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Small tube amp based on 6N6P

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Hello!

I'm thinking of building a small mono-speaker with integrated amp.

The speaker element I will use is a 4", and has a sensibility of 94dB.

Does anyone have a very simple and good schematics or idea for how to build the amp?
I haven't decided if I should go with PP or SE, would you think SE could be power enough?

Maybe this schematic is something to use? The SE looks quite easy, though I don't understand the "Parallel"-thing:
a_qrps.gif


Please comment!

Could this be a good transformer to use?
Link to datasheet

What do you think of these speakers?
Link to product page of speakers

Here are some info on the 6N6P
Introduction to 6N6P

/M
 
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I've looked at the specifications for the 6N6P.
It's an interesting tube and may sound good as the output stage in a SE configuration.
Both sections in parallel.
You'll need another stage or two to drive the 6N6P.
What are your thoughts on the input/driver stage(s).

I've built a couple of SE amplifiers using 6BM8 triode/pentodes and with 6DN7 dissimilar triodes.
I have no experience with the 6N6P tube.

I'd like to know the outcome of your project.
 
I've looked at the specifications for the 6N6P.
It's an interesting tube and may sound good as the output stage in a SE configuration.
Both sections in parallel.
You'll need another stage or two to drive the 6N6P.
What are your thoughts on the input/driver stage(s).

I've built a couple of SE amplifiers using 6BM8 triode/pentodes and with 6DN7 dissimilar triodes.
I have no experience with the 6N6P tube.

I'd like to know the outcome of your project.

Thanks for your very quick reply!
Since this is my first DIY-tube-experience, I'm not sure what I need. I thought the 6N6P tube it self was enough for a so small speaker, I'm thinking 4-6 watt. I might need to study the SE theory first...

I hope you have patience ;)
 
6N6P is roughly similar to ECC99, but with 6.3V heater only. Its electrical characteristics are pretty close to 5687 as well.

http://www.lampizator.eu/UPGRADE/RU-6N6P.pdf

Figuring its rp is about 2k ohms (at most common op points), paralleled you'd get rp = 1k ohms. Plate dissipation for both plates combined is spec'd at 8W. Mu is about 20. Max plate voltage is 300V.

Using that info, you could actually use two 6N6P bottles per channel to make a push-pull-parallel (PPP) amp with B+ supply of 300V. Each 6N6P section should be set to draw 12.5mA quiescent, so each bottle (two paralleled triode sections) would draw 25mA. I figure the grid bias will need to be about -15V. For cathode-bias, the plate-cathode voltage would be 285V. That works out to a bit over 7W plate dissipation per 6N6P bottle.

Since the driver would only need to deliver 30V peak, it might be possible to use a 6DJ8 in a concertina (cathodyne) configuration as the driver -- if you don't use a global negative feedback network around the circuit. The driver stage's plate current would need to be fairly high, since the input capacitance of the 6N6P is fairly high (Cmiller is more than 100pF per triode section, so >200pF per bottle paralleled). Maybe couple a 6DJ8 section to a MOSFET concertina phase splitter?

A 20W PP OPT with impedance of maybe 6k6:VC should work. I'd expect no more than about 3.5W per channel. 8k:VC would give you a little less power, a little lower distortion.

One thing to keep in mind is that 6N6P uses a lot of heater power, 6.3V at 750mA per bottle. If you did the PPP idea above, you'd use 3A of heater power per channel, which is about the same heater power a pair of EL34 or KT88 would use.

Anyway, just thinking out loud. I've used this tube as a single-ended line stage and as a differential PP driver, but not as an output tube. Might be worth a try...

--
 
And 6n6p-I has a 900mA heater.

I have an OTL headphone amp that uses one 6n1p-ev and one 6n6p-i per channel. Works great.

6k6 sounds about right for PPP 6n6p. The 6n6p PP output circuits I've seen used a 12k opt. Edcor's XPP15-8CT-7.6K might be a good one for PPP 6n6p.
 
Hello!

I'm thinking of building a small mono-speaker with integrated amp.

The speaker element I will use is a 4", and has a sensibility of 94dB.

Does anyone have a very simple and good schematics or idea for how to build the amp?
I haven't decided if I should go with PP or SE, would you think SE could be power enough?

Maybe this schematic is something to use? The SE looks quite easy, though I don't understand the "Parallel"-thing:
a_qrps.gif


Please comment!

Could this be a good transformer to use?
Link to datasheet

What do you think of these speakers?
Link to product page of speakers

Here are some info on the 6N6P
Introduction to 6N6P

/M

Let me level with you here. While it's kind of neat to build these cute little under powered amps that may be used in a small surrounding,asking a driver to do the job of an output tube is pushing it..Being this is your first DIY project,why not build an EL Cheapo that has much more versatility in that you can use it to power most any speaker 89db and above.Once you source the power and audio transformers for this project,you are going to have all this mass and expense that may run more money than the higher wattage PP amp and then you will no doubt be defeating some of your intended purpose..I'm not saying don't build the amp in question but it is very limited in what it can accomplish. JMHO.
 

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I live about 20 miles from you.

