Which 2A3 would you build

[colin.hepburn]

Hi All
Well my first amp build is getting closer I have chosen to build a 2A3 but which one I have looked at the 5842/2a3 http://diyparadise.com/5842-2A3.html and this one JE Labs Simple 45/2A3 http://members.myactv.net/~je2a3/simple45.htm plus I like the idea of a 6EM7 Driving a 2A3 anyone got any comments on this 6EM7 version

http://209.85.135.104/translate_c?hl=en ... rl%3D18081
Your ideas all welcome
thanks

[colin.hepburn]

|Hi All
Well I guess no one wants to commit to which 2a3 to build this I can under stand I suppose you just have to build them and see however I have decided to go with the JE Labs 6SL7/2A3

I have a couple of question’s regarding the heater supplies
My mains TX 6.3 v heater supply don’t have a CT can I just use two 100R resistors as a artificial centre tap
Plus the 2A3 heater using the 266M2 TX should I use the 100R pot or the CT of the 288M2 which would be the best way for this
Cheers

[Nick]

I would just use one leg of the 6.3v supply to connect to, I don;t know of anything to be gained by creating a virtual center tap.

I would use the pot on the 2a3, it will enable you to null hum.

[IslandPink]

2 stages of 6SL7 is going to have a 'mental' amount of gain .

Sorry, it's a cathode-follower.
I'll get me coat...

MJ

[colin.hepburn]

Hi All
Sourcing parts for the 6SL7/2A3 build the 880R 25W 2a3 cathode resistor doesn't seem to be a standard value nearest mills is 820R or 910R 50w is this critical or can I use ether of these two values
Cheers

[Nick]

I would go with the 910, you can always parallel a 27k 0.6w to give you the 880

[colin.hepburn]

Cheers Nick
thats made things easer

[steve s]

I would just use one leg of the 6.3v supply to connect to, I don;t know of anything to be gained by creating a virtual center tap.

I would use the pot on the 2a3, it will enable you to null hum.

I have always used a wire wound pot there... with ac heating.. you can reduce the hum..

but i have found only this this week that that pot has been the cause of my humming amps.. i have a couple of 25 ohm resistors in place,
now the hum is much less...

i used these pots when playing with the ob's last year i had one on as a volume control on the lowther.. it worked ok untill i boosted the bass with the extra bass driver.. when i removed it, i found it had really taken away the sound quality.. i felt i had got the lowthere back..

well it had the same effect with the the 2p amp, there has been a step increase in detail and that 'real life' sweet sound that old triodes do..
i had a good listen last night.. i'm very, very happy...
even lesley could tell...


on the 2a3 colin,

i would say that amp would be good

but on my 'simple is better' rule...
that amp is very sensitive .. there is alot of gain..

i would just use one stage.

A cap coupled half a 6sl7 gives a gain around 45ish, if you are using a cd player one stage would do it.. just...

depends on what you want, and your speaker efficiency...
and what you listen too..

I don't like direct couple stages.. I know the theory looks good ??

but what i would do, is not what most would do...
and i'm very much still learning...


steve

[colin.hepburn]

Hi Steve
Thanks for the tips taken then on board this is my first amp build so learning as I go the 2a3 will be running into fostex 126e 94db BLH when I can get them built? I also have a SRPP sch of the JE Labs 6SL7/2A3 I would value your thoughts on this version I guess the thing is to try both
cheers

[andrew Ivimey]

The difficulty here, Colin, is that if you ask enough of us you will get a huge number of replies and be none the wiser.

Your latest posting is SRPP. It will sound different (and not just because there is more gain) to Steve's 'simple' suggestion or the original JELabs scheme you posted.

Which is better?

Of the three, I'd go for the 'simple' solution.

[Darren]

Hi Colin,

I'd have to agree with Andrew on this one, keep it simple. I'm a firm believer that the more parts you add the more you loose.

I know others will disagree though....

[Nick]

Well, I agree with everything said here. BUT...

Steve: I think like Mark, you are missing that the second stage is a CF, so its just the first gain stage.

I don't think a common cathode 6sl7 would be up to driving the 2a3 directly.

As every, as Andrew said, if possible, you need to try and make your own mind up, buting on a breadboad would allow you tro try both, and others.

if you look closely at the two circuits, you will see they have more in common than not, if you consider the top part of the SRPP as a cathode follower, you can see how they are alike.

But to steal a famous quote:

"Make everything as simple as possible, but not simpler."

[steve s]

thanks nick,

i should keep my head down..and mouth shut..

colin should be well confused by now...

just build one and see colin...

when it works you will be very pleased with it..


below is not for colin to read.....
the point for me is.. do you need lots of current on the grid of the valve your driving... i thought you did .... but driving SE i'am not so sure....

in the olden days....
a voltage amplfier was what was used for se
a driver was for driving the grid with variations on the push pull theme.
i know thats not saying much..
but i'm still a little confused...

steve


steve

[colin.hepburn]

Hi Steve s
No need too keep your head down its all part of the learning curve I guess as you say just build it as nick has suggested I will bread board the amp and try out both looks easy enough to change over to try the version SRPP
Thanks

[Nick]

Yes, but in some of those Goldern Ages, the source often didn't have content above about 12kHz, so any HF drop off from driving the grid with a high impedanece source wasn't as much of a problem.

All IMHO of course.