U47 with EF14 tube Build

[rock soderstrom]

the only thing i would ask is on the heater side, would a parallel pot work so i could adjust the volatge to 5.05v or there abouts?

Are you talking about my solution with a LM317? There you can adjust the voltage directly at the regulator with a trimmer. Very flexible, huge range for underheating or exotic filament voltages, if needed.

 

[Spencerleehorton]

sorry my mistake didnt spot the 5k trimmer!!

So on the B+ side on your schematic would i be right in saying for my 170vac after bridge = 238vdc, drop 118v which would be 120k lets say at 1mA.
if i wanted a pot within the B+ i would put it in paralell on the R8, say 100k pot with 50k resistor, first resistor 50k and last resistor at 27k, should give me roughly what i want right?

 

[rock soderstrom]

So on the B+ side on your schematic would i be right in saying for my 170vac after bridge = 238vdc, drop 118v which would be 120k lets say at 1mA.
if i wanted a pot within the B+ i would put it in paralell on the R8, say 100k pot with 50k resistor, first resistor 50k and last resistor at 27k, should give me roughly what i want right?

This would work, but has the disadvantage that the filtering depends on the position of the pot. Try it out, to be on the safe side, take 100uf capacitors, then nothing hums i guess, no matter how the potentiometer is set.

It's been a while since I built this circuit. I think I implemented the voltage adjustment with a following potentiometer as a variable voltage divider back then.

A paralell potentiometer for R8 or R9 should also work in a certain voltage range.

 

[Spencerleehorton]

i would normall put the pot at the R9 position and not have it in parallel, so a 50k then 50k then 25k trimmer.

 

[rock soderstrom]

i would normall put the pot at the R9 position and not have it in parallel, so a 50k then 50k then 25k trimmer.

It is almost the same thing, one advantage is that if something goes wrong with the pot there is still resistance left. Try it out!

 

[Spencerleehorton]

i'll see what bits ive got and hopefully start putting it together

 

[Sorr]

View attachment 115936

for the 170Vac B+ side would this be ok?

Just need to know if i'll be able to use the 6.3vac for the H+?

You should put in a protection zener across the TL783! Say 100V 5W?

 

[rock soderstrom]

You should put in a protection zener across the TL783! Say 100V 5W?

I agree, see Jakobs G9 schematic for reference.

 

[Spencerleehorton]

ive done a bit of LTspice and will go with this config as per rock soderstrom schematic and layout.
i'll just need to do a bit of photoshop to do the traces of the pcb, then printout and iron on, then a bit of ferric chloride and drill some holes.

 

[rock soderstrom]

I would extend C11 in your schematic with more C for extra ripple filtering. (C6/7/8 in my schematic)

 

[Spencerleehorton]

If I had c6,c7,c8 at 1000uf /25v or go with 470uf/25v for them all?

 

[rock soderstrom]

If I had c6,c7,c8 at 1000uf /25v or go with 470uf/25v for them all?

I think both are more than sufficient. Use what you have available. I have built it with both types, even critical microphone circuits with cathode biasing from the heater work fine with them.

 

[rock soderstrom]

You wrote that your heater winding is quite current potent, so your 6.3VAC may be higher and you may have to use R1 (very small value) to distribute the thermal load evenly to all series resistors and the regulator. Then everything stays nice and cool and works forever.

It would also give you some pre-filtering as well

 

[Spencerleehorton]

trying to work out the H+ with the voltage doubler going into the regulator, if 6.3Vac winding of transformer is about 7vac after diodes going into regulator what would i have? can i use the multiply by 1.4v or is it half that? im thinking its about 19vac going into the regulator?

 

[Spencerleehorton]

You wrote that your heater winding is quite current potent, so your 6.3VAC may be higher and you may have to use R1 (very small value) to distribute the thermal load evenly to all series resistors and the regulator. Then everything stays nice and cool and works forever.

It would also give you some pre-filtering as well

what would you have as R1? i have some 5W 25R?

 

[Spencerleehorton]

ive made a few adjustments

 

[rock soderstrom]

trying to work out the H+ with the voltage doubler going into the regulator, if 6.3Vac winding of transformer is about 7vac after diodes going into regulator what would i have? can i use the multiply by 1.4v or is it half that? im thinking its about 19vac going into the regulator?

Possibly, but I think it will be one or two volts less.

I just checked my red book with the measurements I took at the time.

For me it was like this:

Load: 33R Current: 192mA

VAC = 6,93V
VDC pre regulator = 15,33V
VDC post regulator = 8,6V
VDC per filter resistor = 1,14V
VDC at heater = 6,33V

the 6.3V/1.4A transformer was cool, the FIlter resistors lukewarm and the heatsink of the regulator quite warm after 10 hours of operation, everything was ok, but I then fitted R1, very small value, something in the 5-10 Ohm range perhaps, I didn't note it down. After that, everything was perfect, nothing excessively warm, just the way I like it.

Please consider your fatter transformer, your raw secondary voltage will be a bit higher, but not dramatically.

Nothing will smoke or get very hot. Do it without R1 for now, it will work, if necessary and available, install it.

 

[rock soderstrom]

View attachment 116090

ive made a few adjustments

25R is a little big in my opinion. C12 is hanging in the air with one leg in your schematic

 

[Spencerleehorton]

hopefully this is better?

 

[Khron]

Does C7 do anything, with both terminals grounded?

https://en.wikipedia.org/wiki/Rectifier#Voltage-multiplying_rectifiers