Euridice pramp but with 45

[dejanm]

I have seen few schematics for one tube preamp. Usual tubes used in these designs are 5842, but there are some other available choices as well: 26, 27, 10Y, ...

Does anybody have schematic for one tube preamp with 45 (VT52) ? Which transformer should be used at the output ?

Thanx in advance ...

[Zen Mod]

what's gain you need/expect from preamp?

every OPT have transfer ratio ;

just for example - if you're shooting for Ra of 4K and output impedance 600E , thats voltage ratio of 2,58:1 ;

so - presuming that gain of tube in circuit is (optimistically and without even looking in 45 data ) 3 , then you'll have overall gain of 3/2,58=1,16

you'll need either input xformer before tube ( with adequate up ratio ) or to switch to another type - choke loaded 45 , then C coupled to load or parafeeded to load ;

instead of choke you can use CCS , then just cap to load , or parafeed

so - choice is all yours

[dejanm]

Zen,

Thanx a lot for your comment. Actually I do not need a large gain. What I am looking for is the linearity, not so much the gain itself.

If I take "normal" 45 (45's differintiate considerably depending of sub-type) with:

Ua = 250V
Ia = 34 mA
Ug = -50V
Rp = 1750 ohm
mu = 3,5

and if I put the choke (200 H) as a load and have only coupling capacitor at the output (without trannie), I would have output impedance of about 1,8K @ 1KHz. Rcathode would be ~ 1,5 KOhm. Which is quite ok.

If I put a trainnie that you described, I would get a gain of 3,5/2,58 = 1,356 which is more like a buffer than preamp. The output impedance would be about 270 Ohm. That shouldn't be a problem if the power amp has a gain of 29dB and input impedance of 100 KOhm ? It shouldn't be ... Would Lundahl LL 1671/30mA be the right choice for the trainnie ?

http://www.lundahl.se/pdfs/datash/1671.pdf

I was thinking about 45 because it has higher grid bias than 5842. If I connect CD player at input (and I will) which has 2V output signal, which further means pk-pk of even 6V (somebody on this forum explained this when he was discussing this kind of preamp with 5842) it will not overload the tube.

Now one question more: I already have a pot with very high output impedance (it is actually remote controlled unit kit that I bought) of between 20K and 40 K and I am afraid that this will not fit well to 45 ... Comment perhaps ?

[Zen Mod]

Originally posted by dejanm
Zen,

Thanx a lot for your comment. Actually I do not need a large gain. What I am looking for is the linearity, not so much the gain itself.

If I take "normal" 45 (45's differintiate considerably depending of sub-type) with:

Ua = 250V
Ia = 34 mA
Ug = -50V
Rp = 1750 ohm
mu = 3,5

and if I put the choke (200 H) as a load and have only coupling capacitor at the output (without trannie), I would have output impedance of about 1,8K @ 1KHz. Rcathode would be ~ 1,5 KOhm. Which is quite ok.

If I put a trainnie that you described, I would get a gain of 3,5/2,58 = 1,356 which is more like a buffer than preamp. The output impedance would be about 270 Ohm. That shouldn't be a problem if the power amp has a gain of 29dB and input impedance of 100 KOhm ? It shouldn't be ... Would Lundahl LL 1671/30mA be the right choice for the trainnie ?

http://www.lundahl.se/pdfs/datash/1671.pdf

I was thinking about 45 because it has higher grid bias than 5842. If I connect CD player at input (and I will) which has 2V output signal, which further means pk-pk of even 6V (somebody on this forum explained this when he was discussing this kind of preamp with 5842) it will not overload the tube.

