[sashaw]

Just soldered up my board. I replaced 2sk310 with IRL510, and use CV5358 instead of 6DJ8. However, the output gives around 100mv AC and it does not work. Anyone can help? PS: I was buying resistors in a combo, so all of them are 1W rating, will that be the problem?

 

[sashaw]

I have tried the 1K trim pot so that pin3 on LM317 is 15v, however, after 13ohm and 15ohm, it gives 8v instead of 6.3v which is the tube required. can anyone suggest a solution?
 

 

[berserkir]

 
 
Finished mine, just waiting for friend of mine to do some drilling for box.
Used Panasonic FC caps 1 x 3900uF, 2 x 1800uF, 2x 470uF and Roederstein MKT1813 1uF with EH 6922 tube
Did few minutes test driving with some really old headphones and seemed to work well and the sound was awesome

 

[audiowize]

Has anybody cut the trace feeding B+ to the 6DJ8 and fed it with higher voltage?  With a 24v supply feeding the 6DJ8, how much plate voltage is there even (10-15v max??)
 
Incidentally, with the voltage regulator sitting under the fet, you could probably jack the voltage up on both stages. 

 

[nikongod]

The 6dj8 is DC coupled to the output FET. you cant really bump the plate voltage on the tube without increasing the voltage supply to the FET too. 
 
Im not sure if the heat-sinks are large enough to handle the extra heat, or if the various caps are rated adequately, but it would probably be a fun project for someone who wanted to go a little wild with it. 

 

[vmedchagr]

What happens if instead of a 100k you use a 50k or a 10k one ?

 

[curiousmuffin]

anybody tried using this as a preamp? can i wire rca outs parallel to the headphone jack without worrying about hum?
 
and do all resistors get hot? i'd like to sneak in carbon comp resistors wherever i can if i can avoid the value drift. 

 

[Zigis]

I design my own PCB variation of this amp
 

 
 
Tube's socket is on top side, all other parts on other side. PCB are double sided, designed for Alps Blue Velvet pot, 6.3mm headphone socket, large power and output caps, bias trim pot.
 

 
In my prototype amp FETs and LM317 are mounted to enclosure, however vertical heat sink can be used.

 

[sashaw]

Quote:

I design my own PCB variation of this amp
 

 
 
Tube's socket is on top side, all other parts on other side. PCB are double sided, designed for Alps Blue Velvet pot, 6.3mm headphone socket, large power and output caps, bias trim pot.
 

 
In my prototype amp FETs and LM317 are mounted to enclosure, however vertical heat sink can be used.

WOW, nice case.

 

[ludoo]

Quote:

I design my own PCB variation of this amp

 
Great job! Have you got a couple of PCBs to spare?

 

[Zigis]

Boards are double sided, with ground plan, fixed with 2 screws near tube socket and pot's and headphones jack's nuts to front
 

 
 
I have few board left, if anyone wants to try it.
1 PCB shipped are 10 Euro

 

[Zigis]

Thanks ludoo, yes I have few

 

[Zigis]

Quote:

WOW, nice case.

Thanks, actually it is fast prototype, made from piece of aluminum U profile, lot of scratches, some drilling errors. 
Idea is - black anodizing finish and side panels from good wood, walnut or bubinga. 
I made it about year ago, project stopped because of lack of time and I can't find good anodizing service locally. Maybe I go to powdercoating route.

 

[Zigis]

As promised, here are schematic with parts numbers and values for those of you, who building amps with my boards.
 
 

 
There is small differences. At power input I use CRC filter, partly independent for each channel. C4 is shared for both channels, then R8a, C3a go to right channel, R8b, C3b go to left channel.
 
I find with some NOS Russian 6N23P tubes I can't get 15V at input with original 1K trimpot, changing to 2K pot solve problem. Use 2k multiturn trimpot, this is more universal.
 
For power filtering and output I use low ESR 1000uf 35V PanasonicFM caps.
Instead of original 2 parallel R104/R105 I use single 8.2 ohm resistor in each channel. (R7a,R7b on my board)
 
Amp's gain is about 10, too much for my needs. I use at input series resistors x2 - x3 of pot value. This make input signal attenuation and increase amps input impedance. In photo you can see - RCAs are connected to boards input with 100k resistors, instead of usually wires.

 

[KimLaroux]

Clean design, I like it. I've got a few questions though regarding it, mind to educate me? 

 
Is there an audible difference with using a CRC filter? Is the background noticeably quieter?
 
How do you go about calculating the appropriate values of capacitors and resistors in such a filter? Do you use an equation or a simple rule of thumb?
 
Why did you add a 10 ohm resistor to the output of the amplifier? There seems to be a general myth here on head-fi that lower output impedance is best. It's interesting to see someone adding a resistor to the output...
 
Thanks for taking the time to share your experience, it's appreciated.