• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

4P1L DHT Line Stage

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mogliaa

mogliaa

Member
Joined 2009
bartola.co.uk/valves/
michaelvv said:
Hi Ale.

What is the "function" of R1,R2 on 300 Ohm exactly.
They wasn't present when I build my Ver 1..

I have a few "clicks" from my 4P1L throught my Speakers quite randomly.

I'm going to change my cathode resistor to a non magnetic type..

I'm currently using Vishay-Dale 10W, and in generel I'm very satisfied with
my amp, so I'm no into any "big" update right now :)

I thought I will give the Mills MRA-12 a try.

http://www.hificollective.co.uk/pdf/pg16prn.pdf

/Thanks Michael.
Click to expand...

The purpose of the resistors is to keep the voltage of the screen/suppressor grids slightly below the anode. The value is not critical at all and can be between 100 and 300 ohms. I have omitted them in several builds, without any issues :)

If you hear some "dings or dongs" is the natural expansion of the elements during warm up, specially when you run the 4P1L rather hot. I can hear these dings and dongs when I warm up the pre-amplifier and then occasionally now and then, but nothing that disturb me at all.

Now, if it is a click, I'm wondering what have you changed in your setup rather than a capacitor. Are you using a shunt regulator? Have you tested any bad solder, lose connector or even changed the 4P1L? Is the noise perceived on both channels?

Cheers
Ale
 
M

michaelvv

Member
Joined 2014
mogliaa said:
The purpose of the resistors is to keep the voltage of the screen/suppressor grids slightly below the anode. The value is not critical at all and can be between 100 and 300 ohms. I have omitted them in several builds, without any issues :)

If you hear some "dings or dongs" is the natural expansion of the elements during warm up, specially when you run the 4P1L rather hot. I can hear these dings and dongs when I warm up the pre-amplifier and then occasionally now and then, but nothing that disturb me at all.

Now, if it is a click, I'm wondering what have you changed in your setup rather than a capacitor. Are you using a shunt regulator? Have you tested any bad solder, lose connector or even changed the 4P1L? Is the noise perceived on both channels?

Cheers
Ale
Click to expand...

Hi Ale...

The warm up I know the sound nothing to be concerned about...
The Click are quite seldom, and It have been there all the time...

I have changed the Tubes, have +100 of them , so nothing here.

I dont think it's a solder problem, best case with my Clarity MR, it
took me 5 week to have it...

Are you using non magnetic resistor for your cathode ???

/Thanks Michael
 
Rod Coleman

Rod Coleman

Member
Joined 2004
michaelvv said:
Hi Rod...

Thanks for your excellent explanation as usual.

Are you using a "Film Capacitors" for the 47nF, or do you have something
else here ???...

I have some "clicks" in my 4P1L , get worse when i tried the K75-10 pio russian caps in combination with my Vcap- CuFt.

With a Clarity MR and my belowed Vcap it was less frequent.

I'm close to make an order from mouser, so I thought of buying some WIMA MKS4 47nf , and some no magnetic resistor for the cathode.
<cut>
/Michael
Click to expand...

Csn should be small physical size (prevents re-radiation) and stacked film. MKT is fine, or MKP. Even cheap Arcotronics R82 series is fine, and Wima MKS certainly OK.
 
M

michaelvv

Member
Joined 2014
mogliaa said:
I'm using wirewound from Dale, they work nice and sound fantastic.

Do you get the clicks at the same time on both channels?
Do you have a scope? Can you try to see where it is coming from?
Ale
Click to expand...

Hi Ale....

No, The clicks have never been in both channels, and again with and interval
of up to 5 week hard to figure out on my scope...

PS! When I have this "scratch click" I usual take an isolated piece of plastic and
touched the cathode resistor, and It's "gone" for a while :)

Where have you bought these Vishay's ????

I'm using the little little brother mouser - RS0108R000FB12

But as I have said before, the sound quality is not my concern, IT LIKE MY
4P1L so much.

/Thanks Michael
 
Last edited:
indra1

indra1

Member
Joined 2010
mogliaa said:
Hi Indra,
I've done my homework at last, and I think we have a real winner here. I'd run it at 8mA if possible, but surely the 4P1L will beat a 26 in this mode :) . . . .
Click to expand...
Hi Ale, thanks for the trace. :up: Sorry for very late response. I was in China for 10 days, didn't have good internet connection. Still need to stay in Hong Kong for a few days. Beat the 26? Hmmm, can't wait to get my hands on it.
 
M

michaelvv

Member
Joined 2014
mogliaa said:
A new improved loctal socket board to reduce microphonic noise in the preamp. Using silicone rubber layer between PCBs and silentblock. Looking forward to implement it soon:
20140413-184915.jpg
Click to expand...

Hi Ale...

Are these the sockets from JakeBand ???

Are you using them now, or do you have any new favorites ???

/Thanks Michael.
 
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