26 DHT users please comment on what you built & use.

[JandG]

I will post pics later of my 26 pre, been a year or so since I started using this pre. I don't see replacing it anytime soon. I would like to year from anyone running this tube in a pre or as a driver in a 2 stage amp, a 2 stage amp with 26 as driver is what I would like to build next, & run it agaist my best amps for comparison. Maybe a pseudo triode some with 26 as driver..? No 45's ,I allready got that spendy damn critter. I built & run a 26 w/ seperate PS chassis about 5' away from main signal chassis. I used 3/4" oak only for both PS & signal chassis. PS is 2- 6w4's for fullwave then LCLC- 17Hy-4uf PIO-10uf-100uf ASC oiler/ then vr-150 for shunt reg. Then off to extremelly simple RC circuit w/ K-40 as the coupling cap. I also sit the harwood signal chassis on a 120lbs sand filled steel spikes top & bottom speaker monitor stand. the spikes sit center under chassis sides, good use for not bieng used monito stands, Microphnics are basically non issue, unless one would stupidly flick the tube with figger. hum is low on 98 db speakers. Haven't measured it, but doesn't bother me, about as much as my AC heated 45 amp. This all goes into a 300B PP amp, you wouldn't think I would need the gain, I don't. Thing is what is does in sonics has nothing to do with gain. It transforms a o.k. amp into a dynamic machine with speed a clarity & 3d ness that is spookville and don't laugh , but Kenwood 7070 speakers untill my Jubals are finished with woofer re-builds in Seattle. You would not know by any means these were Kenwood speakers if you couldn't see em, trust me on this crazyness. I know there are a few that use this 26 DHT in systems at this very moment & would like to hear from those people..if possible Thanks J & G

[kevinkr]

Hi JandG,
Some years ago I started experimenting with the 26, and to this day I am using them in my transformer coupled line stage. You can see my construction article on this pre-amp at Positive Feedback Online, you can find the link easily on my site under pre-amp projects..

I had quite a lot of trouble with magnetic coupling into the output transformers which are UTC HA-133's - in my mind not yet completely satisfactorily resolved, although it is acceptable, this is the source of all of the slightly audible hum in my system.. The two other big issues were microphonics, which in my current rack is not a problem, and electro-static pick up which I dealt with by shielding the tubes.

I am very happy with the overall sound quality, it is quite transparent, dynamic, and tonally well balanced. It measures relatively flat as well - far better than the transformer spec would have you believe. IIRC it is in the range of 0.1dB from about 40Hz - 20kHz or so which is good enough for my Onken (Iconic woofers, JBL horns for mids and tweeters) based speaker system which really doesn't get much below 35Hz.

I also use mine with a 300B amplifier of my own design, again much like the ones featured on my site..

Mine is in a single chassis, were I to do it again (and I probably will soon) I would put the psu on a separate chassis, and I would use a cage to reduce electro-static coupling from other nearby equipment.

I would use a lot more mass in a new pre-amplifier than I did the first time around, but I don't think I could handle 100+ lbs of pre-amp, my 55 lb sacd player is quite bad enough!

[JandG]

Hey Kevin,
I hear ya on mass loading, 55lbs SACD players is quite insane, but we are all really. The 26 even in simple circuits impresses me. Someday will build yours & OT is the stopper for me now, maybe I'll just have someone wind some up. My 1st 26 was single chassis, I could not get it quiet, then sperated them & much, much better for me. I have ran globe 10 & still like 26 better, it is my fav. Running NU st's at the moment. Are you able to run globe's in yours, I can, but have to sift threw em for good pair, then it gets about the ultimate for me. It really shows me the importance of good PS & good earlly signal tubes. IMO this makes or breaks. Your desighns are very intresting & have them all printed & filed for future referance & builds. Under the TT in pic is the PS & off to right on the stand is the 26 signal chassis. I like the idea of shielding with copper & then grounding that, I will give it a test shot. I know one thing my pre transform's my system into a very pleasant music making machine. A few others that I knw that run 26 also use very heavy & thivk chassis, I am the only one I know of that uses solid harwoods with them so far. Good luck on the new chassis version.

[kevinkr]

Hi JandG.
The 55lb SACD player I referred to is a Sony SCD-777ES which with a few cosmetic differences, lack of balanced outputs, and a different case is essentially an SCD-1. I've modded it, but stuck to the stock topology so far. I got it fairly recently from a friend, and it has low hours so I expect with some care it will be my digital frame of reference for some time to come.

I used CECO globes in my line stage for many years, and thought they were glorious, but I unfortunately a couple of years ago I damaged one, and all of the others I had on hand had some issues. I also have older RCA UX-227 globes, and a variety of ST glass. I am currently using a well matched pair of NOS Sylvania 27's in ST glass and they are very good.

I did get mine relatively quiet despite having the power supply in the same chassis with the 26s and output transformers, but it took a lot of finagling with opt locations to get the noise down to acceptable levels. It still is the noisiest component in the system which is a shame, but the noise is all 60 Hz magnetically coupled into the output transformers, and not much else. The actual noise level at the output of the pre is ~60uVrms, but it is enough to cause trouble with my relatively high efficiency onken based speaker system. I will probably try some additional shielding around the power transformer which is already inside a steel can.