I've looked at the specifications for the 6N6P.
It's an interesting tube and may sound good as the output stage in a SE configuration.
Both sections in parallel.
You'll need another stage or two to drive the 6N6P.
What are your thoughts on the input/driver stage(s).

I've built a couple of SE amplifiers using 6BM8 triode/pentodes and with 6DN7 dissimilar triodes.
I have no experience with the 6N6P tube.

I'd like to know the outcome of your project.

I'm in Saginaw.
 
I played a little with LTSpice studying what I could get with a 6N6P as push-pull.
The tube seems very linear even when driven to A2, so I desided to use op-amp as a driver. The tube is biased to 4W dissipation/triode with 10 V zeners to
have the possibility for A2 drive and direct coupled amplifier/driver.
The result is quite surprising; 7W out with 0.03% THD.
The required drive voltage is about 33 Vpp, which means that NE5532 with max. allowed supply voltage would be sufficient driver.
The grid drive goes some 6 V(peak) positive and LTSpice shows 2.7 mA(peak) grid current. This is quite low value and I am not sure if it is close to reality.

Any ideas/comments ?
 

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I played a little with LTSpice studying what I could get with a 6N6P as push-pull.
The tube seems very linear even when driven to A2, so I desided to use op-amp as a driver. The tube is biased to 4W dissipation/triode with 10 V zeners to
have the possibility for A2 drive and direct coupled amplifier/driver.
The result is quite surprising; 7W out with 0.03% THD.
The required drive voltage is about 33 Vpp, which means that NE5532 with max. allowed supply voltage would be sufficient driver.
The grid drive goes some 6 V(peak) positive and LTSpice shows 2.7 mA(peak) grid current. This is quite low value and I am not sure if it is close to reality.

Any ideas/comments ?


Op amp? Why not simple lowgain tube differential connected ex. 12au7 ?

Papparazzi
 
Which 6N6P model did you use?

.SUBCKT 6N6P 1 2 3 ; P G C (Triode)
*
+ PARAMS:
*
+ MU=17.04
+ EX=1.648
+ KG1=949.4
+ KP=151.26
+ KVB=300.0
+ VCT=0.00
*
* russian manual 21-Nov-2011
*
+ RGI = 2000
*
* Ccg = 4.4P+0.7P=5.1P
* Cgp = 3.5P+0.7P=4.2P
* Ccp = 1.85P+0.7P=3.55P
*
+ Ccg = 5.1PP
+ Cgp = 4.2P
+ Ccp = 3.55P
*
E1 7 0 VALUE={V(1,3)/KP*LOG(1+EXP(KP*(1/MU+V(2,3)/SQRT(KVB+V(1,3)*V(1,3)))))}
RE1 7 0 1G
G1 1 3 VALUE={(PWR(V(7),EX)+PWRS(V(7),EX))/(KG1)} ; (2*KG1) ???
RCP 1 3 1G ; TO AVOID FLOATING NODES IN MU-FOLLOWER
C1 2 3 {CCG} ; CATHODE GRID
C2 2 1 {CGP} ; GRID-PLATE
C3 1 3 {CCP} ; CATHODE-PLATE
D3 5 3 DX ; FOR GRID CURRENT
R1 2 5 {RGI} ; FOR GRID CURRENT
*
.MODEL DX D(IS=1N RS=1 CJO=10PF TT=1N)
*
.ENDS 6N6P

what value of leakage inductance did you use for your OPT...

I did not determine the leakage inductance, just the "K" of the OPT. ( 0.99995)
This should give the same result.

Why not simple lowgain tube differential connected...

Because I wanted to drive the 6N6P to A2 i.e. to positive grid voltages with simple means. This requires current from the driver stage. Can be done with tubes but not that easily as with op-amp.
 
I'm surprised that you can get 7W out from a single 6N6P (two triodes push-pull) at only 0.03% THD. That seems too good to be true. Have you tried running your simulation with different 6N6P models? Or try it with a known-good 5687 model, since that is a very similar tube. If the output power and THD results hold up with a variety of models, then I'd say you have a real winner there!

Edit to add: What is the DCR of the transformer windings? What happens if you reduce the K value to something closer to a less ideal transformer, like 0.99986? High frequency extension will decrease, but THD may be influenced as well.
--
 
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I agree, the THD seems too good to be true. The low value of THD is of course partly due to >12 dB of GNFB.
I also expect much higher grid current than shown by the simulation.
Anyhow, I plan to build a prototype.

If you have an other 6N6P LT Spice model to test, please show here at the forum.
I do not have a model for 5687.

The resistance of the primary (a-a) is 40 ohms.

I tried K = 0.99986. No essential difference.

If you want my amplifier model (.asc), just PM me your email address.
 
music soothes the savage beast
Joined 2004
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I have ordered some edcor se trafos...but it will take some time to arrive. In the mean time i will work on power supply.

Btw. I forgot to update, I did receive edcor SE transformers, and finished the amp, but I never measured power output, since I intended it as headphone amp only, and few watts is plenty...

I did measure distortion, I may have the results somewhere. It was not bad for no feedback circuit!
 
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