Joe, if possible I would suggest that voltage readings be taken both with the Elrogs installed and with the tubes Israel originally supplied installed.
Regards,
-- Al
Regards,
-- Al
Elrog 300B vs Takatsuki 300B tubes
Has anyone heard the Elrog 300B tubes ? I read an article which mentioned that the Elrog 300B delivers 15% less power than a traditional 300B tubes. Can anyone confirm that it is audible ?
I am choosing between Elrog and Takatsuki 300B tubes. I would prefer the Elrog because it is cheaper and supposedly wonderful but if it really sounds less powerful then I have to rethink.
I am choosing between Elrog and Takatsuki 300B tubes. I would prefer the Elrog because it is cheaper and supposedly wonderful but if it really sounds less powerful then I have to rethink.
Showing 31 responses by almarg
06-19-15: Charles1dadHi Charles, Yes, the VAC Renaissance amps run the 300B's hard, but according to Kevin, and also A'gon member "Raquel" (Drake), who as you know is especially knowledgeable about those amps, as long as the tubes are truly WE spec compliant they will have no problems and last for many thousands of hours. As "Raquel" said in this thread: I've owned VAC Renaissance amps for eight years. They require well vetted output tubes. In fact, Sophia used to market a special set of the Sophia tubes for VAC Renaissance amps, which were the basic Sophia tube, but particularly carefully tested at plate voltages that resemble the voltage that 300B's see in the Renaissance circuit. Generally, as for transconductance, output tubes for the Renaissance amps should test in the 3,000-5,000 range [edit by Al: I suspect he meant minimum, as the vintage WE's were rated a bit higher than that]. In addition, the plate-to-cathode voltage is approximately 430 volts dc, with idle current approximately 85 to 90 milliamperes in a self-bias (cathode bias) circuit. Again, this is approximately 5% below rating for the WeCo spec 300B. The milliamp and transconductance testing for purposes of matching must be done at those voltage levels.The tubes in my amp, which are Chinese 300B-98's, I'm pretty certain were purchased from VAC by either the previous owner or by the dealer he sold it to, very shortly before I purchased the amp. Their bases are marked with measured data apparently taken by VAC during their screening process. I've had no problems with them after several years. No doubt I could realize a substantial sonic upgrade by going to one of the upscale brands you've tried, IF I could be certain they could handle the operating conditions the amp would impose on them. But considering the cost of an octet of those tubes, or even a quartet if I were to run the amp in 30/30 configuration with four tubes removed, my recent investment in the DEQX HDP-5 you've probably seen me talking about with others in the current DEQX thread seemed to me to be a higher priority. As does a phono stage upgrade (probably to a Herron) at some point in the foreseeable future. Matthias, thanks for your further inputs. Best regards, -- Al |
Hi Charles, My only knowledge of the 300B operating parameters in my VAC Renaissance 70/70MkIII consists of the values Raquel provided in the thread I quoted from earlier. In which he said that the plate-to-cathode voltage is approximately 430 volts (compared with 484-79 = 405 for the Elrog in this case), with an idle current of approximately 85 to 90 ma (compared with 77 ma for the Elrog in this case). Also, based on those numbers for my amp, 90 ma x 430 volts = 38.7 watts plate dissipation. The numbers George measured for the Elrog seem to me to be moderate. Best regards, -- Al |
Excellent info, Joe (& George). That all seems very comfortable relative to the specified "limiting operating conditions for safe operation" of the Elrog tube. (79V/1.025K = 77 ma). And the plate dissipation which can be calculated from those numbers is actually closer to 31 watts rather than 32. Enjoy! Best regards, -- Al |
Bill (Brownsfan), thanks very much for the nice words. Charles, I suppose it would be reasonable to try that experimentally with an inexpensive variac, perhaps purchased used at eBay, but it wouldn't surprise me if the result was degraded sound quality. Due to both the effects on the amp's sonics of the lower voltage and the effects of the variac itself. Best regards, -- Al |
If it can somehow be ascertained, it would be interesting to know what grid and plate voltages the Lampi operates the 300B at. I wouldn't be surprised if those voltages were considerably lower than in the Franks or other 300B power amps, and if that difference was a major contributor to the Elrog's performance in Dracule's DAC. Best regards, -- Al |
