1. My bad, I assumed that there are some "standard" value inductors in the fans that would fit my circuit... Stupid of me to asume as I didn`t even tell you what trafo I will use, in fact I don`t even know myself as I didn`t look at what I have at home.
2. Yes, sims logical to me to. Anyway I would like to start with the transmitter as "I`m already in." I have receiver already, by the way this is it`s frequency band:
Bands are marked old Yugoslavian way...
DV -DOLGI VAL - LONG WAVE
SV -SREDNJI VAL - MEDIUM WAVE
KV -KRATKI VAL -SHORT WAVE - AM
UKV - ULTRA KRATKI VAL - ULTRA SHORT WAVE - FM
Mainly all old Yugoslavian radios offered all that bands.
I would like to build regen receiver and join it with the transmitter... but frist thing`s first.
3. I was actually looking at one such receiver project before and I saw a thread on radiomuseum (I don`t know if I`m allowed to post links of other forums here.)
It uses PCF801 tube and it immediately catched my attention, but I wanted to hear from others what could be done with tubes on my list and here I am.
Now that I had read your description about such radio, I`m even more impressed about it and also my understanding is better.
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1. Ok. That would be cathode of the triode or the pentode? I would say triode?
2. Short wave on my Savica starts at 5,9mhz, so I will have to listen it in harmonic, at least till I build the receiver.
3. Ok, noted.
4. Ok, also noted.
Now I`m wondering what value resistors / capacitors I should use a a starting point... I understand that it will probably have to be set via trial and error, but for the starting point.
Resistors with 1w power rating should be strong enough for everywhere in the circuit right (Except for the filament drop-down)?
RF chokes... Pair of coils from the second picture from above... I can still try to use them for cathode choke regardless of using PCF802?
That leaves the RF choke below the tank coil and the tank coil. Any specs for making or buying the RF choke? And for the tank coil if I understand correctly I must make it matched it to my xtal? How do I calculate the specs?
If you carefully can dissasemble the two pies from.the antenna in the radio depicted, one of them will be fine for the triode's cathode, and the other for the decoupling choke in the plate circuit. Going deeper, a choke in RF is closely a constant current source device. So there you can have a high impedance to the signal while low DC resistance path to ground.
Triode's grid leak is 100K. Half watt suffices. The plate dropping resistor initially may be 100K too, but it may be decreased in order to get more excitation for the pentode if needed. Here 1W may be necessary.
Previous comments about VOM and the like, refer to PCF802 triode exclusively.
Triode's grid leak is 100K. Half watt suffices. The plate dropping resistor initially may be 100K too, but it may be decreased in order to get more excitation for the pentode if needed. Here 1W may be necessary.
Previous comments about VOM and the like, refer to PCF802 triode exclusively.
ok, thank you... I will see if I can get the coils apart.
Would this power supply be appropriate for the project? I used this schematic in EL84 amplifier build, B+ is 270VDC
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I usually like to be concrete with some comments. In some of them I can, in other no. As you are starting a project whose main components aren't well defined (I undertand you are using aged tubes, so we don't know their state, the activity of the crystal, availability of some materials), I can't. Thus I can't be specific on those things.
When l build my first transmiter using a 6DQ6 from horizontal sweep in TV's, exausted tubes for such a service, were relatively fine for my TX. Class C amplifiers and oscilators need a very short pulse of current plate as intense as the tube can. So, with a new pentode one can obtain 30/35 RF Watts while an aged can do it at 20 or 25. The cloud of electrons generated by the cathode between it and the grid can be sufficient still in an aged tube to perform quite well.
When l build my first transmiter using a 6DQ6 from horizontal sweep in TV's, exausted tubes for such a service, were relatively fine for my TX. Class C amplifiers and oscilators need a very short pulse of current plate as intense as the tube can. So, with a new pentode one can obtain 30/35 RF Watts while an aged can do it at 20 or 25. The cloud of electrons generated by the cathode between it and the grid can be sufficient still in an aged tube to perform quite well.
Yeah. I suggest to add a ceramic .01uF on each 'lytic as they aren't good for RF decoupling. Also add .001 across each diode for the same reason. All may be those ceramic caps @1KV blue colored available in many shops and SMPS to reuse.
Ok, understood. I think that I have enough info for now to start with the build. I had also looked at some other builds and got ideas about values and functions of some components. I will start writting known values to the schematic and see where I am. If I understood correctly those are the coils I will use, right?
Only one thing I'm having hard time with... It's the tank coil... I'm searching and searching, but can't seem to find much info on it.
Should it be something like that?