Now one question more: I already have a pot with very high output impedance (it is actually remote controlled unit kit that I bought) of between 20K and 40 K and I am afraid that this will not fit well to 45 ... Comment perhaps ?

you know what ....... I spent some time thinking about your questions .......
but :

-that lundahl doesn't have needed ratio for xforming impedance for your needs ;

- I think that you can do it much better , either with 12B4 R loaded , Choke loaded , CCS loaded ....... ( mamouth thread here)

or 6V6 in triode , (loading by your choice - look for one or two threads here) ;

6H13C (russian 6080 ) , loading again bu your choice , except xformer load .

with all of them you'll have lesser output impedance

btw - you can go to www.vt52.com , and download few xls files ; they are handy for quickie calcs

edit:

save those 45's for more appropriate purpose ....... or send them to me for proper disposal ..........

[Zoran]

hi,
The 45 tube is quite good for preamp design...
45 is vintage tube delivering vintage sound if the concept is right.
like predecessor of 2A3 tube (maybe even better for preamp),
has one plate and about double internal resistance (1.6K ?)
so it could be about 60Hy
of primary inductance for the output transformer...
for 600 ohm output it is step down ratio of rougly 1.6
that is for I think suficiant total gain (I think that 45 has -A of about 6)
god thing is that bias point is far from signal level, and with low heating voltage,
ensures no hum...
10Y sounds extraordinary but that is on the edge to obtain proper design,
expetialy for the preamplifier, because of need for very high primary inductances,
damaging the bandwidth from both sides...
god luck with Your project
cheers.

[Zoran]

I saw now that 45 have the pretty low -A,
but that is not like a problem, when You going for the realy high end preamp
You could consider Loftin-white topology (one stage before 45, maybe also 45)
then you could go for even lower output impedance like 200 ohm,
and I am positive that, even with a 2 stages, You will have less hum,
against all mediocre, compromising designs of preamps, with opposite phase out,
overaplifiesd signals, low Va to make PS easyer, high transconductaces tubes degrading the sound,
and so on

[dejanm]

Originally posted by Zen Mod



btw - you can go to www.vt52.com , and download few xls files ; they are handy for quickie calcs

edit:

save those 45's for more appropriate purpose ....... or send them to me for proper disposal ..........

@Zen - you have always great ideas. I already downloaded these XLS's and they are quite handy although I am not using them :-)
Did I make a mistake somewehre in my calculations ?

I do not have any 45's yet - therefore I cannot give them to you

And 45's are rather expencieve, especially VT52 that I will try to buy ... WE VT52 has even better characteristics than usual 45, but it can not simply replace 45 - it has Uh of 7 V.

@Zorane - I share your opinion. I like the idea to use 45 as preamp tube in this configuration. For double stage amp I even found somewhere schematics (on VT52.com I believe) but mainly because of the price of the tubes I am not sure that I will go for it.

My main problem at the moment (there are some others as well of course) is to find the right output transformer for 45. I would like to buy Lundahl because I know they are good. But which one ... So any input would be welcomed ...

[Zen Mod]

another (quickie one ) - I presume that this tube isn't too hard to find in Betsch

http://www.tubecollector.org/atp4.htm

definitely sleeper

( I drew these lines long time ago - triode connected , what else )

[dejanm]

Originally posted by Zen Mod
another (quickie one ) - I presume that this tube isn't too hard to find in Betsch

http://www.tubecollector.org/atp4.htm

definitely sleeper

( I drew these lines long time ago - triode connected , what else )

I do not know this tube. Have you ever implemented it ? Experiences ?

It seems to me that you want to discourage me to go for 45 ... why ?

[Zen Mod]

Originally posted by dejanm


I do not know this tube. Have you ever implemented it ? Experiences ?
....

I tried it few times on bench , but I have no need for new line stage then ; it's promising , as I wrote before

Originally posted by dejanm


...

It seems to me that you want to discourage me to go for 45 ... why ?

nope ; but you really need to solve few things - to decide what you need - gain or muscles on output ;

then we can work from there

numbers you wrote are completely OK ; but I think that mentioned Lundahl isn't capable for that task - what you need is at least double ( if not triple ) Ri for primary impedance .