Hi Neskor,
Tricky question and you will find many answers round here. Let me share my experience at least. It will depends on the end to end system first of all and what load you need to drive. The 26 cannot drive high capacitances so in my case struggled to drive my 814 SE amp. This will be also the case if you are looking to achieve loads of gain with a simple 6c45pi or similar high-mu triode gain where Miller will be a problem. This results in treble loss. Coming back to the sound, both are fantastic valves. I have a personal inclination for the 4P1L. It is very consistent from valve to valve, whereas the 26 is not. You are at the mercy of the quality (and variety) of ST and globe valves you manage to get hold of. Both tones and overall response is great and clarity of sound is what you would expect from a DHT stage, if you ever heard one before. It will depend massively on the implementation of the filament DC heating (Rod's boards are highly recommended here). The 4P1L has better bass detail in my experience. Again, hard to compare all versions of 26 and 4P1L I built so far where different (and so was my system).
My recommendation is to try it for yourself and share your experience
Cheers
Ale
Tricky question and you will find many answers round here. Let me share my experience at least. It will depends on the end to end system first of all and what load you need to drive. The 26 cannot drive high capacitances so in my case struggled to drive my 814 SE amp. This will be also the case if you are looking to achieve loads of gain with a simple 6c45pi or similar high-mu triode gain where Miller will be a problem. This results in treble loss. Coming back to the sound, both are fantastic valves. I have a personal inclination for the 4P1L. It is very consistent from valve to valve, whereas the 26 is not. You are at the mercy of the quality (and variety) of ST and globe valves you manage to get hold of. Both tones and overall response is great and clarity of sound is what you would expect from a DHT stage, if you ever heard one before. It will depend massively on the implementation of the filament DC heating (Rod's boards are highly recommended here). The 4P1L has better bass detail in my experience. Again, hard to compare all versions of 26 and 4P1L I built so far where different (and so was my system).
My recommendation is to try it for yourself and share your experience
Cheers
Ale
A slight change of topic here, but ... the plate choke contained in the link below would seem to be perfect for a 26 preamplifier design. However, it has been in a backorder situation for months on the Antique Electronic Supply site tubesandmore.com. The choke is manufactured by One-Electron and sold mainly on the AES site. I have emailed the manufacturer several times enquiring about availability but have yet to receive a reply. Whatever the case, it would seem a good fit for a 26 line stage project ...
Audio Choke - One Electron PRC-3, 225H for Preamp Output | Antique Electronic Supply
-Edward
Audio Choke - One Electron PRC-3, 225H for Preamp Output | Antique Electronic Supply
-Edward
That should still work fine at preamp levels. Maybe try to dial down the current to ensure to stay below 5mA
best to try and measure
Thomas
First up I would like to thank Rui Lourenco for building his fantastic implementation of the 26 DHT Preamp, and secondly for parting with it to enable me to finally get up to speed.
Since it arrived I have enjoyed listening to it, and marveling at the quality of work which has gone into it. As can probably be expected, I have also been musing over what, if anything, I may have done differently if I had built it.
The only real change I came up with was a switch from cap input to choke input on the HT. After this I upped the SSHV2 from 23mA to pass 30mA, and slightly upped the 26 filaments from 800mA to 875mA.
Overall a slightly bigger, more muscular performance with a bit more colour. Nothing huge, but I like the outcome.
Finally, I thought I would draw out the circuit of what I now have. For politeness, if nothing else.
Since it arrived I have enjoyed listening to it, and marveling at the quality of work which has gone into it. As can probably be expected, I have also been musing over what, if anything, I may have done differently if I had built it.
The only real change I came up with was a switch from cap input to choke input on the HT. After this I upped the SSHV2 from 23mA to pass 30mA, and slightly upped the 26 filaments from 800mA to 875mA.
Overall a slightly bigger, more muscular performance with a bit more colour. Nothing huge, but I like the outcome.
Finally, I thought I would draw out the circuit of what I now have. For politeness, if nothing else.
