Chinese 6N2 / 6P1 schematics advice needed

[matose]

Hello all diy-ers,

I bought one diy tube amp from Ebay and I don’t really trust the chinese schematics they send me and I need a second opinion about it. It uses Chinese 6Z4 in parallel for rectifying AC to DC and 6N2 + 2 x 6P1 for the final stage. I will use Sylvania 6C4 NOS instead of 6Z4, Voskhod 6N2P NOS instead of Chinese 6N2 and Svetlana OTK 6P1P-EV NOS (EL82) instead of Chinese 6P1 - already ordered and on the way!

The resistors and transformers they sent in the package are fine for a first tube build, but the capacitors look fake and low quality (will order some from eBay after the final schematics). Will replace the potentiometer with japanese ALPS dual 100k and a bigger aluminum knob.

How can this schematics be modified for the best sound? I only want SE triode connection for the amp, so I’m not interested in other solutions. I prefer to stick to 6N2 and 6P1 regarding the tubes but I’m open to try other solution using better tubes that work at the same voltage (250v): EL84, EL86. I could really appreciate an answer from you if you have the time!

Output transformers (measured): primary (335-336 ohm), secondary1 (2-2.1 ohm), secondary2 (2.5-2.6 ohm)

Thanks a lot,
matose

 

[kevinkr]

Commodity Chinese tubes really aren't that bad, but it is possible that the Russian ones will sound a little better. Make sure that there are no differences in the pin out (used/unused pins typically) before you plug in the new tubes.

 

[artosalo]

How can this schematics be modified for the best sound?

The person who can do that has invented something unprecedented.
Unfortunately "good sound" varies a lot between different listener, days, mood etc,.

The schematic looks OK. That circuit is a basic pentode connected SE-amplifier.
In power supply is one mistake. The first capacitor after the rectifier may not be 220 uF. This big capacitor will ruin the rectifier very quickly.
Usually first cap is from 22 to 47 uF.

 

[matose]

Thanks a lot for the feedback guys
Hmm... what should I do to convert it to triode mode?
Also, I see that EL86 runs at the same voltage and have better specs and power. Should I search eBay for these. It will make a difference or will the 6P1P-EV will be enough?

Other tweaks of tips I should be aware before I start building. I have experience in electronics but very little in tubes, that's why I ask the specialists here.

 

[JMFahey]

Remember that these aren't "designer's designs" if you get what I mean, but product of a bunch of Chinese entrepreneurs who get together and think : "what can we make to sell to American customers and make some money?" so they typically read some Forum to know what may sell , google some schematic, order the parts from their low cost suppliers and offer the kit (or finished product) on EBay .

Don't expect much from such products.

Besides , you paid ..... how much?

They can't even write English !!!!!!

I bet if you quote them what artosalo wrote

In power supply is one mistake. The first capacitor after the rectifier may not be 220 uF. This big capacitor will ruin the rectifier very quickly.
Usually first cap is from 22 to 47 uF.

they'll look at you glassy eyed and answer: ".... huh? "

 

[matose]

I'm not trying to get 10.000 USD of sound from a 100 USD eBay amp, I'm not that naive . I'm just trying the get the best performance I can get from it, so that is what I'm asking you...

P.S: The speakers are JM Lab Laureate with 91dB sensitivity

 

[pcan]

6C4 is a triode, it is not a substitute for the 6Z4 rectifier. According to the 6Z4 datasheet, the maximum value of first capacitor is 8uF, so there is definitely a error in the power supply schematic. I guess that both filter capacitors should be 22uF. 220uF is typical for silicon rectifiers.

 

[matose]

Yes, I figured that myself out... ordered General Electric 6203 / 6X4 instead. Funny because they sent two 220uF in the package

 

[pcan]

Let's say they sent two capacitors with 220uF stamped outside. The real capacity should be measured. I also buy bargain electronic parts from China and not everything is what it looks to be, big capacitors are one of the most suspect parts (I don't buy them from China anymore). But I guess it's a mistake. Most 6N2/6P1 kits have silicon rectifier with 220uF capacitors. A untrained seller may have just put in the bag the usual part.

 

[rotaspec]

Be careful. Chinese 6C4/6Z4 rectifier has a different pinout to 6X4 western types.

 

[matose]

After some more reading I will be building the RH EL84 v2 amp, you have the schematics attached. For starters I will use the JJ 12AT7 / ECC81 for pre and JJ EL84 for the finals.
The only thing different will be the rectifiers. I will be using two General Electric 6203 tubes in parallel for a maximum current of 140mA and a 4uF motor run cap (from the 6203 datasheet).
Please let me know if you have any comments, thanks!

 

[artosalo]

LM317 at the cathode of EL84 can be replaced with a resistor.