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Old 24th March 2007, 06:11 AM   #1
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Default Any Eimac Scematics?

I am looking for any schematics that use 304TL, 250TL, or 450TL output tubes.

The only one i could find is this one:
http://www.alumrocktech.com/drawings...tic-1bit.shtml

I would really appreciate them. I just bought a 450TL, if i could get another and make a very nice set.
thanks
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Old 31st March 2007, 08:52 PM   #2
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I find in this thread: Blue glowing tube
Ken L posted a link to a schematic:
http://www.mothaudio.com/ts-m304tl.html

Unfortunately he does not accept PM's.

If anyone has a copy of the schematic i would be happy for a copy.

thanks
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Old 31st March 2007, 11:39 PM   #3
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Sorry, I don't have any schematics to offer, but will be interested in your progress. The 75TL and 304TL amps that I've seen were pretty simple two stage affairs with interstage transformer coupling. I'm not sure I would use 1/2 6SN7 as a driver. I would probably look for something considerably beefier (lower ra, higher current) to drive the grid of those big transmitting triodes. They ain't EL84's. Most of the work will end up in the power supplies, including the filament supply, which you should not ignore if you want good sound.

In any case, it seems to me that you will need to run the 450TL in A2, i.e. you will need to drive the grid positive during part of the cycle if you hope to get a lot of power out of it. The 75TL, 150TL (two 75TL's in one bottle), and 304TL (four 75's in one bottle) can be biased with enough negative grid voltage that A1 is possible. I'm not sure that's the case with the 450TL, but I could be wrong.

A2 can be very good by most accounts. Just be prepared for it... The 450TL has a somewhat higher mu than the others listed, so the grid swing is smaller by comparison. A direct coupled cathode follower might do the trick. But, direct coupling makes things a LOT more complicated than an interstage transformer. I know there are several people here that will recommend a MOSFET source follower. I haven't tried it, so I can't comment.

-- Dave
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Old 1st April 2007, 01:22 AM   #4
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Hey-Hey!!!,
The 2 75's in the same bottle is the 152. By EiMac's way of numbering, 150 watts dissipation and 2 sections. Scaled up again for the 304.

As Dave said, they're just like other triodes, only bigger. The scale factor isn't always obvious. The 304's 25A of filament current is in another league from the ~3.5A that an 845 would need.

If you go high voltage, which will provide for adequate negative bias and achieving plate dissipation at reasonable currents, you'll need to pay attention to OPT insulation. The challenges are many, and the design is going to depend on how you solve each of them. Laying out a general schematic won't do you much good...the details are going to dictate how it's done.

What have you designed and built so far?
cheers,
Douglas
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Old 1st April 2007, 03:48 PM   #5
Tweeker is offline Tweeker  United States
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They are expensive to find NOS, but the 250TL is suitable for A2/AB2, datasheet gives some audio op points. A1 is also possible with much reduced PO, since much reduced PO is still plenty for driving most speakers rather than RF finals.

The lower voltage settings may be more demanding in driver, but are far easier in OPT design. Lower impedance and less insulation stress.

The cornerstone to such amps is the OPT, cant really recommend a schematic without knowing the OPT you will be using.
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Old 1st April 2007, 09:26 PM   #6
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Thanks for the useful info guys

I got 5 304TL's http://cgi.ebay.com/ws/eBayISAPI.dll...arch%26fvi%3D1

6j5g input 100TH driver?
6j5g input 300B driver?
6SL7?

Just looking for a place to start.
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Old 1st April 2007, 09:51 PM   #7
Gluca is offline Gluca  Italy
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That's you! I was looking at that very auction. I got 4 nos 304Tls a month ago or so. Same price, maybe a few bucks higher. Still looking at 304Tls to see if I had a good deal :-)

I have a 900V/200mA PSU running, I tested the driver (100TH mu-follower with a sandy CCS) and I have all the irons+caps to heat the 304TLs. Output tranny will be a special 10K parafeed OPT made by Mike Lefevre at Magnequest and its companion choke.

For your info, I run the 100TH at 750V/25mA/3.6V and I get 40x amp factor (20x actually as I use a step down IT). If you plan to use 100TH as driver keep in mind that its Rp is 18K so interstage trannies are out of question here (I use a low impedance mu-follower to drive mine). A CCS works just fine. An option is to use a 3C24 by Eimac, lower Rp and lower mu.

I am aiming to a low voltage bias point for 304TL. No more than 900V ... things get utterly dangerous and expensive out there. I should light it on next week or after the Easter break.

You probably know this 304TL amp by Sakuma.

Let me know how things go.

Ciao
Gianluca
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Old 1st April 2007, 10:19 PM   #8
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Hey-Hey!!!,
Be careful with those things...been messing about with 4E27's and find a lot of NOS/NIB to be gassy...
cheers,
Douglas
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