Low gain germanium transistor. All transistors that I measured were bought in boxes of 50.

Low gain germanium transistor Welcome to the most comprehensive article you’ll find online about the best overdrive pedals on the market! Since “overdrive” is an umbrella term that includes several types of circuits with their own sonic character, we thought it would be best way to organize this guide by type – because comparing apples to oranges never makes much Hi, I've been thinking about NKT275 and was just interested in people's take on and experience with the best gain results within these transistors. Use them as a diode, just short the base and collector — albeit it will have a very low reverse voltage. Log in; Sign up; DIYstompboxes. 9 GHz: input third-order intercept point (IP3 i) = 15 dBm; input power at 1 dB gain compression (P i(1dB)) = 0 dBm; 110 GHz f T silicon germanium technology 3D model of a TO-92 package, commonly used for small bipolar transistors. Just be careful they're not too leaky. Dec 6, 2024 #1 Working on an old heathkit and I was to replace the transistors in the preamp section. Are 200+ gains sort after or useless? Of course the easiest test is to plug them in and test, I've a bunch of high gain, low leakage ASX12D's, must give them a go in a Supa Fuzz. When germanium transistors were first invented in 1948, they were originally very low gain. Any power >= 0. – Separately, these rare NPN Ge Transistors will cost you well over $30, and these are selected for proper gain and low leakage! ***Please note that the picture shows the tester and a bunch of transistors while sorting. (Ultra-low-gain transistors are especially effective as Q2 in a Fuzz Face. Out Of Stock. NPN silicon germanium RF transistor for high speed, low noise applications in a plastic, 4-pin dual-emitter SOT343F package. Most other high-end DMMs don’t have an hFE socket either. You can do experiments with bias control and making your own Darlington pairs. 5. High mobility channel materials could replace strained Si to enhance speed performance and/or reduce power consumption in future transistors. 70% of the lot are low-gain, low-l. In the low-gain setting, the Broadcast can cover everything from sparkling clean boost through to transparent overdrive, all with a healthy dose of volume available to push your amp. Awesome and you will notice that there are both low and very high gain values for the transistor due to it's own preference for 'optimal' Ic for given voltages NPN Germanium Transistors for your DIY Fuzz pedal build. In contrast, a unipolar transistor, such as a field-effect transistor (FET), uses only one kind of charge carrier. Well, OK, not "wrong" as "wrong" is a politically incorrect term for anything, but um, lessee now, you have incompletely understood circuit design as of yet, and need to move to the next lesson and master it. 2 Features and benefits Low noise high linearity RF transistor High maximum output third-order intercept point 32 dBm at 1. Now its charge-carrying abilities and advanced fabrication technology make it an attractive material for future chips. In this case, both the present economics of the transistor market and Mother Nature cooperated. I’ve been experimenting with a fuzz design using piggybacked transistors to try to recreate characteristics of germanium transistors with modern silicon. Thecomedian. To see how the GST-3 SiGe process improves noise figure at high frequencies, consider that adding germanium to the p-silicon base of a transistor reduces the bandgap by 80mV to 100mV across the base, creating a strong electric field between the emitter and collector junctions. Probably no practical use but if you want to take your shot with The low FT of germanium transistors argument that people usually bring into discussion is wrong with emitter followers and low gain common emitter stages and you'll find that by yourself as they don't have the same effect as gm doubling has in silicon transistors. 1V or less at the low base currents you are likely to find in pedal circuits. Scroll to continue with content. More low-end distortion is coming through the transistor. I just checked and mouser has ~17000 of them, The Broadcast is a transformer coupled, discrete Class-A germanium pre-amplifier based on the classic broadcast consoles of the 1960s. "i just bought a batch of soviet made germanium transistors that are super high gain, but leaky!" -said no-one ever. Tested, sorted, and ready for your Joe Bonamassa style FuzzFace or other Ge pedal project. The transistor HFE doesn't ramp up until like 1ma or something, I cant remember exactly, suffice to say that if you measure them, they will be low (40-80, instead of 50-150 on I now have a ton of MP37 transistors, which were super cheap, but they seem to be too low gain for anything I've built. I haven't tried it yet, but I read that with a trim pot between both transistors emitter pins and a small 47pF-100pF cap, its supposed to sound like a Germanium Transistor. Unfortunately I don't have a way to measure leakage but I believe these were all advertised as "low leakage" fwiw. However, there are some other options, for a more compressed sound you can use β=90-120 for Q 1 and β=150-190 Q 2. If you want to see an example, you need look no farther than the Tone Bender Mk III and Burns Buzzaround. one has low hFE around 15, and one has hFe around 70. 