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 Post subject: Re: Tube Rolling
PostPosted: July 7th, 2015, 6:39 pm 
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:character-oldtimer: Like J-Rob said, listen to it for a while as-is. Tube rolling should be the very last thing you go for, getting the right amp (or the amp right) is much more important. Think of an amp like a woman, a really good design is like a beautiful woman, a lousy design is like an ugly woman. Tube rolling/boutique parts are like makeup. A beautiful woman is still beautiful without any makeup, and no amount of makeup can make an ugly woman beautiful....

As for the low-end, that's a tough one with tube amps unless the transformers are up to it. At that price point, the transformers can only be so good... :whistle:

Roscoe

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 Post subject: Re: Tube Rolling
PostPosted: July 7th, 2015, 8:24 pm 
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I wrote an extensive reply to this. But couldn't post it because I had to take a phone call from a dying friend. I came back to tweak it and post it, but the site logged me off. When it redirected me to log in again, my post was lost.

Sorry, that was too much work to lose. I'm done here.


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 Post subject: Re: Tube Rolling
PostPosted: July 7th, 2015, 8:38 pm 
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I'm with Stuart...wrote a LONG detailed response and got timed out while writing.

What's up with that?

I'm going back into forum retirement.


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 Post subject: Re: Tube Rolling
PostPosted: July 7th, 2015, 8:41 pm 
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Location: Baltimore MD
There is global feedback that will affect how the amp sounds and would be a place to start to try changing the amount of feedback or removing it completely. Too much feedback can dull things down.
Also coupling cap and resistor to the control grid on the el34 will greatly effect how the amp will sound
Some claim one must consider cathode resistors must be considered to be in the signal path and will also effect the sound
But I agree you should live with it "stock" for a good while, it might grow on you in time.


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 Post subject: Re: Tube Rolling
PostPosted: July 7th, 2015, 11:44 pm 
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Joined: June 4th, 2013, 2:39 pm
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Contra Roscoe, I would suggest some tube rolling before you try modifying the amp. EL34s vary widely, and some can sound flat and dry, especially the cheap Chinese ones. The vintage ones are best but extremely expensive and difficult to find in good condition. The Psvanes (or Treasures) are very nice but will cost from $250-400 a quad, depending on the grade. But they will transform your amp. If you are on a budget I would suggest a quad of Svetlanas, which will set you back $80. They were very well made and have a warm, forward mid-range and slightly rolled top. The Mullard copies were too bright and edgy for my taste. I haven't tried the Tung-Sols.

In terms of 6SN7s, this is a critical tube in this design and will do a lot to set the tone. Again the Psvanes are wonderful--amazingly transparent and spacious but with a clear, vivid mid-range that makes classical and jazz a joy. These go for around $120 a pair and would be well worth the investment. You'll get a lot of the "growl" back with these. I listen to a lot of classical and these lend great authority to cellos and basses. And frankly the vintage 6SN7s sell at such a premium that you'll spend almost as much for something only half as good.

A cheaper alternative is the GE 6SN7GTB grey plate. You can get good strong matched pairs for $50-70 and they are almost as good as the Psvanes. They give you the whole instrument, not just parts of it. Viva Tubes is my favorite and most reliable seller of vintage tubes on eBay and his prices are very fair.

RCA black plates/clear tops from the 60's offer a very clean sound, extra depth and tonal honesty, but I find them too cool. My audio pals here, though, liked them very much when we did some swappping of vintage varieties. Avoid "wafer" bases though. You can get a nice pair for c. $60. The Ken-Rads are great but are simply out of control price-wise.

Guitar enthusiasts rave about the Sylvanias and "Bad Boys" but while they push the mid-range out and give you a lot of "depth," once you hear the phase coherence of the Psvanes you'll quickly get tired of this effect. These are probably great for guitar effects but just so-so for general use.

The 1579s (?) someone else mentioned sound interesting but I'm told that it's hard to find authentic versions. I've never been tempted to risk it.

In terms of 12AU7s, they tend to be much of a muchness, but a pair of 6189s will give you a good bit of extra punch and restore some of that growl.

