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$30 tube preamp kit? What do you think?

Gary Indiana

Gary Indiana

Active Member
There are some ebay sellers from Hong Kong and China offering inexpensive tube preamp kits.
Has anyone try any of those?
What is your opinion?

I'm very tempted to get one to replace the opamp in my CD player.
There is one pictured below for $30 + shipping,
and
High End Class A tube buffer -- for around $60 plus shipping

I have no affiliation with the sellers.
 

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Maybe it's because I don't really understand how you plan to do that, but it seems like starting from scratch would be better.
 
Ive seen these and have been on the fence for awhile.
I have a modular style tube preamp now that some of these cards would swap directly (somewhat) across.
They advertise Marantz 7C phono preamp circuits and line stage etc. boards also.

I dont know about your intentions but the cost isnt outrageous.

:scratch2:

.
 
Gary Indiana said:
There ebay sellers from Hong Kong and China offering inexpensive tube preamp kits.
Has anyone try any of those?
What is your opinion?

I'm very tempted to get one to replace the opamp in my CD player.

[ Peramplifier KIT Tube 6N11 SRP] -- these are around $30 + shipping,
and
[High End Class A tube buffer -- these go for around $60 plus shipping

I have no affiliation with eBay sellers" [QUOTE

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I think you get what you pay for.
Click to expand...
 
wa2ise said:
I imagine you may use it to do something like what I did at my web page http://pw2.netcom.com/~wa2ise/radios/tubedac.htm
Click to expand...
VERY impressive! That was exactly my plan inspired by the Lampizator project.

Looking around the net for parts I came across these really cheap tube kits that look pretty well laid out and ready to stick into the box. I think, I would just stay away from Chinese transformers and probably use better electrolitic caps.

It would be great to hear from someone who used those exact kits.
 
I keep hearing good things about the SP-6/SP-8 preamp from tubes4hifi. You could pick up a PCB for around $90, shop for parts at Mouser or eBay and get a classy preamp for under $200 (or around $130 if you already have the tubes, resistors and caps). This is a lot more than $30, but looks like a solid product.

The good thing about this one is that it uses the stock Dynaco PAS transformer, they're pretty cheap at around $30 compared to what other preamp kits need. Everything else is self-contained on the PCB.
 
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Could you buy the Marantz phono preamp board and upgrade the caps and resistors to make it worth while?The bare PC board would be nice.
 
I will be interested to read your report.Electronic components are expensive,so I would think that you may want to upgrade caps and resistors.How about the power supply?
 
drillher said:
I will be interested to read your report.Electronic components are expensive,so I would think that you may want to upgrade caps and resistors.How about the power supply?
Click to expand...
Will report when it comes. The big caps look like Rubycons in the picture so they might be fine. I might put other caps in audio path though. Resistors look like metal film - so they will stay as well, unless I need to play with their values.

I just ordered a couple of Russian 6N2P tubes for $11.90 (cheaper than ebay) shipped directly from mother Russia. The pins match the Chinese 6N11 that come with the preamp.

6n11.png

6n2p.png


The Lampizator guy raved about the 6N2P so I want to try those.

From what I've seen in the photos, the board needs two AC supplies: 9 Volts and 90 Volts. And it looks like the tube heaters get stabilized 6,3 VDC which would be very nice. For the supply I might connect a couple of 9 Volt transformers with their low voltage terminals together and that way achieve all the Volts required. ;)

Meanwhile, I'm patiently waiting for shipments from Hong Kong and from Russia.
 
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drillher said:
Does the seller have a power supply board for sale as well?
Click to expand...
I think there is a +$15 version including transformer, but I wouldn't trust their transformers.
Plus, the Russian 6N2Ps will require 150 VDC vs. 90 VDC for the "original" Chinese 6N11s.

=== EDIT Feb. 8 ===

My board arrived today - Feb. 8, 2010. So, it took 15 days to arrive from Hong Kong - not too bad.

The packing was rather poor. I expected a small cardboard box, but the whole board with tubes inserted was put in clear shrink wrap and bubble wrap and all put in gray envelope with "Fragile" sticker on it. In a typical Chinese fashion it came with no instruction, schematic or any documentation whatsoever.

It is pretty well made for $30. PCB is well made double sided fiberglass. Each tube's heater has a 6 Volts regulator and the filtering caps are generous size. HV caps are 450 Volts allowing plenty of room for testing different tubes running on higher voltages.

The 6N11 heaters together draw 700 mA at 9 VAC. Nothing on the board gets too hot to work inside a CD player's enclosure, IMO - which is how I intend to use it. I will update this thread when I have a chance to hook 90 VAC to it and take it for a test drive.

Board with its packing material:
10469004.jpg


Shrink wrapped. Tubes are bent out of place but no damage done:
95687342.jpg


The board is well designed to be compact size w. 4 mounting holes:
10272001.jpg


Double-sided fibreglass PCB with plenty of grounded area:
18654795.jpg


These are the unmarked 90 VAC and 9 VAC terminals:
82531837.jpg


Heaters are fed regulated 6 VDC from two separate L7806CV:
65746762.jpg


I traced the actual schematic of a single audio channel...:
6n11preamp2.gif


...and found it remarkably similar to the LAMPIZATOR circuit:
originallampizator.jpg
 
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My 6N2P tubes arrived on Wednesday, Feb. 17.
So it took little over three weeks for them to come from Russia.
Tubes are boxed new, nicely packed in foam wrap and put in plastic envelope.

I'll jump back on this project and update the info when I have time.

6n2p.jpg


===== EDIT Feb. 22 =====

I've had a bit of a problem keeping close to 90 VDC to supply the original Chinese 6N11 tubes, so I inserted a simple 90 Volts DC regulator (blue area in the picture) into the existing circuit. It seems to do the job pretty well. Nothing in the added circuit gets even warm to the touch, so there is no need for a heatsink. I will skip the regulator, or add more Zeners to it for the Russian 6N2P tubes, which require 160 VDC.

voltregulatorblue.png
 
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jaymanaa said:
Yeh, and even if you got twice what you paid for, you would still have a 60 dollar preamp.:D
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cant agree with you guys here. ive opened up quite a few once expensive pieces of audio gear only to discover that i must have let all the magic out because their want much left in the box to justify the once outrageous price.
 
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