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LTSpice model for a commercial toroidal output transformer
LTSpice model for a commercial toroidal output transformer
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Old 15th July 2018, 08:17 PM   #81
45 is offline 45  Italy
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Originally Posted by dch53 View Post
Any suggestions how I can improve the performance of the sim or the circuit?
Let's not call it improvement but another solution.

Disconnect the G2's from the UL tap and give them a separate regulated supply (that one you use for the 6CG7's). Remember that if the CFb is 24% then your actual UL ratio becomes 24+33=56% when CFb is on.
If you disconnect the G2's it will become 24% (modified) ultra-linear. Then disconnect the 27K anode resistors of the 6CG7's from the 505V supply and connect them to the UL tap in cross-coupled fashion (where you get 505V as well minus a few volts for the UL tap DC resistance). This way you will bootstrap the 27K anode resistors (i.e. will multiply their AC value = more swing with less distortion).

Because the UL ratio is less (i.e. closer to pentode) you might get even more power.
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Old 15th July 2018, 08:56 PM   #82
45 is offline 45  Italy
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I have just noticed that you are not using 24% CFb.
So the ratios will be according to the actual transformer you are easing but the idea is the same....
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Old 15th July 2018, 10:29 PM   #83
45 is offline 45  Italy
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If you are using the VDV4070 with 5 ohm load you can do the same with the Polish 4K when you use 24% CFb to get the same primary load.

In fact the VDV has 28.267:1 turn ratio without CFb. It becomes 30.437 in total when CFb at 7.1% is connected. So for 5R this is 4.63K.

The Polish OT is 22.36:1 without CFb. This becomes 29.431 with 24% CFb. That's about the same.....
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Old 16th July 2018, 03:24 AM   #84
dch53 is offline dch53  Australia
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Originally Posted by euro21 View Post
Before you changing anything, look at output tube G1 waveform in the simulator.
About +30V.... -150V swing.

Then look in 6550 datasheet the UL characteristic: 0V... -70V swing.
No comment.
Hi. I have Tung-Sol and Eletro-Harmonix datasheets but I can't find that specification in either. The EH datasheet has no charts at all.

There are some typical UL operating characteristics I am exceeding:

Plate and grid 2 voltage DC: 450V
Grid 1 Voltage DC: -48V
Maximum signal power output: 70W

but these are just "typical".
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Old 16th July 2018, 03:25 AM   #85
dch53 is offline dch53  Australia
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Quote:
Originally Posted by 45 View Post
Let's not call it improvement but another solution.

Disconnect the G2's from the UL tap and give them a separate regulated supply (that one you use for the 6CG7's). Remember that if the CFb is 24% then your actual UL ratio becomes 24+33=56% when CFb is on.
If you disconnect the G2's it will become 24% (modified) ultra-linear. Then disconnect the 27K anode resistors of the 6CG7's from the 505V supply and connect them to the UL tap in cross-coupled fashion (where you get 505V as well minus a few volts for the UL tap DC resistance). This way you will bootstrap the 27K anode resistors (i.e. will multiply their AC value = more swing with less distortion).

Because the UL ratio is less (i.e. closer to pentode) you might get even more power.
Thanks 45. I'll sim this too.
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Old 16th July 2018, 06:42 AM   #86
euro21 is offline euro21  Hungary
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LTSpice model for a commercial toroidal output transformer
Quote:
Originally Posted by dch53 View Post
Hi. I have Tung-Sol and Eletro-Harmonix datasheets but I can't find that specification in either.
GE 6550-A
electron Tube Data sheets - 6
Attached Images
File Type: jpg GE 6550A UL connection.jpg (189.3 KB, 9 views)
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Old 16th July 2018, 07:05 AM   #87
dch53 is offline dch53  Australia
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Originally Posted by euro21 View Post
Thanks. I have that datasheet too but didn't look too deeply because it's a 6550A. Looks the same as the 6550 though.

The negative swing beyond -70V is a result of the cathode feedback. Seems to work in the simulation anyway.
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Old 16th July 2018, 07:13 AM   #88
dch53 is offline dch53  Australia
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Originally Posted by Koonw View Post
Try to increase K factor from 0.9995 to 0.99995, as you probably have too much leakage inductance as shown by the ringing top waveform, esp. at higher output.
According to Using Transformers in LTspice/Switcher CAD III

Lleak = L * (1 - K**2)

For the VDV transformer, L = 813H and Lleak = 2.55mH.

This gives K = 0.999998.
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