[DecentLevi]

Hi m...good question. The 'guide' for this GU50 tube is in fact a raised section that runs 2/3rds the way down its side, denoting the cathode position, and which would therefore fit correctly in the corresponding guide in bespoke holders. But going straight into a socket would need this position marked clearly on the socket itself, so as to marry up with said raised section on the tube. This would obviously have to be pointed out to any 3rd party maker of adapters.... :



The raised guide clearly visible above.

The tube's pins are unevenly spaced, so there are in fact only 2 ways it will fit in the socket, which should limit the chance of incorrect insertion.

And as for that rather strange metal top cover, it obviously can in fact be removed and looks much better for it IMHO!! ...as can be seen below :



(Shan't bother with the LED lights from underneath though, even if it does look 'pretty'!! ).

All I need to do now is work out just how to remove the curved metal cap without breaking the tube lol! ...(just as well I've got some more tubes coming...eventually!!!).

ps. Actually, with these GU50s costing just a few bucks each I'm sorely tempted to make up a neat (not 'Frankenstein!) 2x tube array for each power slot, which should be easy enough to slip in a couple of small leds...with McKintosh blue!...(sounds better the more I think of it lol!! ).

pps. And now with these GU50s beating all comers, I must thank you mordy for providing the extra push for me to test the JAC Music guy's assertion that this tube is 'better' than the KT88...was undecided until then...CHEERS!...CJ

I would wonder if somehow the exterior glass may cause some indirect sonic benefit (such as vibration absorption), so if removing it I personally would do an A/B with one with / without the outer glass shell. At least this would allow an easier fit for a quad GU50 powers setup anyway.

 

[hypnos1]

I would wonder if somehow the exterior glass may cause some indirect sonic benefit (such as vibration absorption), so if removing it I personally would do an A/B with one with / without the outer glass shell. At least this would allow an easier fit for a quad GU50 powers setup anyway.

The only bespoke tube holder that seems available is the open-sided metal 'trash can' type, with no exterior "glass shell"(?). And I think the only benefit was from military ease of use in the field. There are in fact quite a few amps out there using the GU50/Chinese FU50 and they all have the tube by itself, with no holder...

 

[hypnos1]

........................................Important update on the GU50 as driver...............................

OK @mordy and any others interested in the GU50 as driver, not just power tube.

My last post re. the slight noise at certain volume knob settings prompted me to try the KT88 as powers...which I was gonna do anyway lol! Although much less than with the TT21 powers, it was still there to a certain extent. From previous experience with even worse hum/buzz using my 12V supply for the 13V FDD20, I once again connected the negative wire from the supply back to the mains Earth wire et voila!...completely gone!! And so another case of 'grounding issues/loop', which is why many items of hi fi equipment have a specific 'ground connector' in case of such issues.

Anyway, at least this is a problem easily remedied for most folks, if necessary - as described above...thank goodness!...and much cheaper than going for a good quality (grounded) linear power supply .

And which is also good news because as a driver (to the KT88 powers) it is exceptional! Better in fact IMHO than KT88s driving KT88s...certainly in my own system. The volume knob needs another couple of notches, but is no problem at all - even when turned up to ear-shattering levels there's no hint of distortion whatsoever. Stage is even wider, with superlative bass and more mids emphasis. Treble is sweet, detailed and extended, with an even more dynamic presentation overall.

In other words, this GU50 excels not only as a power tube in our amps, but equally as driver. I know of no other amp (or project) that uses this tube in both roles, let alone do so to such a high level of performance.

All that now remains is to see just how well they perform with one (2, rather!) driving the other(s)...and which could possibly be an even more important finding, given the meagre cost of four GU50s (typically $12 to $15, plus shipping!!).

Hopefully, this will be answered in the next couple of days......BFN...CJ

 

[OctavianH]

If we can use KT77 in our amps, can we also use EL34? I guess these tubes are close/similar.

 

[hypnos1]

If we can use KT77 in our amps, can we also use EL34? I guess these tubes are close/similar.

Hi OH. The EL34 is wired slightly differently - ie. grid #3 isn't connected internally to the cathode, unlike the 6L6/KT66/77/88 etc. And so as we need that connection (as triode) you would need to link socket pins 1 and 8, using a piece of thin stranded wire. However, it seems the majority of folks out there prefer the KT77 to the EL34 anyway...but as usual, different strokes for different folks...and equipment lol!!

ps. My GU50s arrived from Romania the other day, so it wasn't too bad really, considering Christmas...

 

[OctavianH]

The question came into my mind while reading this:
https://www.tubesforamps.com/el34-6ca7-kt77-differences

 

[hypnos1]

The question came into my mind while reading this:
https://www.tubesforamps.com/el34-6ca7-kt77-differences

Hey OH...you readin' my mind just like @connieflyer ? Was looking at that very article myself just now lol!!

ps. Re. the need for linking pins 1 and 8 to use the EL34, they're the ones in the adapter's socket of course!!

 

[hypnos1]

Hey @OctavianH ...I've just tested Mrsx's 6L6/7581 adapter, and hers at least have infact been wired with pins 1 and 8 connected, so they should already be OK to take the EL34 after all lol ...

