My Totem Arro 4 ohm load on KT-88 based amp - diyAudio
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Old 12th May 2008, 08:29 PM   #1
r3cc0s is offline r3cc0s  Canada
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Default My Totem Arro 4 ohm load on KT-88 based amp

I have a Yaqin MC-100B which has served quite well

I've played around with only tube rolling and now it consists of:
Tungsol 12AX7s
Sov 6SN7
and stock Shuguang Grade 6 KT88-98

while playing around, I tried the 8ohm taps on my amp and have found a great deal of difference...

Almost more linear, but definitely more prevail ant bass

However the speakers are rated for 4ohm and I don't know if this will cause "issues"

I realize speakers impedance are just a subjective rating & that the way an amp utilizes the whole power transformer circuits running off the 8 ohm taps rather than the 4ohms secondary is likely why I'm seeing this difference.

However... How can I tell if I am pushing the amp to it's limit?
I've had to replace the fuse on it before, but I think it was related to a power spike... but I can't be fore certain

The Totem is rated 87db @ 1w
but is 4 ohm, and has a max power rating of 80 watts

The Amp @ both 4 or 8 ohm taps are 65 UL

So I'm thinking at my typical listening levels of around the 85 db in a relatively small room should not be drawing "tons" of power

but I do think the tubes do run hotter, as the cage gets even warmer...
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Old 12th May 2008, 09:46 PM   #2
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At a listening level of 85-90dB, your amp is basically running at just above idle. I'm assuming you are running the amp in UL, not triode.

If it sounds better to you running from the 8ohm tap, them leave it there and enjoy.

Try removing the cage for better ventilation, although it may not make a difference.

Jeff
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Old 13th May 2008, 06:41 AM   #3
r3cc0s is offline r3cc0s  Canada
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After calling around asking advice.. everyone says: "use what sounds best"

So tonight I again find myself favoring the 8ohm taps

However even after just an hour of playing music at a reasonable range... the cage & the heatsink'd area around the tubes were outrageously hot...

I know that's a "common" thing with tubes, but whilst running the 4 ohms taps at the same volume level (gain)... it wasn't getting this hot

Are there potential issues with this?
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Old 13th May 2008, 06:41 AM   #4
r3cc0s is offline r3cc0s  Canada
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can't remember if I'm posting again or not

anyways, i've been running my amp for the last few hours off the 8ohm taps

sounding great

but after touching both the cage and the chasis (heatsink kind of thing) aruond the pots

I notice it does run quite a bit hotter
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Old 14th May 2008, 04:18 PM   #5
r3cc0s is offline r3cc0s  Canada
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Over the last few days, I've measured the temperature of the heatsink by the tube pots and found that running @ 8ohms at the same gain levels is resulting in a 10c or 20f increase of temperature.

i.e 60 - 70c difference

What I've done was reduce the bia's from 5.8 down to 5.5 and have noticed that I've been able to reduce the temperature to half the rise, to about 5c

However this pot adjustment has gave me a bit more "Fatty" tube sound with a bit less bass presence.

However I'm still not certain whether I should reduce the bia's more to save the tube life?
Or if this increase in temperature is "tolerable" by my amplifier?

Also by reducing the Bia's do I reduce the total amount of current available? Or is that just a transformer thing?
Does reducing the Bias also save the amount of load on the transformer though I'm running the 8ohm taps?

If anyone can reply that'd be great
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Old 14th May 2008, 05:53 PM   #6
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I seriously wouldn't be concerned about the amount of heat radiating from your amp, it has a lot of tubes crammed into a fairly small area.

Bias your amp for the best sound, don't be concerned about tube life. Unless there is a serious problem with your amp, you should expect thousands of hours of listening pleasure before any replacement is required.

I would encourage you to try running your amp in triode mode, either from the 4 or 8 ohm taps.

Jeff
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Old 14th May 2008, 08:01 PM   #7
r3cc0s is offline r3cc0s  Canada
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I enjoy the Triode for intimate listening of Jazz and easy listening style of music

The melodic rich vocals and I think added decay and softness to the strings & piano is wonderful

However UL gives me more extention for other genres of music, plus I think there is added spacial depth
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Old 14th May 2008, 09:09 PM   #8
r3cc0s is offline r3cc0s  Canada
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Message back from Totem:

although we do rate the Arro at 4 ohms, this does signify the minimum impedance

operation they nominally operate at 8 ohms + 90 % of the time. so your findings do make good sense

the HAWK on the other hand is a very constant 6 ohm load.

both loudspeakers are fantastic but the long throw woofer on the HAWK does tend to favor higher powered amplifier (for more control)
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Old 15th May 2008, 05:09 AM   #9
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If it sounds better to you running from the 8ohm tap, them leave it there and enjoy.[/QUOTE]

I'm thinking of bypassing the triode/UL switch on mine... i find it a much better amp in triode. I was also thinking of bypassing the 6SN7 cathode followers.

dave
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Old 15th May 2008, 06:45 AM   #10
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My speakers are also 4 ohm, before I had a Cayin which also sounded better using the 8 ohm taps, now I have a Classic that sounds better using the 4 ohm taps...

Never bothered measuring temperature, just used the best sounding...
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