Hello all,
I've been given a large box of various valves by my grandfather and want to make use of some of them in a headphone amplifier. The snag is that although I know what many of them do in a technical sense (I've looked them up on tdsl and the National Valve museum sites) I don't know my splitters from my pentodes so would be extremely grateful if anyone could give some advice on which of the following valves could be of use. I believe lots of them are government surplus from the war and from RAF receivers and the like.
What I'd like to do is make a very small amplifier, rather like an "earmax", so preferably without output transformers but mains powered (UK 240V). If anyone knows of a schematic (I've checked headwize and liked the Morgan Jones version of the earmax, but thought I'd better see if I could use any of the glass I've got) please throw it my way!
Here goes:
1267
5B255M (x 2)
6H6
6J7GT
6K7
6K8
6SH7
7193
CV51
EABC80
ECC85
EF85
EM81
EZ80 (x 2)
EZ89 (x 2)
MHL4 (X 2)
PCC84
PCF80 (x 2)
PCF802
PCL84 (x 2)
PCL86
PL508
PL509
PL802
PP3/250
PY500A
SC966A
UX281 (x 2)
VP23 (x 2)
VR55 (x 6)
VR57
VR65 (x 4)
VR100
VR101 (x2)
I know a couple of those are tuning indicators, which brings me on to my other question; whether anyone has any suggestions on how to turn one of them into a signal level indicator, as I've seen on another website (URL's slipped my mind) but with a different valve.
Many thanks!
I've been given a large box of various valves by my grandfather and want to make use of some of them in a headphone amplifier. The snag is that although I know what many of them do in a technical sense (I've looked them up on tdsl and the National Valve museum sites) I don't know my splitters from my pentodes so would be extremely grateful if anyone could give some advice on which of the following valves could be of use. I believe lots of them are government surplus from the war and from RAF receivers and the like.
What I'd like to do is make a very small amplifier, rather like an "earmax", so preferably without output transformers but mains powered (UK 240V). If anyone knows of a schematic (I've checked headwize and liked the Morgan Jones version of the earmax, but thought I'd better see if I could use any of the glass I've got) please throw it my way!
Here goes:
1267
5B255M (x 2)
6H6
6J7GT
6K7
6K8
6SH7
7193
CV51
EABC80
ECC85
EF85
EM81
EZ80 (x 2)
EZ89 (x 2)
MHL4 (X 2)
PCC84
PCF80 (x 2)
PCF802
PCL84 (x 2)
PCL86
PL508
PL509
PL802
PP3/250
PY500A
SC966A
UX281 (x 2)
VP23 (x 2)
VR55 (x 6)
VR57
VR65 (x 4)
VR100
VR101 (x2)
I know a couple of those are tuning indicators, which brings me on to my other question; whether anyone has any suggestions on how to turn one of them into a signal level indicator, as I've seen on another website (URL's slipped my mind) but with a different valve.
Many thanks!
I'm about halfway done on a 6N1P variation of the Morgan Jones headphone amp.
It's a tiny push/pull amplifier using twin triodes. You would need three twin triode tubes if you want to keep things pretty. You do have a couple of pairs of triode/pentodes:
PCF80 (x 2)
PCL84 (x 2)
You may be able to build these into a a Single Ended output headphone amp, by using the triode as a gain stage and then the Pentode as a SE output stage. I don't have any schematics in mind though. I think I've got a couple of those tubes myself.
It's a tiny push/pull amplifier using twin triodes. You would need three twin triode tubes if you want to keep things pretty. You do have a couple of pairs of triode/pentodes:
PCF80 (x 2)
PCL84 (x 2)
You may be able to build these into a a Single Ended output headphone amp, by using the triode as a gain stage and then the Pentode as a SE output stage. I don't have any schematics in mind though. I think I've got a couple of those tubes myself.
