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@@garretthead This is one big reason why a properly designed power supply is critical. Many tube amps are designed by borrowing other known designs, with no (zero) actual design work being done. This applies both to hobbyists and commercial manufacturers. We design everything from first principles, checking every component in a design to make sure it's correctly spec'd. This takes both experience and time, and costs money, which is why it's not commonly done any more. Now if an amp has a separate filament switch or a standby switch it should have been designed to NOT over voltage the B+ if the filaments aren't lamped. In a well designed power supply there should always be lots of extra room on the component specifications.

Politely disagree. An amp may have been designed, or even just tested to operate with-in spec for an application, following an intended startup sequence . Then blindly on the advice of a youtube video, someone turns their amps on in the opposite order (ie B+ on cold start) and suddenly the amp is put in a situation it was _not_ designed or tested for. You are right that a lot of amps had questionable designs. Many of those amps happily lived through years of abuse or being operated beyond specs. Now some of those I can think of probably would not survive what you suggest here... at least not many times. I understand your sentiment as an engineer, but pragmatically what you are advising is quite dangerous to many amps... and I wouldn't expect the audience to be able to discern which ones. To suggest intentionally operating other amps not-as-designed because you prefer to design/operate yours this way (for whatever reasons) seems sort of distasteful. I did enjoy some of your content and hope you keep it up. Just something to consider. Cheers.

@@garretthead to clarify, if your amplifier manual says to start your amp in a certain sequence, then follow those instructions. An example of this would be an older Fender amp with a standby switch. In this case the manufacturer didn't want to afford expensive filter caps, so they avoided over voltaging the caps, by first turning on the filaments, then the high voltage B+. However in modern amps, the cost of those filter caps is no longer a significant concern and most amps are simply turned on with one switch. This gives a significant inrush current, but the designer would have had to allow for this. Unfortunately it probably also leads to the shortest tube life. Less commonly amps have the option to turn on the filaments separately from the B+. As shown on our bench testing the lowest inrush current happens when you first turn on the B+, immediately followed by the filaments. This produces effectively a slow startup and the lowest inrush current and probably the longest tube life. Any designer of such an amp would automatically have to ensure the caps can withstand a higher B+. Everyone who has ever properly designed such a power supply over specs the filter cap rating for this reason as well for longevity. The fact that many modern tube amps are simply older circuits they copied, with no understanding of how they operate doesn't absolve the manufacturer of responsibility for ensuring a safe operating amp. Another common method for dealing with the above issues is to build in a slow start circuit. A thermistor being probably the most common. Not something I like to incorporate in our designs, but nevertheless a valid approach. As you can see there are many different approaches to achieving the same goal, a safe operating tube amp. With a read of your manual and some common sense, this is not complicated. The most important thing is to avoid badly designed, cheap tube gear, which we unfortunately see more and more of.

@@el_arte about that, and we invested about $60k developing it, only to discover the retail price point was way more than our average customer could afford. So we went back to the design stage and started off with two key criteria - great sound at an affordable price. That led straight to an OTL design, that impressed us enough to continue developing it. We're waiting for a couple of parts and then hopefully we can call the prototype done. Eventually when the Kit business is bigger, we'll release the original headphone amp.

@@andresmartinelli5276 we specialize in vintage EL34's, and I've never seen a modern one that I would be interested in. Years ago the early production Electro-Harmonix used to be pretty good for a budget option, but the quality of current production isn't as good - so I can't even recommend them.

Which is the least bad based on your experience then ? Thank you!

@@59seank All of our Kits have the RCA In/Out located on the top plate and it works really well. Remember when you bring a low signal into the rear of a preamp/amp chassis it is now located right beside the noisy power supply. Much better to drop it in to the point of the circuit where it is quiet and the wire run is very short. In order to design superior sounding Kits it's important to forget what commercial manufacturers do, and start from first principles.

