need to wire 2 kt88/6550 in class a mode! - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 28th January 2002, 11:40 PM   #11
dice45 is offline dice45  Germany
diyAudio Member
 
Join Date: Jan 2002
Location: Munich, Bavaria
Quote:
Originally posted by GRollins





Bernhard is clearly trying to give me a run for my money in length of posts...




[supergrin] just slips out ... not intended
but it certainly will provoke me to post lengthy again



Quote:






--I don't have any objection to efficient speakers, per se, just the use of horns which tends to lead to compromises that I'm not willing to make.




I am fervently awaiting my Fertin FLB20EX drivers; they are meant to run in an open baffle and they yield 97dB/W/m. Enough for a 45 SET to satisfy with it. The open baffle speaker also is big but nothing compared to a horn.



I was pondering about horn speakers for quite a while but I gave up. I heard extraordinary horn systems; They had in common that the voice coils were vertically aligned to avoid phase mess. Which means that the tweeter horn has 7 cm, the midrange about 45 cm and the bass horn 2 meters or more. I do not have the space for that. However, Tom Danley's Unity horn sounds very nice and is an intelligent approach to the phase thing. Of course, it needs a closed or vented enclosure for the bass.







Using simple tube amps all over and even trying to make them behave like XOs, I refuse to repair the phase mess with a digital XO most horn users are using nowadays.







Another issue are compression distortions. I heard three horn speakers so far not having much of it and few long-term listening fatigue is to be expected: The Unity horn, a German horn speaker from Visaton with a vented bass enclosure and the best, Peter Bahnsen's Maximator, a 3way tractrix horn. The other horns were exciting on the 1st run but fatiguing on the long run ..compression distortion.



Interestingly, the German horn speaker as well as the Bahnsen horn were most pleasant; both are intentionally reduced in efficiency. Hence less compression distortion.



OTOH, the Unity is not and with consequences, but its compression tweeter can be used as weapon substitute with a SET 71A yielding 700mW. See the guys raving about the 71A at the SET Asylum.







Quote:
Add that to the fact that I'm currently playing with line sources--which are rarely so efficient--and anything less than 30 to 50W won't fly for me. Yet. We'll see what happens later when I get time to play with speakers again.


L'Audiophile, Paris, once suggested a line source called Totem. It was using 8 samples of the Fostex FE103Sigma; efficiency was in the 100 dB/W/m range and a buddy reported bleeding ears and shocking dynamics with a SET 300B.



Quote:



--Bias, to a solid state person, nearly always means current. Bias, to a tube person, can mean either the negative voltage on the grid, relative to the cathode, or the current that flows through the tube, essentially the same way that a solid state person would look at things. Unfortunately, the two uses mean opposite things: less bias voltage (a smaller negative number, that is) at the grid means more bias current through the tube, conversely more bias voltage (a larger, more negative number) leads to less bias current. Sometimes I even confuse myself if I get to rushing headlong through these things. If I was unclear above, I apologize. If the original fixed bias (approximately negative 50-odd volts applied at the grid) was left alone, and a cathode resistor was added, then the combination of the two would lead to a net increase (a larger negative number...confused yet?) in bias voltage, which would lead to a decrease in (bias) current through the tube. It is possible to mate the two biasing schemes, but it requires a deft hand to achieve optimal results.






How's that? Did I manage to say it more clearly?




Yes, great! Learned new stuff.



Warning, yours truly is a non-native speaker, has English as 2nd hobby and prefers it to his mother tongue when describing technical stuff and causal relations. English is waaay tauter than German. I use to write my tech specs and my technical notes in English and feel depressed about the result when I have to do it in German











Quote:
... or an Audio Research (I believe they usually use straight plate-to-plate outputs), and I'll fiddle the thing until the cows come home.




ROTFLMAO! added to the repertoire











Quote:
... But a Mac...uh unh. That amp walks a rather sharply defined knife edge, and I'd take it or leave it unless I was intending to use another output transformer.




Agreed. When I read richt's post about his Mac, I get the impression he is atleast as good informed about the amp as we two together, Grey . However, I do not think a normal PP amp has to run in pure class A. From own experience with an EL34 PP amp a friend of mine designed decreasing the bias to a class A operationg point does not lead to improved sonics, but certainly to improved tube wear.











Richt, you are your own bad luck's blacksmith do what you cannot avoid











Quote:





--You don't need to kiss my feet.




phew, was hoping you would say that











Quote:
... I wasn't suggesting that he live with an electrolytic bypass, just try it as an experiment to see if the gain came back. Not having a schematic handy, I don't remember how they handled the cathodes. If they're wired together (i.e. differential) then it wouldn't do much good.






Sorry for assuming you would do. Sorry also for pecking on the differential issue, got another lesson from my friend Manfred this evening about self-bias, fixed bias and self-bias with common cathode resistor which is right in between concerning SOA. Safest operation is with self-bias over two separated cathode resistors.



However, sonically the differential operation with common cathode resistor is very good; if the resisitor is replaced by a CCS, it is PP heaven.







Hell, how could I get Manfred to post here, this would be tube university. The odd thing: he loves this forum and reads it, just generally loathes to post.







Quote:
...



Note that using cathode bias will decrease available power anyway, since it will eat about 50 volts of the potential voltage swing. Fixed bias is a lot more efficient in that respect.


