Ok, them lets just say: a 4P1L driving a 300B driving a gm70 sounds great.
This much I know first hand
I agree, the 4P1l is a very interesting tube, just not convinced that it is a 2A3 alternative for an SET output, more like a 71A for real power comparison.
What about a 4P1L - GU50 (triode)? I can post a sim it looks nice. For my purposes I don't like 3 stage amps, because it takes away the natural 2H & 3H distortion cancellation.
One thing I haven't quite grasped is why we need so much gain when designing an all DHT amp.
I mean you have a 3A5 in front of the 4p1l, but the most the 4P1l is going to swing is ~180V's. So why not just feed it 2ishVrms, its gain is nearly 10 so I am not seeing how the 3A5 is doing anything ?
I'm still learning the all DHT concept vs the good old 6c45p or otd3 or Cgm, 2stage SET. So bear with me
Three stages or two depends on the input voltage and the sensitivity of the speakers. One of the many good things about the 4P1L is that it does have good gain for a DHT, unlike the 71A. So that allows an output tube with less gain, like 2a3 or 300b. It has low anode resistance and can be used in filament bias - very flexible for a driver tube. Most of all it sounds great.
One reason to use a 3a5 is as a tube output from a DAC directly into its grid.
One reason to use a 3a5 is as a tube output from a DAC directly into its grid.
Yes I agree about the flexibility, it is such an interesting tube and I have a quartet I am dying to use. Using the 3a5 for a DAC output makes sense, and it adds more flexibility for a wide range of DAC's/preamps. But for my case with a solid 2Vrms DAC (SS) do you think a 4P1L would have enough gain to push a 6C4C 150V-180 Vp-p, maybe even even a GU-50 triode ? Worse case I would use an input transformer to use the DAC's balanced output and deliver 4Vrms to the 4P1l ?
Thanks your work with all DHT SET's is inspiring. I just figure if I'm doing an DHT oupt it really makes most sense to use all DHT.
A pair of 4P1L in parallel (like pair of paralleled triodes in 2A3 bulb) can give you 5W of clean power in class AB.
Gu-50 has nothing common with 4P1L, even though both were designed by Telefunken for military usage. Gu-50 in triode is not close by linearity to 4P1L. You can parallel 4 of 4P1L to get the same max dissipation power like one Gu-50, with incredible linearity.
2 stages of 4P1L, driven directly by CD player. 5 tubes total. You can use either an interstage transformer, or the method that I used when started this topic: dynamic load and cathode follower. Or a source follower using modern nice depletion mode high voltage MOSFETs.
I would better save Gu-50 for PP amps where they beat common civilian tubes like KT-88 for example.
I'm still waiting for my 4P1L tubes to show up. Been over 2 weeks and I was hoping to build an amp during the Christmas break.
I can top that. I have been waiting for over 1 month for mine......
Fortunately seller has offered to send replacements.
I'm still waiting for my 4P1L tubes to show up. Been over 2 weeks and I was hoping to build an amp during the Christmas break.
How far are you from Pleasant Hill?
You can borrow mine.
One day all the supply off all these fabulous inexpensive Russian tubes is going to come to a halt and we will all wish we had bought 100 of each. Tubes like this one are a deal of a lifetime right now.
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Sorry for my ignorance, can 4P1L be used as preamp? if yes what's the input & output impedance? what's the gain? for SS amp can be used without output transformers if not what are the specs of the output transformer?
Thanks for help, I wish you Merry Christmas & a Happy New Year for all people of this amazing thread.
Felipe
Thanks for help, I wish you Merry Christmas & a Happy New Year for all people of this amazing thread.
Felipe
Yes, 4P1L in triode can be used as a preamp, and it sounds great. BUT - it is microphonic and if that bothers you in your system you will need to take steps to kill the microphonics. Basically you need to mount it on a solid and fairly heavy piece of metal (or mount two on the same piece) and then decouple that from the chassis. You also need to decouple the chassis from the stand it's on. I have been winding teflon plumber's tape around the bottle half way up as well - not sure how much that helps but it doesn't seem to do much harm.
I use a 1:1 OPT straight into my amp - Lundahl 1660/18mA. That's a gain of around 10 and output impedance of around 2k. You need at least 15mA. For a lot of SS amps you would need to step down, so you will lose some of the gain. You may be OK with others - depends what devices are on the input.
But, yes, 4P1L makes a great preamp and it's what I use myself - in filament bias.
I use a 1:1 OPT straight into my amp - Lundahl 1660/18mA. That's a gain of around 10 and output impedance of around 2k. You need at least 15mA. For a lot of SS amps you would need to step down, so you will lose some of the gain. You may be OK with others - depends what devices are on the input.
But, yes, 4P1L makes a great preamp and it's what I use myself - in filament bias.
Hi Dave,
The 4П1Л will drive the 6C4C into clipping easily.
It's very well behaved in pentode mode - there are no sharp rises in screen current, even with the anode down at 50V.
The only big demand is a B+ of 500V. But the current is low, so you can use a voltage doubler to get this high voltage. a tube (damper) rectifer is recommended, to give a slow rise to this level of HT.
Operating condition:
Va(b) = 500V, well filtered LCLC or shunt regulated
Va = 200V
Vg2 = 150V (eg DN2540 CCS into gas tube)
Ra = 10K 14W Welwyn W24
Ia = 30mA
Pa = 6W (7,5 max rating)
Gain is approx gm.RL: about 6 x 10 = 60
So to get 90V zero-to-peak, need 1.5V peak from DAC
IME a single pentode driver sounds much fresher and more articulate than 2-stage triode.
And if you like the sound in pentode, you can convert the stage to shunt cascode later, and get better supply rejection, more gain, and better sound.