10-25-15: Charles1dadThanks for pointing that out, Charles. In looking at the Lampi site, though, I see that Dracule's GG is described as having a choke (i.e., an inductor) as the plate/anode load for the output tube, while the Big 7 which the other two gentlemen have been using is described as using a resistor. I don't know if that might account for any difference in how the Elrog performs in the two designs, but it suggests that it could conceivably be a possibility. 10-26-15: Dracule1There isn't enough information at the Lampi site to be able to say for sure, such as an output impedance spec, but I'd be surprised if there was an impedance compatibility issue here. It appears that all of the currently produced Tortuga passive preamps have input impedances of around 20K or more, regardless of the attenuation setting, which, given that it uses LDRs, figures to be essentially constant as a function of frequency. I'd be surprised if the Lampi's performance would be compromised by such a load. And while the input impedance of your amplifier will reduce the 20K somewhat, depending on the attenuation setting, since you are using a passive preamp I assume the input impedance of the amp is high and will therefore not have a large effect on the impedance seen "looking into" the preamp. On the other hand, though, it appears that the 300B or other output tube that may be used in the GG & Big 7 is used in an anode follower/plate follower configuration, which leaves me a little bit less certain about impedance compatibility than I would be if it were a cathode follower that would undoubtedly have low output impedance. Best regards, -- Al |
While I'm hesitant to question George's recommendations, FWIW I don't understand some of them. According to my documentation and my understanding, the 5AR4 (which he advises against) is two-way interchangeable with, and therefore very similar to, the GZ34 and the GZ37 (which he suggests trying). Also, the filament current drawn by the 5AR4, at least in its vintage incarnations, is 1.9 amps, not 4 amps as stated. 1.9 amps being substantially LESS than the draw of the EML versions of the 5U4 and 274B that are supplied by Lampi according to its website, as well as the filament draw of the vintage versions of those tubes. It is also slightly less than the 2.0 amp filament draw of the 5Z4 and 5R4. Although if the filament current drawn by the tube is too low, as well as too high, problems can result. If it is significantly too low relative to what was anticipated in the design it could conceivably result in the filament voltage that is applied to the tube being high enough to shorten its life. If it were me, without an ok from Lampi, either directly or via some indication on its website, I would be hesitant to use a rectifier whose filament current is significantly outside of the range of 2.4 to 3.0 amps, those being the ratings of the EML tubes the Lampi site indicates they supply. Are 1.9 and 2.0 amps "significantly outside" of that range? Not having knowledge of the specifics of the design, I don't know. Good luck. Regards, -- Al |
10-27-15: Dracule1You're welcome, Dracule. But I didn't say that the site specifies 2.4 to 3 amps. What I said is that the site indicates that the GG is supplied with either the EML 5U4 or the EML 274B. And I said that since those tubes have filament current ratings of 3 amps and 2.4 amps respectively, as can be seen at the emissionlabs.com site, without an ok from Lampi I would be hesitant to substitute a tube having a filament current rating significantly outside of that range. As I see it, doing so would amount to incorporating a design change into the DAC, without any means of knowing what its ramifications may be, in terms of long-term reliability as well as sonics. I couldn't find a datasheet on the Psvane 274B. FWIW, though, the original Western Electric tube that it is intended to emulate was rated at 2.0 amps, although I wouldn't necessarily assume that the Psvane version is the same. Regards, -- Al |
As a point of information, the Big 7 is indicated at the Lampi site as being supplied with one of the following rectifiers. I've determined the filament currents listed for each tube from datasheets that can be found elsewhere on the web: 5C3S (filament current 3 amps +/- 10%) Shuguang 274B (filament current 3 amps) (Optional) EML 5U4G (filament current 3 amps) Other tubes mentioned in Wyan's post just above: 5Z4 (filament current 2 amps) Cossor 53KU (filament current apparently 2.8 to 3 amps) WE 422a (filament current 3 amps) WE 274A/B (filament current 2 amps) Takatsuki 274B (filament current 2 amps) Hope that helps. Regards, -- Al |