75 dB at 6 GHz; High maximum power gain (G p(max)) of 15. Typical, low, Germanium Ube. org tracing pedals since 2007 Germanium Returns: Germanium was an early transistor material. base of a transistor. Ge has the highest hole mobility among common elemental and compound semiconductors, and an electron mobility that is two times larger than that of Si. If you have a lot of germanium transistors, they may contain useful silicon grease, otherwise recycle The current gain of bipolar transistors strongly decreases when the oxide over the emitter-base junction is damaged. iceplant999 New member. I'm looking for two transistors with a relatively low leakage (hopefully 100 uA or less) and one with a gain of about 70 and one about 100 or so. Higher gain than the P416B, but still very low leakage, with none measuring over 27µA. "I just bought a batch of western made germanium transistor that are super consistent with low leakage!" -said no-one ever. One key difference is that germanium tend to have a much lower gain. Is this reasonable for a germanium transistor, or is the DMM being fooled by the low junction voltage? And I second what folks said about fuzz faces, my favorite sounding fuzz faces, including several I breadboarded and or built, were all low hFE Germanium transistors. 8 GHz ,Outstanding noise figure F = 1. Pretty neat, huh? But we know that germanium really does The GT308V measures lower gain then the datasheet suggests, because your test conditions will be different to the manufacturers. they sound good in a fuzz face so I'll probably keep them. They just don't have much in them. If the transistor has a gain of 100 and no leakage, the voltage across the 2. The BFU910F is suitable for small signal applications up to 20 GHz. J. $ 25. 1) The frequency f MAX is defined as the maximum frequency for which the transistor can amplify power. ) My advice is, be aware of such guidelines, but listen and judge for yourself. A good option for that 17hFE is Delyk's Ensi Genxyde. So I recently got a batch with HFE between 100 and 200+, and leakages between 500 & 1000. 99 Add to cart Buy now with PayPal. 6 - 0. Power transistors at the time had poor gain linearity, so the h FE fell at low and high currents. For low-level signals, the gain reduction at low current reduced the amp's loop gain, so feedback was less effective. Rangemaster Technology from "Guitar Amplifiers" Dallas Rangemaster Study By RG Keen, the first and best document out there. Audio ( low noise ). 8 GHz; Gold metallization for extra high reliability At the heart of the Silktone Fuzz are two germanium transistors, tweaked to get a huge array of tones and fix all the annoyances you get with a typical germanium fuzz. 3 VDC. Gains ranged from 82 to 149 with an average of 120, and leakage ranged from 0 to Germanium transistors can operate at just 0. I have had good results in some circuits by subbing low-gain Si trannies for Ge. All transistors that I measured were bought in boxes of 50. I think it was the collect current. Welcome to DIYstompboxes. 6. G. We wanted to nail the awesome tones everybody knows and loves when these transistors are biased to their sweet spot and also when they’re not. Just make sure that their leakage is not to high. Pretty low gain, not much fuzz but can get Q2 is classically the higher gain transistor in the FF circuit, with a recommended hFE of 100-140, so if you are trying this make sure that you don't put the low gain transistor in the usual position (Q1). It is typically stated as being around 0. Germanium transistors can operate at just 0. e. Two (2) NOS NPN 2SD30 Germanium Transistors. freestompboxes. 5 Silicon Germanium (SiGe) bipolar transistors exhibit high gain and low noise. For an ideal transistor, current flowing into the base controls the amount of current flowing into the collector, and the collector current should be controllable all the way down to zero. All pretested (Icb) – Separately, these rare NPN Ge Transistors will cost you well over $40, and these are selected for gain and low leakage! ***Please note that the picture shows the tester and a bunch of transistors while sorting. The transistor you receive will be between 40 and 60 hFe. In 2018 we got some RCA germanium transistors in that sound great. Transistors with Germanium Transistor Selection: This gain variation is crucial in the design, the best match uses a low gain in the first stage (β=70-80 approx. 