I have discovered(or rather rediscovered) some PCL86 tubes in my large tube collection (in the part i had misplaced a few years back, and found a few weeks ago). I originally wanted to build a OTL headphone amp for my old 64 ohm headphones, but never had the time to do so. Sadly due to me studying applied Mathematics and Physics at university, i don't have the time to reteach myself what i new about vacuum tube circuitry. I did find some book in my university's library about the subject, they were being thrown out, and i saved them. Sadly i have little time to read them at the moment, yet i would still like to build a PCL86 headphone amp for my 600 ohm Beyerdynamic headphones. They are currently being driven off a solid state amp.
I searched around the net to find some schematics for a PCL86 amp, but it only tended to turn up amps for 8 or 4 ohm speakers.
...so if anyone here happens to have a schematic i could use for the amp, it would be much appreciated.
I have read the books part on testing tubes, so i should be able to find a matched pair in my collection (i have about 10 or so to test).
If using this tube is a dumb idea, pleas tell me.
I do have experience with electronics and high voltages, so building it isn't a problem for me.
I searched around the net to find some schematics for a PCL86 amp, but it only tended to turn up amps for 8 or 4 ohm speakers.
...so if anyone here happens to have a schematic i could use for the amp, it would be much appreciated.
I have read the books part on testing tubes, so i should be able to find a matched pair in my collection (i have about 10 or so to test).
If using this tube is a dumb idea, pleas tell me.
I do have experience with electronics and high voltages, so building it isn't a problem for me.
PCL86 is for SE or PP for, as You read, amps with transformer output that provides tube load about 5-7 kohm, that is not suitable for Your 600 ohm headphones. Transformer has second coil that accords amps output with speakers 4-6-8.....or 600 ohm.
For Your OTL project You need tubes with inner resistance about 200-400-500 ohm, like 6AS7, 6S19P, ....that are suitable for OTL headphones project.
For Your OTL project You need tubes with inner resistance about 200-400-500 ohm, like 6AS7, 6S19P, ....that are suitable for OTL headphones project.
So basicly i cant use them for a headphone amp for my headphones. I did find a 600 ohm to 8ohm transformer from Hammond, the 119DA, maybe i could build a class A amp with a output transformer for 8ohms, and then connect the 119DA in reverse to convert it to 600. The only problem i see in this, is it may fry my headphones if i turn it up to loud.
I would have wanted to build a SE amp based on them, btw.
I can remember i found a schematic somewhere for a 600Ohm headphone amp using the PCL86, however i have no printed copy, and i cant find the schematic anymore.
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I would have wanted to build a SE amp based on them, btw.
I can remember i found a schematic somewhere for a 600Ohm headphone amp using the PCL86, however i have no printed copy, and i cant find the schematic anymore.
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http://frank.pocnet.net/sheets/010/p/PCL86.pdf
R inner = u/S = 21/10 is 2 kohm.
Maybe You, for OTL, will use parallel tubes in cathode follower mode....that will decrease it inner resistance.
R inner = u/S = 21/10 is 2 kohm.
Maybe You, for OTL, will use parallel tubes in cathode follower mode....that will decrease it inner resistance.
So basically, build a speaker amplifier designed for 8Ohms output impedance, and connect a 8 to 10 ohm power resister over that, and then the headphone to that? I asume i need the output winding were the primary impedance is 5K and the secondary 8?
Also, how did you calculate / figure out that the PCL86 needs a 5K output transformer? I do have some other tubes i would like to play around with (audio wise) but i haven't found a pattern in the designs yet (based on the values in the datasheets)
Also, Thanks for the help!
Also, how did you calculate / figure out that the PCL86 needs a 5K output transformer? I do have some other tubes i would like to play around with (audio wise) but i haven't found a pattern in the designs yet (based on the values in the datasheets)
Also, Thanks for the help!
IMO, main rule, that I use, is inner resistance multiply to 3-5 and receive transformer load. Hammonds have possibility use them with variations of loads, less and more 5 kohm /You need better 7-8 kohm load/.
Res. 8-10 ohm and headphones are connected parallel and this group connect to output by switch.
Res. 8-10 ohm and headphones are connected parallel and this group connect to output by switch.
Thanks for the Reply's! also well that is interesting.
I have also found a YouTube video with the title: PCL86 HEADPHONE AMP
https://www.youtube.com/watch?v=VxVYauTUZSQ
in it the person showed a schematic of a OTL amp that uses the PCL86.
I have drawn up the schematic using Eagle CAD, the pdf is in the attachment.
Also the AKG K601 is 120 ohm impedance, while my bayers are 600, so i dont think connecting them to the 4ohm post will work all to well, but correct me if im wrong.
I have also found a YouTube video with the title: PCL86 HEADPHONE AMP
https://www.youtube.com/watch?v=VxVYauTUZSQ
in it the person showed a schematic of a OTL amp that uses the PCL86.
