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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 05 Nov 2012, 20:05 
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Joined: 05 Nov 2012, 19:48
Posts: 1
All y'all been pretty quiet this year. How are the projects proceeding?

I picked up a couple of the boards locally and am planning on building either an EL34 version with existing iron or picking up some Edcore iron and building the KT-88. I'm leaning toward the KT-88.

I'm planning on using the Edcore TPC 10K/10K or the enclosed version M2M 10K/10K as an inexpensive substitute for the Sowter. I was wondering if anyone else had tried this? Or if anyone used the Lundahl open frame without shielding, did you have a problem with it picking up hum?

Also, if anyone has a set of transformers they will no longer use, I'd like to hear about that.

Dave


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PostPosted: 29 May 2015, 07:08 
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Joined: 08 Aug 2014, 16:35
Posts: 1
Location: Grenoble Alpes
Hi everybody,
Old topic but starting to build my own Millett’s Uniamp monoblocks and hope you can help me.
I have some questions relate to the differences between documentation and PCB :
1- R7 is open or short for unbalanced .
If I use the Sowter 3575 ,with unbalanced 2 pins RCA plug, R7 is a jumper or 1K resistor ?
2-C11 is not installed for choke input filter (LC filter) but if I want a CLC (PI filter)
47uF isn’t a bit high (simulate it in Duncan PSUD2 and have to decrease C11 to reach the good B+ value !)
What have you used and what’s your B+ measurement ?
3-To run a source directly,without preamp, a 50K volume pot would be OK (or a 10K would be better to reduce hum) ?
4-100R resistor of power tube (pin 4 of the socket for triode mode) must be soldered close to the socket and 2 or 3 Watts resistor is OK (no value on schematic) ?
5-R9 (1K resistor).
Saw that some DIYers change the value of R9 (3.3K instead of 1K) to avoid motorboarding,oscillation.
Any issue with 1K value ?
Thanks and sorry for my english (I’m french and 30 years without english lessons….).
Cheers.
Pascal.

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Le mieux est l'ami du bien.


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PostPosted: 21 Mar 2017, 09:17 
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Joined: 21 Mar 2017, 09:13
Posts: 1
Hi everybody... I just became aware of this forum thread.

Just a note about low frequency oscillations:

Generally the cause of this is bias instability of the output tubes. It turns out that 220k for R17 and R18 is too high for most modern KT88 and EL34 tubes (probably 6L6 as well).

I recommend changing these to 47k. That settles the bias down and also raises the -3dB point a bit (but still < 20Hz).

Pete


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PostPosted: 29 Mar 2017, 13:05 
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Joined: 29 Mar 2017, 12:14
Posts: 3
pmillett wrote:
Hi everybody... I just became aware of this forum thread.

Just a note about low frequency oscillations:

Generally the cause of this is bias instability of the output tubes. It turns out that 220k for R17 and R18 is too high for most modern KT88 and EL34 tubes (probably 6L6 as well).

I recommend changing these to 47k. That settles the bias down and also raises the -3dB point a bit (but still < 20Hz).

Pete


Hi Pete.

What an coincidence... I found this thread today when looking for information as I'm thinking of building your amp P2P (I like the old ways with tubes :D). So far I have sourced OPT's and tubes. I will use the Sowther phase splitters. Still to find are 2 mains transformers suitable for the project. Either buy or wind for myself - not decided yet. I believe I got the rest in the bins :).
Looking at the schematic I'm uncertain of when to use what resistors when using balanced input and when not? I will use single ended input at least as a start.

Regards / Seppo


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PostPosted: 31 Mar 2017, 01:14 
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Joined: 29 Mar 2017, 12:14
Posts: 3
I saw that paskwalito asked the same but got no answer. I presume it will be obvious then when I start my build :)

Regards


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PostPosted: 01 Apr 2017, 03:08 
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Joined: 29 Mar 2017, 12:14
Posts: 3
Turbon wrote:
I saw that paskwalito asked the same but got no answer. I presume it will be obvious then when I start my build :)

Regards


Talking to myself here - looking at the schematic made it quite obvious :).

Regards


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