Updated: 26-Aug-01
Doede's Tube Stories...

Using different Tubes on the GOLIDAV: my new KR300BXLS single ended Mono Block AMP

After a week of just playing 24 hours a day, I considered the Amplifiers to have set, find their working point, burned-in, or whatever you want to call it. The sound indeed stopped developing. In the first days, the sound was, as usual, a bit sharp. This has completely gone now and made place for smooth silky highs, without any loss of dynamics. This amp is far from being laid back !!!

So, I was completely happy? sure I was! Why using other tubes than? well, because you never know and it is lots of fun too !!! I still have in my possession a set of AVVT-300B's, Triodes# 56 several 6688's and I have been able to free a local dealer from his AZ11's meshplate version (even at a reasonable price: 40DM)

I have just spent an enjoyable evening, listening to lots of music (Classical, Pop, CD and LP) whilst switching the different Tubes. Well, one thing is clear, there are no losers, all tubes play great and the differences are in a Bandwidth which is clearly smaller than the difference between my old (simple) B300 amp and the new Golidav. But never the less, it is very interesting and even if the differences are not "jaw dropping" they are clearly noticeable and "THERE IS NO WAY BACK". If you tasted the sweetness of for example the meshplate AZ11, you will just let it stick in its position!  But I am jumping ahead.......

In stead of long fuzzy stories, I decide to set up a very simple "table" with the Tubes and what the basic sound differences are. this is all relative to each other and must be read as such of course.... The table is in order of impact to the music. So the top family Tubes are of most importance to the improvement below the table, I still will do some of the fuzzy stuff, hehehe.....

Between brackets the relative impact in points or % or whatever, how I see the impact to the sound.

End Stage Tube (100) TKR300BXLS (140mA) Very dynamic in whole audio range, precise and punchy. Huge Headroom. Very natural and deep sound stage
KR300BXLS (90mA) As above, but without the driving power, more laid back
AVVT-300B As "KR-90mA" but less precise, stereo image less air, vocals color a little bit. Still a class better than most Chinese or Sovtek 300B's
Driver Triode
227 driver Smooth, silky, lots of air in the stereo image
56 driver Same character, but somewhat less spatial and in the back of the stereo image less precision
Rectifier Tube
AZ11 MESH Plate Great all-round Rectifier, very natural and very very smooth in the highs
AZ11 "REGULAR" Idem, but not the extra cream on the cake from the highs.....
Current source Tube
D3A MU Penthode Working horse, power full sound
6688 Little bit less dynamic, but still very good alternative. Sound balance is the same


In the GOLIDAV, I built in a switch, enabling the 300B to operate with an 1kOhm Rk, making the amplifier more flexible. The AVVT found its working point at 400Vk-a @ 85mA. So quite hot; I am not sure if would try this with some cheap Chinese. The AVVT is a real rowdy. powerful sound, dynamic and nice stereo image. Compared to my old Chinese 300B' a different class. After switching to the KR300BXLS a little MMMMHHHHH ! comparable sound in terms of dynamics, nice (warm) bass, powerful etc, BUT: specially the midrange (vocals !!) is cleaner than the AVVT, in comparison, the AVVT has some (very little) coloration in the midrange. So the KR sounds more natural. Further plus is the clearer stereo image in the back. It seems that the KR is doing it's work with more precision! The highs are a bit smoother, again more precision. So, lets go back to the 140mA position (540m Ohm Rk), Well, this is a sudden change. the sheep becomes the wolf now !!! Bass becomes punchy and dynamic, overall dynamics are a class better. Attack! is this still a Single ended tube amp? wow, the extra current let me play music with unprecedented sound levels. A pity, that the KR300BXLS is used in "normal" situations" as "upgrade" in existing amplifiers. With the higher bias (you will need a bigger OPT !!) The hulk gets green and bursts out of his shirt (this for the older readers, hahaha)

56 vs. 227. the 56 is actually the same as a 76, but with filament of 2.5 Volt, So directly swappable with the 227 and 27.... easy eh? the 56 is a great tube, plays great music, but is second to the 227; They produce both a dynamic, natural sound. The 227 however puts more air round the artists and instruments, more pin point. The picture becomes clearer and more contour Both very good tubes, but the 227 stays in its sockets.......

The AZ11 is any way a natural born killer. Very nice tube for the driver section. Not "BIG" enough for the end-stage. The AZ series are very natural. If you compare them with for example an GZ34, the GZ34 is more "solid state" I must admit, that with some heavier pop music, the GZ34 can be a good friend as well! But the AZxx is much more an all-rounder, and that is what I want, I have all kinds of music and software media. The AZxx are also available (big word, you really have to look very hard !!) in MESH Plate. I just bought some (I was lucky to find them !) and this was the moment to try! MMMHHHH This is something again, where there is no way back. The MESH does the same with the music as the KR300BXLS compared to the AVVT: More precision, more air in the stereo image and as extra a smooth silky high !!!! I would guess that the improvement is roughly half that of the AVVT to KR. If I had to chose (bit academically, but who cares) I would rather take a KR with normal AZ than a AVVT with AZ11 Meshplate... That may be puts things in perspective.

I am using the D3A as current source in the MU stage. I was tipped to try this tube and I was lucky enough to buy a whole lot from EBAY for a very reasonable price (below 10DM). The D3A has a 3 times higher transconductance. as the 6688 and therefore works "better" in the MU stage (see my MU article for more back grounds) the 6688 is a very worthy alternative as well and is drop in replacement. This is not always the case with Penthodes, so take care before just plugging other tubes in. The difference is not as impacting as the ones described above, but the D3A bring a little more drive to the sound. Little bit more dynamic. If you cannot find the D3A, no problem, the 6688 is a very good alternative. Can you found some D3A's ? just  plug in and check for your self.....s 

Interesting aspect, is that if you make the combination of the KR Low current with the AZ11 Meshplate, the sound becomes too much "laid back" the AVVT is a bit more aggressive, so this combination makes more sense.

Well, I hope this inspires every one to experiment a bit with different (combinations of) tubes and learn to understand where the strength's and weaknesses are from each individual tube....

I will put some pictures later on on this page......

Happy Listening and Building !!!!

Doede Douma


IMPORTANT: The information provided on this page is intended as guide for DIY activities and therefore free to copy and or publish. If any one wishes to use any of the information from my WEB site, please make sure to refer and footnote to my URL Link as source! Doede Douma