[sceleratus]

plugged it in.
no tubes, no smoke....  that's the good part....
 
put in a pair of 6N6P's and the 6.3V reg smoked.
investigating....
 
at the moment, Vegas likes "C".

 

[sceleratus]

Worked on tracing the source of the curling smoke.
 
I did not properly affix the IC heat sink pad to the board.  It actually continued to work for a while so I could track it down.  No valves, no load, no smoke, no heat.  Add two 6N6P's  lots of heat in a hurry.
 
It could tolerate one 6N6P for a while.... but.... my thermocouple hit 170F before I pulled the plug.  Tomorrow I'm making a new one....

 

[sceleratus]

[size=16.0pt]Good news today.[/size]
[size=16.0pt]I made another 6.3V filament regulator and it works like a champ.  Measured 40 C after 45 minutes.  Well within specs.  The 6N6P’s got quite hot 105 C / 115 C.  Their spec sheet says they are good to 200 C, but that’s hot.  All voltages are spot on, plate, grid, filaments for both the 300B's and the 6N6P's.  I have not tested the 300B's because........[/size]
 
[size=16.0pt]Bad news today.[/size]
[size=16.0pt]I took the 300B’s out of the box and noticed one was cracked. Never applied power to them.  I am very thankful I caught it because if it went “poof” it would be on me.  I hope Brent takes care of it.  I was hoping to hear music…  oops, shouldn’t have mentioned music.[/size]
 
[size=16.0pt]In the photo you will notice a volume control, RCA inputs, and a ¼” jack for headphones.  Wow, just like a real amp.  Stuff is bunched together for the photo.  I also need to correct the lean in the 9 pin sockets.... not easy.[/size]
 
 
 
 

 
Crack in the glass
 
 

 

[sceleratus]

[size=16.0pt]I had nothing to do today due to a lack of functioning 300B’s so I did a couple things to keep me busy.[/size]
 
[size=16.0pt]As I wrote in my previous post one of the 6N6P’s was 10° C warmer than the other.  It was also noticeably brighter.  I decided to measure the current flow to the heaters.  The Russian spec is 750 mA [/size][size=16pt]± 70 mA.[/size]
 
[size=16pt]Sure enough, as one would expect, the valve in question drew considerably more current.[/size]
 
[size=16.0pt]Valve A   758 mA   Bingo[/size]
[size=16.0pt]Valve B   913 mA  ( 0.093 mA beyond the 820 mA limit )[/size]
[size=16.0pt]If I really knew my ***t, I’d reconcile 0.093 mA to [/size][size=16.0pt]10° C.[/size]
 
[size=16.0pt]I sent the measurements to Tom and I actually understood most of his response.  Tom is off the charts smart.  As in Masters in EE, Sr. circuit design engineer for TI.  He also happens to love vacuum tubes.  I usually only understand snippets of his explanations.[/size]
 
[size=16.0pt]Anyway he wasn’t too concerned.   Heater current is not a component used to match a pair of valves like gm and plate curves are.  So The Tube Store did indeed send me a matched pair of 6N6P’s.     Nonetheless they are sending a replacement.[/size]
 
[size=16.0pt]Lastly I tested my mains power switch.  (my design, not Tom’s) [/size]
 
 

 
I want to add that Tom's consulting is not free.  I'm a capitalist and I believe you get what you pay for.  He's got better things to do with his free time than tutor a numbskull for nothing.   His help and patience has been invaluable in both completing this project and understanding "some" electronics theory.  Just setting expectations if you embark on your own 300B.
 
That said,  the Damn Thing goes together pretty good.  Order the right parts and watch Dave Jones 3 part soldering tutorial on EEVBLOG and you are banked.
 
One very cool thing..... Tom's looking to see if the DG 300B can be modified to support my beloved ECC88's and variants.  

 

[eimis]

Wow this project isn't cheap. Good luck. I'm curious on how it will turn out..

 

[sceleratus]

Quote:

Wow this project isn't cheap. Good luck. I'm curious on how it will turn out..

Yo, eimis, for sure.
It's a runaway locomotive.  I blink and it's another $25
Then there's the transformers and 300B valves.  I stopped counting the Bengies.
Just don't want to know.
 
I gained a real appreciation for companies that offer a configuration like this for what I used to think is an outrageous price.
Holy Mac Daddy, and I have no idea if it will sound as good as my Schiit Lyr.  I'm trying to rationalize it and prepare myself for the worst.
I came up with an analogy of your 8 year old child in a music recital.  She really sounds like crap, but you think it's awesome.   

 

[sceleratus]

[size=16.0pt]I promised to itemize the project costs.  Here it is although there has to be another couple hundred in shipping or something else.  Like a new DMM and Solder Station.  Etc. etc. etc.  Those really don’t count.[/size]
 
[size=16.0pt]If I really like the sound that comes out during “desktop” testing I will have the cabinet done up right.  I have some very cool species of wood picked out.  That will be a big chunk.[/size]
 
 

 

[randytsuch]

Since your source is single ended (I think), wondering why you went with input tranny's instead of input coupling caps?
 
