GU15 SE amp prototype

[matejsirk]

Hi,

I am finished my new prototype amp with GU-15 tube. GU-15 is medium power (19W) DHT pentode. More information and some data: http://www.diyaudio.com/forums/tubes-valves/47108-magic-gu15.html.

 

[Wavebourn]

Where did you get 138.44V from?

 

[matejsirk]

My mistake, I posted wrong schematic.

See new schematic. On the scheme are measured values.

 

[saptemari]

Hello, Happy New Tear to all colleagues!

Can you please let me know some more details about the sound? Does it sound like a DH tube (airy and effortlessly)? Did you think about a comparison with 4P1L and/or 6P21S, or maybe even with #45 or 2A3?

From the circuit, I understand Ua is 435 Vdc while the drawn current is only 35mA. Why did you chose this OP?

I saw the docs which were published by Charm from Russian Federation. Do you think getting the tube closer to 19W Pdamax would not be safe?

Thank you very much!

 

[matejsirk]

Hi,

yes it sound like a DH tube -airy and effortlessly. Not so sweet as 4P1L, but with more body. I like this sound.

OP is around 290V/57mA - 16,5W. Where did you get 35mA?

 

[saptemari]

Thank you! I saw written 35 near the OPT primary, but now I think it’s the impedance (3K5).

Anyway, I’ll check the impedance on the diagrams already provided by our colleague

 

[savu]

35 is the inductance in Henry for the primary of the output transformer.

I simulated the schematic in LTSpice... I kinda still don't understand why it works

 

[saptemari]

I am not decided to use this tube, I was only trying to find some more interesting DH tubes which may work in audio. To be sincere, I listened to a 6P21S SE, amplifier, to a 4P1L SE and to my 2A3/#45 amplifier. 6P21S, clearly sounds better than a usual indirectly heated penthode or tetrode, but not that refined as #45 does. 4P1L is much closer to the triode DH tubes.

Anyway, if I will find them for a reasonable price, I will take the chance to experiment

 

[savu]

Kinda off topic:
Saptemari... from your experience are DH tubes good for balanced circuits or just SE? I know that back in the day, because they did not have the concept of global feedback, only open loop, tubes were made with tighter tolerances then now.

I plan to design and build a balanced DHT preamp/line stage for my OTL monoblocks and I intend to use #26 triodes or 4P1L triode strapped.
Sanatate

 

[saptemari]

@Savu, I am not sure about how tight was the tolerance when talking about soviet tubes. For instance, 6C33C was used in MIG”s and their characteristics are very dispersed.

Anyway, I am quite sure your idea is good. I too want to build a push-pull amp using DH tubes. I only built SE amps until a month ago when I finished a PP amp with the classic EL84. It is sounding nice and the extra power made me think about a DHT PP.

I would suggest using a LM317 as a CCS for the cathodes (if using semiconductors is acceptable to you), like Mr. Heran did here: http://diyaudioprojects.com/Tubes/EL84-Push-Pull/ECC802S-SRPP-EL84-Push-Pull-Tube-Amp-CCS.png

You’ll be able to perfectly balance the current between the two tubes.

Sanatate!