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Old 8th January 2008, 08:39 PM   #1
pred is offline pred  Switzerland
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Default Hammond power transformer fillament rating

Hello everybody,

recently I have struck a good deal on Assemblage ST-40. After reducing the feedback and playing with input section tubes I would like to try different output tubes. Instead of EL34 I would like to put some KT88. Output transformer is rated for 40W and with triode strapping I think this will be ok. But the filament current on the power transformer is rated only at 7A. With the current configuration I am using arround 6.9 (4xEL34, ECC83 and 2xECC82). With KT88 in place it will go up 0.4Amps more, so in total 300mA more than the transformer rating. The maker of the transformers is Hammond and I heard that they spec their transformers very conservatively. So do you think it will be ok. I mostly used toroids up to now (tube newbie) and these are EI core ones. So will they buzz if the current is too much, get hotter or what?

Thank you in advance for help.

Pred

PS
I have EAR (tim paravicini) EL34 logo tubes in do somebody has an idea where the source the tubes from, except from their logo there is also G1LE1 on them.
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Old 9th January 2008, 12:44 AM   #2
Jeb-D. is offline Jeb-D.  United States
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If your already going to be running the other secondaries at the max ratings then it probably wouldn't be a advisable. But if you got a couple VA to spare of the transformers total then it may be worth a shot.

EI types can buzz too if over loaded. But usually have to be loaded quite a bit past their rating. Though not as bad a toroids. You can run the transformer past the current rating, but it causes the voltage to sag. The transformer will run hotter but possibly not significantly.

Give it a try and check for
-Buzzing
-Heater voltage to make sure your still within the permissible range for the tubes you’re using. Or if it has sagged too low.
-Excessive heat. Most transformers do run pretty hot, but it would be best to take a before and after measurement. Check with the hammond datasheet to verify operating temp range. But more than likely if it just raises a few degrees you should be ok.
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Old 9th January 2008, 04:30 AM   #3
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Don't run Hammonds, even the 3XX series, at their ratings.

Definitely do not run them, any of their windings (or any other transformer) outside their ratings.

As in, never.

Aloha,

Poinz
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Old 9th January 2008, 06:44 PM   #4
pred is offline pred  Switzerland
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Default thanks for the help

Thanks guys for the answers, I am so confused not to try since the manufacturer designed it so close to 7A so I think that there is a margin. When I now touch the transformer it is warm, like 35 deg maximum. So I will anyway try. Watch like a hawk first hour or so and then will see.

Anyone idea about my EL34 PS tubes with G1LE1 on them?

Regards,
Pred
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Old 24th January 2008, 08:14 PM   #5
pred is offline pred  Switzerland
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Default just to finish the thread

I won some kt88 over the ebay. But I measured correctly to bulb size and it fits but the base of kt88 is much bigger then EL34 and it will not fit the assemblage since the bias test point is toooo close. Bummer

Thanks for the help,
pred
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