jt1stcav Posted January 18, 2004 Share Posted January 18, 2004 Dale brought up a good subject in an earlier thread, one that I think should be posted here: what about tube substitutions and/or equivalents? Is is really safe to use other tube types other than what the manufacturer calls for? I understand about the differences in nomenclature from US makes compaired to European types (US version 6SN7 and the European 6H8C version, both being equal), but is it really safe to switch out, let's say, a 5AR4 for a GZ34 equivalent? For instance, I have a new 8 watt per channel BEZ Model T3B Class A 300B SE power amplifier on its way from Hong Kong. It has a pair of Shuguang factory matched 300B-98 tubes, a pair of NOS Tung-Sol or British military 6K7G pentode tubes, and one Russian 5U4G recifier tube. The builder of my new amp states on his eBay auction that you can substitute a pair of NOS Mullard EF37A (red painted glass) and 6J7 metal or glass tubes for the existing 6K7G radio tubes "to obtain the higher output power". Is it really best to replace the 6K7G (which isn't the best choice using a radio tube for an audio amplifier, so I guess) for the other two choices? And will using either the EF37A or the 6J7 tubes really increase output power to this 8 WPC amp, and by roughly how much? I'm a tube-nube; I thought the 300Bs are what determine the amp's output power. Any advice y'all can give me would be greatly appreciated. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted January 18, 2004 Share Posted January 18, 2004 The EF37A or 6J7 may have a little more transconductance. They may add more gain to the driver stage/stages. Hence more to the output stage, a geuss. I'd listen to the amp for some time before I'd get worried about rolling driver tubes. At least you can derive more gain if desired. Dunno about the reliability or the sound of the Shuguang 300B tubes. I'll be using TJ solid plate 300B's. (Bastard 300B with 2.5 volt filament.) Dunno about the Russain 5U4 reliability, but US NOS 5U4's are quite abundant. Quote Link to comment Share on other sites More sharing options...
Deang Posted January 18, 2004 Share Posted January 18, 2004 Whatever "more" it gets you, it's probably not worth the trouble or extra money. It will also accelerate the demise of the 300Bs. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted January 18, 2004 Share Posted January 18, 2004 "It will also accelerate the demise of the 300Bs" I don't think it would re-bias and make the output tubes run harder,it just gives them more gain. I'm not familiar with the circuit, so I have to claim ignorance. Quote Link to comment Share on other sites More sharing options...
Deang Posted January 18, 2004 Share Posted January 18, 2004 How can you get more output without driving the tubes harder? Well, I'm definitely out of my realm here. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted January 18, 2004 Share Posted January 18, 2004 Don't feel bad, I'm with you. I'm building a Triode amp and can't even explain, That's terrible! Quote Link to comment Share on other sites More sharing options...
Deang Posted January 18, 2004 Share Posted January 18, 2004 LOL That's O.K., I electrocuted myself 3 times in 30 minutes before I figured out how I was doing it. I'm sticking with crossovers from now on. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 18, 2004 Share Posted January 18, 2004 I believe am keep in mind I do not know this circuit at all so I'm like Dean here ! That the new tube type ups the gain slightly in that stage which in effect ups the amps output slightly. I bet it doesn't effect the 300B at all. Craig Quote Link to comment Share on other sites More sharing options...
3dzapper Posted January 18, 2004 Share Posted January 18, 2004 Ow! Ow! Ow! Rick Quote Link to comment Share on other sites More sharing options...