@@darrenfoxwell7831 saying all tube amps are sold with cheap tubes may be subjective but I think a lot of people would agree...if comparing them to NOS tubes & especially Rectifier tubes. Rectifier & driver/preamp tubes seem to be much better with New/Used Old Stock. Just my opinion though & I'm not saying all current tubes are bad. The question is are the sonic differences gained by using NOS worth the extreme premium prices these days? Gotta keep in mind that NOS seems to live much longer as well.

@@darrenfoxwell7831 I agree, what we should have said, is almost all new tube amps sold in the last decade or more are supplied with inexpensive Chinese, Russian and Slovakia made tubes. Those tubes in many cases are inferior to 2nd generation vintage tubes made prior to about 1982. This is based on handling ~5-10k tubes per year and more importantly comments from 100's of customers, who on a daily basis ask questions like "why do my preamp tubes sound so harsh or edgy", "can you recommend a power tube that doesn't die 2 months after I plug it in", "my rectifiers are not lasting more than 6 months" and on and on. The problem with a weekly show that's mostly filmed in one take, is it's not always possible to define everything we say in absolute terms and infinite detail - when we do that the show goes past 30 minutes and we get complaints. Most of our viewers understand this and do more research on their own if they're interested in learning more about something. Or ask questions in the comments section.

@@jeff3575davison actually I did mention that there's at least 2 dozen ways to limit the inrush, but given we get complaints once the Friday episode goes over 30 minutes, we need to push forward sometimes. As a designer, I'm wary of putting anything in current path, the quality of the power supply design substantially affects the quality of the sound. We just replaced the thermistor in one of our Ebike chargers, somehow it blew it's guts to smithereens. I'm not a fan of the thermistor, but obviously there's a place for them - just not in my designs.

@@tubelab194 perhaps make a follow up video to explain the in's / out's, pro and cons? should make for a good video and compelling rational for their non use?

@@jeff3575davison good idea, but a bit beyond our typical audience. Because we tend to only do episodes about tubes / circuits and related stuff that we can get behind (based on actual experience), we don't normally do negative vids and if we talked about the thermistor it would be one of those.

@@tubelab194 doesn't have to be negitive. If you show both sides and explain why you choose not to use them, really is positive, informative, and educational. It would lend to your viewers understanding of their function. Your viewers are probably quite knowledgeable and and capable, don't underestimate them as those who only replace and swap tubes...

@@whome8192 It all depends on the tube, we only talk about things we actually know, and the 5U4G is one example in which some Chinese rectifiers clearly can handle more in rush current than quality vintage production. With other rectifiers it could be the reverse, in fact the GZ34 comes to mind, those vintage mullards are beasts and modern production is junk in comparison. We always design a lower value first cap in our power supplies, typically 47uf with solid state rectification. The UF4007 has amazing specs for a wee piece of doped silicone, but why stress it if you don't need to!

@@ahmadathari3503 you can't, the tubes are different enough that you should not attempt to adapt an 807 for a 6L6 amp. Vintage 6L6's and the Soviet version (6P3S-E) are still available. We have excellent inventory of the Soviet version for very reasonable money.

@@ahmadathari3503 Please visit the store, www.valvesnmore.com for pricing and automatic checkout. Any questions, jist use the contact page in the store.

@@NosEL34 I used to think they were just a good tube with a lovely treble, then we used them in one of our headphone amp prototypes as the input gain stage and they just blew me away with a nice warm full midrange and a treble that was the best we've ever heard. Even though everyone knows tubes are partly dependent on the circuit they're running, it's always worth repeating. Another common problem we see all the time is poorly designed circuits that don't even give the tubes a chance to show what they're capable of - this is a common problem even in expensive amps.

@@tubelab194 very true & well said. I guess I should say that I haven't listened to the clear tops in a circuit that brought out their full potential. They are definitely a very popular tube.

@@liamguitars only one or two, but Caution! make sure that pop can shield doesn't short anything out. Most likely you don't even need the shield unless the tube is close to a transformer or other noisy component.

