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Old 14th April 2012, 01:42 AM   #11
Bismar is offline Bismar  Australia
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Hi guys, really appreciate all your help. Sorry for being a complete and utter newb at this.

As for the speakers, no i am not particularly attached to them.

If however you could suggest me a kit and a drawing for the chassis that is considerably better for about $500, i will probably jump on that instead.
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Old 14th April 2012, 02:46 AM   #12
rmyauck is offline rmyauck  Canada
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For your budget I would stick to George's tubelab.com PP EL84 PP amp for $100 (board and parts to populate the board. You can build a top plate out of aluminum, cutting holes for tubes using a wood base if your handy.

Triode Electronics Z-565 output transformers would be great for sonics as the Output Transformers are what makes a tube amp sound great. Edcor 23% UL 8K 25W ones for about $40 less.

As for a suitable PS. transformer an affordable one may be had from Antek so a total of $200 for transformers using SS diodes to save $ and bass may be better too. Tubes and other parts $100. The rest for a volume pot, shipping and base. There is fixed bias mod that can be done later for a bit more power and improved sonics @ $10 called the EFB mod. LED's could be tried too.

Randy

Last edited by rmyauck; 14th April 2012 at 02:48 AM.
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Old 14th April 2012, 03:18 AM   #13
Bismar is offline Bismar  Australia
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Thanks guys, i think perhaps i should look to getting better speaker kits first before making a decision on the tube amps.

I'm however having trouble finding more efficient speaker kits (without chassis) with a maximum budget of $500.

I've saw some nice kits at Madisound website but their sensitivities seem even worse then the kit i previously had in mind. Or am i getting confused with terminology?

Btw rmyack i can't find any reference to the EL84 PP on tubelab website? I take it its the the Simple P-P amp but all the links are broken.
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Old 14th April 2012, 04:07 AM   #14
roline is offline roline  United States
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I did a home brew similar to the Millet Big Red board. Under $450 complete with case and outputs, 30watts/channel in triode mode. Pete's board can do over 120watts/channel depending on iron and output tubes chosen. I drive 4ohm Orions that dip under 3ohms without issue.
Original St70 Dynaco amps were a little weak, only had about 18watts RMS / channel. With larger power transformers and modern driver PCB's 60+ watt/s channel is possible....

I started a PCB project for KEGGER, tried a combo of tubes and iron, just need to try 4.3k hammonds to finish. With the smaller 6P3S tubes and smaller output iron, 25watts/channel. With 5881, 6550-c- and kt88 tubes pushing 50-60 watts/channel, less in triode mode. Currently playing with 40 watt 6.6k hammonds, 5881 in triode mode. Very respectable combo.
pic attached of PCB being evaluated, Svet 6550 output tubes.

Approx cost of a ST70 clone;
Cost of iron ~$320 40 to 60watt, 4.3k to 6.6k Raa
Output tubes ~$40 for 6P3S-E 5881 Russian
Driver tubes ~ $8
Components ~ $40 can be upgraded for higher $ coupling caps
Alum top plate ~ $9
Chassis wood ~ $10
PCB one sided ~ $5 optional , point to point for purists.
Alps pot ~$30 optional
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Old 14th April 2012, 04:12 AM   #15
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Once you start talking "12" W. tubes, like the EL84/6BQ5, an "El Cheapo" fits easily into the budget. The Triad N-77U (main B+) and Triad VPS24-1800 ("12" V. heater power and B+ boost) work in both "120" and "240" V. zones, thanks to dual primaries. Something will have to be scrounged up to replace the "120" V. only Allied 6K27VF (B- and 12AT7 heater power). Perhaps a Triad VPS24-3300, for all the heaters plus B+ boost and figure out something low cost for B-. The currently recommended filter choke is the Triad C-24X.

Z565 O/P trafos are "Gold Standard" for "12" W. tubes, but Edcor is respectable. Also, "iron" winders are to be found in "Oz".

Any tube in the 6V6 "clan" will work without parts value changes. A low cost option for the O/P tubes is the Russian 6П1П (6p1p), which is electrically equivalent to the 6AQ5/EL90, but is 9 pin mini, instead of 7 pin mini.
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Old 14th April 2012, 06:31 AM   #16
Bismar is offline Bismar  Australia
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Eli Duttman, i take it theres no kits for the El Cheapo?

Also found the speaker impedance curve for the original firesprite i linked.

SB Acoustics :: 6" SB17NRXC35-8

Seems pretty flat.
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Old 14th April 2012, 07:01 AM   #17
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I would suggest Fostex Fe206 or line array.

Tube sound is all about quality passive components (audio-grade foil capacitors, chokes, OTs). Do not waist your time on tubes in case you are limited in funds. Use LM3886 instead you will get a better sounding result in case you are on a budget.

Start with back loaded horn speakers and LM3886. Later on upgrade your signal path with tubes first audio source (TriVista Musical Fidelity for example or google Lampizator) then made yourself a tube preamp-amp.

Otherwise you gonna amplify AB OPAMP output with a pricey inefficient class A tube power amp.
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Old 14th April 2012, 08:54 AM   #18
Bismar is offline Bismar  Australia
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Quote:
Originally Posted by suntechnik View Post
I would suggest Fostex Fe206 or line array.

Tube sound is all about quality passive components (audio-grade foil capacitors, chokes, OTs). Do not waist your time on tubes in case you are limited in funds. Use LM3886 instead you will get a better sounding result in case you are on a budget.

Start with back loaded horn speakers and LM3886. Later on upgrade your signal path with tubes first audio source (TriVista Musical Fidelity for example or google Lampizator) then made yourself a tube preamp-amp.

Otherwise you gonna amplify AB OPAMP output with a pricey inefficient class A tube power amp.
Hi thanks for your advice, but i believe the speakers your recommending are large floor standing speakers.

I am looking for small bookshelf speakers instead.
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Old 14th April 2012, 11:17 AM   #19
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Look around for older second hand speakers, build your own cabinets if needed.

You can find suitable speakers in old record player consoles etc.

I use the old Jensen P10 and P12 type.
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Old 14th April 2012, 12:13 PM   #20
Bismar is offline Bismar  Australia
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Hmm, i seem to find quite a few ST70 clone kits out there.

Is there a particular seller folks recommend? I want to get a feel of how light my wallet will be if i went down that path.

Also is the Dynaco MK3 kit from Triode electronics a viable option?
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