Just for fun: $160 Douk 6N2 + 6P1 tube amplifier kit

[JeffS7444]

There's no particular logic behind this particular purchase, except that I had fond memories of a similar 3-tube amplifier I once owned: Just a few watts of power, but that older amp sounded decent, and didn't radiate too many BTUs into the room, so using it in mid-summer was an option. It may be another month or so before I officially start this project, and am planning on doing it at a leisurely pace

I do like what I'm seeing in this kit! Main part of chassis is brushed stainless steel (shown here still in it's protective wrapping. And they definitely got the nostalgic touches with the burly toggle switch and bakelite volume control knob. I'm not sure what kind of wood the side panels are made of, but the lacquered finish is surprisingly well done. Supplied tubes include a Beijing 6N2, and a pair of Shuguang 6P1s.

Assembly instructions are very basic: Just a parts list, and the schematic as shown. Which is no problem for me, as it's a simple circuit, and I've assembled a number of tube amplifiers previously. Looks to be your basic single ended ultralinear design, and super-easy to tune via the feedback loop.

Minor gripe: The edges of the sheet metal chassis were only roughly finished, and though they won't be visible once the amp is assembled, I spent an hour smoothing those areas, just because.

 

[mhardy6647]

Adorable.
Kind of a minimalist P/S design.
Does the kit use point to point or PC board construction?

 

[DWPress]

Hope you keep this thread updated as you build. Adorable indeed!

 

[mhardy6647]

So... according to the internet -- the 6N2 is a high mu twin triode, functionally very similar to a 12AX7, but with two 6.3 VAC heaters in parallel (only), rather than the center-tapped 12.6 VAC heater arrangement of the 12AX7.
The 61P is a beam power output tube, essentially equivalent to a 6AQ5 or 6V6 but in a 9-pin miniature envelope.

Do "we" know if the Douk outputs are wired as triodes or as pentodes? If the latter, are the run ultra-linear or otherwise?
I cannot quite make out the schematic in the photo posted earlier (translation: I am too lazy to try too hard to read it ).
EDIT: N'ermind -- it was easier to read than I expected it to be.

 

[restorer-john]

It's very cute!

 

[Ron Texas]

Soldering therapy...

 

[mhardy6647]

Soldering therapy...

Rosin core 60/40 smells better than napalm in the morning.

 

[JeffS7444]

Couple of details which are not noted in the schematic:

No specific instructions are given regarding Earth ground, so current plan is to connect Earth terminal to the chassis, and from the chassis, I thought I'd borrow an idea from Pete Millett and connect Earth to power supply ground via a set of series diodes. His writeup of Engineer's Amplifier has a brief description of this "ground loop breaker" circuit: http://pmillett.com/DCPP.htm

Then, there's a mysterious green/yellow wire on the primary side of the power transformer. Not sure, possibly I could connect to power supply ground, else leave unconnected. Manufacturer photos appear to show it soldered to the power supply capacitors.

My original intent was to use all of the original parts. I've never heard of Samxon or Sam Young-brand capacitors, and the latter seems like they're trying to pass as Panasonic parts at a casual glance, but whatever, they're probably fine. But I'm feeling less confident about the main power supply capacitors, which yes, are actually branded as "NAPFCM CEBNYCON".

 

[mhardy6647]

a priori I like your grounding idea(s).
I certainly'd be wary of all of those electrolytics -- but it's "only" $160 for a reason (perhaps for many reasons).

EDIT: Since (as is written in Ecclesiastes 1:9) there is nothing new under the sun, I just looked for threads about this amp (or as close as I could get) at audiokarma. You might (or, frankly, might not) enjoy leafing through this thread:

Douk Audio Tube Amplifier Kit Assembly Advice Needed!

Hi all! I've had the fun pleasure of assembling electronic kits since the P-board offerings from Radio Shack! From there, I've assembled Heathkit and Dynaco kits in the 70's. I was even able to bring an HK A50K back to life, which I had posted on this forum. What they all had in common was that...

audiokarma.org

and/or this much shorter one

Douk Audio Amplifier Kit - It's Alive!!!

Hi all! Drum roll please!! I just completed my Douk Audio Amplifier kit and am ecstatic to report that it is complete...and sounds excellent! I had visions of it going up in smoke when I flipped the power switch, or at least be greeted with lots of hum! The output is hum-free and makes my...

audiokarma.org

I mean, the guy was successful in getting it to work

 

[JeffS7444]

a priori I like your grounding idea(s).
I certainly'd be wary of all of those electrolytics -- but it's "only" $160 for a reason (perhaps for many reasons).

EDIT: Since (as is written in Ecclesiastes 1:9) there is nothing new under the sun, I just looked for threads about this amp (or as close as I could get) at audiokarma. You might (or, frankly, might not) enjoy leafing through this thread:

Douk Audio Tube Amplifier Kit Assembly Advice Needed!