Hi Bill, The upshot of my previous post is that if no one participating here has already done so I suggest that one of the Lampi users ask Lampi if each of the various rectifiers that have been discussed is suitable for use in the Big 7 and the GG. And that Lampi also be asked if the filaments of the output tubes and the rectifier tube in those DACs are supplied by the SAME 5 volt output winding of the power transformer. As opposed to the filaments of those tubes being supplied by separate 5 volt windings in the power transformer. If the answer to the latter question is "yes" I would recommend against using a rectifier tube having less than a 2.4 amp filament current at the same time as an Elrog 300B is being used. If the answer to the latter question cannot be obtained, I would suggest that there is a non-zero risk in doing so. Best regards, -- Al |
Yes, thanks for chiming in, George. After thinking about your comment I agree -- the 5 volt winding for the directly heated 300B and the 5 volt winding for the rectifier must be separate, or the circuits wouldn't work properly. Thanks for pointing that out. I'm still a bit uncertain, though, that it would necessarily/always be appropriate, with respect to long-term reliability, to use a 2 amp rectifier on a winding that is designed with the expectation that it would be used with a 3 amp rectifier. My concern, as I mentioned earlier, being that the filament voltage provided to the rectifier would increase to some unknown degree compared to the voltage that would be provided to a 3 amp tube, due to the lighter loading on the winding. Thanks again. Best regards, -- Al |
Thanks, George. I don't doubt that what you are saying is correct in most and perhaps nearly all cases. But without knowing the DC resistance or low frequency impedance of the filament winding of the particular transformer (which would enable calculation of the voltage that is dropped across it for a given current draw), and perhaps also the +/- tolerance on the transformer's turns ratio, I'm not certain we can say that for sure. Although I will state that I don't have a particular feel for what those numbers are likely to be for the kinds of power transformers that are used in audio components such as these. Again, see the statement by Matthias of Elrog that I quoted in my first post dated yesterday (10-28-15). 10-28-15: Dracule1Yes, certainly as far as the 300B is concerned, given George's point about the separate filament windings. And most likely as far as the rectifier is concerned, although per my comments above I for one am not sure we can say that with certainty. FWIW, IMO, etc. Best regards, -- Al |
It occurs to me that I should perhaps add some clarification to Matthias' statement I referred to just above, which I quoted in my first post of yesterday. That statement was: If an EML 300B XLS is the right choice we have 1.5A heater current at 5V. There is no voltage regulation. A transformer a rectifier bridge and a CLC only. May be the XLS is underheated (so I hope) ore all other (right) 300B are overheated, because they draw 1.2A (some russians and chinese 1.25A)only. This would result a heater voltage above 5V...not so good for any 300B and very bad for an Elrog 300B, because the use of thoriated tungsten for filaments. Higher heater voltage will result a (much) higher anode current and a much lower lifetime...What he is saying is that if the power transformer's filament winding is designed to provide exactly 5 volts to a 300B which draws 1.5 amps, if a different 300B which draws 1.2 amps is substituted the voltage applied to that 300B will be higher than 5 volts, to a degree that might be harmful over time. The reason for that increase in voltage is that the reduced current draw will result in a reduction in the voltage that is dropped across the resistance of the filament winding. Note also that he is referring to a difference in current draw of only 0.3 amps. In principle similar considerations may come into play when a rectifier rated at 2 amps is substituted for one rated at 3 amps. However I suspect that the sensitivity to filament voltage increases of the rectifiers being discussed is considerably less than the corresponding sensitivity of a 300B. Best regards, -- Al |
I've just read through this entire thread, having been referred to it by Tmmvinyl today in another thread. Charles & Bill (Brownsfan), thanks for the nice words earlier in the thread. After examining the Elrog 300B datasheet, and comparing it with a 1939 Western Electric datasheet I have (as reprinted in the book "Western Electric Tube Data," published by Antique Electronic Supply), and also with a datasheet for the Psvane 300B-T (click "additional images" and then "enlarge"), in lieu of a datasheet I couldn't find for the non-T version which I believe is what Israel supplies, I agree with some of the others that there is cause for concern operating the Elrogs in the Franks. While the specs for the vintage WE 300B and the Psvane 300B-T look extremely similar, as was alluded to earlier the Elrog tube has