Thanks, had forgotten that.







Caps: electros are a NoNo in my book except for the heater, as far as tube amps are concerned. The friend who designed the EL34 PP mentioned above found out that in tube amps electrolytics are responsible for the sonic changes during warm-up. Once the electros were gone, no warm-up changes anymore, the amp was on top 2 minutes after switch-on.



Foil caps: try out Siemens/Epcos MKV. And ... don't make me responsible afterwards for consequences on your budget They ain' cheap, they are high-tech. But not insanely priced either. I hope the MIT are better than the Hovlands although reports from buddies tell they are not; cannot tell haven't tried them out myself. But I have A/B-ed the Hovland against the MKV. Forgetabout the Hovland. It is a question of quality, not of taste. (Bernhard, stop crusading!!)
__________________
Greets,
Bernhard
  Reply With Quote
Old 29th January 2002, 12:49 AM   #12
diyAudio Member
 
Join Date: Feb 2001
Location: Columbia, SC
Bernhard,
--You're trying to make me thirsty. Maximator is also the name of a tasty doppelbock, though not my favorite. (I prefer Spaten Optimator.)
--With the exception of my subs, all segments of my current speakers are single-driver line sources. I won't take up space here with all that; it's described elsewhere.
--Your English is better than my German...don't worry about it.
--I've been thinking about rebuilding my tube amps ever since I finished the first pair of Alephs. There are two reasons for this. One is that I've rethought some of the basic building blocks that I used the first time around. The other is that the Alephs are nipping at the heels of my tube amps in sound quality...for about 1/4 the parts cost. The tube circuit wins out in detail retrieval and imaging, but only by a small margin. In all other categories, it's pretty evenly matched.
Hmmm.
Once I get a few other issues settled out, I'm going to tear the tubes down and see what I can do to widen the lead.

Grey
  Reply With Quote
Old 30th January 2002, 01:06 AM   #13
dice45 is offline dice45  Germany
diyAudio Member
 
Join Date: Jan 2002
Location: Munich, Bavaria
Quote:
Originally posted by GRollins



--You're trying to make me thirsty. Maximator is also the name of a tasty doppelbock, though not my favorite. (I prefer Spaten Optimator.)



Cannot refuse commenting that



I was brewer before I became engineer and so I feel somehow qualified to crusade around ... AFAIR the Maximator is from Augustiner Bräu. The Spaten-Optimator has more in common with most bad doppelbock beers and so does the Augustiner. Few breweries resist the temptation to brew a thick, syrup-like fluid with faint rests of carbon dioxide in it and tasting like malt cough-drops. What a pity, market restrictions usual for large quantity lager beers don't apply here (DON'T ever change the taste the customer expects!!!) so the brewmaster could produce a real fancy stuff.



Best doppelbocks come from small unknown breweries. Two exceptions Paulaner (Salvator) and Löwenbrau (Triumphator) do not stick to the cough drop syrup, their dopplebocks are lean and fresh and worth to be called a beer. I pretty much prefer the Löwenbräu Triumphator.



And then there is the fancy Weihnachtsbock from Mahrsbräu Bamberg.



Mahrsbräu's brewmaster makes one lot each Xmas, not more.



It is a bock beer tasting like the finest Pilsener beer you can dream of.



With this beer the brewmaster doe not look on the money; it is meant as a Xmas gift to his customers. He avoids anything usually done to sqeeze the last penny out the raw materials. And he looks for usual brewing mistakes, uses a special procedure, only hops used is flavour hops etc.
..... Result is a heavy but light-tasting bright beerwhich has about the quality of a good Bordeaux wine; just about the same body; you take a tiny sip and have your mouth full. Fantastic! This brewmaster is proving what quality level is possible with a beer!




Quote:
--Your English is better than my German...don't worry about it.



Thank you! As my father uses to pray: sloppy thinking causes sloppy speaking and inverse!
__________________
Greets,
Bernhard
  Reply With Quote
Old 30th January 2002, 03:46 AM   #14
diyAudio Member
 
Join Date: Feb 2001
Location: Columbia, SC
Salvator I've had, and like. In fact, I find it rather similar in taste to Optimator, which leads me to wonder if there are 'export' versions of those brews that are different from the domestic versions. Or perhaps they suffer in shipment.
Note that it's impossible to get doppelbocks here in SC. The Southern Baptists believe them to be bottled sin (along with barley wines, Belgian trippels etc.). Anything above 6% (I believe that's the limit) is illegal. Yes, you can buy wine, port, sherry, Scotch...you expect logic from these people? At any rate, I have to pick up higher alcohol beers on trips to other states, and the selection is catch as catch can.
And now we've managed to shift far enough from the topic that even I am feeling guilty.

Grey
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
New kt88's or 6550 nhuwar Tubes / Valves 35 18th April 2009 02:02 AM
KT88 and the 6550 duderduderini Tubes / Valves 56 28th October 2008 04:47 AM
Driving the kt88/6550 in set mode duderduderini Tubes / Valves 0 15th October 2008 12:38 PM
KT88 or 6550 cjng74 Tubes / Valves 4 25th November 2007 12:33 AM


New To Site? Need Help?

All times are GMT. The time now is 04:45 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2