Now then guys, after checking the GU50s drive KT88s to perfection (with the 12V supply negative wire now connected to mains Earth wire), I put back my GEC TT21s as powers and...WOW!... With sub-bass back (if overall bass/lower mids not hitting quite as hard as with KT88 or GU50 powers, I now realise I myself actually prefer the smoother, more 'refined', better balanced delivery of the GECs (which they're generally renowned for anyway lol!). And the GU50s as drivers help give them just a tad more dynamism and bite...with a soundstage that goes even wider and more 3 dimensional. So for me - and my system - this is now (for the moment at least lol!) my favourite combo. And I suspect therefore that the GU50 quad might not maintain this preferred sound...will know soon (if I can leave this laptop and get back to work lol! ). More likely could well be a GU50/GEC TT21 joined pair per channel (power)...but that'll have to wait a wee while!

Anyway, a pic of my latest 'magic combo' :



ps. These GU50s are undoubtedly the best drivers I myself have ever tried in my Euforia setup......(who'd have ever believed it lol?!...we now have a truly unique amp!! )...CJ

 

[connieflyer]

Looked for the TT 21's but the price for a quad was a bit much! https://www.usaudiomart.com/details...77-production-date-and-batch-matched-rare-wi/
Asking Price:
USD $12345.00

http://www.r-type.org/exhib/aby0019.htm nice info

 

[connieflyer]

Article of interest, "The Story of the Valve" http://www.r-type.org/articles/art-001.htm

 

[hypnos1]

Looked for the TT 21's but the price for a quad was a bit much! https://www.usaudiomart.com/details...77-production-date-and-batch-matched-rare-wi/
Asking Price:
USD $12345.00

http://www.r-type.org/exhib/aby0019.htm nice info

Huh cf...this is the sort of thing that gives our hobby a very bad name IMO lol! Either this guy is totally insane, or worse, the sort that fishes for some poor soul who misreads the figure...there should be one decimal place less in there!!...viz. NOS TT21s usually go on average for about $320 over here (or from elsewhere), so do the math lol! And not only that, but although they're very good, they aren't that good...going by my own system at least. These $3 GU50s for example are only a whisker behind them, and in some ways would suit certain systems and ears better! ...Having about 15 hours on my first GU50 power driven by another (with 100+hrs on), it was interesting today to hear the difference between this and the other channel with GU50/GEC TT21 through my Tannoy XT6f speakers. The latter combo was by no means way ahead...in fact, to some ears it might even seem a tad too soft in comparison, especially if the rest of the system is on the 'dark' side. To tell the truth, it confirmed that I shall indeed probably need to combine the GU50 and TT21 as power duos, assuming any differences aren't too significant and are able to merge seamlessly...stage and PRaT particularly mustn't be too far off each other or will certainly clash, especially noticeable in hi-end headphones.

I should have a better idea soon as to what may be needed as this afternoon I managed to finish converting the 4th GU50, and so now have 2x driving 2x powers. Mind you, it'll still be a while yet, given the long burn-in they need lol! Will keep y'all informed...CJ

ps. Already, the quad of GU50s perform together magnificently .

pps. Blue leds on their way!......

 

[Johnnysound]

Huh cf...this is the sort of thing that gives our hobby a very bad name IMO lol! Either this guy is totally insane, or worse, the sort that fishes for some poor soul who misreads the figure...there should be one decimal place less in there!!...viz. NOS TT21s usually go on average for about $320 over here (or from elsewhere), so do the math lol! And not only that, but although they're very good, they aren't that good...going by my own system at least. These $3 GU50s for example are only a whisker behind them, and in some ways would suit certain systems and ears better! ...Having about 15 hours on my first GU50 power driven by another (with 100+hrs on), it was interesting today to hear the difference between this and the other channel with GU50/GEC TT21 through my Tannoy XT6f speakers. The latter combo was by no means way ahead...in fact, to some ears it might even seem a tad too soft in comparison, especially if the rest of the system is on the 'dark' side. To tell the truth, it confirmed that I shall indeed probably need to combine the GU50 and TT21 as power duos, assuming any differences aren't too significant and are able to merge seamlessly...stage and PRaT particularly mustn't be too far off each other or will certainly clash, especially noticeable in hi-end headphones.

I should have a better idea soon as to what may be needed as this afternoon I managed to finish converting the 4th GU50, and so now have 2x driving 2x powers. Mind you, it'll still be a while yet, given the long burn-in they need lol! Will keep y'all informed...CJ

ps. Already, the quad of GU50s perform together magnificently .

pps. Blue leds on their way!......