I have added quite a lot of damping to the chassis, wood sides, bitumin damping materials inside, and it is pretty dead. Suspending the sockets on bushings would be a nice touch..

Next time around perhaps..

[JandG]

Hey Kevin,
I tried rigged 10K OT's on my 26 & love it. I found a quad of the little TamRadio SE 5k OT's from sony RTR's all matching, so I ran the primary is series & the secondary's in parrallel. for 10k/600.
These have a 600 ohm tap on them. I mounted them on a board external & clipped it up. It was a large improvment in transparency, So my cap's & plate resistors are gone & hard wired it all together with the quad of OT's still external, I like it. Question is what would you do for a $500.00 budget for a pair of 10K/600 OT's & where would you go..? Electra-Print..? MQ..?
I would like to have a USA winder if possible. I could go higher in $ but would like to keep it at 500. Finding the HA's you use looks to be almost impossible.

[planet10]

Originally posted by JandG
Question is what would you do for a $500.00 budget for a pair of 10K/600 OT's & where would you go..? E

I'd talk to Bud @ O'Netics...

dave

[kevinkr]

Originally posted by JandG
Hey Kevin,
I tried rigged 10K OT's on my 26 & love it. I found a quad of the little TamRadio SE 5k OT's from sony RTR's all matching, so I ran the primary is series & the secondary's in parrallel. for 10k/600.
These have a 600 ohm tap on them. I mounted them on a board external & clipped it up. It was a large improvment in transparency, So my cap's & plate resistors are gone & hard wired it all together with the quad of OT's still external, I like it. Question is what would you do for a $500.00 budget for a pair of 10K/600 OT's & where would you go..? Electra-Print..? MQ..?
I would like to have a USA winder if possible. I could go higher in $ but would like to keep it at 500. Finding the HA's you use looks to be almost impossible.

Amazing what a difference transformer coupling makes with this tube. Yes, the HA-133 is pretty much unobtainium at this point, it wasn't all that common 8yrs ago when I originally built mine. Prices are ridiculous - you could pay as much as $600 for a pair of these. Incidentally I don't have one other component in the system that I have used for this length of time without a complete replacement with a new design - so I guess that says something about it. Yes it has changed considerably in that time, but the core remains.

I'd also talk to Jack over at Electra-Print, I've used custom transformers from him in a recent headphone amplifier project and was rather pleased with the overall performance. I've had no direct experience of the O'netics stuff so I can't say - but I have heard good things about them as well.

On a slightly different train of thought I just bought some reproduction WE tube shields on eBay from seller chiluen8 located in Hong Kong. These should be far more attractive than the home brew shields I currently use, and may be slightly more effective given that they are fully enclosed.

I'm going to make some minor changes to mine in order to try and knock the remaining hum down at least a few more dB. I'll probably be moving the output transformers and adding additional shielding around the power transformer. Ultimately I will probably move to an outboard supply which is what I have recommended to everyone else who has built my design.

[JandG]

Thanks for reply. I think I will get quotes from both Bud & Jack. Bud is just up the street from me, well I-5. Yeh my PS is 5' away & is way over kill, but after my single chassis build & almost gave up. I like external. almost impossible without shielding to stop all the craziness, 27's actually give me more fits than 26, but all is well now, I can run 10, 26, whatever. But 26 & 10 are my favorite. 10 is great tube also but to damn expensive & have only 2 vs, way over 50 26's over 100 27's. CECO's are superb I have a single pair of them in globe fashion. Mine is cathode biased w/ 4- NiMH AA at the moment, running 150 plate voltage, What bias voltage would you use going cathode route as I have. - to ground with + to cathode via 22 ohm resistors. I was using 2-AA & swithched to 4 with my upping plate voltage to 150. I am listening to cx-310 at the moment & they perform = to 26 in every way in this pre, but as said, just silly priced & when they blow, that will be it for 10's & me. Well off to get Jacks # I have Buds.
Thanks J & G

[wicked1]

Ive gotta mention....
I got my 300b outputs from BudP. They are small!! About 1/2 the size of other 300b outputs Ive seen. (about 1/3 the size of the Hammonds)
At low levels they are BEAUTIFUL.
If I turn them up, and listen to something bassy, they everything sort of muffles out.. like, all the tones get quiet or distorted for a fraction of a second..
So, something like house music doesn't work well, cause the music cuts out a bit at the bass kicks. (I'm guessing this is saturation)

At lower (normal) levels, or w/ slower music (slower meaning not the FAST attack of a synth line, or kick drum) then they are truly the best sounding things Ive ever heard.

My experience is very limited, as this is my only single ended amp, so something else could be at fault.

I just wanted to throw this in there, as I see many recommendations for Bud, but almost NO reviews of the transformers.

I am quite happy with them for what they cost.

I wish I had the money to buy a bunch of transformers and do a side by side comparison of them... I guess everyone wishes that

[JandG]

Level 1 SE tranny's..? The problems you mention do not sound as if all is well with amp & or etc... What amp did you build.? off topic I suppose , but curiouse as to the why they are doing this. Sounds as if something somewhere is not well at all. Maybe start new thread on this very topic you mention & go for a cure.
J & G