Hi all! I've had the fun pleasure of assembling electronic kits since the P-board offerings from Radio Shack! From there, I've assembled Heathkit and Dynaco kits in the 70's. I was even able to bring an HK A50K back to life, which I had posted on this forum. What they all had in common was that...

audiokarma.org

and/or this much shorter one

Douk Audio Amplifier Kit - It's Alive!!!

Hi all! Drum roll please!! I just completed my Douk Audio Amplifier kit and am ecstatic to report that it is complete...and sounds excellent! I had visions of it going up in smoke when I flipped the power switch, or at least be greeted with lots of hum! The output is hum-free and makes my...

audiokarma.org

View attachment 366719
I mean, the guy was successful in getting it to work

Oof, not a fan of soldered connections floating in mid-air, but nice to know it's working for him!

 

[JeffS7444]

As delivered, the stock RCA jacks and binding posts needed some reworking before I could fasten them firmly to the chassis, and they're not keyed so as to prevent the non-rotating parts of the connectors from being spun about, but hopefully, a bit of adhesive will remedy the latter.

I remembered that I had some turret boards and perf board sitting in my pile 'o junk, and they ought to help tidy up the wiring, and give me plenty of solid anchor points. Because I really don't like "floating points" in my p-to-p wiring.

 

[JeffS7444]

It's time to install the turret board, but I didn't have any standoffs in my junk box, and I wasn't keen to make a Mouser / Digikey order for such small items. So I decided to design and 3D-print my own. They'll be anchored to the chassis with adhesive, and the turret boards will in turn be affixed with cable ties, hence the 4 mm holes.

 

[Stanton]

It's time to install the turret board, but I didn't have any standoffs in my junk box, and I wasn't keen to make a Mouser / Digikey order for such small items. So I decided to design and 3D-print my own. They'll be anchored to the chassis with adhesive, and the turret boards will in turn be affixed with cable ties, hence the 4 mm holes.
View attachment 373410

As delivered, the stock RCA jacks and binding posts needed some reworking before I could fasten them firmly to the chassis, and they're not keyed so as to prevent the non-rotating parts of the connectors from being spun about, but hopefully, a bit of adhesive will remedy the latter.

I remembered that I had some turret boards and perf board sitting in my pile 'o junk, and they ought to help tidy up the wiring, and give me plenty of solid anchor points. Because I really don't like "floating points" in my p-to-p wiring.

View attachment 373033

Looking forward to following your progress in these pages.

I bought one of these just for fun too. I've posted in another forum about it but if it's ok I'd like to also post here.

I've bought this kit in the last few months from Aliexpress for a first valve amp build but am yet to start.

On YouTube, "xraytonyb" has an 11 part series based on building this kit point-to-point.

The series/playlist is titled "Electronics 101½".

He says he didn't choose this kit for any particular reason but simply as an exemplar for demonstrating and explaining valve audio concepts.

While going through the build, where immediately relevant, he digresses into theory with practical "mini-tutorials" that include simple demonstrations and testing.

Overall, as a beginner with a bit of basic knowledge, I found the series very informative and easy to watch.

I purchased this kit after viewing the series.

Of interest to me as an aspiring builder with no more than a multimeter and ancient oscilloscope for test equipment is that he tests an output transformer and concludes that they are of reasonable quality and fit for purpose.

In the final video of the series (Number 11) he does a frequency sweep and distortion measurement of the amp and then runs the viewer through a couple of simple modifications to improve the overall frequency response and significantly lower the total distortion.

I won't attempt to describe or convey those mods here but suggest that others who are interested in either building the kit or have already built the kit, whether pcb or point-to-point, may find some material of interest in the series and particularly in the final video as mentioned above. Xraytonyb also has a marked up cirucit diagram I think in his Video 11 to show the resistor changes that he did.

I'd be interested to know how you go with the build generally and with the power transformer. I ordered a 230V version for Australian mains but received a 220V mains transformer. Also the 6.3V winding is marked as 3A so not sure how the transformer will go in the long run.

 

[JeffS7444]

Looking forward to following your progress in these pages.

I bought one of these just for fun too. I've posted in another forum about it but if it's ok I'd like to also post here.

I've bought this kit in the last few months from Aliexpress for a first valve amp build but am yet to start.

On YouTube, "xraytonyb" has an 11 part series based on building this kit point-to-point.

The series/playlist is titled "Electronics 101½".

He says he didn't choose this kit for any particular reason but simply as an exemplar for demonstrating and explaining valve audio concepts.

While going through the build, where immediately relevant, he digresses into theory with practical "mini-tutorials" that include simple demonstrations and testing.

Overall, as a beginner with a bit of basic knowledge, I found the series very informative and easy to watch.

I purchased this kit after viewing the series.

Of interest to me as an aspiring builder with no more than a multimeter and ancient oscilloscope for test equipment is that he tests an output transformer and concludes that they are of reasonable quality and fit for purpose.

In the final video of the series (Number 11) he does a frequency sweep and distortion measurement of the amp and then runs the viewer through a couple of simple modifications to improve the overall frequency response and significantly lower the total distortion.

