A single stage amp ?

[steve s]

a single output valve driven straight from a CD player.. .

A few years ago i was convinced this would be the way to audio perfection, the trouble was finding a quality valve sensitive enough with sufficient gain and clean enough not to loose some that gain by needing feed back

So, single ended of course, what is the most sensitive valve per watt output?
Any suggestions...

[Dave the bass]

Dunno about 'sensitive' but I've long toyed with the idea too our-Steve.

I'm leaning towards 6c45P spud like AndrewL did, I wonder what other valves lend themselves to spudage?

DTB

[pre65]

I'm leaning towards 6c45P spud like AndrewL did, I wonder what other valves lend themselves to spudage?

DTB

ECL82 if that's not cheating.

[Dave the bass]

Thats 2 active elements in one envelope, deffo cheating (and I've done E/PCL82 already!).

EL86...?

4P1L...?

DTB

[Paul Barker]

The only successful genuine spud has always been the 6c45Ï€.

But you could cheat in my book because what is on the output of the CD player? An opamp?

Right, what about "converting the Cd player output to a 5687 cathode follower" then you could drive such as an 811a, which due to it's gain will give you a reasonable level of sound.

This cheat is allowable because you said you wanted it driven by a CD player, and such as a 5687 just happens to be a typlical valvification mod to a CD player.

Now if you wanted a spud amp capable of being driven by a 300mv sensitive old piece of kit, not a snowballs chance in Hell.

[steve s]

All fair points, but far too much outside the box thinking..

Two stages phil.. Tut tut..
i was thinking in the lines of a sensitive pentode that could make 10 watts driven to quarter of its capacity...

I really only have old valves.. so thats whre i've looked towards..

It is possible i would guess to get a couple of watts ultra linear with no feed back, some of the older pentodes quoted at maximum output at only 7% distortion, quite close to some triodes.
And if not using full signal it would help the distortion tremendously

[Steptoe]

I too only have old valves, nearly all of which were developed for radar. Those which I have tried as a single stage include KT 44, 12E1, CV72, 19BG6 and CV 57. As I said before they all sound the same (good to me) but I don't know if that is because my ears are past their use by date. A pair in parallel gives a slight increase in volume but no change in quality, even when two different valves are used, which again calls into question my hearing, but does have the advantage of halving the TR of the output transformer. I use a 12: 1 ratio for all the valves mentioned, with no feedback. As a beginner I ran into all sorts of trouble trying to make even 2 stages work well but am pleased with this system, although it is limited in volume and probably full of nasties which I can't hear. I would be really grateful for your thoughts.
Best wishes, Steptoe. PS. My apologies to Paul and Steve who I got mixed up in my mind. Seems like its not just my ears which are worn out.

[ed]

y'all just knew I was going to say something...

I guess it depends which is most important to you, the single stage bit or the valve bit.

I have one(single stage), and it's been in my main system since the last Owston. It's not my best amp, but it's close enough, and it's single ended, and there's no feedback.....but it's not valve, alas.

In comparison to it's peers it really does excel in some areas....so if you ever do find a valve Steve, then there's a good chance of good results.

edit: there is the Michael Rothacher SIT amp which is single stage and I have been working on as a side project for a while. The curves for the sony SITs are true triode curves...I really must get it finished

[Will]

Brian watsisname Clark? who did the spud amp bought a pair of graphite 801's off me for his 801 spud using a stepup t/x 1/60 built by sowter....I think ha! ...
like me he just lerved the 801 sound..

.

[steve s]

Brian watsisname Clark? who did the spud amp bought a pair of graphite 801's off me for his 801 spud using a stepup t/x 1/60 built by sowter....I think ha! ...
like me he just lerved the 801 sound..

.

Thats a good idea will, a 4-1 step up would just do it
Its what was in common use in the 30's
Those graphites you use are up to the levels of a px4 as i remember... No wonder you love them..

[Dave the bass]

I'm guessing we're talking step up input TX here yeah? If so, do they rely on the assumption that the source driving the i/p TX has a modicum of drive current?

DTB

[Mike H]

I've seen single EL84 for record player, sensitive enough for crystal cartridge AND tone controls, must be pentode mode though to get the gain, I've no doubt.

HTH

[Will]

Brian Clark died 2 years ago aged 68, Essex boy from Ongar ..
I found a nice write up about his life on Lenco Heaven.
RIP Brian..

[Steptoe]

E55L has a gm of 45 but the cathode and grid are so close that many of them fail the various tests due to manufacturing difficulties. A better option may be KT33C with a gm of 10, which also looks like a proper valve, while E55L has a definitely effeminate appearance.
With regard to the input transformer, I use a 3:1 step up input with surprisingly weedy results. I have been informed that to double the volume it is necessary to increase the power 10x, yet another illustration of Sod"s law, as if any was needed. Steptoe.

[Alex Kitic]

Here is a different proposition altogether... 6JD5 (or one of the same family of tubes, like 6HS5, 6HV5A, 6HZ5.

This compactron tube is rather strange (beam triode) and as such offers some characteristics like high gain that are conducive to the project mentioned.

Let us assume that you are not afraid of high voltages - it is about low currents anyway...

Next step is, operating point - Ua 1000V, bias (cathode) just above 2V for 30mA current draw. If you assume a 15k load an approximated loadline would go up to 900Vpp, which means about 6W RMS into the 15k load.

The input sensitivity of the tube (input swing) would be maybe 4Vpp, meaning less than 1.4VRMS - that is what you can easily get from any contemporary line source like a CD player.

You would not need an input transformer, the grid could be directly coupled to the input, just like with any "normal tube" (an EL84 comes to mind). All you need is a 15-20k output transformer capable of 30mA DC... but with a good isolation since we are talking about 1000V B+. The rest of the amplifier need not be complicated... a nice CLC filter... even the current draw of the tubes heaters is not all that troublesome (around 2.4A 6.3V) and the tubes are indirectly heated.

Granted, I have not calculated the distortion... but I guess at a couple W it would not be necessarily higher than your average SE2A3 experience. And the tube should be cheap and easily sourced... I believe?