1st build, need a little help

DFMoore · Post by **DFMoore** » Fri Jan 06, 2012 12:56 pm

OK, There is a short jumper wire from the resister to ground, It gets washed out in the photo.

I removed the wire, from the 68K resister (from the input) and probed it. It pops and gets louder as I adjust the volume, however it is still the very, very low volume I have been getting.

I reconnected the above, removed the wire from pin 7 (that leads to the volume pot) and probed. It pops as well.

Tillydog · Post by **Tillydog** » Fri Jan 06, 2012 2:04 pm

DFMoore wrote:There is a short jumper wire from the resister to ground, It gets washed out in the photo.

Ah, OK.

Sorry if I've missed it, but have you tried it with a different speaker & speaker cable?

I know it was suggested above, but have you tried disconnecting the NFB? (The wire back from the output jack to the 22k resistor.)

Check for shorts at the output jack (I can't see very well from the photos, but the solder on the tip lug it looks very close to the jack sleeve, itself.

Other than that, it's going to be worth re-flowing / remaking most of those solder joints.

I'll butt-out now!

Andy

DFMoore · Post by **DFMoore** » Sat Jan 07, 2012 5:32 pm

I tried a different speaker and cable with no change in results. When I remove the NFD I get a constant low volume hum.

I plan on re-flowing the solder joints.

Thanks for the input.

DFMoore · Post by **DFMoore** » Sat Jan 14, 2012 5:16 pm

I finally got a chance to get back at it. I have cleaned up the solder joints and i have traced back over the schematics. I have pins 2 and 7 reversed from the schematic, but the original layout i used had these reversed. Just to be sure can someone advise me if these two pins indeed are reversable on a 6h2n-eb tube?

tubeswell · Post by **tubeswell** » Sat Jan 14, 2012 5:33 pm

DFMoore wrote: Just to be sure can someone advise me if these two pins indeed are reversable on a 6h2n-eb tube?

Trying to find 6h2n-eb is like looking for a needle in a haystack. Got a link to the datasheet handy?

DFMoore · Post by **DFMoore** » Sat Jan 14, 2012 5:56 pm

Try this

http://www.tubes.ru/techinfo/HiFiAudio/6n2p.html

tubeswell · Post by **tubeswell** » Sat Jan 14, 2012 6:04 pm

Pins 2 and 7 are the respective grid pins for each triode. Are you wiring the triodes in parallel? If so, then you connect pins 2 and 7. But if you are using the triodes separately, then keep the grids wired separately.

martin manning · Post by **martin manning** » Sat Jan 14, 2012 6:07 pm

You can straighten this out yourself with a little knowledge. Pins 2 and 7 are the grids of the two triodes in the tube. The two triodes have plate, grid, and cathodes connected to 1,2,3, and 6,7,8, respectively. You can use either triode for stage one and the remaining one for stage two, but you have to swap all three terminals. The input stage gets the 68K from the input jack tip (pin 2 or 7), has a 1.5k resistor to ground (pin 3 or eight), and a 0.02uF coupling cap and 100k resistor from the plate (pin 1 or 6). If your amp is laid out like the diagram at the beginning of this thread, it looks like it'd be more convenient to use the 6,7,8 triode for the input stage.

Edit- in this picture, you're using the 123 triode for the input stage, and the plate and cathode connections look correct.

DFMoore · Post by **DFMoore** » Sat Jan 14, 2012 6:18 pm

OK, i got it. The layout is used does use pins 1,2, and 3 for the input stage.

Thanks for the bit of knowledge.

David

RJ Guitars · Post by **RJ Guitars** » Sat Jan 14, 2012 11:48 pm

For those not familiar with the 6N2P tubes, they are Russian tubes that use the same tube pin out as a 12AX7, except the heater circuit is 6 volts... basically you don't use pin 9.

Structo · Post by **Structo** » Sun Jan 15, 2012 12:01 am

Here is a data sheet for the 6N2P tube

http://www.mif.pg.gda.pl/homepages/fran ... 6/6N2P.pdf

Looks like pin 9 is a shield between the triodes.

Structo · Post by **Structo** » Sun Jan 15, 2012 12:19 am

So do any of you guys have much experience with these 6N2P Russian tubes?

You can get them pretty cheap like this ad, 8 @ $12+ shipping.

http://www.ebay.com/itm/6N2P-Tubes-QTY- ... 830wt_1059

DFMoore · Post by **DFMoore** » Thu Feb 16, 2012 3:41 pm

It's Alive!!! After walking away for a few weeks and a little more trouble shooting she is singing. I found that the output tranny was fried....I'm sure it was my doing. I can't believe how loud this little amp is, I wasn't expecting this much power out of a simple circuit.

I need to thank all of you and RJ for all of the help. I can't wait to start my next build.

David

playonit · Post by **playonit** » Thu Feb 16, 2012 5:45 pm

Saweeeeet!!!!!!! way to go.............

RJ Guitars · Post by **RJ Guitars** » Thu Feb 16, 2012 6:48 pm

Congrats - that is awesome. I can recall similar struggles with some of my early efforts and when you finally get to hear it, it such a sweet sound. No doubt you have learned a ton.

There is an old saying that 5 watts is as loud as a trumpet... pretty stinking loud if you have it in your face. Lots of other facts and folklore about Led Zeppelin recordings and Eric Clapton recordings using single ended amps similar to these. Loud and they can sound pretty cool. A great tool to have in your arsenal and in case you don't have a roadie it's easy to carry the amp yourself.

Good work!

rj

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