Phono Frustration

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IslandPink
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#16 Re: Phono Frustration

Post by IslandPink »

Does G1 float up towards G2 ?
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izzy wizzy
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#17 Re: Phono Frustration

Post by izzy wizzy »

IslandPink wrote: Mon Mar 04, 2019 9:39 pm Does G1 float up towards G2 ?
Dunno. Didn't measure G1 only G2 at about 125V. For giggles, I'll measure it before I bung the battery in.

Edit. G2 134V Anode 168V and G1 -0.9 to -1V with G1 floating (no battery).

Cheers,
Stephen
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#18 Re: Phono Frustration

Post by RhythMick »

izzy wizzy wrote: Mon Mar 04, 2019 9:42 pm
IslandPink wrote: Mon Mar 04, 2019 9:39 pm Does G1 float up towards G2 ?
Dunno. Didn't measure G1 only G2 at about 125V. For giggles, I'll measure it before I bung the battery in.

Edit. G2 134V Anode 168V and G1 -0.9 to -1V with G1 floating (no battery).

Cheers,
Stephen
Does measuring G1 when it's floating actually tie it to ground though, via the meter?
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Nick
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#19 Re: Phono Frustration

Post by Nick »

Yep, you would need to use a electrometer or similar to measure the grid in those conditions. I would assume its working because of leakage resistance and capacitive coupling across the input transformer.
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#20 Re: Phono Frustration

Post by izzy wizzy »

Nick wrote: Mon Mar 04, 2019 10:16 pm Yep, you would need to use a electrometer or similar to measure the grid in those conditions. I would assume its working because of leakage resistance and capacitive coupling across the input transformer.
I don't happen to have one of those handy. And yes, I reckon it produced sound due to leakge capacitance. I was surprised at just how much audio I got.

Anyway normal service has been resumed by just sticking the stoopid batteries in. All this could have been easily avoided :roll:

Now I would like to play with the bias hence questions a while back about cathode bypass caps and this mistake has shed some more light on biasing pentodes ... I think.

Cheers,
Stephen
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#21 Re: Phono Frustration

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'Welcome to the next level'
"Once you find out ... the Circumstances ; then you can go out"
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#22 Re: Phono Frustration

Post by izzy wizzy »

IslandPink wrote: Mon Mar 04, 2019 11:31 pm 'Welcome to the next level'
You mean remembering to stick the batteries in?
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#23 Re: Phono Frustration

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:D
Sound Practices, man !
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#24 Re: Phono Frustration

Post by Nick »

Trying to get my head around your output stage. Its a very small cathode resistors for a cathode coupled phase splitter. I know the transformer in the anode will do a lot of the heavy lifting.
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#25 Re: Phono Frustration

Post by izzy wizzy »

IslandPink wrote: Mon Mar 04, 2019 11:40 pm :D
Sound Practices, man !
Well I got much inspiration from them things. JC's siren song changed my outlook for one. Not the circuit as such but his approach.
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#26 Re: Phono Frustration

Post by RhythMick »

izzy wizzy wrote: Tue Mar 05, 2019 7:46 am
IslandPink wrote: Mon Mar 04, 2019 11:40 pm :D
Sound Practices, man !
Well I got much inspiration from them things. JC's siren song changed my outlook for one. Not the circuit as such but his approach.
That was one of my inspirations too. Might try building it one day.
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#27 Re: Phono Frustration

Post by izzy wizzy »

Nick wrote: Tue Mar 05, 2019 12:00 am Trying to get my head around your output stage. Its a very small cathode resistors for a cathode coupled phase splitter. I know the transformer in the anode will do a lot of the heavy lifting.
It doesn't look technically right does it. I don't think of it as a phase splitter which is picking nits. I had a PP 1660 tx and wanted to try it there instead of parafeed which I had been using. I could only use it PP. Everything else was there so I only had to bung it in. There was a thread hereabouts on it. It's been a dilemma do I fork out for an SE one? It used to be direct coupled so the 8k2 dropper was in the tail. I had tried a CCS in there in the past, a Gary Pimm one so decent. I couldn't hear the difference. In the model the distortion profile now is very similar to a SE circuit at small levels which is where this is. So for now, until I get a spare £200, the PP one stays as I like it. Unless anyone has some other ideas on it? I'm a bit allergic to caps compared to iron coupling. That one in the phono is the only one I have but I understand why people prefer caps.

Cheers,
Stephen
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#28 Re: Phono Frustration

Post by izzy wizzy »

RhythMick wrote: Tue Mar 05, 2019 7:55 am
izzy wizzy wrote: Tue Mar 05, 2019 7:46 am
IslandPink wrote: Mon Mar 04, 2019 11:40 pm :D
Sound Practices, man !
Well I got much inspiration from them things. JC's siren song changed my outlook for one. Not the circuit as such but his approach.
That was one of my inspirations too. Might try building it one day.
According to JC, it wasn't really meant to be built coz it's direct coupled and very hard to get right which is why he was forced to do the Mk2 ... coz peeps built it and had problems.
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#29 Re: Phono Frustration

Post by RhythMick »

Re the output stage. Have you considered (or tried) separate cathode resistors with bypass caps? I recently changed my transformer coupled 26 PP stage to separate cathodes and found it opened the sound up, much more revealing of "microsounds" in the signal. More tonal expression, more atmosphere especially on live recordings.

I suspect it's down to better DC balance, leaving more of the transformer flux for signal coupling. With the shared cathode the 26s would quite often be at 6.2 & 5.2 mA. Swapping them around made little difference, the stronger one dominated. With their own cathodes they self adjust and are usually within 0.2 mA of each other.
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#30 Re: Phono Frustration

Post by izzy wizzy »

RhythMick wrote: Tue Mar 05, 2019 8:08 am Re the output stage. Have you considered (or tried) separate cathode resistors with bypass caps? I recently changed my transformer coupled 26 PP stage to separate cathodes and found it opened the sound up, much more revealing of "microsounds" in the signal. More tonal expression, more atmosphere especially on live recordings.

I suspect it's down to better DC balance, leaving more of the transformer flux for signal coupling. With the shared cathode the 26s would quite often be at 6.2 & 5.2 mA. Swapping them around made little difference, the stronger one dominated. With their own cathodes they self adjust and are usually within 0.2 mA of each other.
I had thought of that but it slipped backwards. Be easy enough to try. Thanks for reminding me.

Cheers,
Stephen
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