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Old 27th April 2013, 09:24 PM   #21
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excuse me...what?????? No one asked for any hand holding. And guessing what a problem is (your first contribution) or making idle unrelated comments is not learning anything or helping anyone.

I am puzzled why you found a need to make this comment and one that is snotty, tacky, and rude...if your serious about learning. You found this to be helpful? Who do you think you are?

I have been in electronics for 35 years...do I know it all, NO...either do you. Isn't THAT what this forum is for? So, tell me just how you have helped.

Do me a favor and refrain from helping.

DF96 may have some helpful critical points, maybe not. But I would not trash someone's amp in the process of commenting, suggesting good parts are not worth putting in this amp. Do I find oddities in the design...yes I do, but Randell Smith is not an idiot, nor are his engineers.

So, what is this site, a gentlemans club, dishing club, or a fight club? It costs nothing to have manners in a gentleman's club or fight club.

I think I shall look elsewhere for some ideas.
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Old 28th April 2013, 02:22 AM   #22
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I'm very sorry to have offended you. Certainly wasn't my intention.

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Old 28th April 2013, 01:06 PM   #23
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Thank you. You are a gentleman.
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Old 28th April 2013, 01:51 PM   #24
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For all to see I will add, not just on this topic thread, but on many I see that the real subject wanders off and folks start getting judgemental and darn offensive with replies just as one sees on political blogs. I use to read some very well informed and technically detailed replies from members on this site and other sites, but they don't post or rarely post anymore....I was about to join them.

I was hoping to see names like Eva, gootee, conrad hoffman, and some others join in on this topic. These folks know alot about caps, power supplies, and applications and use technical details to support their posts.


So, I will try to get this train back on tract with my original question: has anyone used DC-Link caps in a power supply of a tube amp.

If one sorts out all the posts here, the secondary question emerges....why does this amp sing like a prized canary in every setting but not in full 'all out' pentode? This is the root of this topic thread. What is going on in pentode.

If this amp sounds like a jaw dropping champ to folks who have heard it in triode and triode-2/3 pentode mix, why would the phase inverters and drivers tubes suddenly be the culpret? Are two more tubes in pentode vs triode (at 3/3 pentode) more than the 12ax7s can handle? Maybe, but if there is a post to that affect, some details on the how and why should back back that position up. It does not matter if 6L6, 5881, el34, kt66, kt88 or any other tubes (vintage or new issue) this amp is able to run, in pentode there is a grainy presence. This 'grainieness' is less so with vintage tubes, which again brings me back to the screens which new tubes can have a problem vs old ones. If you had a battery radio, and the batteries were loosing steam, the grainy strain heard on the speaker is in this neighborhood.

Why not poor or inadiquate screen control...regulation or to low capacitive reserve power supply for pentode? To me, seeing a pair of 47uf caps in series (making what 23uf) seems very shy for the task of screen control of six tubes. I see old Fisher, Scott, Mc's and many more that used a full 47 to control the screen and sometimes screen stoppers as well on just two tubes. I have already pointed out that, to me, 800uf supply for the B+ seems shy for power in the pentode mode.

I would like to read comments on this pentode/screen point before even thinking of someother part of this amp as being suspect. The horse does not have a broken leg, it just doen't like playing hard rock or heavy metal....yet.
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Old 28th April 2013, 03:33 PM   #25
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Probably more unwanted comments, but...

[1] Since your "stack of electrolytics" is not directly providing power to the six-pack of pentodes, any (very slight) differences in audio-band ESR between them and a creative, oversized stack of film caps ... is going to be invisible to your amp. And ears.

[2] You may find though, after the "replace-the-caps" activity, that your amp will sound rich and beautiful and wonderful in ways that you hadn't heard before. Since you can't "A/B" test the PS mod (it would be remarkably unwieldy to do so) ... the Pride of Completion of a Theory Put Into Practice factor will be coloring your opinion. Its OK! We all have it!

[3] The comments by DF96 and others regarding the "candidate for most inappropriate use of the 12AX7" is candid, valid, and from my read of the schematics, entirely justified. On one hand, I'm amazed you get good sound out of the amplifier. On the other hand, there's enough gain through the various component chains that I understand why the amp actually performs as it is claimed to do.

