djn111

Re: V-241 from scratch
« Reply #140 on: January 27, 2019, 11:49:18 AM »
Hi,

Very nice build en inspiration :-)

But if you ever build a other one, I will give you a nice Elma switch for the gain switch ;-)

DJN


DaveP

Re: V-241 from scratch
« Reply #141 on: January 27, 2019, 05:22:33 PM »
Too late, the second one is almost finished!

Thanks anyway :D

DaveP
Soundcloud: Delayed Action.

Murdock

Re: V-241 from scratch
« Reply #142 on: March 10, 2019, 12:37:58 PM »
Hey Dave,

have you looked at the Lorenz V41 preamp?
It is the predecessor to the V241 and V72 preamps.
As I was lucky enough to get two original V41 output transformers for 50€  ::) I would like to build a blend of the V41 and V241.
I thought about using the same tubes as the V241 but the gainswitching of the V41.
How would you implement the gainswitch in to the V241 schematic?
Would it be as easy as just to put it after the output cap (C9 in the V241 schematic) or before as you did it? 

« Last Edit: March 10, 2019, 12:41:31 PM by Murdock »

DaveP

Re: V-241 from scratch
« Reply #143 on: March 10, 2019, 06:18:22 PM »
Quote
I thought about using the same tubes as the V241 but the gainswitching of the V41.
How would you implement the gainswitch in to the V241 schematic?
Would it be as easy as just to put it after the output cap (C9 in the V241 schematic) or before as you did it? 
Yes, I know about the V41, the gain switching of the V76 was developed from it and is almost the same.   It is an elegant combination of feedback and cathode bypass gain changes.

Wise to use a later pentode type as the EF12 type has a much higher g2 current (partition noise), check the data sheets.

Breadboard the circuit, then try connecting before and after the cap, the results may well be different.  I think I found some instability coonecting after the C9 cap.

Note that the feedback string is in an earthed metal box and that C17 has been put in for a reason maybe to tailor the response or cure a stability issue or both.

Find a triode that has the same spec as the E12 triode wired. An EC90 is close, but there are many other possibles.

Good luck

DaveP
Soundcloud: Delayed Action.

Murdock

Re: V-241 from scratch
« Reply #144 on: March 10, 2019, 07:42:35 PM »
Yes, I know about the V41, the gain switching of the V76 was developed from it and is almost the same.   It is an elegant combination of feedback and cathode bypass gain changes.

Wise to use a later pentode type as the EF12 type has a much higher g2 current (partition noise), check the data sheets.

Breadboard the circuit, then try connecting before and after the cap, the results may well be different.  I think I found some instability coonecting after the C9 cap.

Note that the feedback string is in an earthed metal box and that C17 has been put in for a reason maybe to tailor the response or cure a stability issue or both.

Find a triode that has the same spec as the E12 triode wired. An EC90 is close, but there are many other possibles.

Good luck

DaveP


Hey Dave, thanks alot for your answer!
I wanted to use EF86/E80F and ECC85 like the V241. Already got a suitable choke and don't want to buy two more.
I saw that your (V76) gainswitching was similiar but that also adds two more electrolytics... Can you maybe explain why?
In the orignal there is only one electrolytic in the whole circuit and I wanted  to try to keep it that way, maybe even use a wet tantalum for that spot.

Also in one Maihak V41 they tied the input transformer secondary directly to grid without caps. Can you maybe explain the difference between the Lorenz and the Maihak input topolgy?



DaveP

Re: V-241 from scratch
« Reply #145 on: March 11, 2019, 04:49:36 AM »
Quote
I saw that your (V76) gainswitching was similiar but that also adds two more electrolytics... Can you maybe explain why?
In the orignal there is only one electrolytic in the whole circuit and I wanted  to try to keep it that way, maybe even use a wet tantalum for that spot.
I copied the V76 circuit as far as possible, I figured if its good enough for them, its OK for me and not directly in the audio path, for that I used poly prop caps throughout.  Tantalum has not got a good reliability record.

Quote
Also in one Maihak V41 they tied the input transformer secondary directly to grid without caps. Can you maybe explain the difference between the Lorenz and the Maihak input topolgy?
I can only guess really, I can think of two reasons. 1: they used a different input transformer that had some secondary effects that needed correction (after the war everything was in short supply so you just used what you had). 2: It was developed for a studio environment that had a lot of stray fields like tape machine bias or camera scanning so it needed to be filtered out.

On that subject: notice the chokes are all in boxes (mine too) as if they radiate back to the input circuit you get an unwanted feedback path and possible oscillation.

The V76 was connected directly so I would copy that version, resistor thermal noise on a grid is bad news, 10M is to be avoided!  It is not easy making ratios like 1:18, so they have tried to correct the response I guess.

DaveP
Soundcloud: Delayed Action.

Re: V-241 from scratch
« Reply #146 on: March 21, 2019, 12:10:20 PM »
Also in one Maihak V41 they tied the input transformer secondary directly to grid without caps. Can you maybe explain the difference between the Lorenz and the Maihak input topolgy?

Hello,

the first tube in the ÜV268 works with grid leak bias (W1 10 MΩ).

Andreas