substantially lower transconductance and amplification factor, substantially higher plate resistance, lower output power under similar operating conditions, and correspondingly different parametric curves. It also has a considerably higher (better) maximum safe plate voltage rating. I'm not 100% certain, but I believe that the net effect of these differences will be to cause the Elrogs to self-bias to significantly different bias points in the Franks than the Psvane or original WE tubes would bias to, and in the direction of being more stressful. And based on a quick look at the disparities between the numbers, I'm not sure that even changing the 1K resistor to 1.2K would be enough of a change for comfort. Charles, what I would suggest is that you follow up the response from Israel, in which he cited the 400V and 28W numbers, by providing him with a link to the Elrog datasheet and asking him if he can provide a rough indication of what those numbers, and also the bias current, would change to if Elrogs were used in place of the Psvanes he supplies the amp with. Also, unrelated to that, I'm wondering if Mk (Matthias) can provide a link to the WE datasheet from which he gets the maximum ratings cited for the WE 300B in his post above. Rather than the 36W and 400V numbers he cited, the 1939 datasheet I am looking at specifies "limiting operating conditions for safe operation" (what would probably be called "absolute maximum ratings" today) of 40W and 450V. Although it is made clear that those conditions and the 100 ma max current spec for self-bias should not be considered to be simultaneous. And a separate table defining numerous possible operating conditions indicates maxima of 450V @ 80 ma, which does correspond to 36W. But still, I don't see how to reconcile the 450V number I see in the datasheet with the statement by Matthias that "the old datasheet of the 300B says 400V Anode voltage as MAXIMUM." Best regards, -- Al |
Thanks, Charles. I'm still fairly early in the process of "dialing in" the DEQX, which is a somewhat complex and lengthy one especially given that I've chosen to do it all myself without utilizing the optional service they offer of assisting remotely via Skype. But it's proving to be educational and fun, and even without its speaker and room correction features it's already providing significant sonic benefits just as a preamp and DAC upgrade. Matthias, thanks for providing the link to the WE datasheet, which as you had indicated does state 400V, 36W, and 100 ma as maximum ratings, with the words "design center values" added. So it seems that between issuance in 1939 of the datasheet I have, and issuance of the one you linked to in 1950, WE made their specs more conservative, for whatever reason. And thanks also for the rest of your post, all of which sounds right to me. Best regards, -- Al |
07-07-15: BrownsfanThat is the standard in the USA for household AC, as measured at the service entrance. The upper limit of that range corresponds to 126 volts. With due respect to George, I must admit to some skepticism about the requirement of 122V max. I would expect that the designs of the power supplies in equipment marketed in the USA would in most cases be targeted to supply optimal DC voltages to the tubes and circuits for an AC input of exactly 120V. And I find it hard to believe that an increase of 1.67% from that figure would be the upper limit of acceptability. Also, I don't see how a statement as specific as "over 122V AC is a game changer for these or any other 300B tubes" can be defined in such a universal manner, apparently with applicability to all 300B-based designs, given that I would expect significant variation among different designs in the +/- tolerances of the transformers and other components in their power supplies. Not to mention in how hard the tubes are driven. Best regards, -- Al |
A point to keep in mind regarding the AC voltage measurements some of you have been making: Although a digital multimeter may provide 4 digits or more of resolution (i.e., to tenths of a volt when reading voltages in the vicinity of 120), its readings are by no means necessarily accurate to anything remotely close to tenths of a volt. For example, the B&K 2703C, which lists for $46 and is produced by a very reputable company, provides 0.1 volt resolution on the scale which would be used to measure AC power, but its specified accuracy on that scale translates to +/- 2.9 volts when measuring 120VAC! Which reminds me, I've got to order myself a good Fluke DMM. My old Triplett analog multimeter just won't cut it when it comes to accuracy :-) Best regards, -- Al |