And I know the designed said he used Solens for the interstage cap, but I used them a long time ago, and was not that impressed at the time.  I think you might want to try something else there in the future,  what's a few more $ at this point .
 
BTW, I have a Lyr too, but matched with HE500's.  I am currently working on a new source project, but I wanted to try a DHT amp in the near future, thanks for sharing your project.
 
Randy

 

[sceleratus]

Quote:

Since your source is single ended (I think), wondering why you went with input tranny's instead of input coupling caps?
 
And I know the designed said he used Solens for the interstage cap, but I used them a long time ago, and was not that impressed at the time.  I think you might want to try something else there in the future,  what's a few more $ at this point .
 
BTW, I have a Lyr too, but matched with HE500's.  I am currently working on a new source project, but I wanted to try a DHT amp in the near future, thanks for sharing your project.
 
Randy

 
Hi Randy,
 
For now, I'm just an idiot with a soldering iron.  I am following a design from Tom Christiansen.    Here is the link:  Tom Christiansen's web site.  Tom posts all the schematics and components including DigiKey part numbers.  He only sells the boards.  Here's some text from his site that may answer your question.
 
 
"The driver architecture is as follows: Input transformer (TR1) → Gain stage (TU1B) → Current driver (TU1A) → Output stage (TU2).
The input transformer, TR1, provides conversion from the differential input to the single ended topology of the rest of the amplifier.
For those not needing differential input, the circuit has provisions for placing an input capacitor instead of the transformer."
 
Here is is diyAudio thread where he discusses the design more.
 
 
EDIT:
 
Are you going to the LA meet?  Or does LA stand for Louisiana? 
 
[size=small]EDIT 2:[/size]
[size=small]I looked at Mundorf but they would not fit.  That was the only component I considered changing.  Otherwise I followed the BOM to the letter.[/size]

 

[randytsuch]

From the same website, in the 300B driver section
The input transformer, TR1, provides conversion from the differential input to the single ended topology of the rest of the amplifier. For those not needing differential input, the circuit has provisions for placing an input capacitor instead of the transformer.
 
LA stands for Los Angeles, live in Brentwood, work by LAX to be more exact.
 
When/where is the LA meet?
 
Randy

 

[randytsuch]

Nevermind the LA meet question, I saw the thread about it.

 

[sceleratus]

Quote:

From the same website, in the 300B driver section
The input transformer, TR1, provides conversion from the differential input to the single ended topology of the rest of the amplifier. For those not needing differential input, the circuit has provisions for placing an input capacitor instead of the transformer.
 
LA stands for Los Angeles, live in Brentwood, work by LAX to be more exact.
 
When/where is the LA meet?
 
Randy

Not to be snarky.....  but I put the exact same passage in my post.
 
That said, upon re-reading your question, Tom's explanation, and Wikipedia,  I have learned a bit.  More than anything this is a learning exercise for me.
Upon completion, I want to hit the books more and the soldering iron less.
Easier said than done due to learning issues.
 
I'll bring the 300B to the meet if it is worthy.

 

[sceleratus]

More on my capacitor choice.
 
Along the way I've read that caps do make a difference and discovered that there are some highly touted upgrades available.
As I said, I thought the Mundorf's looked cool but they are huge.  I then found a capacitor shootout thread (someplace)
and, as I recall, the Solen's were rated very high.  Hence, I stopped looking at other caps.
 
When the dust settles I may experiment a bit.  At the moment, I'm simply hoping to hear music.

 

[randytsuch]

Quote:

Not to be snarky.....  but I put the exact same passage in my post.
 
That said, upon re-reading your question, Tom's explanation, and Wikipedia,  I have learned a bit.  More than anything this is a learning exercise for me.
Upon completion, I want to hit the books more and the soldering iron less.
Easier said than done due to learning issues.
 
I'll bring the 300B to the meet if it is worthy.

 
 
I guess I should actually read a post before replying to it.

 
It would be cool if you could bring your 300B, if it's ready. 
If you do, would you mind if I brought my source and my HE500's to try with it?  I could also bring my K1000's.  5 watts should drive them.
 
I don't know what the rules are, but I am guessing this won't violate the meet rules (or I won't do it if it does).
 
Here is a REALLY long group buy thread for my current source
http://www.diyaudio.com/forums/quanghao-audio-design/228755-dac-end-r-es9018-full-assembled-board.html
 
I use USB only for the DAC input, with the  Amanero module.  I am still working on the output stage, going to try a transformer output.
And you have to promise not to laugh at it, it is in a case that has been reworked many times, so there are holes all over the place.
 
Randy

 

[randytsuch]

Some capacitor reading
http://diy.ecpaudio.com/p/some-notes-on-coupling-capacitors.html
 
In the beginning, he also linked to other capacitor comparisons.
 
And I agree to get sound from your amp first before you worry about things like the best cap to use.  It's just in looking at the rest of the design and components used, IMHO a solen cap is the weakest link .
 
Randy