[aryntha]

So, a lot of folks have talked about the hum with the stock tubes in the 336SE...

And indeed with the stock 6N8P, there was hum - though not a whole lot.

I can get rid of the hum completely with RCA 6SN7GTBs; but - using an adapter and VT99/6F8Gs, the hum can be - lets just say - heard across the room via my Senn HD600's...

Has anyone, anyone at all, successfully gotten VT99/6F8Gs to work in this amp? I've got a bunch of NOS 6F8Gs, and was hoping I could use them with a 6SN7 sub adapter with this amp but so far, seems, no way.

Has anyone had any experience with this configuration?

 

[aryntha]

Well this is discouraging. Out of about 20 6SN7s, probably 11 of them hum monstrously, and 9 are silent.

Out of 8 6F8Gs, one doesn't hum.

Is this normal for this amp? I'd hate to send the thing back to China if it's somehow defective, but it seems like the 336SE is amazingly picky about tubes? (Or is it just my particular one....)

 

[aryntha]

Okay, so here I am replying to my own thread but:

I did the "fitz mod" with 220uF Nichicon caps; -- ALL THE HUM IS GONE.

On every tube.

I can use any 6SN7, or any 6F8G.

Now... I have to ask folks:

1) Is there any detriment to this mod? Will the amp blow up in 100 hours?
2) Why isn't this installed at the factory on the 336se???

 

[paara]

I actually talked to the people at darkvoice about this when I ordered my 336se from them. They said that they could not do any changes to my 336se.

 

[aryntha]

Well, I understand they wont make any requested changes to a single order, but I wonder why they won't integrate this into their design?

Makes me wonder if there's some kind of detriment to the fitz mod?

It just cant be a cost issue. Not two caps. The rest of the amp seems to be competently designed... If hum is this easy to alleviate, I don't understand why it isnt part of the design?

 

[paara]

Yes, I can agree with that, but it is not very customer friendly to refuse to add 2 capacitators either.

There are probably no reason other then that they are satisfied with their design, and that the chinese tubes do not produce any hum in the unit. Since "the DV people" have limited english capabilities they probably do not understand that it is a big problem either.

Or they just choose to ignore it. Customers are always wrong

the communistic way of thinking. ( if you have lived in a former communistic country you will know what I mean)

 

[aryntha]

Interesting... Maybe it is something along the lines of Promoting Glorious People's Chinese Tube. Or just saving face. I don't know...

Well, hopefully my fitz-modded 336se won't go up in a cloud of smoke in 100 hours.

Nice to be able to use all the Tung Sol 6SN7s and Raytheon 6F8Gs I had on hand.

 

[jamato8]

What is the fitz mod?

 

[Oskari]

Quote:

Originally Posted by jamato8 /img/forum/go_quote.gif What is the fitz mod?

http://www.head-fi.org/forums/f5/dv-...tz-mod-353079/

 

[jamato8]

Interesting. Well I would use 470uf as I have found this the best balance of bass and mids in a cathode cap. Also, while voltage doesn't matter, a lot, I find that using an electrolytic closer to the working voltage to be better sounding than using something like a 100 volt or 50 volt cap. Unlike film caps that sound better when rated at much higher voltages. I also prefer nonpolar caps as in the Black Gate 470uf nonpolar. I would also replace the resistor with a good carbon comp as they use cheap power resistors as a cathode bias resistor and a carbon will impart a smoother and more refined sound.

 

[Skylab]

It really seems hit or miss on the hum. My 6F8G's don't hum in my 336SE at all. But I had a 6SN7WGT that did (and another that didn't).

The Fitz mod will indeed resolve this problem completely, however.

 

[atbglenn]

Quote:

Originally Posted by Skylab /img/forum/go_quote.gif It really seems hit or miss on the hum. My 6F8G's don't hum in my 336SE at all. But I had a 6SN7WGT that did (and another that didn't). The Fitz mod will indeed resolve this problem completely, however.

Which makes me wonder why Darkvoice hasn't incorporated this, or similar mod?

 

[Skylab]

Quote:

Originally Posted by atbglenn /img/forum/go_quote.gif Which makes me wonder why Darkvoice hasn't incorporated this, or similar mod?

That is a VERY good question.

 

[jamato8]

Some designers don't like to use a cap on the cathode. I find that it adds a little fullness to the sound and prefer it and I would say it is more normal than not to use a cathode cap. Why, if it gets rid of a problem, they don't use one is poor reasoning and design decision.

 

[Tridacnid]

Well, my amp hasn't gone up in smoke, and I don't think it will, so you should be safe.