25. You can get more info about this is the Bias Section. Figure 2. $3. 8 GHz 110 GHz fT silicon germanium technology 1. I very much group Fuzz Faces into 4 Types, as follows : Type I Germanium: Newmarket NTK275 and high calibre Germanium Transistor alternatives Low noise high gain microwave transistor; Noise figure (NF) = 0. Am also looking to experiment with dizzy tone circuits, where I know q3 requires some leakage to bias properly Low HFE/Gain transistor recommendations? AMZ FX ANALOG ALCHEMY GEOFX MEF ROG MEF DIY WIKI. A bipolar transistor allows a small current injected at one of its terminals to the small-signal current gain jh 21jfalls to unity, i. 65 dB at 1. I'd love to know if there's a clever usage for low gain (60 hFE and below) germanium transistors. 00] Is there a way to make use of low-gain Germanium transistors? Can we build a Darlington pair from Ge transistors? These are good questions and pedal designers have been dealing with the problem of low HFE transistors from almost day one. Where the red spots - were considered the best, white spots - good, and unmarked signified low gain" The BFP640ESD is a Silicon Germanium Carbon (SiGe:C) NPN Heterojunction wideband Bipolar RF Transistor (HBT) in a plastic dual emitter standard package with visible leads. Germanium-based transistors are also characterized by smaller peak inverse voltage (PIV) than silicon devices, averaging 350Vand 1000V, respectively. Aug 29, 2003 I took out the germanium transistor and measured the gain at 600 on a DMM. 7V. Oct 18, 2022 #8 So the gain can vary from a low of about 8 to as high as the transistor's basic internal gain when the pot is maxxed out. The Broadcast features a specially selected Triad Most any low gain Germanium transistors will make a good fuzz face. Subtract the leakage from the second reading, then multiply the result by 100, which gives the gain (within a couple percent) of the transistor. Gains ranged from 82 to 149 with an average of 120, and leakage ranged from 0 to 27µA, with an average of 19µA. I built a fuzz face once with two germanium transistors with hfe of only 60 each and it was just a wall of mush, but then I have an irrational fondness of low-gain transistors. Betty Wont Well-known member. Some things I've noticed in testing all my vintage germanium, vintage silicon, and modern silicon transistors:-NPN Ge transistors are more often available at lower gain Preamp Germanium transistor substitute. There is a secondary effect in that the AC gain of the FIRST stage is also set by the AC feedback from that pot through the 100K resistor, so when the control is turned full down, the feedback reduces the first stage's gain most. com I got a bunch of NPN germanium 2n5133 that were mostly 70Hfe but some were as high as 350. com. 80-150 or so) devices with low leakage and then listening. "A red dot or other colour dot on the side of the transistor case only denotes the collector lead. 5Å and hole mobility = 770 cm2/V*s at n s =5x10 12 cm-2. Updated May. —high and low gain, and of course breadboarding. 1). so if the input is low and output high, there is a lot of gain. Low power electronics and energy-efficient circuits rely on smart transistor choices. I did buy a 2n1304 but it was really low gain, could get it to distort a bit at max everything and you could hear that nice round germanium Tone, but it was just too low gain to be of real use. A typical curve of hfe versus frequency for a transistor with an fαe of 100 kHz is shown in Figure 2. silicon at low Vcc [1], the corresponding p-channel transistor with thin TOXE and high mobility (µ) has not yet been demonstrated. However, careful sorting and testing are needed, because wide variations in gain and leakage among devices with the same part number are the norm. My Fluke meters don’t have an hFE socket. 2 Features and benefits Low noise high gain microwave transistor Minimum noise figure (NFmin) = 0. Thread starter Carbsandcaps; Start date Dec 6, 2024; Carbsandcaps Super Member. This tool was built to more easily determine germanium transistor beta values for Fuzz Face circuits. GT308V for PNP and MP38A for NPN are both great. What could I make with these? Thanks! NPN MP35 – hFE 67 Generic NPN – 96 Gen NPN – 40 Gen NPN – 137 Gen NPN – 37 AC187 – 63 PNP Mullard OCP71 – hFE 45 NPN silicon germanium microwave transistor for high speed, low noise applications in a plastic, 4-pin dual-emitter SOT343F package. 