Not to step on toes, but I would NOT mess with the feedback. These Chinese amps are reasonably well-designed, the transformers are decent and I wouldn't mess with that. Since this is a direct-coupled design (the first stage is direct-coupled to the 6SN7 driver) I would take the advice of another poster and check the bias points for the driver and output stages, especially if you do some tube swapping. The voltage relationship between the first two stages is very important. An incorrect setting for the 6SN7 could cause unsymmetrical plate swings and add harmonic distortion. This is the same basic design I use for my PP 300B amps so I'm pretty familiar with it.

If you want to get into mods I would start first and foremost with the coupling caps (C2 and C3). The Mundorf Supremes are a superb buy, the best I've tried for the money, about $16 a piece, and might well give you a lot of extra magic. To my ears they are very balanced and musical.

Hope this helps.


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 Post subject: Re: Tube Rolling
PostPosted: July 7th, 2015, 11:55 pm 
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PS. I see the Psvane 6SN7s now go for either $80-90 for the standards or $180 for the black-glass Treasures. Go for the Treasures if you can but the standards will still beat any NOS variety, IMHO.


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 Post subject: Re: Tube Rolling
PostPosted: July 8th, 2015, 12:18 am 
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PPS. Since this has a solid-state rectifier power supply, some better rectifier diodes in the PS would also improves matters for a very small investment. The difference between standard diodes and UF (ultra-fast) diodes is pretty big. This is something for experienced builders, though. Perhaps someone in the group could take a look at it and do some simple mods for you.


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 Post subject: Re: Tube Rolling
PostPosted: July 8th, 2015, 11:48 am 
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Joined: March 12th, 2013, 1:49 pm
Posts: 216
A lot of good suggestions here, I would go with J-Rob first and give it a listen (properly biased of course) before making any changes to anything and get a good idea of the sound quality before any changes are made. One can drop a lot of money doing basic parts upgrades and get very little in return so that is something to consider. And tubes even more so! My experience with more recent tube amps of the Chinese (and Audio Research) variety is that they tend to have a "thin" sound in going for a tonal palette that is accurate and fast above all else, the Cary amps tend to sound "full" while retaining detail and speed. I think that a lot of the thin sound may be attributed to the wholesale use of metal film resistors, when vintage amps are restored with all metal films, they too start sounding "thin" rather than full as they once did. Such sound quality can be affected by the use of good quality carbon films in the feedback loop or so I have been told. There are a lot of "flavors" that are present in tube amps that vary depending on driver tubes and output tubes and even tube rectifiers, and since audio is a subjective thing, the sound you may like may be in a certain type of amp/tube combination. Take it slow and enjoy the ride and learning!


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 Post subject: Re: Tube Rolling
PostPosted: July 10th, 2015, 9:26 pm 
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Location: Highland, MD
Yes, I vote to wait a while before changing. I think it was Broskie that said, "I haven't met a distortion I didn't like - at least for 2 weeks."

Sometimes new things sound good because they sound different, so it pays to listen for a few weeks at least before mucking about. You'll have a good idea of things you like and things you don't.

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 Post subject: Re: Tube Rolling
PostPosted: July 11th, 2015, 3:00 pm 
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Joined: October 21st, 2013, 6:53 pm
Posts: 270
Grover Gardner wrote:
Contra Roscoe, I would suggest some tube rolling before you try modifying the amp. EL34s vary widely, and some can sound flat and dry, especially the cheap Chinese ones. The vintage ones are best but extremely expensive and difficult to find in good condition. The Psvanes (or Treasures) are very nice but will cost from $250-400 a quad, depending on the grade. But they will transform your amp. If you are on a budget I would suggest a quad of Svetlanas, which will set you back $80. They were very well made and have a warm, forward mid-range and slightly rolled top. The Mullard copies were too bright and edgy for my taste. I haven't tried the Tung-Sols.


Hey Grover,

Thanks for the advice! I found Psvanes on ebay for around $150/quartet. Are these not the high quality versions you referred to?

While I was waiting for responses from the forum, Yen audio on ebay recommended some Genalex tubes and I bought them. I probably should have waited for some more responses before I bought, but I guess I'll just see what happens.

Chris


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