I won't attempt to describe or convey those mods here but suggest that others who are interested in either building the kit or have already built the kit, whether pcb or point-to-point, may find some material of interest in the series and particularly in the final video as mentioned above. Xraytonyb also has a marked up cirucit diagram I think in his Video 11 to show the resistor changes that he did.

I'd be interested to know how you go with the build generally and with the power transformer. I ordered a 230V version for Australian mains but received a 220V mains transformer. Also the 6.3V winding is marked as 3A so not sure how the transformer will go in the long run.

Thanks, I had a look at those videos - very detailed, and I like how he does a bit of circuit analysis and measurably improves the amplifier's performance. But as "xraytonyb" himself states, the videos are not intended as step-by-step assembly guides to assist you in building that specific kit, and there's a bunch of small details which he has omitted

Mine is a simpler 3-tube kit, chosen partly because it it shouldn't make the room uncomfortably warm during the summer months. Among other challenges with this kit are the holes which are pre-drilled in the chassis: They make for loose-fitting binding posts and RCA jacks, which xraytonyb mentions, but seemgly addresses off-screen.

The output transformers had some minor paint scratches, so I repainted them. I thought the bolts used to fasten the OPTs down to the chassis really needed some additional washers, so I dug those out of my parts box. Then I decided to chemically blacken + paint the lot. Now I'm fretting over whether the bluish color of the zinc-plated tube socket bolts looks awkward against the brushed stainless steel chassis. Yes, fussy little details, but they're sometimes what gives gear a higher-end vibe.

Am also stalled pending a parts order. Nothing fancy, I just wanted to use electrolytic capacitors of a known quality, but then there's the matter of which performance parameters I should prioritize: ESR? MTBF? Ripple current? And so on.

 

[WizardWG4]

Here are a few pics of mine I which I just started testing this weekend. Since I had some spare Electro-Harmonix EL84s and 12AX7s I decided to do a clone build of Dave Gillespie's modified Magnavox 8600.

https://audiokarma.org/forums/index...t-of-the-8600-series-a-lot-more.665735/page-5

Outside of the chassis and transformers, the only components I used from the kit are the rectifier, power supply caps and dropping resistor. I'll be ordering some nicer RCA connectors and speaker binding posts. The rectifier and filter caps are working fine but I may change those out eventually.

So far so good and it sounds great. It's putting out about 3.3 watts of clean power right before clipping.

One of the downsides to these kits is they ship with 110v power transformers. I have to set my variac to 112v to get the heaters right at 6.3v. That gives me a plate voltage of 238v with about 6.5v at the cathode and a 130ohm resistor. I'll end up either using a bucking transformer or resistors to drop the heater voltage and then use the extra B+ to squeeze a few more tenths of a watt out.

If I didn't already have the spare tubes I would've built as per the schematic with the 6N2 and 6P1s. I have another kit running 6P1s in triode mode. It sounds very good as well but only puts out about a watt so.

 

[mhardy6647]

One vote for bucking transformer from me!

 

[Stanton]

Thanks, I had a look at those videos - very detailed, and I like how he does a bit of circuit analysis and measurably improves the amplifier's performance. But as "xraytonyb" himself states, the videos are not intended as step-by-step assembly guides to assist you in building that specific kit, and there's a bunch of small details which he has omitted

Mine is a simpler 3-tube kit, chosen partly because it it shouldn't make the room uncomfortably warm during the summer months. Among other challenges with this kit are the holes which are pre-drilled in the chassis: They make for loose-fitting binding posts and RCA jacks, which xraytonyb mentions, but seemgly addresses off-screen.

The output transformers had some minor paint scratches, so I repainted them. I thought the bolts used to fasten the OPTs down to the chassis really needed some additional washers, so I dug those out of my parts box. Then I decided to chemically blacken + paint the lot. Now I'm fretting over whether the bluish color of the zinc-plated tube socket bolts looks awkward against the brushed stainless steel chassis. Yes, fussy little details, but they're sometimes what gives gear a higher-end vibe.

Am also stalled pending a parts order. Nothing fancy, I just wanted to use electrolytic capacitors of a known quality, but then there's the matter of which performance parameters I should prioritize: ESR? MTBF? Ripple current? And so on.

Well, I made a rookie error there confusing a 3-valve amp for a 6-valve amp. Never mind the circuit configurations!

For me at the moment the main thing is to learn skills and have some fun. A well-known amplifier designer, in another forum, once advised someone agonising over the choice of a first build more or less to not worry about circuit choice and just build something that works; then enjoy the success and learn something along the way. That way they would enjoy their first success and be encouraged to keep going.

I have just received my order of axial capacitors and other components from Digi-Key. I mainly chose components on price for this first build.

I'll be interested to see how the 220V transformer goes on 230V along with the 3A heater winding running maxed out. I have a NOS Australian made transformer from the 1960s that may be a good substitute if required.

Looking forward to following other's builds here too.