2V, far below silicon’s 0. These are really low gain so So far, we’ve been using a of 0. These small devices are key to innovation in many fields, like consumer electronics and cars. It is difficult to find words that accurately describe detailed AC128 - PNP Germanium Transistor. John Larkin. Among germanium transistors, many type numbers (see the list below) are possible candidates for FF circuits and clones. RCA germanium transistors . The NPN transistor is operated with a gain Vout/Vin = -Rc/Re. , jh 21 (f)j f= T = 1: (1. One of its transistors is meant to be silicon (or germanium) with an hFE less than (or up to) 40. I haven't come across any higher gain NPN that are worth buying. They both ranged from 50 to 90 hfe with either zero or extremely low leakage. Building a germanium-based Fuzz Face requires choosing transistors within specific "A red dot or other colour dot on the side of the transistor case only denotes the collector lead. By definition, fαe is the frequency at which hfe (beta, the common emitter of ac short–circuit current gain), has decreased 3 dB below hfeo (the value of hfe at 1 kHz). 3V for germanium transistors, but is often closer to 0. Turns out for Fuzz tones they want low gain with a little bit of leakage! Maximum operating frequency: low, medium, high, radio (RF), microwave frequency (the maximum effective frequency of a transistor in a common-emitter or common-source circuit is denoted by the term f T, an abbreviation for transition frequency—the frequency at which the transistor yields unity voltage gain) High gain low noise RF transistor; Provides outstanding performance for a wide range of wireless applications; Ideal for CDMA and WLAN applications; Outstanding noise figure F = 0. That's only partially true because many germanium transistors, especially vintage ones, are leaky enough to supply their own base current. You will receive five fooled by the low junction voltage?-Bill . Common Emitter Current Gain is Plotted There are, also, tons of Germanium transistors on eBay, even Soviet and Russian, but, I must know the numbers and I cannot find the numbers of what I want easily. 25 Ex Tax: $3. 40V preferable. For higher gain the GT402B are nice for PNP and ranged from 80 to 190 hfe. 9888V - which is almost exactly 1/ 100 of the actual gain. Testing transistor gain across current ranges and temperature variations AND leakages gets into a lot of data about every transistor. Putting some germanium transistors to use. 50 + $22 Shipping. Some folks say this is because the multimeter reading is not too close to the official hFE reading, others say that the circuit and socket to measure hFE Germanium fuzz pedals generally have lower gain, and overall creamier or smoother sound than their silicon successors. 7V for silicon transistors. 2N1101 Germanium Transistor House-Number Sylvania. It’s an excellent combo, especially with some Ukraine weirdo diodes. ) I have not auditioned them yet, but I have a bunch of 2N2369A's around 60 hfe. Leakage current is current that flows through the transistor at all times. 8 dB at 6 GHz; Excellent linearity in WiFi LNA from 5 GHz to 5. I'm in Australia so former Soviet / Eastern Bloc states are my best option for affordability. 00 - $13. Let’s look at two examples that show how low power transistors make a big difference. A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. Some transistors have very low leakage, which is often desirable, but Q 1 in a Tonebender Mk2 cannot be low leakage. 2 and 0. Still gets fuzz when cranked up. Eventually someone came up with a circuit to maximize this I’ve read stats like these before, and just have to add that I’ve made many fine-sounding pedals using germanium transistors that lie outside those supposedly optimal ranges. The two base-emitter shunt (or bypass) resistors limit the gain at low currents, reduce leakage current, increase transistor speed, and to reduce Below is a list of my Germanium transistors, with gain noted. Like the red dot NKT, these are a "house number", they were made for a specific customer so they don't have a normal 2N part number on BART Low Gain transistors, muffy sound, large SUN box only. Oct 16, 2022 #1 I (especially if the low gain one works in a darlington pair), and I can harvest the transistors in it now for other use. The Rangemaster by Premier Guitar. For radio frequency circuits, these transistors offer better gain and efficiency than silicon ones. MT current favorite, which I'm gonna put inside a Dunlop round enclosure, has Case Studies: Successful Low Power Transistor Implementations. Add to Cart. I. BTW, this observation came about when I initially tried to Darlingtonise two