I have also tested with a different transformer which gives 6.1v ac at 1A
As follows with one valve connected
7.75vac supplied
8.2vdc at input pin
4.7 vdc at output pin
6.02vdc offload output pin
0.06vdc measured across resistor on load
With original transformer
10.2 vac supplied
11.5 vdc at input pin
4.7 vdc at output pin
6.02 vdc offload output pin
0.06 vdc measured across resistor
I have checked several times they are 6v regulators and also changed the bridge rectifier. I have to conclude the regulators must be bad so I've ordered some more
As follows with one valve connected
7.75vac supplied
8.2vdc at input pin
4.7 vdc at output pin
6.02vdc offload output pin
0.06vdc measured across resistor on load
With original transformer
10.2 vac supplied
11.5 vdc at input pin
4.7 vdc at output pin
6.02 vdc offload output pin
0.06 vdc measured across resistor
I have checked several times they are 6v regulators and also changed the bridge rectifier. I have to conclude the regulators must be bad so I've ordered some more
I think your problem is in your supply... 7.78VAC makes more than 8.2VDC unless you have VERY lossy diodes or your transformer is current limited.
Same for 10.2VAC*1.414=14.42VDC without diode loss.
Perhaps your transformer is just too small.
Same for 10.2VAC*1.414=14.42VDC without diode loss.
Perhaps your transformer is just too small.
Or else the 4700uF input capacitor is bad, and not filtering enough, or at all.
Try a different capacitor there. The regulator seems ok.
Try a different capacitor there. The regulator seems ok.
Last edited:
That's why I tried a different transformer and bridge rectifier, I still get voltage drop when a valve is connected, you may be right about the capacitor as Kodabmx pointed out 10.2v rectified should make more than 11.5v ! I'll wait till the new regulators ( from UK ) arrive and order a couple of new capacitors as well, thanks for all the input I'll post results later, my brain is hurting from all this, it all looks so simple on paper !!!
Take the 1000uF capacitor that is at the output, and put it on the input.
The output only needs 10uF to 100uF at most. A 1000uF at the input should be
able to let the regulator work ok on at least one tube filament.
The output only needs 10uF to 100uF at most. A 1000uF at the input should be
able to let the regulator work ok on at least one tube filament.
Final attempt tonight, added 1000uF, input voltage up to 12.3vdc, output from regulator 4.6vdc so no change, still think it's the regulator. Offload 6vdc.
I think the fact that you get 6.02 V with no load means that the regulator is working. I think you're either in current limit or foldback.
The regulator was sold rated at 1.5A, with one valve the current draw is only approx. 365mA ! It gets warm but not too hot to touch as you would expect if at 6.3v. What do you mean by foldback ?
Foldback is the regulator protecting itself from a combination of current through and voltage across it that would cause failure in the output transistor. I think you have high Vin and a low impedance load at startup so the regulator folds back to a survivable combination of voltage and current and sits there. The only way to exit foldback is to remove Vin and restart.
One thing you could try is to start up as you are, remove Vin and very quickly restore it - less than a second if possible. That way the filament would already be hot. If it starts up that way you're definitely folding back... and like they said in Jaws you're gonna need a bigger boat.
One thing you could try is to start up as you are, remove Vin and very quickly restore it - less than a second if possible. That way the filament would already be hot. If it starts up that way you're definitely folding back... and like they said in Jaws you're gonna need a bigger boat.
I measured the DCR of cold 6DJ8 ECC88 tubes and got about 3.5 ohms cold, which results in 1.8A inrush current at 6.3Vrms input. That will kick the feet out from under a 7806 regulator. Slo-o-owly over time, the tube will heat up and the current will drop to the specified 300mA, at which time the 7806 will resume normal regulation.
Today I swapped the valve for first a resistor of 18R and then 10R - I still got voltage drop about to 5.4v with the 18R and more with the 10R. I also lowered the input voltage to around 8vdc as I have read the input voltage should be no more than 2vdc above, don't know how true that is but either way it definitely was not regulating to the specified 6v. Should soon get some more from a different UK supplier and will update later !!
"I have read the input voltage should be no more than 2vdc above"
No, the input voltage must be MORE than 2V greater than the rated output voltage.
No, the input voltage must be MORE than 2V greater than the rated output voltage.
I've tried 8vdc 10vdc 12vdc and 20vdc with different transformers and resistors on the ac transformer output, nothing came close with valves or resistive loads.
As you still haven't achieved a result after all the help you have been given Jabiri --lets recap -
First --is your circuit exactly like this -
6 Volt regulator circuit using 7806-Voltage regulator IC
especially the way the CIRCUIT earth runs .
I ask this as I have come across HR earths and incorrectly wired earth that can cause this .
First --is your circuit exactly like this -
6 Volt regulator circuit using 7806-Voltage regulator IC
especially the way the CIRCUIT earth runs .
I ask this as I have come across HR earths and incorrectly wired earth that can cause this .
In my experience threads like these drag on because the OP deliberately or mistakenly omits important basic details.
What is the part number of your regulator? Did you find its datasheet? The Lite PCB is expecting an LM7815 and uses a CRC to drop that to 12VDC. What are the other parts used to populate the circuit? Did you make any assumptions on how to substitute your regulator for an LM7815?
What is the part number of your regulator? Did you find its datasheet? The Lite PCB is expecting an LM7815 and uses a CRC to drop that to 12VDC. What are the other parts used to populate the circuit? Did you make any assumptions on how to substitute your regulator for an LM7815?
Circuit is exactly that other than having larger output capacitors which if you google the 78 series circuits some show capacitors up to 470uF on the output ( most show much lower ) the regulator ( I bought a pack of 5 and have tried 3 ) is marked LM7806CV, I have swapped out the bridge rectifier and the resistor is 0.12R which I put in just to make the connection. I'm going to remove the output capacitor and put a small value in - give me half an hour and I'll post back !! Last gasp attempt
You've got a point Leadbelly , I have never had a problem with genuine LM voltage regulators , some part of the construction of the circuit cant be right.
Hang on did you say LM7806----CV ????
SGS -Thomson Microelectronics website has this marked down as a -----
500ma regulator ---NOT a normal 1.5 amp LM regulator .
IF ---that is the case then the valve/tube isn't far short of the regulators limit and as several posters have said ---"is it LIMITING " ?
SGS -Thomson Microelectronics website has this marked down as a -----
500ma regulator ---NOT a normal 1.5 amp LM regulator .
IF ---that is the case then the valve/tube isn't far short of the regulators limit and as several posters have said ---"is it LIMITING " ?