What quick replies! Thanks chaps.
whitelabrat: I did think that as I've got quite a few 'ones' of the valves I'd find a workable circuit and if necessary buy the extra few valves. So those PCFs and PCLs are both triodes/pentodes? I assume that means I wire them with or without a common cathode? I'm afraid I am not confident in my ability to design an amp around the valves...would it be a very difficult exercise? Are there resources around or should I stick to either gentle modification of an existing design or something tried and tested? Bear in mind I've only built a preamp and a 300B SE so far :S Could I mod the design of the Morgan Jones to accommodate those twin triodes?
Andy: That looks a great site - I certainly haven't come across it! Thank you very much.
whitelabrat: I did think that as I've got quite a few 'ones' of the valves I'd find a workable circuit and if necessary buy the extra few valves. So those PCFs and PCLs are both triodes/pentodes? I assume that means I wire them with or without a common cathode? I'm afraid I am not confident in my ability to design an amp around the valves...would it be a very difficult exercise? Are there resources around or should I stick to either gentle modification of an existing design or something tried and tested? Bear in mind I've only built a preamp and a 300B SE so far :S Could I mod the design of the Morgan Jones to accommodate those twin triodes?
Andy: That looks a great site - I certainly haven't come across it! Thank you very much.
Take a peek at tubedata.org. You'll get a better idea of what you have in your stock. If you're really set on doing the Morgan Jones design, I'd say just go with the ECC88's. I think they're a bit pricey for me so I've gone with a 6N1P design instead and I may use a 6bq7 on the input side just for giggles.
I don't have any good tools for design, aside from my brain which isn't very reliable. You would likely have to do some serious adjustments if using anything other than the ECC88. For example the 6N1P needed a lot more voltage to get it's best performance. That and the heaters draw a lot more power. Bruce Bender's variation on the Morgan Jones design uses a similar topology, but different values on many of the parts. I believe they used pspice to calculate appropriate adjustments? The upside is the much cheaper 6N1P's.
I suppose it may be misleading to suggest that a triode/pentode could be fudged into a Morgan Jones design. Far beyond my skill, but perhaps not impossible. You would need about four PCL84's to do a push-pull I believe.
I don't have any good tools for design, aside from my brain which isn't very reliable.
You would likely have to do some serious adjustments if using anything other than the ECC88. For example the 6N1P needed a lot more voltage to get it's best performance. That and the heaters draw a lot more power. Bruce Bender's variation on the Morgan Jones design uses a similar topology, but different values on many of the parts. I believe they used pspice to calculate appropriate adjustments? The upside is the much cheaper 6N1P's.I suppose it may be misleading to suggest that a triode/pentode could be fudged into a Morgan Jones design. Far beyond my skill, but perhaps not impossible. You would need about four PCL84's to do a push-pull I believe.
I'm not set on anything at the moment, it's just the Jones is the most useful schematic for me I've come across so far. I want to do this on the cheap, with the stock I've got, or at least based on it. I'm afraid my brain, while not exactly reliable either, hasn't the requisite knowledge to infer what does what from the data I've already gleaned from tdsl et al! I'll try tubedata though and see if I get further. I'm looking at buying Morgan Jones's book in case that makes things clearer... I wouldn't really want to fudge too much...it's probably a little too much to ask! I expect another basic design would be more appropriate to my needs. I was taken by the small size though...
I'll try tubedata though and see if I get further. I'm looking at buying Morgan Jones's book in case that makes things clearer... I wouldn't really want to fudge too much...it's probably a little too much to ask! I expect another basic design would be more appropriate to my needs. I was taken by the small size though...
Wavebourn: That's a very cool idea. I wanted to make this because I hope to soon get some Grado headphones and wanted them to feel at home. Probably the SR60s as the SR80s with their harder foam earpieces were rather uncomfortable for me. This gives me an impedance of 32 Ohms and a sensitivity of 98dB/W/m. I wouldn't know what relation that would have to the necessary power...what would you advise?