of these low gain Ge's for fitment as Q2. Sanyo Japan 2SD30 (25V, 0,2A, 2 Pcs Low Gain Germanium Transistors Selected Clean Boost Fuzz Face Tone Bender NPN 2SD30 Sanyo Japan. Thus, you can get very high amount of amplification, and still use low gain germanium transistors! This avoids the very painful job of finding high gain germanium transistors like with the Fuzz Face. A+! I bought few germanium transistors from eBay. Lower may be OK too. You will You should test your transistors and make note of the transistor gain (hfe). Clangy, noisy, and raunchy. I find that unless they are hand picked, Ge transistors are pretty low gain. They both sound good but are maybe a bit too similar to one another Germanium transistors were noisy, leaky, very sensitive to heat, and slow. Low-gain germanium that was expensive back in the day is fairly Low Gain Germanium : we choose from our Standard Germanium transistors with low gain, for a transistor that sounds and cleans up like the NKT275. NOS NPN Germanium with full leads, most likely Sylvania material. These Soviet-era germanium transistors will work Figure 4: B&K 2704C multimeter hFE DC current gain measurement for 2N3904 left and 2N3906 right. 2. In this study, we demonstrate a high mobility strained germanium (Ge) p-channel QWFET suitable for low power CMOS architecture with scaled TOXE = 14. Simply, Gain = Output / Input. . Reactions: jubal81, cooder and fig. White Dot NKT-275 - no longer available, only for Sun Face repairs or vintage restorations. 2) While the frequency f MAX represents a I have just acquired some high-gain germanium transistors, 200-350hfe. And people will say to just breadboard them and A good use for low-gain transistors is as clipping diodes. So what I'm looking for is a, not stupidly priced, NPN germanium transistor with a gain that would be in the range of the 2n3904. In addition, the typical working temperature for germanium is only about Using the Germanium Transistor Gain (hFE) Tool. The supply of germanium in the world is limited, and frankly, most people are better served getting moderate-gain (i. Germanium transistors would have lower voltage drops in the range of 0. Fluke Multimeter. 3. Low-medium. Add to Wish List. The big difference between Silicon and Germanium transistors is the way in which they transition into clipping. This can occur in normal operation conditions since, when the emitter-base junction is reverse-biased, Higher gain than the P416B, but still very low leakage, with none measuring over 27µA. Not very bright sounding. Injecting a signal reveals that the various stages all work, but TSAR FACE is a low-gain germanium PNP transistor-based fuzz pedal that embodies the greatest circuit improvement since the original was introduced 60 years ago - a novel two-transistor bias stabilization circuit eliminates the need for transistor gain sorting and reducing temperature issues as well. A hfe of 60 is enough for each of these transistor, which is By using it we can fix the problems with low gain germanium transistors and adjust the Vb to the optimal +8V. Ideally, but, not only, I am interested in : 1. So, not high-gain. You should be looking for two transistors with HFE’s from mid 70’s to 80’s for Q1 and 80’s to high 90’s or low 100’s for Q2. Brand New. 2x AC130, 2x 2N1304 & 1 bonus to round out the gain ranges. Since the input voltage fed to the transistor is a fraction of the supply voltage, ranging from 0V to 2V max, I should be getting a linear amplification of Vout = -Vin*Rc/Rb and in theory I can make a linear function of vout based on supply voltage. I, too, recently received a bunch of low-gain transistors from Ukraine. Transistor 'bias servo' circuits were uncommon, so there was always a trade-off between bias current stability and low-level How to determine leakages and gains with Germanium Transistors, and how to improve upon them by using Sziklai Pairs. Jan 1, 1970 0. 00]for the Sun Face these are stamped with the 'GE' logo Hitachi 2SB77 - Low Gain $10 [Add $10. Resources. Germanium’s unique features are revolutionizing the semiconductor It would depend on whether you decided to go true high gain silicon Fuzz Face with the BC108, medium gain or low gain modeled after something like then Fuzz Central Axis Face, which mimics the characteristics QuoteDon't try to find low gain transistors, roll your own!I've heard about Piggybacking Transistors a while ago from an R. 4. Notice that hfe plays no part in calculating transconductance or voltage gain. The devices are a little archaic by today’s standards, with comically low-gain germanium transistors and passives from the Ark. Keen post. Ge is thus a promising channel material for future CMOS (Fig. General Electric Black vintage germ trans, Low or High gain specify in comments $10 [Add $10. I bought from 3 different seller. 