Hi everyone 🙂. So I've been disassembling some old tv's and radios and i came across a PCL86 tube and its audio transformer. I've gathered the components and designed a PCB. So far so good. The problem I've stumbled upon is the power supply for the tube. Everything else i have but i don't have the 1:1 isolation transformer for the power supply. I'm looking for different options for supplying the 250VDC needed by the tube.I'm open to suggestions for both the PSU and the amplifier circuit itself . I'm uploading the circuit i'm working on.
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Except for heater voltage, the PCL86 is the same as the 6GW8/ECL86. Look for 6GW8 circuits.
An inexpensive Triad N-68X isolation transformer's O/P can be "full wave" voltage doubled to obtain approx. 300 VDC. Given its dual primaries, the N-68X is "universal".
An inexpensive Triad N-68X isolation transformer's O/P can be "full wave" voltage doubled to obtain approx. 300 VDC. Given its dual primaries, the N-68X is "universal".
In my early days in tube project and with small tube amps using PCLs (82/84/86) , i was used to take 2 xformers with same voltage ratio and power connected back to back , providing filaments and hv supply .. if you have a pair of 230 / 13.5 V xformers you can do that.
here's an exaple unfortunately only in Italian 🙁
Termoionica Applicata: L'Insulto Finale!
here's an exaple unfortunately only in Italian 🙁
Termoionica Applicata: L'Insulto Finale!
Yes i already tried using two transformers second one being backwards but they turned out to be pretty weak and the output voltage dropped to 60V once loaded. I even tried it with 3 transformers (2x 220V - 8V 8VA and one 220V 16V 35VA) and it seemed to be working, with output voltage standing steadily at 160V but unfortunately the two ,,driving'' transformers are too weak and get hot. I don't think this solution is stable so i abandoned it. Now i am thinking of something else. I found a PY88 tube in the junkbox and I'm thinking of using it to rectify the mains directly. Any advices and tips here? I'd appreciate an exemplary circuit of such a rectifier 🙂
Forum rules prohibit discussion of transformerless circuitry attached directly to the AC mains. Please cease mention of the very, very, dangerous practice.
Buy a N-68X!
Buy a N-68X!
Advice: DON'T. Please reread the forum rules, any discussion of this dangerous practice is prohibited here. Unlike normal electronic hazards which will just kill the ignorant or careless experimenter, this can easily kill innocent bystanders.Lol i had no idea it's restricted to discuss transformerless circuitry. Anyway that was gonna be my last resort. I know the dangers and if I had been forced to to it that way i would have taken extreme precautions. What other options are there?
You could use one of these cheap step-down isolation xfmrs backwards from 120V to get around 230V out (from the 250 V winding). (the 115V winding would be more like 125V actually, usually up-designed to make up for xfmr loss.) Or voltage double off the 190 V winding. (probably 175 V out in backwards mode)
Herbach & Rademan, electric motor, power supplies, timing motor, solar panels, fans, transformers, H: 115VAC 200VA Output, 190, 210-250 VAC 60 Hz Input Continuous Duty Step Down Isolation Transformer
Herbach & Rademan, electric motor, power supplies, timing motor, solar panels, fans, transformers, H: 115VAC 200VA Output, 190, 210-250 VAC 60 Hz Input Continuous Duty Step Down Isolation Transformer
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I was thinking of something a little more complex, but way more practical. How can i design a joule thief of a sort to boost a 12VDC input to the needed voltage (250VDC)?
Yes it's Bulgarian. Unfortunately the tv itself doesn't contain an isolation transformer. It's based around direct rectification, so no luck there. Yes i failed to mention i live in Bulgaria, so our mains is 230V. I don't want to use this technique though, despite it being the easiest to implement. I can probably get the choke from the TV and maybe a few HV capacitors, although i don't see a point in taking them, since they're archaic and quite bulky. I can also salvage the potentiometers, some of which seems to be specially designed for the amplifier. I'll try and salvage anything that's worth it. I also found a PY88 tube and I'm wondering what can i do with it. It's a single diode valve. I'm trying to make it with as much as tubes as i can.
Hot chassis is an extremely dangerous practice.
Always use an isolation transformer. Back in the day when I was playing with those 5 tube AC/DC radios that were so popular in the 50s and 60s I was dam near killed when the plastic tuning knob broke and I touched the metal tuning shaft while I was hooking up an external antenna/ground wire. I would have been about 7 years old, and had no clue about isolation but learned very quickly. I had one of those razor only outlets installed in my bedroom for my days of SWL and AM DX listening with vintage tube gear. Those Razor outlets were nothing more than a 1:1 isolation transformer. Today my work bench has a large 700VA isolation transformer on it, and I refuse to work on anything unless it is fully isolated from the AC mains.
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