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Old 2nd Feb 2020, 8:59 pm   #21
Syrinx1
Pentode
 
Join Date: Feb 2018
Location: Nottingham, Nottinghamshire, UK.
Posts: 225
Default Re: Grade 1 Class H winding wire

Thanks,

I might be able to move to something bigger. Is their a rule of thumb regarding interlayer insulation thickness?
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Old 2nd Feb 2020, 10:22 pm   #22
kalee20
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Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,059
Default Re: Grade 1 Class H winding wire

Not really. It depends whether you want interlayer materi9al to reduce capacitance, or to prevent breakdown.

Or occasionally, just to keep an even winding level!

Kraft paper 0.00075" has been used (I've probably got some) but I have never found it necessary to use it myself, with modern Grade 2 wire.

But I have specified 0.002" Nomex sheet, to keep the winding base level, layer by layer, on a cheekless bobbin winding.
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Old 6th Feb 2020, 9:27 am   #23
Syrinx1
Pentode
 
Join Date: Feb 2018
Location: Nottingham, Nottinghamshire, UK.
Posts: 225
Default Re: Grade 1 Class H winding wire

Hi,

The saga continues!

The transformer I intend to wind is for EL91 in push pull. I'm trying to make a low wattage version of a Soldano slo guitar amplifier. The original amplifier ran a quad of 6L6's using s high definition transformer with low frequency 20hz limit, so more like s hifi output. To get the same frequency response with a pair of EL91 it looks as though the transformer needs a primary Inductance above of around 140H due to the high impedance of the EL91 anodes. I'm not sure jow I can achieve this practically. Can anyone suggest any alternative low wattage pentodes that could give about 5W output but more manageable output impedance? I could probably revoice the smp to enhance bass and use EL91 but I will presumably end up with significantly more bass distortion than in the 100W version of the amp.
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Old 6th Feb 2020, 10:49 am   #24
kalee20
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Default Re: Grade 1 Class H winding wire

If you are going to 20Hz at low power, you'll be looking for the same sort of inductance WHATEVER low power valves you use.

Loading for pentodes and beam tetrodes is largely determined by HT voltage and standing HT current. Virtually independent of the valves.

And inductance is then determined by load resistance and frequency. So changing valves won't help, unless you use beefy ones at lower HT and thus higher current.

Output transformers are not easy if you want wide frequency range.

You might be resigning yourself that you'll be winding lots and lots of turns.
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Old 7th Feb 2020, 12:07 am   #25
Syrinx1
Pentode
 
Join Date: Feb 2018
Location: Nottingham, Nottinghamshire, UK.
Posts: 225
Default Re: Grade 1 Class H winding wire

Thanks,

I think I'd need a huge core to have space for sufficient primary inductance for 20Hz, so I'm going to go ahead with my original design and see what happens!
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