The Russian equipment Г807 (G807) is also great

@@ahmadathari3503 no the 6CG7 is a completely different tube (medium gain) compared to the high gain 12ax7. The only acceptable tubes to sub for the 12ax7 are the slightly lower gain 12at7 or the higher spec'd 7025.

@@tubelab194 thank for your answer, what ablout 12sl/sn7 instead of 12ax7 with converter socket?

@@ahmadathari3503 again it's a very different tube. And adapting from a larger octal tube down to a miniature 9pin is not practical. Going the other way, mini 9 pin to octal is fine structurally. The 12ax7 is a unique tube and should be replaced with 12ax7's. We should still have stock of some excellent vintage 12ax7's. Note if you sub a different tube in a phono preamp the EQ will be changed.

@@daviddabbs1234 completely different tubes, the 6n1p is a twin triode with medium mu (gain) and the 6n2p is a high gain twin triode that's so similar to a 12ax7, I call it a 6ax7. EV is the higher spec version, similar to the Western "mil spec" variants.

@@tubelab194 thank you for the information

@@cobar5342 Thanks, we don't have a tube collection, only the store inventory. We once were roasted by someone online for hording precious tubes. But nothing could be further from the truth, we sell everything we have available. However as inventories of quality vintage tubes head to zero, Charles has suggested we start reserving examples of some of the rarer types, the Sylvania 12SN7 "Bad Boys" for one - probably the best sounding preamp tube ever made - unfortunately not as robust as the later higher spec'd 6SN7GTA.

Good choice !...............this tube does even not have a barrier cathode issue ...performance will stay for decades wheb used correctly ........sound may even get better over time . With the stock version sounds marvelous , that's the right starting point to upgrade components, wiring, connectors and volume pot ...etc . Only a very good design will benefit from this , not a design with flaws to try to hide the flaws ... I even do not use RCA connectors .....straight out and in with Neotech 1220 OCC AG wiring , no selector switch or whatever , only a Duelund tinned copperfoil on the output , Preheating and post heating of the filaments ........RGN1064 mesh rectifiers . Shinkoh 2 watt resistors and A/B......Black Gate capacitors....and Lunfdagl chokes. Sockets mounted on rubber suspension and point to point wiring. Rhodium IEC inlet and switchable bypass for the fuse ( at your own risk ) Do not forget to bias the heater voltage above the ground potential; No plastic isolation on te caps , .........copper foil to replace the plastic foil. BG needs long hours before revealing their magic , unequaled by any other brand , voices come out totaly free out of space of the recording .......layers of instrumentsfloat in gthe air beside, higher or lower, closer or further away..all will have body and air arround them and be separated one from another.....microdynamics will appear and shine without false upfront presentation........you can not buy a preamp with the same musicality in commercial totaly overpriced preamps ! Good luck and happy building . PS : Quality silver RCA plugs /Quality solder (AN or WBT )....lining the inside of the chassis with CU foil/quality noval socket ( military nos - AG)......shield cable for heater wiring. ../ better volume pot than the usual Alps ...Etc ... You will be rewarde with a totaly and silent black background.for the music .......no noise even better than SS ...........and a dramaticaly expansion of the dynamics from micro to macro level.

@@frankgeeraerts6243 Yes , this one rewards a bit of attention to detail. I was almost startled about the dynamics in this one, I perceived some extra punch via this one for sure. I did not go with raised voltage on heaters, but I went with filtered and regulated DC for the heaters. I use that voltage also for nice quality Japanese relays for input switching. I need 4 inputs you see. I went with RCA sockets, of the KLE type, which is basically same style as WBT. I also have full shielding of the circuit beneath my 2mm copper base-plate and I have both steel and copper in the transformer and choke housing. Also mounted a stepped attenuator built on Seiden swith and Takman carbon film resistors. All inn all very happy with it, thus I ordered a set of spare tube, they also sounds wonderful in my Crack HPA.

