Cheap Chinese 6P3P kit

Big & Pink

Active Member
I found this kit through another DIY forum in their vendors section.
(NO affiliation)
http://www.siliconray.com/index.php/low-price-6p3p-single-ended-tube-amplifier-kit.html

For the price it looks interesting.

The schematic is on the site. I’m curious if anyone here has had any experience with the 6P3P tube. From what I have found on the net the 6P3P is equivalent to the 6L6.

I don’t have high expectations for the amp. It looks like it would be a fun father/son kit to play with.

Thoughts and opinions?
:scratch2:
 
It looks very clean and neat. I'd like to know more about it myself. Thanks for posting this! Hope someone here can offer a qualified opinion on it.
 
I will add; I had a question about the power transformer working for US (220 to 110V) because I skimmed past that part and the seller replyed within three hours!

It looks clean enough under the hood that any future upgrades could be done with ease.
 
I like the inclusion of a choke. The circuit sucks, I'd steal from something more modern like the RH84 or a Kegger variant. In particular I dislike the giant feedback loop from the OPT secondary to the cathode of the preamp tube (as indicated by the 10K resistor at the top of the schematic).
 
I like the inclusion of a choke. The circuit sucks, I'd steal from something more modern like the RH84 or a Kegger variant. In particular I dislike the giant feedback loop from the OPT secondary to the cathode of the preamp tube (as indicated by the 10K resistor at the top of the schematic).


Because I dont know enough, how could the feedback loop be fixed? Could the 10K resistor just be removed?
 
I like the inclusion of a choke. The circuit sucks, I'd steal from something more modern like the RH84 or a Kegger variant. In particular I dislike the giant feedback loop from the OPT secondary to the cathode of the preamp tube (as indicated by the 10K resistor at the top of the schematic).


So, I better wait for the AK "Indignia" Tube Amp?
:D


>>>
 
The output iron doesn't have UL taps, so your final will either be run as a pseudo-triode, or a true pentode (where G2 is hooked to B+ or thereabouts). A decent example of a good true pentode amp would be something like the RH84/807 amp, which has a much shorter feedback loop (a 100K resistor). I'd just use the RH807 schematic and call it a day. I'd even try it with the original tubes from the amp. I'd be prepared to switch out the front-end tube for a 12AT7, but the finals would likely stay.
 
Schematic


6P3Psch.jpg
 
Because I dont know enough, how could the feedback loop be fixed? Could the 10K resistor just be removed?

I would say no...because the penthode is a high impedance device..its need the feedback to provide low output impedance. However it could be triode coupled...then it would work with less or no feed back but the output would be reduced to 3,5W

The schematic shown here employes ultraliniar OPT...much better than clean penthode but would require another OPT...
best
 
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This, I believe, is the schematic for the kit in question as it comes from the maker. You can see the lack of UL tap and the 10K resister that Squidward was objecting to. I think. Correct me if I'm wrong here.

6p3p-sch.jpg
 
Everything can be modified...however this amplifier I think work best as it made. The goal is a cheap amplifier and so it is. They could have made an UL option...that should not have bin to costly.
 
This kit looks like a huge bargain to me. It's probably a great way to get started fooling around with tube amps.

I'm not a big fan of amp designs that leave the OPT outside the feedback loop. That's often a sign that the OPT is so poor that the amp would oscillate if it was included, and load coupling is likely to be rather loose. This design includes the OPT, and does so without any circuit tweaks to patch up stability problems. The feedback network is just a simple resistive divider. The tradeoff is probably that total feedback or 'loop gain' is not very great, which could lead to some audible SGD (spectral growth distortion), but who's to say without buying in?
 
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The output iron doesn't have UL taps, so your final will either be run as a pseudo-triode, or a true pentode (where G2 is hooked to B+ or thereabouts). A decent example of a good true pentode amp would be something like the RH84/807 amp, which has a much shorter feedback loop (a 100K resistor). I'd just use the RH807 schematic and call it a day. I'd even try it with the original tubes from the amp. I'd be prepared to switch out the front-end tube for a 12AT7, but the finals would likely stay.

If I am interpreting you correctly, I would essentially be trying to polish a turd unless I abandon the original schematic, go with the RH807 scheme, use UL OPT and sub the 6N1 with the 12AT7?

I am a luddite. If you would, explain "G2". Are you referring to the second ground, next to the rectifier?

I went ahead and bought the kit. My plan is to build the kit as it is, listen to it, understand or learn why the circuit is or is not a POS, and then make any suggested changes. This kit looks sparse enough that it could be gutted with relative ease and reworked.

Any suggestions for OPT with UL? Edcore perhaps?
 
Go ahead and build it with the original schematic, you're out nothing there. An upgrade path would possibly be the RH807 schematic, but BinaryMike brings up concerns that the original schematic is based on an inferior output transformer and would be best used as presented.

The RH schematics do not use a UL tap, I suggested them to use what iron is available. If one did go the RH route, they might consider experimenting with the input tube, hence the suggestion of the 12AT7 (which the RH schematic specifically calls for).

G2 is the second grid of the pentode output, it's a physical feature of the tube.

Go ahead and get the kit and experiment, looks like a good deal to play with tubes!
 
Thanks Squidward.

I will build it as is. Then I will study the RH807 schematic.

Shematics are my weak point. This is not my first tube amp. I built one of Bob Latinos ST-70's, but I learned nothing about schematics from the build. His instructions are very well laid out, like a paint by numbers kit. Solder this, solder that, check the volts here, bias there & listen.

Just so I can be crystal clear...

BinaryMike brings up concerns that the original schematic is based on an inferior output transformer and would be best used as presented.

The Chinese scheme or the RH? I'm assuming the Chinese one.
 
I'm sure it can't be beat for the price. I think there are only two wires to move if you do change to 12AT7.
 
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