An externally hosted image should be here but it was not working when we last tested it.
Hello,
the preamp really looks good in the pictures, congratulations. Just a small question, after all these chokes and the capacitors in the HV supply, was the regulator really needed? I do not know, but I do not think that much ripple has been left for the 12mA of current and after multiple 10 and 30H chockes and 50uF capacitors... Did you try without?
Best regards,
Pred
the preamp really looks good in the pictures, congratulations. Just a small question, after all these chokes and the capacitors in the HV supply, was the regulator really needed? I do not know, but I do not think that much ripple has been left for the 12mA of current and after multiple 10 and 30H chockes and 50uF capacitors... Did you try without?
Best regards,
Pred
It'll work like a charm without regulator. Because the filament is held in a double nelson by the filament supply it's beneficial to tie down the other end too. If both ends were freely drifting on the mains things would probably work out fine too, but how to assure drifting in equal amounts? All for less distortion
Hey all, just wanted to give you all a tip on a great-sounding 26 balloon tube, made by Sparton. Apparently Sparton (from the Sparks-Withington company, hence the name) made very high-end radios in the 1930 and 1940s and also manufactured their own tubes, according to some antique radio websites. I procured three of these tubes on e-bay a while back (two of which test as new) and just got around to trying them out. For info purposes, I'm running them at 7mA and 1.5V filament V using Coleman regulators, with 9V battery bias applied to the grid through an input transformer.
Wow. These sound better than the Cunningham CX-326 I was using. They have a very seductive warmth to them while also retaining the famous 26 detail and clarity. Highly recommended!
PS: I considered keeping this a secret but I just had to share with my 26 preamp buddies. Now watch the prices shoot up!
Wow. These sound better than the Cunningham CX-326 I was using. They have a very seductive warmth to them while also retaining the famous 26 detail and clarity. Highly recommended!
PS: I considered keeping this a secret but I just had to share with my 26 preamp buddies. Now watch the prices shoot up!
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Interestingly, according to The Radio Museum, Sparton made their own tubes for several years to avoid RCA's patents, then signed an agreement with RCA to use their tubes. So, these 26s could be Sparton-made or they could be re-branded RCAs. Their construction resembles RCA 26s, with a few minor differences. Whatever they are, they sound very nice.
The price might not shoot up at all, the 26 crowd seems to have moved on to 4P1L, that's the rage now.
Agreed, no intention of building another preamp here, unless it's for another house some day...
I still find 26s for pretty cheap prices; I bought a box of assorted balloon 26s at Kutztown a couple years ago for about $5 per tube. I even got to test them before purchase! I must have a total of 20 or so balloons and a bunch more ST. Enough for several lifetimes at preamp usage rates.
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The price might not shoot up at all, the 26 crowd seems to have moved on to 4P1L, that's the rage now.
Yes - I moved to the 4P1L over a year ago. The 26 has a special place in my heart - it was my first love for DHTs. My jaw dropped when I heard it - couldn't believe it. I think I said out loud "THIS is what I've been searching for all my life!"
I still have a box full of good specimens. I think it was the added clean quality of the 4P1L and the treble that won me over. I always found the 26 just a trifle soft in the treble.
I think "soft in the treble" depends on the circuit and system. With a CCS load and nickle core autoformers on the output I don't detect any softness. My speakers do tend toward brightness with some electronics, too so perhaps there's a synergy going there too. And of course all of us hear differently.
Soft in the treble does probably depend on the system. I don't have a CCS load and I can well imagine that can brighten the sound. In a direct comparison both with LL1660 OPTs I do find the 4P1L cleaner, a bit more dynamic and clearer treble. I always use the LL1660 in 1:1 to keep the gain, if that's relevant. The line stage is actually in the 2-stage amp chassis of my PSE 4P1L, not a separate preamp. The 26 will always be seductive in the mids - has that special magic.
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Look in here: Bartola Valves | All about electronic valves and hi-fi
You'll find plenty of information.
Good luck.
Cheers.
