• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6418 tube preamplifier - Oatley Electronics

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Hello,
I just finised my tube entry project
the AN6418 Valve (Tube) Preamplifier / Headphone Amp Kit
its quite nice and really affordable, for the sound it self I subjetively must say it sound very clear I was missing nothing, therefore im satisfied with the kit.
see the image of the amp here http://hex.dan.sweb.cz/minitubeamp/DSC_0837.JPG

does anyone here made it as well?

For the begining I builded it as it came, but I would lilke to make a few changes so I would like to get the experience from someone else as well.

Cheers,
Imagios
 
hello,
I bought it on australian Ebay: K272 - STEREO TUBE PREAMPLIFIER - HEADPHONE DRIVER KIT - eBay Tube, Valve Amplifiers, Amplifiers, Audio, Electronics. (end time 18-Dec-09 15:46:10 AEDST)
as Oatley Elec. do not ship to Czech Republic.

Its easy to build, sound for a amateur nice. But I never lisened to a tube amp therefore please take this with some distance. newer the less I have a headphone amp self made from a kit based on the TDA7053 chip and personaly I like these tubes more than the chip. (but this must say nothing)
Im not much knowledgeable in electronics, so I build only kits. But I would for sure change some parts on the board. a potentiometer would be fine...

I would be interested to know the THD at the amp... but have no equipment to measure it.

But as a introduction to tubes I think its great 1-easy to build, few parts that you can hardly mix up, 2- low voltage (Im not skilled egnouth to play with deadly voltages) 3- good sound (subjetively on common headphones) I will as well conect this as a preamp to mi tripath amp from 41Hz to see what difference it will make.
Never the less I was not sorry to instal golden cinch to the amp and a quite expensive jack connector as you might see here http://hex.dan.sweb.cz/minitubeamp/DSC_0836.JPG

as well for thouse who might be interrested the "shine" of the petodes:
(ISO 200; 30 seconds exposition)
http://hex.dan.sweb.cz/minitubeamp/DSC_0845.JPG

the biggest problem with the amp is the ring sound comming from vibrations they suggest to use rubber grommets, that I dont have and that are not a par of the delivery(thats a pity) but I dont know how much bether it will become. I can not imagine to use this as a travel amp in a bus,car, train as I think it would ring... but to have it on stable place makes it a quite nice travel amp, desk at work, library, waiting room, what ever ...
One common 9V battery can power the amp for good 10 hours without loose of "power"
but I think to buy a Li-ion batery and make it a travel amp with rechargable embeded batery. Quite easyer than to exhange bateries.
 
Anyone know about Oakley's K261 preamp Kit.

It seems to use a smal smps to supply the 30v HT.

Oatley Electronics
 

Attachments

  • K261.jpg
    K261.jpg
    130 KB · Views: 1,371
I have one too and decided to upgrade some of the mediocre quality parts since I want to use it as a preamp with my mini Aleph in the living room.

Here's my BOM
Resistors: all resistors 1% metalfim types
Caps: C1,C2,C4,C5 MKP1837 0.1uF C7,C8 Elna Silmic ARS 220uF 25v
Trimpots: Piher 1M
Opamp: OPA2134PA

I replaced the opamp socket with a better one and connected a decoupling cap (a "104") to the supply pins on the reverse side of the PCB.

For the tubes I came up with a diy socket. I butchered a large IC socket to make two 5-in-line sockets for the tubes. Tube (re)placement now is quick & easy.

The Elna's are 12.5mm diameter and they just barely fit. I plan on using MKP1837 0.01uF bypass caps on the Elna's once I have them.

As for tube dampers I use a short piece (~32mm) of clear silicon tubing with the side cut open.
 

Attachments

  • DSC_0362.jpg
    DSC_0362.jpg
    143.8 KB · Views: 1,448
  • DSC_0363.jpg
    DSC_0363.jpg
    54.3 KB · Views: 1,258
  • DSC_0366.jpg
    DSC_0366.jpg
    91.9 KB · Views: 1,248
  • DSC_0367a.jpg
    DSC_0367a.jpg
    120 KB · Views: 1,250
Last edited:
Anyone know about Oakley's K261 preamp Kit.

It seems to use a smal smps to supply the 30v HT.

Jameco Electronics sells the power IC for $.40 each. Had to look around to find it.

Click the red (and hard to read) button on the Oatley page for this board for complete info (PDF) including a schematic.

Looks cool but shipping is nuts to North America IMHO.

Best online info about SMPS for tubes is here:

http://groups.yahoo.com/group/NEONIXIE-L/
http://groups.yahoo.com/group/NEONIXIE-L/files/Power Supply Designs/
 
Last edited:
For the tubes I came up with a diy socket. I butchered a large IC socket to make two 5-in-line sockets for the tubes. Tube (re)placement now is quick & easy.

Kewl -- Cut up SIP 'header' strips (see: 5x 40-pin Female Headers 0.1" spacing *fcbusa 5 x pcs - eBay (item 360131819147 end time Feb-09-10 12:04:59 PST)) work good too.

As for tube dampers I use a short piece (~32mm) of clear silicon tubing with the side cut open.

Wow -- great idea :) -- is it just garden variety fish tank tube? Doesn't the tube get too hot?? thx.
 
Kewl -- Cut up SIP 'header' strips ...

Check the fit of the tube leads in those 'header' strips first. I'm not sure if they will make and keep good contact.

Wow -- great idea :) -- is it just garden variety fish tank tube? Doesn't the tube get too hot?? thx.

Yup, it's just a piece ordinary silicon tubing, the open side allows for easy removal. Don't know if those tubes get hot in normal use, I have only tested mine with very cheap headphones for a short while.
From the manual:
The warmth in this preamplifier can certainly not be attributed to the heat given off by the filament: The 1.2V filament draws just 10mA! You can barely see it glow in a very dark room.
 
I built one of these, albeit I dont have a tube amplifier (yet) to compair it against, I though it sounded dead smooth and tight.

cheaper to buy from their website directly, but shipping takes best part of 3/4 weeks to the UK

I have a spare kit (I bought 3 lol) if anyone from the UK wants one that wont take 3 weeks to arrive.

drop us a PM. (I do have feedback elsewhere i.e. avforums, ebay etc)
 
Administrator
Joined 2004
Paid Member
Surely that's a mistakeon the schematic?

No, not necessarily - the effective bias for both tubes should be the same, note however that the effective plate voltage isn't because that filament is floating 1.2V above ground. I think there might be a bit of an issue with the first tube's bias as well, but apparently it works well enough in practice.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.