lynnm Posted January 18, 2004 Share Posted January 18, 2004 I assume the 300B amp in question is running in Class A in which case the 300B's are running essentially flat out at all times. If the amp is well designed the plate voltage will have been set a below maximum and therefore a slight increase in drive should make no noticeable differenc to the 300 B tubes. A large increase in drive might well be a different kettle of fish however. Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted January 18, 2004 Author Share Posted January 18, 2004 Thanks, guys for all the responses so far. Not knowing the circuit (which according to Edmund Lam is Class A single ended), then it would be a safe bet not to be doing any tube substitution, but to keep them as they are. That's fine with me...I'd hate to pop in the wrong type tube and screw the whole thing up. If I do any tube rolling later on down the road, I'll continue to use the same type; just exchange the stock tubes for their NOS equivalent. The 5U4G rectifier is common, so finding a NOS or used US made 5U4G will be easy...same for the 300B, albeit expensive (I hear the new Electro Harmonix 300Bs are satisfactory along with the JJ Electronics, with both the KR Audio and TJ 300B mesh anode globes being one of your better choices...although the replica Western Electric 300Bs are out of my league). But I wonder why the builder decided on using a pentode designed for radio use like the 6K7G for his amplifier design? Is it less effective than another tube type better suited for audio amplifier use, or is its use negligible? Or was it just a cheaper alternative? Maybe he aquired a huge stockpile of these 6K7Gs and wanted to use them to keep his overhead (and prices) down. Your thoughts please... Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted January 18, 2004 Author Share Posted January 18, 2004 ---------------- On 1/18/2004 8:20:52 PM mdeneen wrote: ..."It's an inexpensive way to get lots of gain in one chunk. To get the equivelent gain using triodes would require two cascaded stages, or a dual unit cascode stage. These tubes - 6K7G - are normally used as RF amplifiers, hence the term "radio tube". ---------------- I guess as long as the overall sound of the amp isn't compromised because of the 6K7Gs, then I'll stick with NOS versions of this tube when and if I ever do any tube rolling. I suppose if I was to ever replace the 6K7Gs with the red painted EF37As or the metal or glass 6J7s, I'd have some piece of mind knowing its use wouldn't affect the existing circuits or biasing any. Quote Link to comment Share on other sites More sharing options...
Dale W Posted January 19, 2004 Share Posted January 19, 2004 I've noticed a lot of the asia tube amps are being advertised as self biasing. Like a lot of the "DARED" lineup. Just plug in your favorite 12au7/ ax7 /bh7 etc and away you go . Don't know how any of this stuff sounds but its sure being sold cheap on e-bay. Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted January 31, 2004 Author Share Posted January 31, 2004 So I've learned thus far: A) It's not a necessity to exchange the original tubes selected from any given circuit for their substitutes due to what little benefit (if any) they may provide. Damage may result if not properly researched. For tube rolling, it's best to stick to the original tube's equivalents, whether it be new, NOS, or used. As in A), know your circuit's schematics. C) Know your circuit's proper voltage to ensure best usage of any given tube in your component. As far as the venerable 300B goes, I assume that I can exchange the original Chinese 300B for a better equivalent from other manufacturers, i.e. TJ, JJ Electronic, KR Audio, Electro Harmonix, etc. Are the mesh anode globes from these and other makers also acceptable for my amplifier, or is it best to stay with the typical standard shoulder-glass types? Quote Link to comment Share on other sites More sharing options...
mike stehr Posted January 31, 2004 Share Posted January 31, 2004 The difference in a glass globe, or a shoulder type is only in the cosmetics. Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted January 31, 2004 Author Share Posted January 31, 2004 So the mesh anodes on these particular balloon glass 300Bs are nothing more than a prettier lightshow than on the standard shoulder (or coke-bottle) glass 300Bs with the conventional solid metal anodes? See, this is why I get so damned confused with all these specialty 300B tubes out there...maybe I should just stick to the base Chinese 300B, but I always read that there are other much better sounding 300Bs out there! I know that one 300B from brand "A" might sound great on a particular amp and sound thin and sizzly on another amp; the same with different 300Bs on my particular amp, but which one would be the best choice? I haven't the funds to buy several pairs of 300Bs from different manufacturers and literally try out each make to see which sounds the best. I'd prefer to purchase the best 300B within my budget that'll sound the best with my amp, but I guess that's not really possible. The only way to really judge what's best sounding for my BEZ amp would be to experiment when I can afford to do so. Alas, this is not a poor man's hobby... Quote Link to comment Share on other sites More sharing options...
banned Posted January 31, 2004 Share Posted January 31, 2004 "So the mesh anodes on these particular balloon glass 300Bs are nothing more than a prettier lightshow than on the standard shoulder (or coke-bottle) glass 300Bs with the conventional solid metal anodes?" The shape of the glass envelope shouldn't make any sort of difference at all, the internal structures(electrodes)inside the tube are what make the differences. I'd do like you said, just listen to the tubes that come with the amp, they are probably voiced and set-up with the amplifier topology of the Bez amp in mind. Save your sheckels while you burn those up for a higher quality 300B down the road. There always Ebay.... Alas, this is not a poor man's hobby... It can be, but it depends how deep you want to go with the hobby. There a few old-timers out there building tube amps for the price of a can of dog-food, it's from years of collecting parts. Quote Link to comment Share on other sites More sharing options...
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