[lupoal]

Hi, I've checked and... it was my tester that in case of electrical continuity but with high impedeance doesn't biiip ... so, ok I've the same situation except for the resistor value that is 4,9 instead of 5,1

... what I don't understan is why they elevate the EF95 heater, that is not critical, and do not elevate that one of the high tube in the SRPP which is much more critical... I have the doubt the thay have done so with EF95 to take under control possible huummm and left floating those about the two 6N6, that could be the other possibility instead of elevating them... does make it sense?

 

[drteming]

As far as hum reduction goes, elevating the cathode of the EF95, the voltage amplifier, is more important. However, elevating the cathode by only 5 volts or so is kind of silly as it won't achieve the desired goal. Not elevating the upper triode of the 6N6 is probably ok, as the voltage is still within spec of Vhk of 100V. Your guess is as good as mine as to the thinking of the designer of the amp.

 

[lupoal]

I would like to rebuild mine but... optimised for C3g as driver and 6SN7 as power tubes, it is how I’m using it right now and it sounds a lot better then with 6N6P and 6AK5 (not the stock tubes but other better)... I’m wondering how it could sounds if tailor made on tubes I’m using

 

[Datun Walnut]

I would like to rebuild mine but... optimised for C3g as driver and 6SN7 as power tubes, it is how I’m using it right now and it sounds a lot better then with 6N6P and 6AK5 (not the stock tubes but other better)... I’m wondering how it could sounds if tailor made on tubes I’m using

I use 6sn7s now on adaptors. I couldnt go back to 6n6s

 

[lupoal]

6SN7 are completely at another level... at the moment I’m running two Russian 6H8C (year 1952 real NOS) and two 6BE6W Brimar (EF95), they are not so extremely good as C3g + GE but, in any case, far superior to 6N6P

 

[lupoal]

@drteming
did you measure the load, I mean current and voltage, at the output of high voltage section of the transformer under load?
I'm asking you because I'm going to assemble an external "block" with better transformer and two separate stage linear DC supply to heaters, I discovered that LD underpower the filaments with a voltage of only 5,6Vac (average) with 220Vac from the wall... that's bad as it should be not less 5,7Vac but, better, 6,0Vac

so, as the filament temperaure has an important rule in sound quality I will remove the tranformer from the LD2 and add something external connected via terminal blocks on additional pcb... having possibility then I will also add an additional switch, in the transofrmer box to manually switch by hand to valves power only after some seconds after the voltage will be applied to filaments... or maybe something that will do that automatically

someting like...

plus (but a switch is much easier obviously)

and seems that filaments temperature/voltage also have an important rule in lifetime of the tubes... 6N6P and 5654 are, at decent quality, in the market for few bucks but C3g and 6SN7, those I use, are in total roughly 200 bucks and some of them are not so easy to find, so I would avoid troubles

 

[lupoal]

@drteming
did you measure the load, I mean current and voltage, at the output of high voltage section of the transformer under load?

I've done that... it should be 151Vac output with input of 220Vac ... but it is only 144Vac, so 5% lower then target

anyway, here is the picture of the trafo

 

[drteming]

@drteming
did you measure the load, I mean current and voltage, at the output of high voltage section of the transformer under load?
I'm asking you because I'm going to assemble an external "block" with better transformer and two separate stage linear DC supply to heaters, I discovered that LD underpower the filaments with a voltage of only 5,6Vac (average) with 220Vac from the wall... that's bad as it should be not less 5,7Vac but, better, 6,0Vac

so, as the filament temperaure has an important rule in sound quality I will remove the tranformer from the LD2 and add something external connected via terminal blocks on additional pcb... having possibility then I will also add an additional switch, in the transofrmer box to manually switch by hand to valves power only after some seconds after the voltage will be applied to filaments... or maybe something that will do that automatically

someting like...



plus (but a switch is much easier obviously)



and seems that filaments temperature/voltage also have an important rule in lifetime of the tubes... 6N6P and 5654 are, at decent quality, in the market for few bucks but C3g and 6SN7, those I use, are in total roughly 200 bucks and some of them are not so easy to find, so I would avoid troubles

The filament voltages were right around 6.3 volts, but the mains voltage was 123V at my house. Undervolting filaments definitely reduces tube life. I saw a graph a while back showing that undervolting is worse than overvolting, but I can't find it again.

As for delaying the high voltage: http://www.valvewizard.co.uk/standby.html

 

[lupoal]

@drteming
... so, my external LPS using two LM317 is finished and running fine supplying now, at the end, the correct voltage to all the tubes
... now looking again at pictiures about your rebuild... did you use DAC Type stepped actuator instead of potentiometer? which one? this (10k of course)? how did it work compared to the ultra-cheap pot used inside the LD ?

 

[drteming]

That's the stepped attenuator that I used. It worked great. Well balanced, no appreciable noise. I used that attenuator because I had previously swapped the cheapo pot out, and it fit the original noard. Without a PCB, there's no constraint on the pot that one can use.

 

[lupoal]

ok thanks, I will buy and try

 

[lupoal]

@drteming
question: why did you change from 0,68uF to 4,7uF? did you measure both and the second one works/plays better?

 

[drteming]

@drteming
question: why did you change from 0,68uF to 4,7uF? did you measure both and the second one works/plays better?

Nah, I just had a couple of good 4.7uF caps lying around. If you have good low ESR electrolytic, then 0.47uF is likely all you'll need. I listened to a bunch of different value caps and couldn't really tell a difference, so I kept the 4.7uFs in there as I didn't have any other applications for them. In my big headphone amp based on 6AS7 output tube, I have really low ESR 470uF electrolytes bypassed by 0.47uF Russian PIO caps.

 

[lupoal]

ok, thks

 

[lupoal]

my big headphone amp based on 6AS7 output tube

... interesting... OTL? will you share project/details about that?