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Old 30th August 2006, 09:55 AM   #1
afriend is offline afriend  United States
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Default Seek for your comments/advice to newbie on Tube world

Hi,

I currently use solidstate amp, and sometimes use tube only for pre-amp section. I started having a look to a tube SE integrated amp, however, it seems the cost (or price) of tube amp is significantly costly than a solidstate one while delivers low watts.

As a newbie to tube world, could you let me know ;

1). Why you love/currently tube amp?
2). Can the 3.5 watts SE amp is enough to drive a 2-ways speakers (88dB/w/m) in 4x4m room?

3). Is the attached circuit good to try ( the overall could be ~ US$200-250) ?

Thanks.
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Old 30th August 2006, 11:10 AM   #2
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Default Re: Seek for your comments/advice to newbie on Tube world

Quote:
Originally posted by afriend

2). Can the 3.5 watts SE amp is enough to drive a 2-ways speakers (88dB/w/m) in 4x4m room?
No.

Quote:
Originally posted by afriend

3). Is the attached circuit good to try ( the overall could be ~ US$200-250) ?
Yes.

best regards
Andreas
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Old 30th August 2006, 12:45 PM   #3
Sherman is offline Sherman  United States
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It depends on how loud you like your music. My first thought is that you won't be happy with that combination of speaker, power and room size.

That said I have spent a lot of time listening to a SE EL84 amp wired in triode mode giving only about 2 watts per channel. I have used the amp with 89dB speakers though my listening distance from the speakers is only 2 meters. It sounds very good on softer acoustic music but honestly doesn't cut it for live performance volumes.

The schematic you posted is a nice, easy first amp. Cost should be about what you think. If you can get used transformers that will help with the cost.

You may want to search this forum for Mikael's SE KT88. That schematic is just as simple as the one you have and will give you about twice the power.
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Old 30th August 2006, 01:17 PM   #4
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Hello,

the schematic looks like a good place to start. There are some points I would propose to change:

The ECC83/12AX7 gives you an input sensitivity of about 0,1V for full output which is a bit much considering a modern CD player puts out 2V. I would replace the input tube with a ECC82/12AU7. This gives you an input sensitivity of about 0,6V and will sound a lot better! Use a 47K wirewound anode resistor >3W and 1.2K at the cathode. In this case R13 and R14 should be around 2K.

R17 and R18 do not have to be larger than 1.5K.

I would replace R14 with a choke of 5-10H (like Hammond 159Q) because otherwise ripple rejection will not be sufficient for hum free operation.

Make sure you don't have much more than 250V on the plate of the EL84, which means you need about 270-280V out of the power supply.

Once up and running you might like to experiment with triode and pentode connection.

Wheter this amp is adequate to drive your speakers depends on your volume requirements and the characteristics of the speaker but it might be worth a try.

Best regards
Michael
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Old 30th August 2006, 02:02 PM   #5
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Sometimes it's better to find out what output transformer you can get and then choose the output tubes to suit.
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Old 30th August 2006, 02:19 PM   #6
afriend is offline afriend  United States
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[AndreasS]

Thanks for your comment. My listening area is open, only 2 metres from the speaker + having a new born baby, so I cannot listen music too lound for sure.


[Sherman]

Do you mean the schematic on the 2nd post of Looking for Mikael's KT88 Schematic ?

If so, my concern is about the output transformer. Getting it from vendor mentioned may cost me a lot on the shipment cost ( I am in Thailand now). Can I use the off-the-shelf one ( see the model "P-50", 4.6K push-pull transformer, http://www.sacthailand.com/transSilk.html ) ??


[tubemaster]

Thanks for point this out (as I said, I know every little on tube amp). I am very curios if the 3.5Watts and 6Watts difference on tube amp will be siginifcant in this case. -- because from my observation from solidstate, the average power for normal listening is ~ 1 watt only. Besides the clipping behavior of tube amp is pretty nice :-)
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Old 30th August 2006, 06:00 PM   #7
Sherman is offline Sherman  United States
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Yes, that's the one. Extremely simple, good sounding and a bit more power than the EL84. The KT88 output tubes can be had in the US for about $24 each. I have some Valve Arts that I got in a 'matched quad' for $79 US. Might be cheaper for you.

About the OPT, I would think that in Thailand you could purchase the James 6123HS for even less than I paid (about $100 US each). However you could use any 3.5K to 5K primary OPT that has an ultralinear tap (often referred to as a screen tap).

Edcor in the US has a trafo that would work for about $18 US, though I don't know about shipping to Thailand. The Hammond 125ESE doesn't have a UL tap otherwise it might be a reasonable choice.

Also there are a couple of sellers from China on eBay with suitable trafos for $49 US plush shipping. Again, might be less expensive for you.

Anyway, the OPT is something you can always upgrade later. Get one with the right impedance that can handle about 80mA of current and worry about getting a $500 OPT later!
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