Pins 1, 2, and 3 are the triode (the skinny side) and pins 6, 7, 8 and 9 are the pentode (the fat side). The pentode can be operated as a triode as well (I think) depending on the circuit. To illustrate what we're dealing with, imagine taking half of a 12ax7 (twin triode) and a mini EL84 (Pentode) and smushing them into a single tube. The neat thing about the triode/pentodes is that you can drive the pentode side with the triode side and have a single tube mono amplifier as Wavebourn has demonstrated. Two of these tubes would give you stereo.
You'll only need two tubes for Wavebourn's design.
20mw would have you rock'n pretty good. 1w would likely blow your Grados into the next room!
You'll only need two tubes for Wavebourn's design.
20mw would have you rock'n pretty good. 1w would likely blow your Grados into the next room!
whitelabrat said:Wavebourne, very nice.
I don't suppose this could be adapted for other triode/pentodes.
6KT8'sand 6GH8's?
It may be adapted to any usable triodes and pentodes. 6KT8 may be used (it's triode part) on less current, while it's pentode part is too weak for the output. The same about 6GH8: a triode is better for your application, but a pentode is too weak.
Kaidanovsky said:So I've got a 170V DC supply on the right, with the input on the left, output centre right. I would have thought 120dB from a pair of headphones was impossibly loud if not brain-bleedingly unpleasant!
Power wise, if the current's 70mA then it's outputting 15mW?
70 mA / 1.4 = 50 mA for a maximal sinusoidal signal.
50 mA*50 mA * 32 Ohm = 80 mW
Plenty of headroom!
Why the LEDs on the cathode of the first stage? Just in lieu of resistors?
No, a LED has sharp curve, and very low dynamic resistance. They are used as low noise Zener diodes to stabilize working point so your amp will much less depend on brand and age of tubes than another one without such stabilization.
Kaidanovsky said:
No, depending on how many internal elements they have. A triode has one anode, one cathode, and one grid. Pentode has 2 more grids, so it has 5 electrodes total. Accordingly, tubes with 2 internal electrodes are named diodes, with four -- tetrodes, and so on.
Kaidanovsky said:
This topology gives several advantages:
1) Safe against tube-rollers
2) Deep bass, less dependence on output capacitor used (safe against cap-rollers )
3) Quieter pops on switch on/off than without a feedback from a headphone out
4) No so called common-mode distortions than with feedback to cathode that introduces them
5) Longer life of tubes (self-adjusted bias)
6) Nice glow of LEDs when tubes are ready to sound
One disadvantage: reversed polarity. But who hears that?
By the way, for stereo may be used 6N1P (left tube) and 6N6P (right tube); the same number of tubes, but differently arranged.
Something like IRF610 may be used instead of a right tube, so only one 6N1P is needed for a stereo amp.
1) Safe against tube-rollers
2) Deep bass, less dependence on output capacitor used (safe against cap-rollers
) 3) Quieter pops on switch on/off than without a feedback from a headphone out
4) No so called common-mode distortions than with feedback to cathode that introduces them
5) Longer life of tubes (self-adjusted bias)
6) Nice glow of LEDs when tubes are ready to sound
One disadvantage: reversed polarity. But who hears that?
By the way, for stereo may be used 6N1P (left tube) and 6N6P (right tube); the same number of tubes, but differently arranged.
Something like IRF610 may be used instead of a right tube, so only one 6N1P is needed for a stereo amp.
Kaidanovsky said:
VR55 and VR101 may be used as the left triode (voltage amplifier), just ground anodes of both diodes: you don't need them. They need 6.3V filament voltage. MHL4 will need 4V filament voltage, and is probably in demand by owners of hundred years' old radios. VR65 may be tried in the cathode follower (right part). Anyway you will need to tweak that 4.7 Ohm resistor to get about 80 V on cathode of the cathode follower.
But in such case you will have a bar of bottles instead of couple of tiny tubes. How about your small size requirements?
More about tubes: http://www.john-a-harper.com/tubes201/
Wavebourn said:
Well known to tech people, but for ones that wonder why such names, the answer is these are Greek composite words. First part is number*, rest is ''way''. So diode = two way, triode = three way, tetrode = four way, pentode = five way.
*dyo = two
tria = three
tessera = four
pende = five
0dos = way
ano = up (anode=way up)
kato = down (cathode = way down)
I did some Greek with my Latin A-Level but wasn't aware of 0dos, ano or kato - I realised the numerical prefix but didn't know the reasoning behind the "ode". It makes a lot more sense now - thank you! I had some hazy idea it was to do with pins so I couldn't understand why my 300Bs are triodes but with four pins! I should have guessed, what with diodes and all that that internal element number is much more sensible.
So I'm using each tube to drive itself, effectively, meaning two for stereo? So your diagram actually shows two halves of one valve? If so I'm getting close to understanding.
So does this mean that there are for example dual pentodes with 1/2 the valve per pentode, like there are dual triodes?
I wouldn't be using the VRs for my one, I thought if this worked out well I'd knock up another with my brother using them to see what happens...
I should have guessed, what with diodes and all that that internal element number is much more sensible. So I'm using each tube to drive itself, effectively, meaning two for stereo? So your diagram actually shows two halves of one valve? If so I'm getting close to understanding.
So does this mean that there are for example dual pentodes with 1/2 the valve per pentode, like there are dual triodes?
I wouldn't be using the VRs for my one, I thought if this worked out well I'd knock up another with my brother using them to see what happens...
There are a few dual pentodes in one bottle, but at least 10 pins are needed to bring out all the connections - so some have elements tied together, which reduces your design options.
For anyone else that wants to build this circuit, the 6DX8 (common and cheap) is the same tube as the PCL84 but with a 6.3V heater. With different pin connections, the 6CX8, 6JE8, 6EB8, 6HF8, 6GN8, 6LQ8, 6LY8 should work as well, and maybe the 6AU8, 6BH8 and 6AW8 would do at reduced plate current.
For anyone else that wants to build this circuit, the 6DX8 (common and cheap) is the same tube as the PCL84 but with a 6.3V heater. With different pin connections, the 6CX8, 6JE8, 6EB8, 6HF8, 6GN8, 6LQ8, 6LY8 should work as well, and maybe the 6AU8, 6BH8 and 6AW8 would do at reduced plate current.
I wouldn't put ANYTHING on my head that was remotely connected to a valve, but there's no accounting for taste.
For anybody contemplating it, you should first read about some of the safety issues as discussed somewhere on this guy's site:-
http://www.tubecad.com/
It's quite interesting generally on the subject of tube design.
w
For anybody contemplating it, you should first read about some of the safety issues as discussed somewhere on this guy's site:-
http://www.tubecad.com/
It's quite interesting generally on the subject of tube design.
w
Kaidanovsky said:I've ordered the parts - watch this space...
Good luck!
By the way, you need 30 VA transformer for B+ and 40VA for 15V (if you did not calculate yet)
I've googled for Morgan Jones, it consumes less because it is loaded on a modulated current source instead of on a plain resistor. But it is more critical to tubes used. Also, a current source load is overmodulated, so plate resistor's value should be decreased a lot. I personally would implement a feed-forward modulation of CCS instead of a feedback one like in Morgan Jones, so the thingy would work much better on the real complex load that differs from a plain resistor. If you don't afraid of adding transistors to tube gear I'll show you how.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.