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#26 pre amp

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Joined 2004
Paid Member
Hi!

I never had to apply any such screening to DHTs in linestages. never had an issue with hum or other noise pick up. I have used 26, UX201A, UX112, 801, 10Y and others.

I keep the PSU separate with power transformers with electrstatic shields.

Only in an experimental all-DHT phonostage I had to shield the tubes in the very first stage.

Best regards

Thomas

I do much the same in my own projects, but found that close proximity to other ungrounded, but powered metalic objects (like my tuner and SACD player) resulted in electro-static coupling. My environment is quite possibly much less benign than yours, and using HE speakers that roll off well below 40Hz probably doesn't help me much either.. :D
 
Hi!

the 26 is a real pickup


As I wrote: not in my experience. For example this preamp is totally quiet. Some people who use such preamps from me said that it has much less noise than their previous ones using indirectly heated tubes.

VinylSavor: 801A / 26 linestage with output transformer and TVC

No screening on the tubes. All metal parts and capacitor enclosures are properly grounded. Also the subplates which hold the tube sockets are grounded.

Power supply is external and well filtered (passive multiple LC stages). Filament is LCL. More photos with external PSU here:

VinylSavor: 801A / 26 linestage with output transformer and TVC

I suspect it has more to do with the surroundings of the tube if there is noise pickup. Especially plate chokes can pick up noise.

Best regards

Thomas
 
#27-#26-6c33

this is my project now
source-DAC pcm58- nos--resistor- i/v converter
gain-#27
driver-#26
output-6c33 1w SE OTL cathode follower
Speaker Lowther EX4 in Hedlund horn
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Frugivo, I can tell you are a speaker guy. I am willing to chip in to buy you some copper foil, Reynolds wrap has no place covering an antique classic tube:xmasman:

I love that you are driving the 6c33's at 1W with the #26, I can't think of a harder tube to drive than the 6c33 and you are doing it with a #26! I had another thread veiled in disguise touching on this topic, I believe your sucess is dependant on the <1W output cause you aren't swinging many volts into the 6c33 grid and hence don't need a lot of driver current, your post gives me encouragement for my plans with the #26. You wouldn't happen to have a freq response plot you could post ?

Fascinating that you chose the PCM58, I bought one of mouser's last pair of PCM56K thinking of a similar route, just combine the DAC to the amp, I mean with a DAC gain stage why the hard target of 2vRMS? Causes more trouble than it is worth. My concern with an NOS dac like this in combo with the #26 driver is the potential for the #26 to get dragged down by pushing all the unfiltered ultrasonics from the NOS DAC, if you do the math the #26 is seeing a nasty load above the sampling freq and my concern is this could hurt the #26's exemplary linearity. Miller effect must take care of it in the gain stage? You may want to consider a small cap between the plate and grid of the #27 to reduce the ultrasonic content heading to the #26, but only if you want to experiement, your design is creative and a real inspiration. Thanks for the post.
 
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iko

Ex-Moderator
Joined 2008
I would expect the 26 doesn't work so well in the second stage. I was looking myself at a small power amp, 26 choke loaded followed by a 47 (triode connected), gyrator (dn2540) loaded, possibly with a third stage which I've yet to decide, perhaps two paralleled 4P1L. The first two stages look promising so far.
 
I would expect the 26 doesn't work so well in the second stage. I was looking myself at a small power amp, 26 choke loaded followed by a 47 (triode connected), gyrator (dn2540) loaded, possibly with a third stage which I've yet to decide, perhaps two paralleled 4P1L. The first two stages look promising so far.

Yes 1W may be pushing it, I'm still determined to try a #26-45 headamp, would only need to drive the 45 with a 20v volt swing or less, milliwatt output, thinking slew rate wouldn't be much of a factor at such a low output. My fabrication skills to build a vibration dampening platform as vinylsailor innovated has been holding me back, don't want it to look like a hack job, his work sets a high bar!

On paper it would really seem that if the #26 is amplifying any ultrasonics from a filterless DAC that it would be pushed out of linearity. But this is fairly uncharted territory, and I admire this PCM58-#27-#26-6c33 design, its unique, a bit ground breaking with the whole integration.
 
Frugivo, I can tell you are a speaker guy. I am willing to chip in to buy you some copper foil, Reynolds wrap has no place covering an antique classic tube:xmasman:
I simply experiment
True, I am sorry to wrap the tubes
but the goal is that my ears do not detect anything I do not want
the easiest way and with minimum components
I can not offer frequency response curve
try to do some measuring
I have decided to change the 27 for another 26
to get 1 watt in the 6c33
need to balance 14 vpp
with a bias of 270 mA
-13 To -16 volts grid
67 volts on the plate
on the oscilloscope can not see anything strange
got the sound is great
I'm sorry but I can hardly express myself in English
I have to give thanks to google translator

to feed the dac uses lithium batteries
a full charge for one month
 
Hi Gluca,

I'd say this depends on the surrounding cicuit not only on the tube. Also what you want to drive with it.

In my comparisons the 10Y/801A family of tubes beats the 26. The 10Y/801A in my favorite DHT. The 26 is more forgiving in terms of filament PSU, still critical, but it does not react as strong as the thoriated filament tubes IME.

In my universal linestage which can accept 26, UX112A, UX201A and 10Y I prefer the 10Y

Best regards

Thomas
 
ok! it's time to go 26DHT for me , i have built a DIY 6n6P /AD1 amplifier and i 'll change it to a 26/AD1 soon

my plan
AZ4 tube rectifier
separate LCLC and separate RC for each tube
Capacitor all MKP
CCS filament for the AD1
CCS filament Bias for the 26 ( thanks you for the idea!!)
RC coupling interstage ( i'm a beginner ...)
automatic bias for the AD1
2.5K hashimoto output transfo
25K PEC carbon volume pot

i will post picture in few weeks and post the schematic if it sounds good, the 6N6P/AD1 combo is not so bad anyway :)
 
Hello,

I love too the 26 line preamp, and work about it since many months trying to get it better !

Recently I install the Rod supply and it is really good. Superb sonic performance.
It replace a current reg with LM350 witch sounded good, but a bit too noisy (the DC should be better filtered with inductors).

I have a question to Rod : actually I connect the negative output of the filament PS on the cathode bias side, is it OK ? (this sound fine).

(Sorry if this question has already been asked...).

I tried grid bias with battery but I prefer cathode bias (not tried Duracell brand), filament bias either.
The componants are important in cathode bias : Black gate FK + Shinko resistor (or Riken).

In the HT supply I like the tube dampers (2 x 6AX4, no solid diodes) with LCLC filtering (low impedance choke like old Stancor), and low value ps cap (ASC oil polypro and Leclanché).

Actually this is a resistor load (Mills) on the plate, but choke plate will be tested, and a friend will lend me a pair of LL 1660 18mA to play ;)

This tube is really good, very transparent, living, and with all the mods, it can sounded in pretty different ways...

Have fun !
B r u n o
 
Hi Bruno,

Yes, it's OK to use negative Filament terminal as the cathode.... but it is worth the time to try the positive side, and compare. Sometimes, the sound is more enjoyable! The cathode resistor should be higher value - augment by (0,75V / Ik) Ohms.

I am pleased to hear that you like the sound of the Filament Regulators!