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Old 6th October 2003, 03:41 AM   #1
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Default Wave av-8 hot hot ??

How hot should the transformer of my amp get.

The transformer closest to the tubes seems to get quite hot, I can leave my hand on it, it just seems a little hot.

I am using a 6 ohm speaker am I pulling too much current for the transformers? or is it just the heat from the tubes ?

Adam
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Old 6th October 2003, 03:52 AM   #2
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If you can hold your hand on it, it's not that hot.
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Old 6th October 2003, 05:25 AM   #3
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Default so how hot is too hot

And is it ok to use a 6 ohm speaker on the waves ??

Thanks...
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Old 6th October 2003, 10:44 AM   #4
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Most amps that I have checked run in the neighborhood of 115-120 degrees on the transformers. This is warm enough to feel but not quite hot enough to cook with.

Joe
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Old 6th October 2003, 10:48 AM   #5
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Hi,

Quote:
And is it ok to use a 6 ohm speaker on the waves ??
Just hook them up on the 8 ohm tap.
Powertransfer won't be ideal but it's no real problem.

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Old 6th October 2003, 10:51 AM   #6
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Default Re: so how hot is too hot

Quote:
Originally posted by adharvey
And is it ok to use a 6 ohm speaker on the waves ??
It's usually quite OK (speaking generally; I know nothing about the wave 8's), but you might want to try both 4 and 8 ohm taps to see which sounds better. IME, nominal 6R loads usually sound better on the 4R taps, but it depends on what the Z curve of the speaker looks like.
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Old 6th October 2003, 04:34 PM   #7
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Default Wave - 8

Hi,

Just installed a pair of wave 8 and have noticed the same phenomenon. It is hotter then what I usualy see in tube amps of my design. Two things can be the contributing factors, the tubes are radiating heat on the output transformer (being painted black it acumulates this heat) and the other is a small power transformer that gets hot by itself. Possible cures: reduce the voltage to the tubes filaments to 5.7 v via resistor this will minimize the amount of heat from the tubes, and add a filament transformer under the hood (there is room for this there) to take the load off the main one. Anothr way is to put an aluminum foil on the output transformer facing the tubes, this will radiate the heat back out BUT will hurt cosmetics so it is up to you.

Good luck.

Glass painter.
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Old 6th October 2003, 08:01 PM   #8
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Hi,

Quote:
Possible cures: reduce the voltage to the tubes filaments to 5.7 v via resistor this will minimize the amount of heat from the tubes,
Sorry to say so but reducing heater voltage is NOT a good idea.

The cause of the heat in the xformer(s) is quite likely a thinnish wire gauge in the xformer(s) with respect to the current draw.

Nothing much you can do about it.
Just put the amps in a well ventilated place, not inside a closed cupboard and plan on replacing electrolytic caps every other 15 years.

Other than that it's nothing I'd worry about.

Cheers,
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Old 7th October 2003, 09:02 AM   #9
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Hi Frank,

Can you add info regarding why reducing filament voltage by 10% is not a good idea?

According to Steve Bentch work and based on my experiance I have not seen effects on sound, distortion or any other for that matter because of this action (I have several amplifiers running this way). In addition, the manufacturer states that the filament voltage should be the nominal (6.3v) plus or minus 10%.

Thanks.

Glass painter.
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Old 7th October 2003, 09:53 AM   #10
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Hi,

Quote:
Can you add info regarding why reducing filament voltage by 10% is not a good idea?
First of all I assumed the WAV amp uses IDHTs.

While I mostly agree with Steve Benchs' experiments, what you do when starvings DHTs for voltage is that you create a new set of curves for the DUT.

This is fine for experimental testing but I can't imagine a manufacturer who's had to use a loadline to determine optimal operating points having this kind of condition in mind.

If ever you have the chance to run some experiments on IDHT triodes you can actually see that you can burn in tubes at reduced heater voltages or increased ones and end up with non-standard curves.

For instance, taking the ubiquitous 6DJ8 and testing it at 5 V on the heater and you'll notice a much reduced emission of the cathode.
Leave it at this voltage for hours in a row and you'll have a dull and lifeless sounding tube for the rest of its life.

Now let's use the same type and put the heater at 7 V. At first the cathode emission will be way too high showing much increased transconductance.
About 10 to 15 minutes later you'll notice an emission that's decreased to about 100% of what you'd see for a 6DJ8 at 6.3 V.
If you now test that same tube that was heated at 7 V but retest it with 6.3 V n the heater you'll notice the DUT won't even come close to what is to be expected. It's emission is only about 70% if we're lucky.
Moreover it will quite probably never return to normal emission.

If we now plot the curves of both DUTs we'll notice that neither one will show a typical curve.We just wasted two perfectly fine tubes...

Tube manufacturers allow for +/- 10% of heater voltage variation to ensure the tube will still work as expected.
And yes, it will work...just NOT optimally.
Also note the word variation used which does not mean permanent deviation.

Now, imagine we'd feed that tube at -10% already and the mains fluctuates another 5-10%, where do we end up?
Outside manufacturer tolerances I reckon...

This applies mainly to all IDHT I know of, the higher the transconductance the more obvious the effect.

DHTs are a different kettle of fish all together, I've seen 2A3s that were dull sounding at 2.5 V and came to life at 3 V and lasted for many years. YMMV.

Hope this helps,
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