BIII with Broskie Unbalancer vs. EE Minimax Plus - My experience - Page 8 - diyAudio
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Old 21st March 2013, 06:47 PM   #71
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Hi Bud,
I did a quick search for the optimal operating points for the 6SL7/12SL7 and according to kevinkr it is best at 1.5-2ma.
Here's another interesting 6SL7/12SL7 thread.
Let's take 1.8ma with a lowish 240v B+, to get 1.8ma you need to adjust the resistor of the LM334.
The 82K for the plate is a guess: Broskie uses 120K for the 12AX7, the 6SL7 has 2/3 of the internal resistance of a 12AX7, so 2/3 of 120k is about 82k.

The best way for finding the resistor values for the operating points is to simulate it with a Spice program like LtSpice, install the spice models, start from an existing spice tube circuit and adjust it to the Broskie Unbalancer.

That's how I started :-)
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Old 29th March 2013, 01:52 PM   #72
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Is anyone finding that V1/V2 and V3/V4 are getting slightly different filament voltages?

eg. on V1 and V2 (both 6n23p) I read 6.12v on V1 and 6.42v on V2. The plate/cathode readings also differ: 132.3v on V1 and 134.8 on V2.

I'd have thought each tube should be identical?
I have similar problems on V3 and V4.

On another note, normally to look at plate curves we can measure the voltage across the cathode resistor, then also take the plate voltage. This is ok for V3 and V4 (eg. I get 120v on the plates and 2.5v across the cathode resistors R13 and R14), however how do we take these measurements for V1 and V2 given there is a LM334 controlling the situation?

Last edited by lordearl; 29th March 2013 at 02:08 PM.
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Old 13th July 2013, 11:52 PM   #73
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Is it possible to put an unbalanced signal into the unbalancer? I might need use an adapter cable, but want to test another dac.....
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Old 25th September 2013, 04:42 AM   #74
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I have neohm resistors in the four I/V positions. Do you think it would be worthwhile to add to other resistor positions? If so, which ones (please add the unbalancer position number).

Also, is there any need to replace the 0.22 uF wima caps in the C2 positions with higher quality film/foil capacitors?

Thanks

Kris
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Old 25th September 2013, 04:53 AM   #75
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Wow - long time since this thread was updated.

I am using neohm iv resistors, and recently changed R3,R4 and R13,R14 to Caddock MK132 which seemed to 'lift' the sound in terms of clarity and definition.

I settled on 6N23p-EV as input tubes and tungsram E88CC as output tubes. Hope this helps.
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Old 25th September 2013, 04:04 PM   #76
kvardas is offline kvardas  United States
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What values did you use for R3, R$, R13, and R14?

Thanks

Kris


Quote:
Originally Posted by lordearl View Post
Wow - long time since this thread was updated.

I am using neohm iv resistors, and recently changed R3,R4 and R13,R14 to Caddock MK132 which seemed to 'lift' the sound in terms of clarity and definition.

I settled on 6N23p-EV as input tubes and tungsram E88CC as output tubes. Hope this helps.
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Old 25th September 2013, 08:29 PM   #77
Ryssen is online now Ryssen  Sweden
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What PSU are you using with the unballancer?
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Old 26th September 2013, 12:03 AM   #78
kvardas is offline kvardas  United States
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What PSU are you using with the unballancer?
I am using the Janus regulators power supply. I think it delivers around 270 volts.
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Old 26th September 2013, 03:04 AM   #79
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Quote:
Originally Posted by kvardas View Post
What values did you use for R3, R$, R13, and R14?

Thanks

Kris
I used R3 = R4 = R13 = R14 = 300R

It works well because with 300R you can use any of the tubes in broskie's manual!
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Old 26th September 2013, 06:31 AM   #80
kvardas is offline kvardas  United States
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Thank you for the reply.

Is there any value of replacing the wima caps for C2 with film/foil caps?
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