• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Simple ECL86 amp

Jump to Latest
#41
ECL82 vs ECL86 are different tubes no substitutions.

Derek Walton PCL86 (*NOTE: different heater, same tube)
"Therefore, you can use PLCL86 valves with the heaters in parallel or you can use ECL86 with the heaters in series."
You will probably have to substitute transformers, but the layout, wiring, etc. will help.
https://web.archive.org/web/20070106213517/http://www.iol.ie/~waltonaudio/pcl86.html

http://www.r-type.org/exhib/aai0028.htm

1656082647538.jpeg
 

Attachments

  • 1656082365616.jpeg
    1656082365616.jpeg
    114.3 KB · Views: 342
  • 1656082443470.jpeg
    1656082443470.jpeg
    105.3 KB · Views: 326
  • 1656082514226.jpeg
    1656082514226.jpeg
    40.1 KB · Views: 321
Last edited:
#42
ChrisABC said:
ECL82 vs ECL86 are different tubes no substitutions.

Derek Walton PCL86 (*NOTE: different heater, same tube)
"Therefore, you can use PLCL86 valves with the heaters in parallel or you can use ECL86 with the heaters in series."
You will probably have to substitute transformers, but the layout, wiring, etc. will help.
https://web.archive.org/web/20070106213517/http://www.iol.ie/~waltonaudio/pcl86.html

http://www.r-type.org/exhib/aai0028.htm

View attachment 1066348
Click to expand...
The web archive schematic shows negative feedback with a switch, this schematic shows no feedback. Why?
 
#43
ChrisABC,

No negative feedback . . .
That is right - if you are looking for Schade feedback, output transformer secondary to Cathode feedback, or Global feedback, it is not there.

But, there is Local negative feedback:
Triode Wired Mode
Ultra Linear Mode

Note: The schematic in Post # 41:
The Ultra Linear Tap shows more B+ to Screen Turns, versus Screen to Plate turns.
If actually wired that way, a 40% UL tap becomes 60%, and a 25% UL tap becomes 75%.
(Probably the schematic editor did not have a correct model for an actual UL output transformer).

Pentode/Beam Power is 0% Ultra Linear
Triode Wired Pentode/Beam Power is 100% Ultra Linear.

I have used 40% UL tap, 100% Triode Wired Beam Power mode, and 0% Beam Power mode for push pull outputs.

I have used 20%, 50%, 80% UL taps for single ended outputs,
as well as 100% Triode Wired Pentode/Beam Power mode, and 0% Beam Power mode.

Have fun building and listening.
 
  • Like
Reactions: stenak
#44
Sorry to dredge up an old thread, but on post 34 of this thread, there is a youtube video and a schematic.
The schematic shows R5 and R6 as being in series between pentode cathode and ground, with a connection between the two going to the triode cathode.
In the video, the author connects R5 to the pentode cathode and earth, and R6 between the pentode and triode cathode, with no connection to R5, apart from the socket terminal (16:10 on the video).
Can anyone enlighten me as to which is correct?
 
  • Like
Reactions: peacocksuit
#46
patrickblue said:
Can anyone enlighten me as to which is correct?
Click to expand...
That connexion provides a degree of positive internal feedback.
When carefully chosen the result can be zero internal impedance on the amp speaker terminals.
But depending on other circuit constants, in particular the OPT, instability may result.
The amp will also be a lot more sensitive to PS ripple. That hookup should be avoided except by the knowledgeable.

Schade NFB is not a cure all either. Again, such an amp is more susceptible to PS B+ ripple. 😱
 
#47
Novarria's OPTs are rubbish. Once a friend came to me with one of their kits wandering why it sounded so bad. Hooking up the oscilloscope was enough to show a very poor frequency response and lack of inductance. Because the circuit looked reasonable, I convinced him to open the OPTs up to see what was so bad about them. I can tell with 100% confidence that most power transformers would be way better in the same application! Some schemes might have mistakes. Given the non-educated typical audience they were made for, I don't think that circuit was supposed to be used with positive fbk.
 
#49
jhstewart9 said:
That connexion provides a degree of positive internal feedback.
When carefully chosen the result can be zero internal impedance on the amp speaker terminals.
But depending on other circuit constants, in particular the OPT, instability may result.
The amp will also be a lot more sensitive to PS ripple. That hookup should be avoided except by the knowledgeable.

Schade NFB is not a cure all either. Again, such an amp is more susceptible to PS B+ ripple. 😱
Click to expand...
Sorry, I'm a total novice when it comes to feedback circuits.
Which hookup should be avoided?
The one in the schematic, or the one in the video?
 
#53
patrickblue said:
Not yet, I will in the very near future
Click to expand...
I'm currently building it as per the video with a 20v laptop power brick and boost converter for HT supply. I've started a thread. Had a few issues, probably down to my lack of experience but I'm getting there. I ended up starting again with another, much simpler schematic using PCl86. I've just stripped it down again to start over with the schematic from the youtube video.
It's a steep learning curve but it's good fun.
 
#55
What are you seeing that's different between the video and schematic? It was R6 and R5 that were confusing me (not difficult) until I looked at it properly.

Just had a look at your thread, you seem to be having some fun and games. I'll let you know how I get on.

Good luck
 
#57
By eyeball, that connexion puts a short across R5. 😱
In some circuits R1 is used to maintain stage gain while the cathode cap across R6 is eliminated.
But as usual, nothing is free. Some of the audio power out that should have been at the
OPT primary is now dissipated in R5.👎
 
You must log in or register to reply here.
Top Bottom