Kaidanovsky said:I'm not set on anything at the moment, it's just the Jones is the most useful schematic for me I've come across so far. I want to do this on the cheap, with the stock I've got, or at least based on it. I'm afraid my brain, while not exactly reliable either, hasn't the requisite knowledge to infer what does what from the data I've already gleaned from tdsl et al!
I don't believe you are going to drive Morgan Jones' headphones, I believe you are going to drive yours?
I suggest you to start from research: what power need headphones, and what impedances do they have. Depending on that you may design an optimal topology for set of headphones you are expecting to use, with tubes already available.
Kaidanovsky said:
Be careful with numbers: 98 dB/ 1 mW!
You can blow out your brain applying 1W.
Let's say, you need 20 mW only. So on max power voltage will be square root of 32*0.02 = 0.8V
It means peak voltage = 0.8V * 1.4 = 1.12V
Current = 0.02 / 0.8 = 0.025A,
peak current = 0.025 * 1.4 = 0.035A
What that means?
That means any available tube from your collection when used with output transformer can drive them, but when used without transformer it must work well on idle current of 35 milliamperes (70 milliamperes for a headroom).
Pentode part of PCL84 can do that, that's why I suggested to use it.
You may use a triode part of it for a voltage amplification, while a pentode part may be used as a cathode follower.
Here is it: http://www.r-type.org/pdfs/pcl84-1.pdf
Now, you need to provide power. The simplest way is to use 2 small door bell transformers with 15V secondaries: you will use one transformer to obtain 15V for filament, and another one to obtain from 15V again 120V, but isolated from the outlet. Rectified it will be 170V, enough to drive your tubes.
Have I got it wrong? I thought sensitivity/efficiency was measured in decibels per watt per metre distance from the speaker. Is that not 98dB/W/m?
Obviously 98dB coming through a headphone earpiece would not be pleasant! 98 was the figure quoted on the Grado website. Are you working backwards from that, assuming I need XdB, which would be Y% of a Watt, P=I^2R etc.?
I apologise for all the questions but I'm trying to learn and understand
So the PCL84s would be fine with no output transformers, but as an exercise I could find the idle current flow of the others and use 70mA as the necessary figure.
Why is the idle current of the valve the peak current of the headphones, not the same on each (idle current=no sound, peak current=loudest sound)? Or am I getting muddled...
Thank you very much for your continued help - it's much appreciated.
Obviously 98dB coming through a headphone earpiece would not be pleasant! 98 was the figure quoted on the Grado website. Are you working backwards from that, assuming I need XdB, which would be Y% of a Watt, P=I^2R etc.?
I apologise for all the questions but I'm trying to learn and understand
So the PCL84s would be fine with no output transformers, but as an exercise I could find the idle current flow of the others and use 70mA as the necessary figure.
Why is the idle current of the valve the peak current of the headphones, not the same on each (idle current=no sound, peak current=loudest sound)? Or am I getting muddled...
Thank you very much for your continued help - it's much appreciated.
Kaidanovsky said:
No, 98 dB in specs are given for 1 mW output, directly to your ear.
Read carefully! It is sometimes dangerous!
I assumed you need up to 120 dB max, a jet airplane motor level of sound.
Now, you have a schemo for your tubes and for your headphones.
Build and try, or discuss with other people on the forum who has many different tastes!
Kaidanovsky said:
A positive peak will be provided by a tube, while a negative peak will go from the resistor in it's cathode. To get it you have to divide a idle voltage on it minus a negative peak by that resistor's value: more of a negative swing it can't give.
Probably, 70 mA is too much since headphone speakers are less reactive than guitar speakers so unlikely they will draw twice of current.
In the schemo I've designed for you working point and an AC voltage gain are determined by feedbacks (2 loops: one for AC, another for DC)
Tweak R3 to balance between negative current peak and power consumption.
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?
Why the LEDs on the cathode of the first stage? Just in lieu of resistors?
Power wise, if the current's 70mA then it's outputting 15mW?
Why the LEDs on the cathode of the first stage? Just in lieu of resistors?
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