• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

#26 pre amp

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#5,441
merlin el mago said:
Really Sowter 9063 doesn't have two input coils it's a center taped....
Click to expand...
Incorrect...
https://www.sowter.co.uk/specs/9063.php
Sowter says "Two chamber bobbin provides full geometric balance for the ultimate in noise rejection and phase splitting performance." so the schematic is correct.
I use these transformers in my line-drivers:

zeus-lineamp-vmos-pp-iptx-sowter9063-1x4-dn2535n5-optx-sp-gaped-1x1-front-1-800.jpg
 
#5,445
merlin el mago said:
primary is always CT
Click to expand...
Yes, you are quite correct.

The primary signal is always across both windings, otherwise the output won't be symmetrical because each output is on a separate section.
The schematic you are referring to also does not show the sectioning... it is not a physical representation of the winding stackups.
I have been using the 9063s since 2006, and have a couple in a box at my feet which are just about to go into a new line-driver.

And yes, Happy New Year everyone. 🙂
 
#5,446
H
kevinkr said:
Ring of two type CCS? This is my general preference as well for bipolar transistors. In general I have avoided CCS in the audio path of my own equipment. I am experimenting a little with some of the IXYs devices - SY, Doug and a couple of others think very highly of these which has my curiousity piqued.

I was thinking perhaps I had a specific preference for bias approach but I think I might be almost close to agnostic. I use cathode bias with tubes like the 6J5/6SN7/6SL7 almost exclusively, fixed (grid) bias in power stages and with DHT types in general or and some high transconductance types like the 5842. I have also employed LED bias with 5842 and D3A with choke loads or tube based gyrators. I've found the LED bias sounds good in these applications sans CCS. Using high transconductance types with LED bias in particular means that you need to pay close attention to matching and target plate current vs supply voltage (since I don't currently use CCS).

Fixed bias seems to work really well with low transconductance dhts and results in reasonably predictable Ip which generally is not the case with higher transconductance types which need to be tweaked to achieve the desired operating point.

I guess there are about as many ways to do this as there are designers. 😛
Click to expand...
 
#5,447
15 years is a long time ago particularly for a quote. Since I made those comments I have moved on to cascode CCS typically with depletion mode mosfets and in low voltage applications JFETs. I also use cascode bipolar CCS with LEDs as references in some headphone amplifier and discrete op-amp designs.

Rod Coleman as always remains an excellent reference on all things CCS.
 
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#5,453
witch LL transformer??? Transformer model is in the comments column 1692, 1692AM and 1660AM (not 1662 - typo), all 10mA dc rated
Secondary not connected? How did you measure this then? These measurements were done on the first anode
Which configuration for the interstage are you using? that is recommended by Lundahl, Alt Q SE Line Output, will check later for Alt S SE to SE Interstage
The aim was to determine low cut, caused by the inductance of the primary winding. It looks that 95-100H is not enough
 
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#5,455
dimitri said:
Alt Q SE Line Output, will check later for Alt S SE to SE Interstage
Click to expand...
ALT Q is better choice (10Hz...55kHz) ... if you have low (below 2k) impedance tube (in this case inductance is only 95H).
In this operating point #26 has 7k6 output impedance.

Using #26 with inductive load is the nightmare.

BTW Vinylsavor wrote here about this problem.
 
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#5,459
euro21 said:
ALT Q is better choice (10Hz...55kHz) ... if you have low (below 2k) impedance tube (in this case inductance is only 95H).
In this operating point #26 has 7k6 output impedance.

Using #26 with inductive load is the nightmare. BTW Vinylsavor wrote here about this problem.
Click to expand...
Thomas was just concerned about the output impedance which he wanted to be 300R rather than 600R to drive a TVC. But yes, tubes like 26, 27, 37, 56, 76 need the right load. I use a resistor but it needs to be at least 39K or more if possible. I remember using a 135H plate choke with the 26. Can't remember any special problems but can't remember what it was like either.
 
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