I have drawn up the schematic using Eagle CAD, the pdf is in the attachment.
Also the AKG K601 is 120 ohm impedance, while my bayers are 600, so i dont think connecting them to the 4ohm post will work all to well, but correct me if im wrong.
Also, based on your formula, Zt = Ra * 3, were Zt is the impedance of the Output transformers primary, and Ra is the resistance of the anode, the PCL86 would need about 15KOhm's of output impedance.
Could you give me a actual mathmatical formula? not a word formula. Because it seams that i have misunderstand your word formula, sorry about that.
Could you give me a actual mathmatical formula? not a word formula. Because it seams that i have misunderstand your word formula, sorry about that.
Ri of PCL86 is about 2 kohm.....There isn't exact formula....You can multiply to 3-5, depending what You want,....more bass, less distortions - 5, or little bit more power and more distortions - 3. I know, acc. my skill. I hope DIYs think like me.....Your load must be about 6 - 10 kohm /2 x 3-5 = 6-10/.
I think 8-10 kohm will be fine. This load has Hammond and EDCOR. If You want use amp for headphones and Speakers /4 or 8 ohm/, buy with outputs for 4 or 8 ohm, If You want to use only for headphones - buy with output for 600 ohm.
I like more Hammonds....IMO.
Your schematic is with cathode follower, like I though. Quality of sounding depends from quality of output cap. I don't recommend You use two parallel caps, IMO, signal cross two different phis. media. Better use one electrol. cap with high quality for more money, than cheep....cheep cap - cheep sound.
Are You from?
I think 8-10 kohm will be fine. This load has Hammond and EDCOR. If You want use amp for headphones and Speakers /4 or 8 ohm/, buy with outputs for 4 or 8 ohm, If You want to use only for headphones - buy with output for 600 ohm.
I like more Hammonds....IMO.
Your schematic is with cathode follower, like I though. Quality of sounding depends from quality of output cap. I don't recommend You use two parallel caps, IMO, signal cross two different phis. media. Better use one electrol. cap with high quality for more money, than cheep....cheep cap - cheep sound.
Are You from?
Well to the power needed to drive headphones, i can only quote my beyerdynamic T1's datasheet, it can handle up to 300mW. I have however seen ones that need in the Watts (if i recall the HifiMan HE560 is one such example. Also i just checked the value for the Audeze LCD-3, that thing can handle 15W!! That is insane!.
Also i have found a Schematic for a PCL86 SE OT Amp, maybe i can adopt it for headphone use: PCL86 Piccolo Triode Amplifier
The Schematic uses a 5K output transformer, not the 10K you said. Also i like less distortion in my audio.
btw, i mostly listen to music using headphones, i do have a speaker system, but i rarely us it at the moment. Also the speakers in it are rated at 50W so a PCL86 couldent power them, i was thinking of a KT88 amp for them, however.
Also i have found a Schematic for a PCL86 SE OT Amp, maybe i can adopt it for headphone use: PCL86 Piccolo Triode Amplifier
The Schematic uses a 5K output transformer, not the 10K you said. Also i like less distortion in my audio.
btw, i mostly listen to music using headphones, i do have a speaker system, but i rarely us it at the moment. Also the speakers in it are rated at 50W so a PCL86 couldent power them, i was thinking of a KT88 amp for them, however.
The level required for listening and the level (up to watts) the headphones can handle are very different matters.
According to Beyerdynamic's specs the sensitivity of the model T-1 is 102 dB/V.
Since the impedance of the phones is 600 ohms, the sensitivity is some 100 dB/mW.
According to Wiki the threshold of pain is (at 1 kHz) some 125 dB and hearing damage (over long-term exposure) can take place at the level of 85 dB.
According to above numbers 1 mW should be sufficient power level required from a headphone amplifier for these headphones.
But is it so ?
According to Beyerdynamic's specs the sensitivity of the model T-1 is 102 dB/V.
Since the impedance of the phones is 600 ohms, the sensitivity is some 100 dB/mW.
According to Wiki the threshold of pain is (at 1 kHz) some 125 dB and hearing damage (over long-term exposure) can take place at the level of 85 dB.
According to above numbers 1 mW should be sufficient power level required from a headphone amplifier for these headphones.
But is it so ?
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PCL86 works in this schem. in triod and in UL /Ultra Linear/ mode, by switching second grid. If it in triod mode,
Ri is less than 2.2 kohm, that mean Load can be less 8-10 kohm /in schem. it is 5 kohm, that is close to enough, but for UL mode 5 kohm is Small, IMO, You will have more distortions/.....Choice is Yours...
5 kohm is good for PCL82, ECL82. Don't forget, heating of PCL86 is not 6.3 v.
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