@@RaviNewfarm Nice .........thank you for reply . I also heard some good things about the Crack ! KLE is great ! ( use them also ) Tackman carbon sounds very good without ruiniing the budget .....

@@dakata2416 almost anyway you can think of (that's safe), the only delicate part is the glass, the electronics are in a vacuum so the internal components basically stay in the same condition they were manufactured. We regularly run Sylvania tubes made in the 1930's and 40's and other than the pins needing a clean up they're basically brand new (if NOS - new old stock). Sometime soon we'll do an episode on this, but in general anywhere safe from breakage inside your house is good. If you have boxes great, make use of them and then store your boxes in a shallow cardboard tray. If you don't have a box, wrapped in a layer of mini bubble wrap with an elastic around it is good, and again in a shallow tray. The most important thing is to make sure that wherever your tray of tubes is stored they can't accidentally get broken.

@@tubelab194 what about environmental conditions?

@@dakata2416 normal household conditions are ideal. What would cause problems is if you live near salt water - in which case sealing the tubes in a ziplock would significantly reduce pin corrosion. We store our store inventory in an unheated garage in clear 16L bins and ziplocks and they're perfectly fine. Now don't take a tube at freezing and plug it directly into an amp, that would be asking for trouble, first bring it inside and give it time to reach room temp.

@@kwacz keep looking, it may just take some time to find someone who has a bunch of them AND will test them. Note all quality vintage tube sellers test and match. Or rewire a new octal socket for the 6K6 which is electrically equivalent with a different base.

@@tubelab194 all the major tube websites give you what they give you. No matched sets for nos. Only current production tubes have option for matched sets

Anyhow i put them in anyway and they sound fine. Just as good as the ones currently in there. No different. The radio is from 1942 so dont know if that matters. I dont know if they even did matched tubes back then.

Not practical, my recommendation would be to drive them with a tube output stage coupled with a multi tap output transformer. We actually have a complete headphone amp prototype that would be perfect, as the lowest tap is 8ohms. If you want to experience an OTL amp, I'd recommend thinking about higher impedance headphones. Large selection starting at 150 and 300 ohm. But first find the amp you want, then the headphones, that way you'll know for sure they're compatible. We're currently developing another Kit Headphone Amp and it should be a good match for 150/300 ohm cans.

@@tubelab194 thank you

Yes this is a nice linear tube, however lots of triodes have similar plate curves. And it doesn't matter what kind of circuit you run it in, you will always have distortion, maybe lower distortion, but it'll be there. We currently have a preamp in development and are running each section at 242vdc 8.5mA and it's working perfectly and sounds amazing (Voskhod 6N1P-EV).

I have three…

We haven't fully bench tested and spec'd the new pre yet, but almost certainly it would be a good match. Input impedance will be 100k ohm and every modern dac I've ever looked at will have very low output impedance (I've seen as low as 32ohm!), so the input side should be no (zero) problem. And your AVR has a reasonable input impedance of 42K ohm and the new pre will have an output impedance of less than 1k so again a good match. The output impedance is the one spec that needs proper bench testing. One of our goals for our new affordable Kit Preamp, was to give people a good pre to use as a buffer and given the sonics, I think this will make an amazing main system Preamp or Buffer.

​@@tubelab194 How does this sonically sound vs your current Universal 6or12SN7 Dual Mono PreAmp? Any comparison you can offer - even subjectively between the 3 pre-amps putting cost aside?

With all due respect, listening, I mean really listening is a far more valuable tool than any sweep. Now that said, we do sweep our Kit designs during development and it can provide valuable information. But ultimately critical listening is far more useful in tube rolling and amp design, in our experience. I was an audiophile in the 70's when all we wanted was the specifications and the sweeps, and our equipment had the life sucked out of it by designers relying on what their screens were saying, instead of what their ears were hearing - never again.