5751!

[pinkmarkos]

Hey everybody- I just wanted to share my experience with a 5751 in V1 of my express and liverpool. It is awesome! I have reads many posts about taming the gain with the TW amps and I have tried many of the suggestions about cap and resistor value changes (probably almost all of them )The 5751 really cleans up the hairiness without sacrificing the TW tone IMO. Added bonus is a bit more usable headroom ( I really dig the clean tone of the express.) Also, in the interest of full disclosure, I changed R7 to 56K and C8 to 4700pf. This combo sounds great to my ears in both the Express and Liverpool. Also, my other tubes are: V2 and V3- National brand (Yugoslavian- Tesla/EI?), Mullard xf2 in the power section. Still looking for the tungsrams, I hear they are very good. Thanks again to everyone who helped me. Hopefully this will help someone else to "get there".

[Zippy]

Also, in the interest of full disclosure, I changed R7 to 56K...

To increase the gain??? Was that before or after you swapped V1?

[pinkmarkos]

i noticed that changing these values got rid of some of the higher end "fizziness", and that is what i hear, definitely. and i'm pretty sure that these changes were recommended to reduce gain, but i could be wrong- i will have to look back and verify. all i know is what i hear- it sounds full and i have more usable headroom than before.

[Zippy]

Thanks, Markos.

I'm working from memory - not a schematic. Is the resistor that you cite, the cathode of the cathode follower? If so, I thought that 100k was unity and anything less increased the gain.

[dayn]

I am loving a 5751 in v1 on my Komet 19. More clean headroom, smoother but still aggressive distortion, without any loss in dynamics, harmonics, feedback, feel, etc.

Also a 12at7 in the pi.

[pinkmarkos]

Per Zippy-

Is the resistor that you cite, the cathode of the cathode follower? If so, I thought that 100k was unity and anything less increased the gain

I have read a few descriptions of a cathode follower stage because my grasp of this kind of circuit is not very good. I think I do understand however that the net signal gain of a CF circuit can only approach one. So lowering the R7 resistor between V1a and V2a would lower gain right? I do know, as I stated before that 56K here and 4700pf at C8 seems to smooth things out to my ear.
dayn- i did try 5751 with 12at7 at the PI but i thought it took just a little too much away for me. i am sticking with 12ax7 there. how is the komet 19? I saw it on their website- looks very cool. Mark

[soma_hero]

There is no cathode follower in the Express or Liverpool. The resistor you're talking about, R7, goes from grid of stage 3 to ground. Decreasing this resistor will decrease the gain.

[Zippy]

There is no cathode follower in the Express or Liverpool. The resistor you're talking about, R7, goes from grid of stage 3 to ground. Decreasing this resistor will decrease the gain.

My bad. I've been so Rocket-centric lately that I translate everything that says "Trainwreck" to "Rocket".

Yes, lowering the value of R7 pulls the voltage closer to ground.

[pinkmarkos]

that's what i thought because from the descriptions i read about CF's, (if i have this correct) the signal/load is applied to the cathode of the next stage, not the grid as in the express/liverpool. and the purpose of this is to provide the next stage with more current (tone stack e.g.) rather than signal gain. thanks for the clarification soma hero.

[soma_hero]

In the Cathode follower, one half of the valve feeds signal from its plate to the grid of the second half of the valve. Now output signal is taken from the cathode of that second half and fed to a tonestack/phase inverter.

[Zippy]

In the Cathode follower, one half of the valve feeds signal from its plate to the grid of the second half of the valve. Now output signal is taken from the cathode of that second half and fed to a tonestack/phase inverter.

The cathode follower configuration is independent of what half of the tube it occupies. The other half of V2 in the Rocket is unused (which drives some people crazy).

[pinkmarkos]

thanks for the correction- i just looked at the rocket schematic and i now understand the difference in the context of an entire preamp. thanks for tutoring a newb.

[dayn]

dayn- i did try 5751 with 12at7 at the PI but i thought it took just a little too much away for me. i am sticking with 12ax7 there. how is the komet 19? I saw it on their website- looks very cool. Mark

Mark,

The Komet 19 is really incredible. I am enjoying it more than the Liverpool clone I used to have...by FAR! Sounds and feels way better.

With the (2) 12 ax7s in the K19 preamp the distortion came on a little too quickly and was not as smooth as I prefer. With the 5751 and the 12at7 it has more clean headroom and a distorted tone that is still very aggressive but smoother to my ears.

The nice thing about the K19 is that is will give up the goods early (reasonable volume) or be very loud, all with tube selection and the "Saturation" knob. Very diverse tonal range and great bottom end for el-84's.

[soma_hero]

Have you had a peek inside it?

[dayn]

Have you had a peek inside it?

Yes, but I am no amp builder (yet, trying to read and learn what I can here!)

True PTP inside. Also, very cleverly put heat-shrink wrap on about 10 resistors to hide the values from clever cloners