07-08-15: TmmvinylGiven that the meter displays four digits on that scale (for example, 120.1 volts), the accuracy of readings that are in the immediate vicinity of 120VAC would therefore be: +/- ((0.012 x 120) + (10 x 0.1)) = +/- 2.44 volts For your worst case reading of 123.1 the accuracy would be +/- 2.48 volts So the actual voltage when you measured 123.1 could have been anywhere from 120.6 to 125.6 volts. This information comes from the Takatsuki Denki website for the Takatsuki 300B tube.These numbers, representing maximum ratings, are identical to those which appear in the 1939 datasheet I cited earlier for the original Western Electric 300B. My impression is that the 1930's WE 300Bs are among the most robust 300Bs ever produced. Kevin Hayes designed the VAC Renaissance amps based on the characteristics of those tubes. And as noted earlier those amps drive the 300Bs extremely hard, yet tube life is MANY thousands of hours for tubes which are truly WE-spec compliant. I can share the test results for one of my matched pairs if that would be helpful.... The plate volts Ep vdc test result was 300 for each tube; DC plate current lp mAdc was 73 and 73.1 for each tube; AC plate current lp mAac was 6 for each tube, Bias volts G1 vdc was 60 for each tube; Grid #1 leakage uA was 0.29 and 0.27 for each tube; Tube gain Mu was 3.6 for each tube; Plate resistance RP ohms was 0.6K for each tube.I don't see any concerns in those numbers, and the numbers for which corresponding figures appear in the 1939 WE datasheet are roughly similar. Although these are results of tests that were performed at a plate voltage of 300, and we don't know what the results might have been if the test would have been performed at 390 volts (474 - 84), which George measured across the tube in Joe's Franks. Also, the plate dissipation in the Franks which can be calculated for the Takatsuki from George's measurements is 32.0 watts (rather than the 33W that was indicated), and the plate current can be calculated as 82 ma. Those are reasonable figures, although not on the gentle side of the spectrum. Although of course George measured a line voltage of 119.4, and I have no particular feel for how much those numbers might increase if your line voltage actually approaches the upper limit of your measurement +/- the meter inaccuracy. Finally, we have to consider that we can't say with 100% certainty that your particular tubes, or other Takatsuki 300Bs for that matter, conform to Takatsuki's published maximum ratings, especially given that the indicated tests were performed at a plate voltage considerably less than the voltage the tubes see in the Franks, and much less than the maximum ratings. So the bottom line seems to be that there are considerable grounds for encouragement, but there are no guarantees. Apart, perhaps, from the warranty :-) Best regards, -- Al |
Slight correction to my slight correction :-) When I said in the long post prior to the correction: So the actual voltage when you measured 123.1 could have been anywhere from 120.6 to 125.6 volts.I should have said: So the actual voltage when you measured 123.3 could have been anywhere from 120.8 to 125.8 volts.Best regards, -- Al |
10-27-15: Dracule1The 5R4 tubes and the GZ34 are approximately 2 amps, although the GZ37 is about 2.8 amps. I’d question whether George really meant to indicate that you should stay away from tubes drawing significantly more than 2 amps, given that all of the tube choices Lampi supplies with the Big 7 are around 3 amps, and the choices provided with the GG are 2.4 and 3 amps. And if he did really mean that, I would want to know what his reasoning is. The 2 amp draw of the Takatsuki you are using will result in some increase in the voltage supplied to the filament of that tube, relative to the voltage that would be supplied if the tube were drawing a higher current, due to the lighter loading of the 5 volt winding of the power transformer. Matthias of Elrog made exactly that point, although in connection with a 300B used in a power amp rather than a rectifier used in a DAC, in a post in this thread dated 6-19-15 when he said: If an EML 300B XLS is the right choice we have 1.5A heater current at 5V. There is no voltage regulation. A transformer a rectifier bridge and a CLC only. May be the XLS is underheated (so I hope) ore all other (right) 300B are overheated, because they draw 1.2A (some russians and chinese 1.25A)only. This would result a heater voltage above 5V...not so good for any 300B and very bad for an Elrog 300B, because the use of thoriated tungsten for filaments. Higher heater voltage will result a (much) higher anode current and a much lower lifetime...Now that increase in filament voltage in this case might be small enough to not matter, or it may not be. We have no way of knowing, and I’m not sure that George does either, with respect to the specific design of the Lampi. And given that a 300B and these rectifiers both have 5 