Or more like that?
Distance between the two coils must be adjustable?
I had also seen small coil over bigger one and ferrite core inside that moves up and down to change inductance. Would that fit?
Just to confirm on the smaller coil, upper end would go to antenna and lower end to ground or not connected?
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Tank coil may have any form. For tube circuits generally are air cored but no allways. From a single layer of wire to copper tubing inside them running water for cooling, at very high power. Remember the old times when short wave emmiters had 500 to 1000 KW. Our one will be more like the one wired over a white plastic tube. But have patience. First take the oscillator running and let time yourself to enjoy building the project and familiarize with circuit topology. Tubes and solid state are different in several aspects but similar in others.
In the coil of the first pic, try to leave the dual pie coils over the bobbin alone. If possible, get rid of the other coils.
In the coil of the first pic, try to leave the dual pie coils over the bobbin alone. If possible, get rid of the other coils.
Ok, thank you for explanation. I tought that I need it to get oscillator running... If I take a look at a circuit and taught about how it works, it's clear that I don't need it...
Well with that out of the way I can start building the oscillator. I will have to wait till the monday so I can get the resistors & caps, but will look if maybee I can source everything at home.
Will get rid of other coils, no problem.
There is an application for audio, and it was published in Linear Audio Volume 6. Title: Multiplied transconductance Amplifiers. Author: Frank Blöhbaum.
I liked the article quite a bit because it combined tubes with semiconductors in a way to make the best of both, to achieve very low distortion while maintaining the famous sound signature (mainly 2nd harmonic) of a single ended triode amp. Probably the best part has yet to be published: using a cascode with medium power MJT "below" and power triode "above", such a stage attains close to 50% efficiency while maintaining that characteristic triode sound signature.
Most tubes can perform better than datasheets mention. Very long ago I made a low power oscillator with a 6D6 (Variable u pentode) on batteries and the 6V for the heater also was used for anode and screen supply. Using a loudspeaker for microphone, it was my first AM transmitter. Also, tubes for 9V can be run on 6V as long as the tube is working far enough below the maximum specifications. There even exist passive mixer circuits with tubes (they don't need power supply apart from heater).
True, rectifying the 6.3V heater supply did the job. Before semiconductors took over, car radios were fitted with tubes designed for low voltage, like the ECH83. Although designed as (noisy!) frequency changer (mixer) it could be the perfect tube for a "safe" (no dangerous HV) yet sensitive regen RX.
I had made the oscillator. But I need to get probes for oscilloscope because I can only apply 50vpk max with :1 probes.
B+ is 300vdc and falls to 295vdc when tube warms up... Is this good or to high?
What is the maximum frequency of crystal that I could use?
My radio goes from 5.9mhz to 7.45mhz... So I cant listen either at 4.433mhz or the harmonics... I can hear that radio gets a bit quieter at around 6.6mhz when I turn on the oscillator.
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You can make a natural attenuator for RF. Only take about 10~15cm of copper wire plastic or enamel isolated. Peel both ends. One end to the tip of the oscilloscope. The other end to the ground clip (usually an alligator clip). Give it the form of a round loop.
You surely will think its a simple shortcircuit and this is thus, useless.
Halt: This is true for DC and low frequencies, but NO at radiofrequencies!!!. You had built a secondary single turn of a RF transformer whose primary may be any wire conducting RF: the choke is the best primary. But any conductor in the circuit conducting RF currents radiate it. Why not to try it?
300V for a crystal oscillator is too high. 150DCV is more proper. This may be adjusted with the decoupled anode resistor. Crystal may be any whose frequency may be received in your SW set.
You surely will think its a simple shortcircuit and this is thus, useless.
Halt: This is true for DC and low frequencies, but NO at radiofrequencies!!!. You had built a secondary single turn of a RF transformer whose primary may be any wire conducting RF: the choke is the best primary. But any conductor in the circuit conducting RF currents radiate it. Why not to try it?
300V for a crystal oscillator is too high. 150DCV is more proper. This may be adjusted with the decoupled anode resistor. Crystal may be any whose frequency may be received in your SW set.
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I did make the attenuator, but my o-scope is no good. It's a cheap portable one and it only reads up to 200khz...
However if I set it up to 5mv and 5ms I can see the 50hz from mains and when I turn the oscillator on it flattens that 50hz pickup, so it must be doing something....
I did managed to get 6mhz crystal so I can try it with the receiver, there was silence below about 6.5mhz yesterday when I was listening thru the band, but maybee I will be able to hear some difference...
I will figure out the resistor value to get 150vdc....