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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

EL84 amp

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#43
I use ECL86s and they are indeed half of a 12AX7 plus an EL84 (just limited to 9W dissipation). They work perfectly in EL84 amp designs, biased a little cooler. I'm pretty sure a PCL86 is the same, but with a different heater voltage.

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#44
pcan said:
If your insulation transformer is toroidal, you may even remove the filament transformer, just wrap the required number of 15awg copper wire turns around the core. On the 117-6060 RS Components transformer each turn is 0,275 volts; so 12+12 turns will make 6,3V center tapped. Copper enameled transformer wire may be sourced from a old transformer.
Click to expand...
I'm almost 100% that I will get torodial transformer, i that case I will use this trick thank you very much for telling me this. I will also wind another loop for leds. Looks like I can't do anything without involving blue leds hehe.

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#45
AquaTarkus said:
They're will be no damage to the tube, just the possibility of a little hum. It's also advisable to adjust the position of the output transformer relative to the power transformers to minimise pickup of hum. You can use the "headphone trick" for that purpose.

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Click to expand...
Ok, thanks for info. I just did a research for headphone trick. Well no I know for my next build.

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#46
matejsirk said:
Hi diy1995,

If you need anything you can contact me (I am also from Slovenia). I have a lot of components in my private stock (more then 6000 tubes, etc...).

I can send you some PCL86 (halve ecc83 and halve EL84) in one tube:

http://www.mif.pg.gda.pl/homepages/frank/sheets/030/p/PCL86.pdf

Contact me on PM.
Click to expand...
Hy, I will contact you if I will need anything, I'm little tight on budget tight now. I guess we need to talk in english because of forum rules?

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#47
Well I was thinking that front of housing is pretty empty so I will add analog dB meter from old hitachi tape player. I just glued window on. I will use blue leds for backlight. I'l finish and post another photo tomorrow.
7f1eff83383d2434ac16a5f7c75d76ad.jpg


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#53
Hello,
I have finally builded the amp and it`s not amplifying anything!🙁🙁😕
The sound I get from it it`s loud the same, that connecting source directly to the speaker.
It`s quiet if amp is off and when I turn it on it`s getting louder as tube is warming up like it should, when I turn off the amp sound it`s getting quieter and quieter with alot of distortion at the end like it should.
B+ voltage is 270V, cathode voltage (pin3) is 7v, heater voltage is 6,29v.
What could be wrong? How to troubleshoot this problem? Thank you
 
#54
I have measured output transformer and resistance between middle wire and upper wire is 547ohm (i have upper wire connected to pin7 and between pin7 and pin9 i have 100ohm resistor) resistance between middle pin and lower pin is 33ohm (lower pin is disconnected)
Should i remove 100kOhm resistor that goes from pin2 to ground?
 
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#55
I assume that you connected the pin 9 (g2) to anode, so triode mode is selected. At first, compare the cathode current with the datasheet value to see if the tube is exausted. Your current is 7V / 270 ohms = 26 mA. The Mullard datasheet says that for a triode connected EL84 with 250V anode the current should be 34 mA. So the tube is still working, but emission is not very strong anymore. Then check again the datasheet and see if the measured g1 (grid) voltage value relative to cathode is about the same as the value proposed from the manufacturer. Mullard says -9v for a triode connected EL84 at 250V on the anode, you says 7V (so g1 is negative, -7v), this also checks ok because the tube emission is weak. Now you should measure the amplitude of the input signal and compare to the datasheet. The average headphone output is between 1 and 2 volts. On the datasheet we find out that on triode mode at 1V input signal output power is 50mW, so just about the same power as the internal phone speaker. But if you change the pin 9 connection to pentode mode, as in your original amplifier, then the amplification is 3 times greater. So the quick fix is easy, just disconnect the 100 ohm resistor from anode and connect it to B+, to put the EL84 in pentode mode. It would be better to increase the value of the resistor, 1K or 2,2k are common.

Edit: I corrected a few mistakes on original reply.
 
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#56
pcan said:
I assume that you connected the pin 9 (g2) to anode, so triode mode is selected. At first, compare the cathode current with the datasheet value to see if the tube is exausted. Your current is 7V / 270 ohms = 26 mA. The Mullard datasheet says that for a triode connected EL84 with 250V anode the current should be 34 mA. So the tube is still working, but emission is not very strong anymore. Then check again the datasheet and see if the measured g1 (grid) voltage value relative to cathode is about the same as the value proposed from the manufacturer. Mullard says -9v for a triode connected EL84 at 250V on the anode, you says 7V (so g1 is negative, -7v), this also checks ok because the tube emission is weak. Now you should measure the amplitude of the input signal and compare to the datasheet. The average headphone output is between 1 and 2 volts. On the datasheet we find out that on triode mode at 1V input signal output power is 50mW, so just about the same power as the internal phone speaker. But if fou change the pin 9 connection to pentode mode, as in your original amplifier, then the amplification is 3 times greater. So the quick fix is easy, just disconnect the 100 ohm resistor from anode and connect it to B+, to put the EL84 in pentode mode. It would be better to increase the value of the resistor, 1K or 2,2k are common.

Edit: I corrected a few mistakes on original reply.
Click to expand...

I dont get it... I completely remove resistor and connect B+ to g2 (pin9)?
Or I leave resistor so it`s: b+>resistor>g2 (pin9)?

I can`t messure current right now, i destroyed current meter on my DMM by accident last time :S
Thank you

I don`t belive that tube is exhausted as it was in original setup.
 
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#57
It's b+>resistor>g2 (pin9). The resistor should be increased to 1k - 2k
By measuring the cathode voltage, you indirectly already measured the current (Ohm's law). If your measure is correct, then the tube is partially exhausted. That's very common on vintage equipment that has been used.
To get the full power you still need a preamp stage.
 
#58
pcan said:
It's b+>resistor>g2 (pin9). The resistor should be increased to 1k - 2k
By measuring the cathode voltage, you indirectly already measured the current (Ohm's law). If your measure is correct, then the tube is partially exhausted. That's very common on vintage equipment that has been used.
To get the full power you still need a preamp stage.
Click to expand...
Thank you, tomorrow i will go and buy 1k.
Acurate voltage of cathode was 7,50v, it jumped to 7,70v after few second of playing music. Now it`s playing music for about half hour and voltage slowly rised to 7,80v. I also belive that it became a little bit louder, but not much.
I measured input signal voltage and it`s around 0,80v.
I think that I will use ic preamp for now.
 
#60
diy1995 said:
What does merely bling mean? My first language isn't English.
Click to expand...
Bling:
"denoting expensive, ostentatious clothing or jewellery, or the style or materialistic attitudes associated with them."
Ostentatious:
"characterized by pretentious or showy display; designed to impress."

Nothing wrong with bling, if that is what you like, but it is not the same as genuine high-tech - which is all about performance rather than appearance.
 
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