It doesn't, unless you claim to have golden ears..
You simply wire the speaker terminals back to front so the + and - are reversed.
kind regards
Marek
You simply wire the speaker terminals back to front so the + and - are reversed.
kind regards
Marek
185V is the absolute bare minimum for the glow tube to strike. A bit higher would allow some leaway; mains voltage variation for one.
With fixed bias, the grid resistance is a lot lower than for self bias to prevent runaway. Your circuit is very high.
With fixed bias, the grid resistance is a lot lower than for self bias to prevent runaway. Your circuit is very high.
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Thanks for reply.
That's right. In fact I wanted to avoid putting a capacitor in the circuit. It is so as not to have a capacitor at the cathode coupled to a resistance that I opted for this solution.
That's right. In fact I wanted to avoid putting a capacitor in the circuit. It is so as not to have a capacitor at the cathode coupled to a resistance that I opted for this solution.
Hello,
I have two questions regarding polarization:
1) What are the advantages and disadvantages of using a series of zener diodes at the cathode. adding a small capacitor (1nf for example could help remove any noise)
2) I saw that we could also connect a battery to the entrance of the grid. What do you think please?
Regards,
Marco.
I have two questions regarding polarization:
1) What are the advantages and disadvantages of using a series of zener diodes at the cathode. adding a small capacitor (1nf for example could help remove any noise)
2) I saw that we could also connect a battery to the entrance of the grid. What do you think please?
Regards,
Marco.
1. Zener diodes for the kind of voltage for biasing preamp tubes are not noisy, but they have too much effective dynamic (1kHz) impedance: as much as 25Ω for a 5V6, or 85Ω for a 3V9. Around 6V8 the impedance is probably low enough, but varies with current, at least a little, so there will be added distortion. 6V8s are noisier than lower voltage zeners (2V7 and 3V3 are quiet enough for other supplies in preamps).
2. Battery bias works well, if precautions against unwanted charging are undertaken, there are lots of posts on diyAudio you can look up.
2. Battery bias works well, if precautions against unwanted charging are undertaken, there are lots of posts on diyAudio you can look up.
Thanks for your reply Rod Coleman.
Perhaps i will need your regulators for a futur project :
a type 30 preamp.
But now i want to finish my 4p1l.
Pictures will come later.
Perhaps i will need your regulators for a futur project :
a type 30 preamp.
But now i want to finish my 4p1l.
Pictures will come later.
Good evening,
here is the progress of my 4p1l project Everything is handmade with salvaged things. (the boxes are offcuts of Jatoba flooring). For now I'm building it with a variable cathode resistor and a bypass capacitor, I'll see if I change later. I will be able to find a working point in this way. Transformers: 5k / 600ohm. primary resistance 450 ohm Supply voltage 150v. I think the OPt will be around 35ma. Critics are welcome.
Regards
Marco
[url=https://goopics.net/i/70KGa]
[img]https://i.goopics.net/800/70KGa.jpg[/url][/IMG]
[/url][/IMG]
here is the progress of my 4p1l project Everything is handmade with salvaged things. (the boxes are offcuts of Jatoba flooring). For now I'm building it with a variable cathode resistor and a bypass capacitor, I'll see if I change later. I will be able to find a working point in this way. Transformers: 5k / 600ohm. primary resistance 450 ohm Supply voltage 150v. I think the OPt will be around 35ma. Critics are welcome.
Regards
Marco
[url=https://goopics.net/i/70KGa]
[img]https://i.goopics.net/800/70KGa.jpg[/url][/IMG]
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Hi Andy,
Slightly late reply to your post #1381 ...this actually looks like something I could build...got 2P29Ls, got Hammond 126Cs, got FT-3 220nFs, have a variable preamp power supply...need to know:
1. What's that decoupling cap in the HV supply line?
2. Is this filament bias?
3. What is R1 on Rod's board?
4. What else do I need to know?
Tough to keep up with your experiments/changes, but they are definitely inspiring!
Just trying to get into the mix. Hope my questions are not too *OLD*.
Thanks and Best,
Robert
I've switched to DC Link caps for HV and especially cathode bypasses. Kemet C4AQ. No bypass here - it's in filament bias. For Rod's board, best to ask him - he updates regularly. I looked up my old files and found this schematic, which is probably what I built.
Attachments
Hello,
If you need 150v at the entrance of your transformer (Hammond 126c)Why don't you use a 150v voltage regulator tube please ?
If you need 150v at the entrance of your transformer (Hammond 126c)Why don't you use a 150v voltage regulator tube please ?
Yes - that's an idea. Maybe I designed it that way to allow for that. I read somewhere that plate chokes don't mix well with glow tubes - no idea what that's all about.
En ce moment j'ai 2 projet de préampli dht en cours (désolé, mais je me disperse beaucoup):un WOT 4P1L preamp et un 2p29l avec mu follower. Je cogite également sur un phono dont j'ai construit la boîte. Si vous le voulez, je peux vous informer de mes avancées sur mes projets.
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1. I would build a 26 preamp not a 4P1L
2. Why do you want a mu follower with a 2P29L? Just put 15mA current through it. The Ri is low enough at around 3K. Keep it simple and the sound pure.
I am doing my experiments and I want low output impedance. I was thinking of using the 6j52p for this.