how much I want to spend on this experiment. It also depends on who offers the biggest discounts at the upcoming Chinese New Year sale. I don't look forward to the shipping delay, but I do look forward to the discounts. The ones from Jurrasic Shop Store seem to be the ones that come with the higher-priced versions of the kit. Only $84 USD per pair including shipping to the USA, before any discounts. Not bad.
I bought a 15W SE from Amplifier and Transformer Store, pretty pleased with it.
I'd add HiFi Exquis, for me they are the best one, but not cheap anymore.
I'd add HiFi Exquis, for me they are the best one, but not cheap anymore.
Are these the ones you bought? These are on my spreadsheet.
https://www.aliexpress.us/item/2255800712700882.html
$155 per pair delivered to the USA, minus any special Chinese New Year discounts.
https://www.aliexpress.us/item/2251832645242697.html
$147 per pair delivered to the USA, minus any special Chinese New Year discounts.
Because discounts never apply to shipping charges, I'm only expecting about $8/pair off with discounts, but that's enough to at least cover the sales tax. 😉 The ones priced at $105-$118 are probably where I'll end up.
The D. Pierce article seems very solid, but concentrates on effects at fundamental resonance, and doesn't include effects through crossover region(s), where source impedance also has an impact. Still, very good work and generally applicable.
A ballpark estimate of a valve amplifier's source impedance can be made by spitballing the impedance at the output valve(s) anode(s), dividing by the OPT's impedance ratio, and dividing again by the negative feedback factor. For a pentode output stage anode impedance is dominated by the reflected load impedance; for "UltraLinear" the valve(s)' contribution is roughly equal to the load's; and for triodes the valve(s) actual contribution can be found on its characteristic curves (slope of a tangent to grid voltage line at operating point). Actually, an exact answer can be found the same way for pentodes and UL, but it gets clumsy in practice.
Graphically, the valve's transconductance is found in a vertical line drawn at its operating point, and mu is found on a horizontal line, so anode resistance, mu divided by transconductance, is slope.
All good fortune,
Chris
A ballpark estimate of a valve amplifier's source impedance can be made by spitballing the impedance at the output valve(s) anode(s), dividing by the OPT's impedance ratio, and dividing again by the negative feedback factor. For a pentode output stage anode impedance is dominated by the reflected load impedance; for "UltraLinear" the valve(s)' contribution is roughly equal to the load's; and for triodes the valve(s) actual contribution can be found on its characteristic curves (slope of a tangent to grid voltage line at operating point). Actually, an exact answer can be found the same way for pentodes and UL, but it gets clumsy in practice.
Graphically, the valve's transconductance is found in a vertical line drawn at its operating point, and mu is found on a horizontal line, so anode resistance, mu divided by transconductance, is slope.
All good fortune,
Chris
I love my "Huaji Audio" EL84 PP amp that I built last year. It uses pentode output. I have no problem with it. It's
Because pentode output is so widely demonized and hated almost universally among stereo enthusiasts, it isn't so easy to find good information on it. I found out that single-ended pentode has been reasonably popular in Japan and China for some time, where it is not so widely demonized. Recommendations on discussion forums that I found there indicated that attaching the screens to B+ isn't the ideal approach.
Suggestions there were to use a separate power transformer, or at least a separate node/section on the power supply, or a regulated supply. The regulated screen supply is the one implemented in my Huaji Audio, and that may be one reason why I like it.
I have all of the parts for the regulated screen supply sitting here, except the PCB, so I ordered the PCB set for $11 from China. It will fit perfectly inside the chassis and give me regulated 300V out that can be adjusted with three Zener diodes if needed. I'll wire the choke externally and then tee off of the non-regulated portion with another R-C section for additional filtering. Of course, triode and UL are simpler configurations, but for $11, what the heck, I might as well try it with regulated screens, and the PCB is very nice.
Something like this:
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Can't get the link, I'm right now in China, it tells me "cannot be delivered to your location"
The ones I bought are not listed anymore, but there are similar ones, will shate later the details.
