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Old 10th Apr 2021, 9:13 am   #21
qualityten
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Default Re: Mullard 3-3 voltages query

Thanks Andy. Iím going to look for a variable capacitance box.
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Old 10th Apr 2021, 9:21 am   #22
Diabolical Artificer
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Default Re: Mullard 3-3 voltages query

You'll find you only really need a range of about 1p to 1n so you could build your own in 100p steps but a decade box is really useful, mine was £20. When do the 1khz/10khz square wave test you might find a 560p is good at 1khz but when you jump to 10khz it needs lowering or whatever. It's just a case of mucking about till it's good compromise for both.

Andy.
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Old Yesterday, 9:18 pm   #23
qualityten
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Default Re: Mullard 3-3 voltages query

Thanks Andy, I've dug out an old tuning capacitor that gives me a range from about 0 to 380pF. At the moment, square wave testing shows a HF boost on an otherwise nice square wave. My build does not have tone controls. I guess the treble cut control would see to that.
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Old Yesterday, 9:41 pm   #24
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Default Re: Mullard 3-3 voltages query

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Originally Posted by qualityten View Post
gives me a range from about 0 to 380pF
Does it really go down to '0'?

I think that's rather unlikely myself.
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Old Today, 7:51 am   #25
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Default Re: Mullard 3-3 voltages query

That sounds good, a bit of HF boost is handy,the opposite is often the case. You might need a tad more capacitance so could try a 220p or 330p with your varicap in series, I've attached a quick guide to give you some idea as regards square wave testing.

What I've found is at lower frequency square waves you can dial in the FB cap to get a nice sq wv but at 10khz might have to trim it back a bit. It is an interesting exercise though to do this, tweeking the capacitance & watching the response change.

Lastly a bit of a faff but you could fit a switch to shunt out the FB cap to give you a crude HF boost,very handy to have for old ears.

Andy.
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File Type: pdf square_wave_testing.pdf (102.4 KB, 6 views)
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Old Today, 8:35 am   #26
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Default Re: Mullard 3-3 voltages query

Contrary to the belief that the layout is ultra critical I can say without a shadow of doubt it's not.

Be sensible with the layout. My stereo 3-3 uses two busbars, one HT the other ground and returned to chassis at one single point. Its hum free and bang on spec, it works beautifully with any combination of EF86/EL84 even Russian valves. I also have a 3-3 test amp that only has 250v HT although it's only just over 2 Watts the distortion level is only marginally raised and sounds excellent, they are actually less effected by low HT than some think. I've made many 3-3s now and for a single ended amp are brilliant, knocking spots off those two grand triode amps with 300B valves. I did a comparison last year with the stereo 3-3 and a 300B amp with a HiFi dealer and he came away shaking his head after the comparison. He even asked me to go into production and make some, which I declined.
Why not try an EF37A & EL34 3-3?
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Old Today, 8:40 am   #27
murphyv310
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Default Re: Mullard 3-3 voltages query

Quote:
Originally Posted by Diabolical Artificer View Post
That sounds good, a bit of HF boost is handy,the opposite is often the case. You might need a tad more capacitance so could try a 220p or 330p with your varicap in series, I've attached a quick guide to give you some idea as regards square wave testing.

What I've found is at lower frequency square waves you can dial in the FB cap to get a nice sq wv but at 10khz might have to trim it back a bit. It is an interesting exercise though to do this, tweeking the capacitance & watching the response change.

Lastly a bit of a faff but you could fit a switch to shunt out the FB cap to give you a crude HF boost,very handy to have for old ears.

Andy.
Hi Andy.
My 3-3s all have treble boost rather than cut. Easy to do with a fixed value cap and 500 oum pot. Great for us pensioners with cloth ears.
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Old Today, 9:41 am   #28
barrymagrec
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Default Re: Mullard 3-3 voltages query

Quote:
Originally Posted by murphyv310 View Post
Contrary to the belief that the layout is ultra critical I can say without a shadow of doubt it's not.

Be sensible with the layout. My stereo 3-3 uses two busbars, one HT the other ground and returned to chassis at one single point. Its hum free and bang on spec, it works beautifully with any combination of EF86/EL84 even Russian valves. I also have a 3-3 test amp that only has 250v HT although it's only just over 2 Watts the distortion level is only marginally raised and sounds excellent, they are actually less effected by low HT than some think. I've made many 3-3s now and for a single ended amp are brilliant, knocking spots off those two grand triode amps with 300B valves. I did a comparison last year with the stereo 3-3 and a 300B amp with a HiFi dealer and he came away shaking his head after the comparison. He even asked me to go into production and make some, which I declined.
Why not try an EF37A & EL34 3-3?
I made mine with an EF36 and a KT61 - worked a treat.
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