Telefunken RS241 Design Help - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 29th January 2014, 12:20 PM   #1
bsgd is offline bsgd  Brazil
diyAudio Member
 
bsgd's Avatar
 
Join Date: Jan 2008
Location: Belo Horizonte - MG
Cool Telefunken RS241 Design Help

Hi all,

So, I just got my hands on 2 TFK RS241 tubes and I'm planning on building a SE amp with them. But I dont know exactly where and how to start.

I have found this schematics:

RS241

I have also read about running these tubes in Class A2 to get a little more power. Thing is, I have absolutely no experience in desingning this.
I also do not understand why the schematics above use a 1:1 tranny instead of a capacitor for coupling (just a desing decision maybe?).

I am completely new to these very old tubes like the RS241 and I'm looking for some help and advice on what to do to make the best sounding amp possible with these!

Any input is welcome
  Reply With Quote
Old 29th January 2014, 12:54 PM   #2
Banned
 
Join Date: Jan 2014
Location: Jalan Kayu, Singapore
hi bsgd,

i'd highly recommend this site where the author talks about running 801a into class A2. you can apply the same theory here on your rs241.

801A Amplifier

cheers!
  Reply With Quote
Old 31st January 2014, 03:52 PM   #3
bsgd is offline bsgd  Brazil
diyAudio Member
 
bsgd's Avatar
 
Join Date: Jan 2008
Location: Belo Horizonte - MG
Hi Tubeworld,

Thank you for the link. That looks like a great reading and should get me started!
  Reply With Quote
Old 1st February 2014, 11:55 AM   #4
diyAudio Member
 
Join Date: Nov 2012
Location: Kaiserslautern
Hi bsdg,
congrats you are a happy guy cause theselittle beautys are very rare.
Jim de Koort uses an IT to avoid a coupling cap.
I prefer ITs too - sound becomes clearer.

Hilmar
  Reply With Quote
Old 1st February 2014, 04:20 PM   #5
45 is offline 45  Italy
diyAudio Member
 
45's Avatar
 
Join Date: Dec 2008
Location: UK
Quote:
Originally Posted by bsgd View Post
Hi all,

So, I just got my hands on 2 TFK RS241 tubes and I'm planning on building a SE amp with them. But I dont know exactly where and how to start.

I have found this schematics:

RS241

I have also read about running these tubes in Class A2 to get a little more power. Thing is, I have absolutely no experience in desingning this.
I also do not understand why the schematics above use a 1:1 tranny instead of a capacitor for coupling (just a desing decision maybe?).

I am completely new to these very old tubes like the RS241 and I'm looking for some help and advice on what to do to make the best sounding amp possible with these!

Any input is welcome
You can run it into class A2 but I don't think the schematic in that link will work well enough, unless one likes a lot of distortion....
First I suggest you use fixed bias. Second, I suggest you use a step-down interstage like the LL1692a/18mA ALT Q connection (i.e. 3.5:1) with a triode wired 4P1L. You can run the 4P1L at about 220V/20mA and with 95H primary inductance you will have plenty of clean drive. This way the 4P1l can pump quite some current into the grid and will have a Zout of only 120 ohm. The overall gain will be 2x, just a little less than the 71a with 1:1 but the performance will certainly be into another league (i.e. a lot better).

Cheaper solution for class A2 is DC coupled cathode follower or mosfet source follower. As voltage amplifier you will have plenty of choice.
  Reply With Quote
Old 1st February 2014, 10:05 PM   #6
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Hi,

This one looks interesting enough:

https://www.telok.fi/doku.php?id=projektitutkivahvistin

Ciao,

P.S. I'd forget about Class A2 and run it in Class A tout court.
__________________
Frank
  Reply With Quote
Old 2nd February 2014, 08:41 AM   #7
diyAudio Member
 
Join Date: Nov 2012
Location: Kaiserslautern
Hi Frank,
its the schematic from Jim de Kort .
RS241
I think its worth to try.
I haven´t build it since the RS is very rare and the prices are out of my range

Hilmar
  Reply With Quote
Old 2nd February 2014, 11:00 AM   #8
45 is offline 45  Italy
diyAudio Member
 
45's Avatar
 
Join Date: Dec 2008
Location: UK
Not a brilliant idea to use the RS241 in class A1. It doesn't get better than 1.5W output (for example running at 400V/20mA with that 12K load) while having high requirements, especially regarding the OT. It has a max dissipation of 15W like the 2A3 but given its characteristics the max plate voltage of 400V is not high enough to get some decent power in class A1 to compete against a 45!!
The 801A can rely on a max plate voltage of 600V, for comparison. Although the 801A gets better into class A2 as well at least one can have at least up to 4W in class A1.
If class A2 has to be avoided than it could be better used as a driver for the 300B or 211/845 with 1:1 or similar interstage for class A1 or light class A2 in some cases. Thanks to its high gain should make the rest of the amp rather easy. In that case 400V plate voltage at -15V bias for 20mA anode current would be a very good starting (and probably definitive) point. Having about 130H primary inductance like the Lundahl LL1692a with 4:3.5 ratio (connection ALT S) it could swing up to 300 V p-p for class A1 drive and somewhat less for mild class A2 drive without issues, depending on the power tube.

Last edited by 45; 2nd February 2014 at 11:05 AM.
  Reply With Quote
Old 2nd February 2014, 11:22 AM   #9
45 is offline 45  Italy
diyAudio Member
 
45's Avatar
 
Join Date: Dec 2008
Location: UK
Actually the Lundahl LL1692a is a winner in any case. One can try both solutions for the RS241: driver or final. Used as output device together with the 4P1L driver could be a starter with 3.5:1 connection for class A2 operation. The 4P1L is very chaep and extremely good (and possibly even more linear than the RS241 itself!). For using the RS241 as a driver, maybe at a second stage, one rewires the LL1692a for 4:3.5 ratio and can try the 845 in class A1 at 1250V plate voltage for 30W power output.....
  Reply With Quote
Old 2nd February 2014, 03:25 PM   #10
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Hi,

@Hilmar: I saw Jim's work with the RS only after I posted my reply.

If I only had one pair I probably wouldn't do anything with them at all....

Ciao,
__________________
Frank
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Telefunken TL710 HPH Multi-Way 0 17th December 2010 06:14 AM
Some really old tubes, mostly Telefunken ilimzn Swap Meet 2 9th March 2009 03:33 PM
Telefunken tubes gianis Swap Meet 0 25th March 2008 10:58 PM
Telefunken? Swalabr Tubes / Valves 7 19th June 2004 07:26 AM


New To Site? Need Help?

All times are GMT. The time now is 03:21 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2