Negative grid current WTF?

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Cressy Snr
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Re: Negative grid current WTF?

Post by Cressy Snr » Wed Jul 04, 2018 8:19 pm

The TV is going through it at the 'mo but it seems better in terms of dynamics, HF performance and low level detail, on speech and incidental music. The lack of space and low level detail Richard was complaining about at Owston in comparison to the NVA clone, may have been down to the oscillation problem.
I'll try some serious music later.

I took the time whilst I was in there, to change the rectifier socket to a B5, drop the rectifier heater to 4V and use one of my beautiful, gorgeous, Mazda UU4 British rectifiers. The small current draw of the little PCL86s makes the 120mA UU4 a viable rectifier to use. It is one of the best looking valve rectifiers I know and deserves to be seen glowing.

Also, the HT ramp-up with this is sloooow. :)
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Mike H
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Re: Negative grid current WTF?

Post by Mike H » Thu Jul 05, 2018 10:13 pm

Cressy Snr wrote:
Wed Jul 04, 2018 6:06 pm
What a screamer! :shock:

L channel with the negative grid current is off the scale.
Flippin' 'eck. :shock:

Your display (and timebase knob) seems to be saying 50 uS per division, 9 cycles on the screen so I make it slightly under 20 kHz*. Not RF but still undesirable.


* Or am I talking borrocks Image
 
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Cressy Snr
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Re: Negative grid current WTF?

Post by Cressy Snr » Thu Jul 05, 2018 10:24 pm

I bet it drove the dog barmy, poor thing. :shock:

I couldn't hear it with my old ears though.
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Nick
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Re: Negative grid current WTF?

Post by Nick » Thu Jul 05, 2018 11:08 pm

However if it was 20kHz, then any result that damps it will likely affect the audible bits.
Resistance isn't futile it's V / I.

Cressy Snr
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Re: Negative grid current WTF?

Post by Cressy Snr » Fri Jul 06, 2018 11:22 am

At the risk of sounding thick - my probe was set to x10, so does that make it 200KHz, or does that setting only affect the displayed amplitude?
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Re: Negative grid current WTF?

Post by Nick » Fri Jul 06, 2018 11:31 am

Only the amplitude.
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Mike H
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Re: Negative grid current WTF?

Post by Mike H » Fri Jul 06, 2018 6:18 pm

Yes. :D

Loaaa-dsa Volts then. :D
 
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RhythMick
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Re: Negative grid current WTF?

Post by RhythMick » Mon Aug 13, 2018 9:25 am

Well done sir.

I'd like to have a beginners go at working out what frequency the curve on your scope shows, in the hope the more experienced folk will put me right and I'll learn from it.

Your time dial is set to 2ms (2nd picture), so each small block represents 2ms. The curve is approx 3.5 blocks between peaks, so around 7ms. That would make the frequency around 143Hz (1/0.007).

The first picture (with the clearer image) shows 8 cycles in the 10 blocks of the screen, with the time dial set to 50uS, so each cycle is approximately 62.5 uS (10x50/8). Approx 16k.

How did I do ?
Last edited by RhythMick on Mon Aug 13, 2018 9:36 am, edited 1 time in total.

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Re: Negative grid current WTF?

Post by RhythMick » Mon Aug 13, 2018 9:33 am

How did you decide on 68k grid stoppers Steve ?

Cressy Snr
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Re: Negative grid current WTF?

Post by Cressy Snr » Mon Aug 13, 2018 10:22 am

They were what I had to hand so I bunged them in and hoped.
All very scientific. :lol: :lol:
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Re: Negative grid current WTF?

Post by Mike H » Mon Aug 13, 2018 1:26 pm

RhythMick wrote:
Mon Aug 13, 2018 9:25 am
Well done sir.

I'd like to have a beginners go at working out what frequency the curve on your scope shows, in the hope the more experienced folk will put me right and I'll learn from it.

Your time dial is set to 2ms (2nd picture), so each small block represents 2ms. The curve is approx 3.5 blocks between peaks, so around 7ms. That would make the frequency around 143Hz (1/0.007).

The first picture (with the clearer image) shows 8 cycles in the 10 blocks of the screen, with the time dial set to 50uS, so each cycle is approximately 62.5 uS (10x50/8). Approx 16k.

How did I do ?
Not bad. :D
 
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