volt filaments, perhaps the design even utilizes the same transformer winding to power both, which would result in the 300B seeing more than the 5 volts it is designed for. That suspicion is heightened by the indication you provided that the Lampi applies AC to the filament of the 300B. So regarding your statement that "I'm afraid to try my EML 5U4 (3 amps) with my Elrogs," it seems very conceivable to me that using a rectifier having a 2 amp filament current draw might be more stressful to the Elrog than one having a 3 amp draw. Especially given the very high 600 volt plate rating of the Elrog tube, which together with Matthias' statement quoted above would seem to indicate that it is more vulnerable to a filament voltage increase than to a B+ voltage increase that might result from a rectifier change. There are undoubtedly other significant differences in the electrical parameters of these various tubes, which I haven’t taken the time to study and which don’t seem to be available in all cases. But I would certainly expect that between those differences and differences in the value of the filament voltage resulting from differing current draws there would be significant differences in the DC voltages supplied by the rectifier circuit to the rest of the DAC, including the output tube. Which can certainly be expected to result in sonic differences, for better or worse, even apart from differences in the intrinsic sonic characters of the tubes. But not having knowledge of the specific designs we have no way of knowing what the long-term effects on reliability might be. As I said earlier, changing a rectifier to one that draws significantly different filament current than the one the unit is supplied with amounts to incorporating a design change into the unit. As an electronic circuit designer (not for audio), it goes against my grain to implement a design change without having either a means of understanding its ramifications, or an ok from the designer or some other source having specific knowledge of the design. Bill (Brownsfan), it looks like the CV387 is a small pentode, so you may have mis-typed that number. Otherwise, though, given that I see on Brent Jessee’s site that the VU-71 is equivalent to the 5U4GB, and given the rest of the facts stated in your post, including operation at a lowish line voltage, I don’t see that you have any issues. Enjoy! Best regards, --Al |
Thanks very much, Jet. Could you give us a rough idea of the magnitude of these voltage changes that you see in your particular amp? I did a few minutes of research trying to find specs on the resistances of filament windings of transformers that would be used in these kinds of applications, and came up pretty much empty. It is surprising that such specs aren't commonly provided, which makes it hard to pin down the issues being discussed in any kind of quantitative manner. Which opens the door to speculation and differences of opinion. Not to mention that it seems highly unlikely that data would be available for the particular tubes being discussed, or most other tubes for that matter, which would quantitatively indicate how their MTBF (mean time between failure) varies as a function of filament current, among other application dependent variables. In fact the only conceivably relevant data I was able to find was for some military grade 60 Hz filament transformers specified in MIL-PRF-27 and its associated documents. For transformers intended for applications that are roughly similar in terms of voltage and current those documents generally indicated filament resistances in the area of 0.1 to 0.25 ohms. Which seems reasonably small **IF** the transformer and its turns ratio are chosen by the designer based on a loading assumption that is at least roughly in the general ballpark of the actual load. Best regards, -- Al |
Thanks very much for providing that info, Jet. I've done some fairly lengthy calculations based on it, the results of which are listed below. These results assume (as I would expect) that the dropping resistor you mentioned is on the primary side of the transformer, that its setting wasn't changed during these measurements, and that the tubes were reasonably warmed up for the measurements. The results of my calculations are as follows: Filament winding impedance at 60 Hz (which I would expect to be not greatly different than its DC resistance): 0.33 ohms. Open circuit output voltage of the filament winding (i.e., the voltage it would put out if zero current were drawn from it): 5.46 volts. The 0.33 ohms is just a bit higher than the 0.25 ohm spec I had mentioned for one of the MIL spec transformers for which I found specs, that transformer being reasonably comparable in terms of its voltage and current ratings. I note that in contrast to most manufacturers EML actually indicates a tolerance on the 5 volt filament specification of their 300B-XLS, that being +/- 5%. Kudos to EML for providing that. Although I still wouldn't count on prolonged use of the tube at or near the upper limit of that tolerance to not result in some degradation of MTBF (long-term reliability). 