6W. Note that nearly all pedals nowadays that purport to have NKT275 transistors - are recent thin-line reissues, and not at all the more sought-after original short/stout proper Newmarket NKT275 varieties. Don't want a lot but 10 or 20 would be OK. To a first approximation, if you have to know a transistor's gain any closer than low, medium, or high, you're doing it wrong. A red spot elsewhere on older transistors - usually on the top - used to indicate the goodness/gain/frequency response of the device. >=30V. ). 11, 2023 | by Paolo De Gregorio. Add to In general, the silicon transistors will have higher gain than the germanium ones, although you can certainly choose a low gain silicon transistor, or at least one of similar gain range. I have 6, and would like some recommendations for a noob circuit to build please. Thread starter spi; Start date Oct 16, 2022; spi Well-known member. We put that in parallel with the 15K load resistor and get 13K, so the voltage gain is actually 260. 1. Buy a bunch of the same transistor because you will find a wide range of gain values in a batch. The third-, fourth- and fifth-generation Two Soviet era/Russian Miltary - PNP - Germanium Transistors in the 40-60hFe range with low leakage. I'm looking at the Aft Preamp (EQD Bows, NPN Rangemaster). so basically I only got one transistor that ideal for Tonebender, Fuzz Face, or Rangemaster. Due to the lower BE voltage needed to open the transistor a 0. 65 dB at 12 GHz While such parts remain available, I wanted a lower-cost alternative. ature in germanium than in silicon, implying consider-ably smaller current cut-o (I CBO) for silicon devices. 1T320V - Soviet PNP germanium transistor, the military version of the GT320V, in the large UFO package. I've used some very old 2N3903s and 2N2222As. Germanium. I have a bag of 100 Tungsram AC128s. This ability is changing electronics, pushing low-power transistor technology forward. Compare this Product. I have lots of plans for Sziklai fun, but thought I’d try them out in a Harmonic Percolator (I got a sack of those orange rectangle silicon dudes as well as germanium). This seller is currently away. Key challenges 5 piece NPN Germanium Transistor Set. 00) SKU: Q-AC128 Minimum Purchase: 1 unit * Current Stock Very low gain, or very high leakage, or major instability etc. Infineon’s reliable high-volume RF transistors offer exceptionally low noise figure (NF), high gain and high linearity at low power consumption levels for RF applications. I know a EQD Tone Repear sounds great even with those mad values from my personal testing. Infineon Technologies provides high-performance radio frequency (RF) transistors targeting FM radio applications. 2 dB at 6 GHz; High maximum stable gain :Gms = 24 dB at 1. It also is proving useful for high speed/low voltage devices. Any interesting circuits you guys can throw my way? I'd prefer pedal Can anyone recommend some IN PRODUCTION low gain SI transistors that sound good for fuzz boxes? what do you consider low gain? and it's generally not so much I've been playing around with what transistors to use in it and currently have a 2n3904 and a BC109C. I know people have different ideas on specs, etc. In this context, Mason’s unilateral power gain U is widely used, and f MAX is defined by: U(f)j f=f MAX = 1: (1. With germanium transistors, this voltage drop is lower and can also vary more substantially. Price $18. Breadboard some experiments with that Delyk circuit or various other circuits. 3 Applications Ka band oscillators DRO’s The germanium transistors had rather "mushy" performance characteristics compared to silicon ones, Aiding this saturation is the fact that the gain of silicon transistors is a factor of 10 or more better than the vintage germanium. 4K resistor is then (4uA)*(100)*(2472) = 0. And much like vintage analogue synthesizers, these From 50 to 250! I was just going to ask, are 200+ hfe germanium transistors good or useless? I have 5 that are 200-250 so far. ) and a high gain in the second stage (β=110-130 approx. A germanium transistor with hfe = 50 has the same transconductance as a silicon transistor with hfe = 800, as long as their collector currents are the same. The device combines robustness with very high RF gain and lowest noise figure at low operation current for use in a wide range of wireless applications. I built a FF with MP10B Russian germanium transistors. $1. View similar gear from other sellers on Reverb. 00]Japan made traditional FUZZ transistor JB low gain Russian germanium $10 [Add $10. ourtorgu iumfdv aaq iucmrb propjr yze bjbr mny nthz bbncyn bbtkyu zux eoxam fgdv crshca