The SOHA II Tube Thread
Nov 30, 2009 at 9:03 AM Post #62 of 99

regal

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Quote:

Originally Posted by kostalex /img/forum/go_quote.gif
Please, recommend some tubes for SOHA II > W5000 combo. Music are blues, jazz, jazz vocal.


The best tubes so far I've found are Amperex 12AU7's.
 
Nov 30, 2009 at 9:06 AM Post #63 of 99

sachu

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As Don was mulling, can someone try running 6Cg7s in them..if it works..a pair of cleartops should do brilliantly in this powerhouse of an amp.
90 volts on the plates is plenty..jsut make sure your heater can deliver atleast 700mA at 12.6 volts or 1.5 A at 6.3 volts if you run them in parallel.
 
Dec 1, 2009 at 7:13 PM Post #64 of 99

dBel84

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Well I did more than mull and I have to say that the 6FQ7 has now surpassed all tubes in this amp - I imagine with a little tweaking to get more current on the cathode, this would be even better. It is still not up to the level of my former amp but it is almost there.

an analogy might help - SOHA II with 6FQ7 = High Def iMax imaging, former amp with 6FQ7 = iMax 3D

I can now enjoy my music once again..dB
 
Dec 2, 2009 at 12:51 PM Post #65 of 99

regal

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Quote:

Originally Posted by dBel84 /img/forum/go_quote.gif
Well I did more than mull and I have to say that the 6FQ7 has now surpassed all tubes in this amp - I imagine with a little tweaking to get more current on the cathode, this would be even better. It is still not up to the level of my former amp but it is almost there.

an analogy might help - SOHA II with 6FQ7 = High Def iMax imaging, former amp with 6FQ7 = iMax 3D

I can now enjoy my music once again..dB



Does the stock heater supply handle this much current the 6FQ7 requires?
 
Dec 2, 2009 at 5:02 PM Post #66 of 99

eruditass

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I have tubes that say RCA 5963 on the box, but have green writing on the tube itself that say Sylvania 5963. Any experiences / comparisons with Sylvana 5963? Also, I'm interested in the 6680 and 8416 if anyone has more specific comparisons.

And for tubes with a higher heater current, how much larger heatsinks are required? Any recommend low profile ones? Maybe that tail current mod will make me happy enough.
 
Dec 3, 2009 at 7:17 AM Post #67 of 99

dBel84

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Quote:

Originally Posted by regal /img/forum/go_quote.gif
Does the stock heater supply handle this much current the 6FQ7 requires?


The reg is a 1.5A regulator , mine has a larger heatsink but I don't think this will make much difference. In normal operation, you are running most tubes at 12.6V in parallel - ie 12.6V with 300mA + 300mA = 12.6V and 600mA. The 6.3V tubes run in series and thus the voltage is additive but the current remains the same - still 600mA.

That is if I am thinking about this logically..dB

@DoomzDayz : the 6680 is the closest to the 6FQ7 of the tubes that I have tried - Tungsol 12AU7, philips 5814, amperex 8416, sylvania 5963
 
Dec 3, 2009 at 8:23 AM Post #68 of 99

Alcaudon

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Maybe a bit offtopic, I'm sorry, but since you are already discussing about current issues here...
tongue.gif


dBel, do you know how much is the total current draw from the entire amp? I'm going to add in the same case as the SohaII an alien DAC that I have laying around and a TPA Darwin selector.

The Darwin needs a 5V 60 mA ps, and I was planning to use one of the 3 leds for this (adding a regulator, or maybe a σ25), am I safe using the bom's 1A transformer or should I go for something beefier?

Thanks!!!
smile.gif
 
Dec 3, 2009 at 1:52 PM Post #69 of 99

regal

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Quote:

Originally Posted by dBel84 /img/forum/go_quote.gif
The reg is a 1.5A regulator , mine has a larger heatsink but I don't think this will make much difference. In normal operation, you are running most tubes at 12.6V in parallel - ie 12.6V with 300mA + 300mA = 12.6V and 600mA. The 6.3V tubes run in series and thus the voltage is additive but the current remains the same - still 600mA.

That is if I am thinking about this logically..dB

@DoomzDayz : the 6680 is the closest to the 6FQ7 of the tubes that I have tried - Tungsol 12AU7, philips 5814, amperex 8416, sylvania 5963



I don't know, the way I read Runelights webpage he is saying max 300 mA 6.3 V tubes. pS give the Amperex 12AU7 at try they are incredible.
 
Dec 3, 2009 at 7:47 PM Post #70 of 99

runeight

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Almost.
smily_headphones1.gif


Most 12.6V tubes that work in this amp are 150mA. Two in parallel is 300mA.

Most 6.3V tubes will be 300mA. Two in series will be 300mA.

Thus the design center for the heater supply is 12.6V/300mA. This handles most of the trubes.

However, 12bh7 for example is 300mA. Its draw in parallel will be 600mA.

The regulator can manage most of this range. However, R3P is there to drop some voltage and burn some power so that the reg doesn't have to do it. If the current draw gets too high the drop across R3P will cause the regulator to de-regulate. Hence, if your draws are higher than 300mA or so you should remove R3P.

But, then the reg will burn much hotter hence the need for off board heatsinks.

I don't know if this answers any of the questions, but hopefully it helps somehow.
smily_headphones1.gif
 
Dec 3, 2009 at 8:35 PM Post #71 of 99

dBel84

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much appreciated, my math was correct just the current draw of a regular 12.6V tube was off.

My amp does not have R3P and has beefier heatsinks, thus the ability to use these tubes in my amp..dB
 
Dec 3, 2009 at 11:49 PM Post #72 of 99

regal

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Quote:

Originally Posted by dBel84 /img/forum/go_quote.gif
much appreciated, my math was correct just the current draw of a regular 12.6V tube was off.

My amp does not have R3P and has beefier heatsinks, thus the ability to use these tubes in my amp..dB



Does this negate your ability to run 150 mA 12.6V tubes like the 12AU7's?
 
Dec 4, 2009 at 5:24 PM Post #74 of 99

dBel84

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Quote:

Originally Posted by regal /img/forum/go_quote.gif
Does this negate your ability to run 150 mA 12.6V tubes like the 12AU7's?


No I was thinking they ran higher currents - ie 300mA not 150mA so I had calculated that in parallel they would use 600mA routinely as opposed the the 300mA that they do. Thus my comment that the 6FQ7 would add no greater load in series while in fact they double the load - and I am sure that statement is more confusing than just thinking about it all
tongue.gif
.

I did some further testing and although the heatsinks can tolerate the 6FQ7, the chassis gets very toasty - too much so in fact . So good ventilation is also key for higher current demands.


and runeight addressed the heatsinking issue already.

..dB
 
Dec 12, 2009 at 9:15 AM Post #75 of 99

regal

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Quote:

Originally Posted by regal /img/forum/go_quote.gif
Here's how to get the most of your tubes on the SOHA II. The issue I was hearing on some of the 12AU7s and 6DJ8's was a slight weakness or thinness. So here is how you can safely get more current thru the tube:

1. Set B+ to 85V
2. Add another 18k ohm resistor on top (parallel) of R4L&R (makes it 9k ohm)
3. Add another 200 ohm resistor on top (parallel) of R6L&R (makes it 100 ohm)

Adjust P1L&R to give .550 V across R6L&R

Check to make sure you have at least a 19V drop across the top CCS (adjust P1 until you do)

This gives 2.75 mA thru each tube section.


.




I found that some tubes pull down the CCS a little more than others and it causes the E12 to trip. I recommend setting B+ to 80V which cured this issue with this high current config.
 

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