5.06/5.00 is an increase of about 1.2%, which seems very comfortable, at least in terms of reliability if not sonics. But I suspect that you have done a very wise thing in using a dropping resistor to correct for your relatively high (although certainly not uncommonly high) line voltage. Even if the transformer is designed for an input of 120 volts, as opposed to say 117 volts, 124/120 is a 3.3% increase all by itself. And the MIL specs I looked at generally indicated transformer tolerances of +/-2% or more. The sum of those two deviations, if not corrected for as you have done, would already exceed EML's 5% tolerance recommendation if the deviation in the transformer happens to be in the upper half of its +/-2% range. Turning to rectifiers, for a 3 amp tube obviously a winding having a somewhat heftier rating than the 3 amp rating of the one you are using for the 300B would be used, so chances are its resistance would be a bit less than the 0.33 ohms. Let's say 0.25 ohms, the rating of one of the MIL spec transformers I looked at. Substituting a 2 amp tube would result in a voltage increase, relative to use of a 3 amp tube, of 0.25 ohms x 1 amp = 0.25 volts = 5%, which does not take into account line voltage variations, transformer turns ratio tolerances, and other factors that could further increase the voltage applied to the tube. Not an immediate disaster by any means, but certainly undesirable and a cause for significant concern over the long-term. Thanks again. And I hope that some of those reading this thread will find this analysis to be helpful. Best regards, -- Al |
P.S: A sharp-eyed reader may notice that at one point in my post just above I kind of juxtaposed EML's +/-5% tolerance with the 5.06 volt measurement Jet provided for the Sophia tube. I'm assuming that had Sophia provided a +/- tolerance on the 5 volt supply, the number would have been similar to EML's. Best regards, -- Al |
Excellent comments by Jet just above, regarding the power rating of the replacement resistor(s). And I note in this schematic, which was referenced earlier in the thread, that a 25 watt rating is shown for the present 1K resistor. In general, it is good practice to "derate" a resistor's power rating (i.e., to have the rating exceed the expected actual dissipation) by at least a factor of 2 and preferably more. Rob, thanks for the kind comment :-) Best regards, -- Al |
Ecx123 2-25-2017A 5U4GB can **handle** a somewhat greater output current load than a 5U4G, but their specs are otherwise pretty similar. The website description of the Franks Mk II indicates 5U4G, however. Perhaps the description isn't up to date. A 5U4GB will just about always be a suitable substitute for a 5U4G. A 5U4G will be substitutable for a 5U4GB in some designs but not in others. Charles1dad 2-25-2017The GZ37 is equivalent to a 5AR4. It will often and perhaps usually be a suitable substitute for a 5U4G, and it will be a suitable substitute for a 5U4GB in some designs but not in others. There was some discussion of the 5AR4 near the bottom of page 9 and near the top of page 10 of this thread. (Those page numbers apply if posts are sorted most recent last). Best regards, -- Al |
Ecx123, thanks for the additional info. I see what you are referring to in EML’s note 4, which states in part: Replacing 5U4G with 5U4GB may result in higher rectified voltage, so should never be done. Replacing 5U4GB with 5U4G may result in lower rectified voltage, and may result in damage of the 5U4G rectifier.However, here are vintage datasheets for the 5U4G and the 5U4GB. Note the statement in the first paragraph of the 5U4GB datasheet that: The 5U4-GB ... may be used as a replacement for either the 5U4-G or 5U4-GA.Also, while the detailed parameters indicated in the datasheets do suggest that substituting a 5U4GB for a 5U4G will result in higher rectified voltage, the difference does not appear likely to be major. Finally, my older Sam’s Tube Substitution Handbook lists the 5U4GB as a direct substitute for the 5U4G (while of course not listing the reverse). I have never known its listings to be inaccurate, and I have often found them to be overly conservative (i.e., to err on the side of caution) if anything. In any event, all of this is of course superseded by the indication from Israel and in the manual that the 5U4GB should be used in the Franks. He should update the website description of the Franks, though, which indicates 5U4G as I mentioned. Enjoy! Regards, -- Al |