My First Tube Preamp

[cjkpkg]

I would go with these

These boards allow for 4 output MOSFETs and even cascoding the JFETS if you ever wanted to crank up the voltage more.

A nice big 600VA 18V secondary with 4 output devices is a pretty sweet setup though and can be built on the "relative" cheap.

Biggest problem these days would be getting the JFETS but there is probably someone around still selling matched sets.

 

[Einric]

Oh WOW! I didn't even know there was a Diy Store here.
Thanks I will order this and start gathering parts.
Does the board come with a pick list for parts?

Nevermind - I found the BOM

Sweet thing is I can supply all of those resistors in Carbon Composition from my resistor files of NOS Motorola resistors.

 

[Einric]

Analog Metric sells J74 w/ K170 as a pair! WOOT!

 

[Einric]

What is the difference between the V and BL versions of the K170 & J74?

 

[cjkpkg]

Current rating, you want the BL version of the K170s...the J74 from what I understand are a little less critical.

For MOSFETS I ended up with the Toshiba 2sk1530 / 2sj201 and have been very happy with the performance.

 

[Einric]

Alright, where are some places for suitable heatsinks?
I already have Heatsink USA.

 

[Einric]

Would this heatsink do if I split it down the large fin in the middle?
Each heatsink would be 17x4.5x2.5.

 

[PreCD]

I have been looking for a 6DJ8 preamplifier because I have a ton of those tubes. Can you elaborate on what you had to do to this design to get it to pair well with the ECC88s?

Another path that would ABSOLUTELY give you fantastic results is the Aikido. Specifically the Octal or 9-pin All in one kits.

While certainly more expensive that the ebay reference, you will be blown away by the results.

The kits come with very detailed instructions, all the parts to stuff the boards, and support here is widespread - many here have built them and quite a few more than one.

Just add a pot, RCA's, power inlet/fuse, some type of chassis, and a Xformer and you will have a very competent line stage.

AIKIDO

HERE IS MINE

 

[Einric]

I used 2 pair of 6CG7's.
All I needed to do is follow the recommended parts in the manual for my tube selection and it worked PERFECTLY.
I had a couple of brain farts that were not the fault of the Aikido or the manual.

Just follow the manual, pay close attention and don't rush.
I'm certain it will work well for you also.

Any help needed and I will be happy to share any knowledge I have.

 

[Einric]

Here is the B+ Page from the 9 Pin All in One Kit Manual.
Look at low voltage operation all the way to the right.
It shows your 6DJ8's for all four tubes.

 

[Einric]

@CJ, or anybody else that knows.
Would two 300VA dual secondary transformers suffice?
I have enough MUR860's on hand to build separate power supplies to make a "Dual Mono" F5c.

 

[PreCD]

Very nice. I may just build the little jewel.

Here is the B+ Page from the 9 Pin All in One Kit Manual.
Look at low voltage operation all the way to the right.
It shows your 6DJ8's for all four tubes.

 

[cjkpkg]

That could allow you to go true dual mono which has advantages but is more costly and complex. You would then need two psu sections.

 

[Einric]

I've got parts on the way.
Hopefully I will have my current speaker project completed by the time all my parts arrive.

 

[macdelf]

Subsonic DC

Has the slow DC on output been resolved?

I built a 9-pin dual mono with a ps3 (unregulated supply, 12AU7 and 12BH7). All sounds great. I'm using a 2.2 uF output cap and driving two power amps in parallell (about 100K each, and a subwoofer crossover (~75 Kohm)). Recently I disconnected the sub, and the protection circuits on the main amps went off. I hooked the preamp up to a scope and observed some faitly random, but smooth subsonic noise whith rare peaks (~0.1 v, usually around 20 mv). I am currently using PS1 from glassware with a choke. I look at the input to the grid in the PSR circit and I see sharp spikes where the largest swings take place but not following the smoot nature of the noise. Qestions:
1) Is this a power supply issue?
2) should I go to a regulated B+?
3) Have I just used too large of a coupling cap?
4) Should I increase the size of C6 in the PSR leg?

I think I have too much capacitance for the load and am picking up the house fluctuations. My scope won't let me measure B+ directly.

 

[cjkpkg]

2.2uF sounds awfully big to me. I would probably keep it between 0.22uF and 0.68uF.

 

[Einric]

The heaters were starved at 3.15V and never really warmed up the tubes.

 

[cjkpkg]

The heaters were starved at 3.15V and never really warmed up the tubes.

Did this happen to you?

Same thing happened to me and it was an incorrect value cap in one of the 10,000uF ones. I accidently put a 470uf one in that looked identical.

Check the diode orientation and the voltage divider resistors that set the regulator.

 

[Einric]

Not exactly, I did notice the 10,000uf capacitors were only 16V and I was pumping 18.6V rectified into them.
I replaced them with some 10,000uf 50V caps and now I don't worry anymore.

I set my regulator for 6.3V output since that is what my tubes need.
Unfortunately I also set the heater jumpers for series which starved each heater with only 3.15V.

I then corrected the regulator output to 12.6V and left the jumpers alone.

That solved my problems.

 

[cjkpkg]

Excellent...

The first time I played the all in one was as the gain stage for my Moskido power amp. After all the hype I was like...hmmm...it kind of sucks...

Probing with the DMM uncovered the low heater voltage which I thought might be bad NOS tubes...same thing...

Finally found the cap issue and then I was truly blown away!!! The 6SL7 6SN7 combination is quite a workhorse.