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Old 9th March 2013, 03:09 PM   #1
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Default 1.5K 200W output transformers? What tubes?

I'm in the process if acquiring a pair of 1.5K 200W outputs. They have 40% taps.

Clearly PPP arrangements is the way to go, but what tubes would be optimal here?

6 X KT88

8 X EL34

8 X 6L6GC

Other options? Sweeps, etc.?

I have a few options for PS voltages.

A 1.2KV CT transformer that can be used with choke input for 520-560V at 500mA. Obviously KT88 or 6550 variety for UL here.

A pair of transformers that will probably do 3A or so at around 330-360V. Thinking 6L6 or EL34 for this.

Suggestions?

Thanks!

Blair
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Old 9th March 2013, 05:04 PM   #2
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4 x JJ EL509, PL519 or 6P45S gives >200 W in pentode connection.
This reguires 120...150 V regulated screen voltage and 450...500 V at anode.

I just few weeks ago built this circuit and tested it also with EL509 with 4k to 8 ohms OPT and 120 V at screen, not UL. I got 100 W.
Just douple the output tubes and reduce screen series resistors to some 47...100 ohms.
That's all.

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Old 9th March 2013, 06:06 PM   #3
Ketje is offline Ketje  Belgium
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With two EL509/519 a 200W amp can't survive very long,Pa max=35W !
Input power 300W with classB, 2/3th (200W) to the output lieves 100W (50W pro tube) to be dissipated.
It could be possible with a pair of YL1350 (sold by Ask Jan First).The Pa max= 75W.
Only small problem,heater on 12,6V.
Mona
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Old 9th March 2013, 06:55 PM   #4
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Quote:
Originally Posted by artosalo View Post
4x JJ EL509, PL519 or 6P45S gives >200 W in pentode connection......
Four (4) not two.
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Old 9th March 2013, 07:00 PM   #5
Ketje is offline Ketje  Belgium
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Oh,yes,excuse me.I only looked at the schematic and there are two tubes.
Next time I will read first.
Mona
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Old 9th March 2013, 07:33 PM   #6
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An awful lot depends on the topology selected. Only 4X KT88s/channel is "right", if either Williamson or Mullard style circuitry is employed. Magnetic headroom is needed to cope with the deep bass error correction signal. It's VERY bad if the O/P trafo core saturates.
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Old 9th March 2013, 07:51 PM   #7
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Eli is right. Saturated cores sound awful, been there done that. 160 watts would mean less distortion and still plenty of power. How many secondary taps do they have? The 1.5k primary sounds a bit low? What about KT90?

The Amateur
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Old 9th March 2013, 08:18 PM   #8
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Right,

I'm not bent on the 200W output as much as 150-175. They are Sowter, so they are rated at full power at full bandwidth, but avoiding saturation is a good thing.

The 1.5K A-A is why I'm leaning towards an 8 pack of EL34s or 6L6 tubes. I cannot find the UL data for 6L6 though. I was thinking at around 340-360V in UL, if each pair is good for 30W, then 8 should get me 120W. The GC variety even more.

The EL34 is attractive because its easier to drive and 8 should give me 150W or better.

Regarding the oddball YL tube, I have two filament windings, so a 12V tube is no big deal.

Thanks!
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Old 9th March 2013, 09:24 PM   #9
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Have you contacted Sowter to find out what tubes they had in mind when designing those transformers?
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Old 9th March 2013, 10:08 PM   #10
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Hi,

Yes, that's where I got the data, but they are 20 years old and Brian said he did not remember or have documentation of the tubes intended.

They have a static DCR of 11.5 ohms across both primaries, so I would think they can handle a good amount of current making the possibilities a bit mor open.
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