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Old 4th December 2003, 03:33 AM   #1
navin is offline navin  India
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Default EL 34 parallel push pull (quad)

I have been thinking abiut building a tube amp. recently i heard my brother in law's consonance (in singapore). it left me not so much impressed (maybe the spendor speakers had something to do with this).

The other part of tubes that worries me is the large audio trannies. building good audio trannies from what i gather is an art that is dying.

i live in india most of the year and getting these trannies in india are hell. importing them is crazier they weight 3-4 kgs per pc if not more. that is a lot of iron.

as a tube newbie living in a warm country i guess my best bet is a parallel push pull el 34 (quad tubes). it is relatively simple and can drive my 4 ohm speakers 87db speakers to about 95db and still have enough headroom.

are there any tubes amps that do not use output transofrmers (OTL) that can drive low impedance loads (I can redesign my speakers to 8 ohms)? How much power do they put out? are they simple (as simple as the EL84 and EL34 ckts i have seen on the net)?
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Old 4th December 2003, 03:51 AM   #2
cm is offline cm  Singapore
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I have a Consonance EL34 amp that was built from a kit. You are right that the sound is not as you would like it. I have done a lot of work upgrading it and it had improved by leaps and bounds.

The circuit is very simple, and all you need really is to change the cheap components on the board into better grade components for drastic improvements to be heard.

Top of the list, just rid of the stock 12AX7 in the preamp. A much better tube would be the 6922 ( my opinion ). You can compensate for the loss in gain by adding a good cap to the cathode resistor of the preamp, which improved details, soundstage, and whole lot of body to the sound. You need some surgery for this mod as the 12AX7 are 12.6V filament voltage as compared to the 6.3V.

Finally, triode mode connections at output stage reduces power but improves clarity. Chaging the cheap reisitors to Kiwame and the MKPs to PIOs will give another quantum improvement.

I like making circuits and see almost instant results. No joy for me in making chasis etc. Hence moding is a lot more fun. I know nothing on tubes theory, I just know enough not to smoke anything, and then depend on my ears to instruct what stays and what goes.

KT88 sucks in my opinion.
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Old 4th December 2003, 04:00 AM   #3
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Default OTL's

Hi Navin,
You might be right about PP amps being best for this place. OTL's can sometimes be a problem and with difficulty in getting replacement speaker drivers and tubes ( not to mention cost ) , it might best be avoided. I read something on the net about many of them just breaking down. I guess the speaker goes along with it. I also get the impression from various posts that they can be fussy amplifiers.

PP on the other hand seems to be far more reliable. Many swear by SE's but other think most are too soggy and of course low powered. I heard some SE's long ago and thought they were nice but didn't really critically evaluate them at the time. The bass limitations and limited power is enough for me to avoid them.

EL34's are very well regarded . Did you think of a triode like the 2A3 ? You could make a PP out of that. Power will not be too much . But it will be a true triode amp. Someone once said that they liked the 2A3's sound over the 300B . I guess this is hard to say because there are so many different manufacturers and so many implementations.
Cheers.
Ashok.
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Old 4th December 2003, 05:15 AM   #4
SHiFTY is offline SHiFTY  New Zealand
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If you are a tube newbie I would recommend buying a vintage amp (perhaps two identical mono amplifiers) and restoring them with a few modern components.

You can pick up these amps reasonably cheaply, just search around, ask any old electronic repair stores, broadcasting studios etc. You can get some good bargains on eBay sometimes too.

I wouldn't worry too much about power, anything above 5W is enough for comfortable listening levels.

I would go for a PP EL34 or EL84 design, for decent power. If you want a cheap NOS alternative to an EL34, use an 807. They are closer to a 6L6 but are a grunty and cheap tube.
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Old 4th December 2003, 06:15 AM   #5
navin is offline navin  India
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Quote:
Originally posted by cm
I have a Consonance EL34 amp that was built from a kit. Top of the list, just rid of the stock 12AX7 in the preamp.....
Finally, triode mode connections at output stage reduces power but improves clarity. Chaging the cheap reisitors to Kiwame and the MKPs to PIOs will give another quantum improvement.
ok i just asked my BIL (he was in a meeting so i did not get much of an answer from him) he said he is using a EC88 for the pre and has Vishay resistors and solen caps. remember i said i did not like it. he seems happy. i found the bass a bit tubby (not tubey). i wil be doing a critical listening session tonight. more on dec 7th (PST)when i get my next connection.

for me an amp must feel like the better music halls i have heard (NCPA in bombay, Lincoln Center in NY, Bard College NY State, the music hall at Berkely CA, The Oper in Frankfurt, etc...)

no i have not considered the 2A3. last time i saw tubes was in 1977 (i went to a place called Radio Bhavan those of you from bombay might remember).

more later.
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Old 5th December 2003, 04:40 PM   #6
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EL34, 2A3 have more distortion than KT88, but one has to move up a notch in design work to use a KT88. Vast experience is needed to use KT88, so it may not suitable for most people.

2A3, you have to contend with hum problems too.

I would suggest the EL34 in triode mode as your best solution. Price of tube and design is very reasonable for those on a budget.

Hope this helps.
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Old 5th December 2003, 06:19 PM   #7
zobsky is offline zobsky  India
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if output transformers and budget are a concern, you might consider building a tube preamp first, since they are cheaper and don't necessarily require OPTs.

It will be a good learning experience, the parts will be readily sourcable (relatively speaking). will inject tubed sound into your current system and you can either use the preamp with a tube amp if you decide to build one later or build the power tubes into the same chassis if you want and have the space.

other more knowledgable folks on this board can suggest circuits / tubes depending on the sound you are trying to achieve.
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Old 6th December 2003, 02:48 AM   #8
navin is offline navin  India
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now that is what i was wondering. does a tube preamp sound bter (mate better) to atube power amp and so with solid state. i see a lot of guys using solid state preamps with tube power amps. if you want teh tube sound wont a tube preamp be a cheaper option?
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Old 6th December 2003, 04:48 AM   #9
zobsky is offline zobsky  India
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Quote:
Originally posted by navin
i see a lot of guys using solid state preamps with tube power amps.
that seems like the worst of both worlds, .. IME, I thought the opposite was more common, at least in the US.
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Old 6th December 2003, 06:10 AM   #10
navin is offline navin  India
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me too. so now i am wondering if it would make more sense to make a preamp first
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