[4] Th question of poor or "inadequate" screen control is a bit of a canard: you say the amp sounds great. Why bother questioning adequacy of a 24 F cap (equiv) at doing the job, when it is doing the job apparently quite nicely?

In short, you asked, "what do y'all think of my substituting film caps for a stack of electrolytics?" We looked at the design, and with various attribution, we came up with "why?" and "gee, that's an odd design", and "though off-topic, these tubes would be better" and "use parallel HV caps, if you're going to make a substitution".

My own opinion is similar, with an added caveat: Use a small-value high-voltage insulated choke leading to your caps from the rectifier bridge. Rectifier, choke, caps.. The choke's value should be around 0.1 to 0.5 H. Non critical. The effect of this little helper is to radially (3-4 orders of magnitude) reduce switching tank oscillation. This will be especially useful if you go all out and buy a couple of hundred dollars worth of film caps. Further, if you decide the "film cap experiment" was doomed for some other reason, and you aim to restore the elecrolytics ... the little choke still will deliver good results.

So there you are. An modest opinion, amongst my betters.

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Old 28th April 2013, 04:41 PM   #26
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Hi Goat Guy,

Thank you for all that. Appreciated, and understood....

#1) but not exactly this: Since your "stack of electrolytics" is not directly providing power to the six-pack of pentodes I do get that the ERS may not have much of a difference. Impedance may be a different story for the ears. But power to the six-pack, what do you mean, please?

#2) yes in search of the holly grail is the main reason I was considering MKP film if I have to redo (atleast part of) this supply. I have done MKP in small amps, vintage amps, guitar amps and yep...it is a eye opener hands down and you suddenly understand that music does pass into, through, and out of the power supply and all the colorations tag along in an endless round and round cycle. Bit like thinking your in love vs knowing you are, or a single day that is so crystal clear that the sunlight is like nothing you have seen before.

Your item #3 is just how I look at it, but it is 'apparantly' doing a good job and I hesitate altering it unless I can be convinced that is the source of the pentode issue and it won't change was the amp is doing right in triode.

#4) Again, the amp sounds wonderful [U]except in full pentode[/U] and maybe hinting grain in 2/3 pentode. The screens are not in the circuit except in pentode. Otherwise the screens are tied to the plate ( the switch may appear as in a 'no state' position, but the switch is either locked in triode or pentode. So, I do not know if the cap is adequately doing it's job in pentode...that is my question. I suppose I can up that and see if it begins to solve the grainy artifact.

Yep, the idea of yanking the power supply out and redoing it with big fat parts and the associated 'murphy's law' surprises, logistics, etc., is a serious matter that must be weighed...and not by whim. Even subbing one or two higher uf and vdc value caps for the 4700@100, means taking out the supply board...a matter of nothing fits in this shallow chassis ( the transformer bells are under the board)

I will look at the choke idea, I don't think I have any that small of a value (I'll see what Hammond or Erse has), but I think you have hit on the most simple idea for a first attack, and maybe saved the last two hairs on my head.

Thanks...and glad you took time to put in your modest opinion!
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Old 28th April 2013, 04:54 PM   #27
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hi folks, i have used many times vishay DC link MKP in my tube amp .
and they work very well, in fact they have so low ESR and are so fast that sometimes i prefer a good old film in oil for the power supply and keep the Vishay DC for cathode bypass.. the big advantage here is their size...
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Last edited by juanitox; 28th April 2013 at 04:56 PM.
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Old 28th April 2013, 04:59 PM   #28
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Hi Juanitox,

are you refering to the box style DC Link and not the round? I was ??? the box style because of the tight corners and long sides and how the film would behave. They are hard to find in the USA.
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Old 28th April 2013, 05:03 PM   #29
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i used vishay MKP 1848 i don't know round one?
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Old 28th April 2013, 05:11 PM   #30
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yep, that is it. They are not in the USA yet. Farnell UK has just started to stock them but not Newark USA.

Thank you for the input.
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