I'd probably take the quoted power figure with a pinch of salt.
Transformers add their own distortion so if you want 10watts, I'd buy a 15w+ transformer.
Also they aren't quoting (presumably) the bandwith at max power nor showing a frequency response graph?
I just can't bring myself to buy anything more from Aliexpress after losing money on an Android car unit which failed to meet the advertised claims but only came with a90day warranty and Paypal wanted me to pay the return postage.
At least ebay provides better protection and also have used ones listed.
In the UK we have this seller of iron at reasonable prices:
https://www.ebay.co.uk/str/thatsaudio
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Indeed. There are Watts and AliExpress Watts. But there are some good products there, just require some homework and managed expectations.
The Chinese prices aren't necessarily as great as they seem. Musical Power Supplies, Matt, in the US has some nice SE outputs in his HiFi range at comparable prices. I've used the 10W outputs with SE 6V6 at 4W and the FR was -3dB at 1W at 15Hz and 65kHz. About $100/pr. He also has some 20W rated SE outputs. I have a pair but haven't used them yet. Just thought I would mention as I'm a satisfied customer. He is also very responsive to emails.
Measurements by another person:
https://hifihaven.org/index.php?threads/5k-tape-machine-ots-tested.7454/page-2#post-213645
Measurements by another person:
https://hifihaven.org/index.php?threads/5k-tape-machine-ots-tested.7454/page-2#post-213645
Fortunately, we have a review and measurements of the OPTs that come in the higher-priced version of this kit and most of the pre-built versions.
Freq. response down to 8 Hz at 1 watt. He ended up getting about 7.5 watts/channel. 2% distortion at 1 watt. Time-stamped video.
I may just get those. There is always a temptation to get something bigger, but they would get the job done for $84/pair delivered to the USA, minus whatever sale discount I can get. It's hard to beat the price and we at least have some idea of how they perform. The GNFB was designed (no idea how well designed) for those.
The next step up would be $105/pair minus any sale discount. Physically larger and heavier. 3.7 lbs each vs. 2.9 lbs each. 87 Ohm lower DCR on the bigger ones. https://www.aliexpress.us/item/3256803332384152.html
Why do values for grid stopper resistors on the input vary so widely? I arbitrarily/randomly penciled in 330 Ohms as an option. They aren't included on my Chinese amps, and I wonder if they are even necessary. I'm one of those "crazy people" 😵 who doesn't like to put things directly in the signal path unless there is a real reason to do so. They are supposed to be soldered directly to the driver tube socket to keep out RFI, correct? That seems like a valid concern, but how real is it given well-shielded interconnects, grounded chassis, etc.? Maybe I'm missing something. Then there is the issue of what type to use, if using one. People seem to have their own preference for carbon vs. film. A guitar amp forum said this resistor can "cause hiss."
Freq. response down to 8 Hz at 1 watt. He ended up getting about 7.5 watts/channel. 2% distortion at 1 watt. Time-stamped video.
I may just get those. There is always a temptation to get something bigger, but they would get the job done for $84/pair delivered to the USA, minus whatever sale discount I can get. It's hard to beat the price and we at least have some idea of how they perform. The GNFB was designed (no idea how well designed) for those.
The next step up would be $105/pair minus any sale discount. Physically larger and heavier. 3.7 lbs each vs. 2.9 lbs each. 87 Ohm lower DCR on the bigger ones. https://www.aliexpress.us/item/3256803332384152.html
Why do values for grid stopper resistors on the input vary so widely? I arbitrarily/randomly penciled in 330 Ohms as an option. They aren't included on my Chinese amps, and I wonder if they are even necessary. I'm one of those "crazy people" 😵 who doesn't like to put things directly in the signal path unless there is a real reason to do so. They are supposed to be soldered directly to the driver tube socket to keep out RFI, correct? That seems like a valid concern, but how real is it given well-shielded interconnects, grounded chassis, etc.? Maybe I'm missing something. Then there is the issue of what type to use, if using one. People seem to have their own preference for carbon vs. film. A guitar amp forum said this resistor can "cause hiss."
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