Bigbottle Phonostage Builders thread

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#141
slav said:
To be honest with you I'd stick with transistor circuit was designed around unless there is something really wrong , sometimes we can miss how some little changes affect whole circuit , another option is to simulate it in Spice for example , saves soldering and de-soldering .

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Alan and I have just come to that exact solution.

I believe what I gained from the 170's came from them being well matched. That is one area I haven't been able to compete with the BF861C's, as a jig for such things is a pain.

However, I have one on order and will then set about matching up some 861s I have and see if that provides the positives I got with the 170s

It's been a worthwhile experiment but ultimately some things just cant be improved on through no fault if their own
 
#142
691Ftoj.jpg

It shows a simple circuit with which you can select JFETs and also match them if necessary. The tester feeds current into the source or connects the source to ground to measure the essential parameters of the device. In position 1 (switch in counterclockwise position), the source is connected to −10V through a 1M resistor. This feeds the source with approximately a 10μA current, which you can consider the cutoff point VP for the JFET. (Data sheets specify lower values, but this gives you a more practical value for measurements.) The voltmeter now indicates the pinch-off voltage VP for the device.
The next two positions measure the VGS for the device at given drain currents. These positions give practical readings for design purposes, and you can choose the constant-current sources for the values you need. The push-button switch shorts the source to ground, and the mA meter measures IDSS.
If you wish to measure only VP and IDSS, you can permanently wire the source to −10V through the 1M resistor, which gives you VP, and then short the source to ground with the push-button to read IDSS.
 
#146
slav said:
You can safely connect 230V to blue and blue
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Thanks, it worked. Connected the board and measured the voltages without tubes. They are very wrong, actually same as mentioned by Marra:
Marra said:
I have connected the L/V side of things and my unloaded heater voltages across pins 4 and 5 are 6.49v. With the valves in place the heaters glow and the voltage drops below 6.3 volts. Using 6DJ8's with Craigs suggested mod.

With the H/V connected I have the following readings all measured to ground :- V1 pin 1 135.2V pin 2/3/7/8 0V pin 6 135.2V

V2 :- pin 1 149.9v pins 2/3/7/8 0v pin 6 150.2v

V3:- pin 1 236.3v pin 2 17.25v pin 3 16.69v pin 6 236.3v pin 7 17.17v pin 8 16.67v. I forgot to say the led's do not light up.

TIA
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I wonder, if solution was found.
 
#149
nielsek said:
Thanks, it worked. Connected the board and measured the voltages without tubes. They are very wrong, actually same as mentioned by Marra:

I wonder, if solution was found.
Click to expand...

I tried to reply to your pm but for some reason can't seem to send them.
With valves in my voltages seemed to be within range and I had nice sound for a few LP's. Developed a fault so is being for sent for sorting.
 
#151
Bigman80 said:
Alan and I have just come to that exact solution.

I believe what I gained from the 170's came from them being well matched. That is one area I haven't been able to compete with the BF861C's, as a jig for such things is a pain.

However, I have one on order and will then set about matching up some 861s I have and see if that provides the positives I got with the 170s

It's been a worthwhile experiment but ultimately some things just cant be improved on through no fault if their own
Click to expand...

Once you reverse it back to BF861 can you measure at the same points if not too much trouble
 
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