Hey CJ...another of your great tube discoveries !! And a significant one it seems, if a $ 3 GU50 tube is able to even approach the performance of a $ 250 thoroughbred, then I really LIKE this one !! But, no adaptors available...(?) Regarding the external PS, well, the fuss of setting up one is worth the effort, and (remembering our old LDMKIII) I do have the laptop 12V P.S. along with the voltage regulator we used to adapt the big 6AS7Gs, to precisely 6.3 volts. The GU50 is 12.6 volts DC, so it looks like, say, a 15V (or more) PS, plus regulator to 12.6 V should be a more precise fit. However, I do not think that the .6 volt difference could seriously affect performance...or it will ? Amperage is another matter, GU50s have very low current draw at 0.7 Amp each, (revealing their military nature). Now, standard 12V laptop PS will give about 40W, which is 3.3 amps at 12 volts...enough for 4 tubes, but, It will get hot for sure. I am a true believer in oversized power supplies for great audio, and my bet is that the GU50s would sound best at their precise 12.6 v design spec, plus at least 30 or 40% power supply headroom.
Anyway, with no adaptors commercially available, all this is just speculation on my side...great work CJ !!

 

[Johnnysound]

Reading about CJs Euforia stellar performance with 2 x GU50 plus 2 x TT21 as powers, driving his very nice Vincent SS amp, and a pair of gorgeous Tannoy speakers, or CFs Euforia driving his also super nice Anthem SS amp to great SVS speakers, I am much more in tune, and able to understand that kind of performance. With my dual mono NAD powers, and US made LSA 2.1 floorstanders (out of this world) Euforia sounded mightily dynamic, impressive, and as I have said dozens of times, there is almost nothing that even comes close to an OTL tube preamp driving an SS amp....save for a good, powerful tube power amp, which is like entering into a whole new, “Alice into Wonderland” magic territory...

 

[hypnos1]

Hey CJ...another of your great tube discoveries !! And a significant one it seems, if a $ 3 GU50 tube is able to even approach the performance of a $ 250 thoroughbred, then I really LIKE this one !! But, no adaptors available...(?) Regarding the external PS, well, the fuss of setting up one is worth the effort, and (remembering our old LDMKIII) I do have the laptop 12V P.S. along with the voltage regulator we used to adapt the big 6AS7Gs, to precisely 6.3 volts. The GU50 is 12.6 volts DC, so it looks like, say, a 15V (or more) PS, plus regulator to 12.6 V should be a more precise fit. However, I do not think that the .6 volt difference could seriously affect performance...or it will ? Amperage is another matter, GU50s have very low current draw at 0.7 Amp each, (revealing their military nature). Now, standard 12V laptop PS will give about 40W, which is 3.3 amps at 12 volts...enough for 4 tubes, but, It will get hot for sure. I am a true believer in oversized power supplies for great audio, and my bet is that the GU50s would sound best at their precise 12.6 v design spec, plus at least 30 or 40% power supply headroom.
Anyway, with no adaptors commercially available, all this is just speculation on my side...great work CJ !!

Hi J.

Well mon ami, with about 45 hrs on one GU50 and 24 hrs on the other as powers, plus many more hours on 2 as drivers, my listening session just now has got me in total disbelief. Already this is by a good margin the best (overall) sound to come out of my setup...in any area you care to name - bass; mids; treble; clarity; precision; PRaT; liquidity; balance; control...and with a soundstage that is simply phenomenal. The $350 GEC TT21 may have a tad more sub-bass that you can actually feel thru headphones, and its softer delivery ideal for gentle choral such as Voces 8 material, but in most other respects the $3 GU50 surpasses it (in my own system, of course).

Although it's still early days for the last 2 tubes, their crisp, detailed energetic delivery is the most exciting I have yet encountered, and is really scrambling my brain as to whether I prefer this, or the more laid back delivery of the GECs...and I simply refuse to keep changing tubes to suit the genre! All I can hope for is that duelling (or, dualing even!) them might just achieve a satisfactory compromise, and so confirms my decision to give it a try...fingers crossed lol!

Just how this amp is able to pull off this major miracle I simply don't know, but obviously runs this tube to what must be near - or at! - perfection...as both power AND driver.

And so I cannot wait to see how they perform with a good few more hours on the last 2...(I do hope they don't change for the worse - which can happen alas, even if only rarely!! But my gut instinct is that they can only get even better! ...).

Time for an updated pic of the super quad in question......complete with blue leds, just for you @connieflyer (! )...OK...for me too lol!! - (they do make these tubes look more attractive...the final touch being when I can get those darned metal tops removed ).



ps. My 12V "LED strip" power supply is feeding the heaters perfectly, without getting too hot (even after 10+ hours' continuous use). Mine is rated at 6 amps and so has plenty of spare capacity, given the 4x GU50s' 2.8A total draw....IMO no need whatsoever for a higher V unit plus a voltage regulator. It also actually outputs 12.3V, and worked flawlessly with the 13V FDD20...apart from the fact this kind of power block must have its 12V DC negative wire connected to mains supply earth to kill any hum/buzz distortion!!

 

[gimmeheadroom]

Looked for the TT 21's but the price for a quad was a bit much! https://www.usaudiomart.com/details...77-production-date-and-batch-matched-rare-wi/
Asking Price:
USD $12345.00

http://www.r-type.org/exhib/aby0019.htm nice info

Ah that 12345 was probably just a default price

I didn't check but I guess the shipping cost was 678910