Directly Heated Triode preamps, anyone own one?

invalid

Just wanted to get someone's take on the sound quality of these kind of preamps, I've never been able to get my ears on one.

mhardy6647

Hmm... not many DHT small signal tubes, although in the modern era there are some pretty weird tube choices being used in preamps Most of the classic small signal tubes (e.g., the 27, 56, and 76, progenitors to the 6J5 and thus the 6SN7) all have indirectly heated cathodes.

http://vinylsavor.blogspot.com/2015/06/tube-of-month-27.html
http://vinylsavor.blogspot.com/2015/08/tube-of-month-56.html
http://vinylsavor.blogspot.com/2015/09/tube-of-month-76.html

I've been playing with a "Berman" style (documented in Joe Roberts' legendary Sound Practices magazine) preamp built by my friend Alan -- no DHTs in it, though; it uses 76s (which are microphonic as all getout) and 6J5s (IIRC).

DSC_0121 (2) by Mark Hardy, on Flickr

One interesting exception to the "not too many DHT small signal tubes" was a bevy of odd (by modern standard) little tubes made for old-time portable battery radios. Many of them had directly heated 1.5 V (DC) filaments -- not so many of them were triodes, rhough -- but some were (e.g., the "1B5", see data from RCA RC-18, below:



The two diodes were for the "radio" circuit and can be essentially ignored if one wanted to use a tube like this as an AF amplifer.
By and large, they're not "hifi" tubes, though.

The direct heated 3S4 is (was) used as the active element in Doc Bottlehead's adorable little "Quickie" preamp. The 3S4 is a "power pentode" (albeit a kind of wussy one), though.

mhardy6647

Do you have any specific preamps in mind -- and, if so, what DHTs are they using (and in what roles in the circuit)? One is most curious.

Oh, the Berman-esque preamp above does use a 5R4(WGY) "potato masher" for HV rectification... that's direct heated, but of course not a triode

No electrolytics at all in that bad boy, either

invalid

Bottlehead also has a 300b tube preamp kit. Coincidence has a 101D preamp called the statement that has gotten good user reviews as well as professional reviews. The 101D tube is kinda cool looking, I believe it's called a tennis ball style tube.

mhardy6647

The 101D is, yes, a real,and very early, DHT
Not sure how easy to find those tubes as NOS in 2020 AD, though?

I do know of that Bottlehead preamp, now that you mention it... but I cannot see the real wisdom in using a 300B power triode (and a pretty serious, and expensive one, at that) in a preamp. I'm funny that way. OK, I am funny lotsa ways, but particularly when it comes to using 300Bs in preamps

I was pretty favorably impressed with a little "Quickie" that someone brought over here once. The 3S4s also tend to be microphonic, but overall it sounded good (especially for the price).

invalid

You can get current production 300b tubes for $150 a matched pair, about what I paid for my nos 6sl7 tubes.

invalid

I guess nobody has one of these preamps.

txcoastal1

I own the Melody Valve HiFi Pure Black 101 Preamplifier with the 101D Triode Tubes

invalid

txcoastal1 wrote: »

I own the Melody Valve HiFi Pure Black 101 Preamplifier with the 101D Triode Tubes

Those look cool, and I believe it is point to point wired if I'm not mistaken. I'm wondering how different it sounds than an octal tube preamp?

invalid

txcoastal1 wrote: »

I own the Melody Valve HiFi Pure Black 101 Preamplifier with the 101D Triode Tubes

Do you have any problem finding the 101D tubes, and are they expensive?

GlennDog

This puppy's FS and can be used as a pre . . . Lampi is VG Kit. Deep pockets may apply lol

Uses DHT 45, 203 and 300B

https://www.usaudiomart.com/details/649809974-lampizator-big-7-se-mk2/