Brilliant.Will wrote:Move the first section into a separate box and call it a Pre-Amp
Next Single Ended build
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Paul Barker
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#76
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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Paul Barker
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#77
I'm not sure if I have the maths but I think the value today has risen considerably beyond the rpi.
Against an index of 100, 1965 was 0.15 and 2013 was 236.
I think that means 86pence was worth £5.79 in the base year and £5.79 then is worth £13.68 in 2013 the last date we have records for. Correct me if I am wrong.
Against an index of 100, 1965 was 0.15 and 2013 was 236.
I think that means 86pence was worth £5.79 in the base year and £5.79 then is worth £13.68 in 2013 the last date we have records for. Correct me if I am wrong.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
#78
I agree with your result, but not your workings, that should have beenPaul Barker wrote:I'm not sure if I have the maths but I think the value today has risen considerably beyond the rpi.
Against an index of 100, 1965 was 0.15 and 2013 was 236.
I think that means 86pence was worth £5.79 in the base year and £5.79 then is worth £13.68 in 2013 the last date we have records for. Correct me if I am wrong.
1965 was 15.1 and 2013 was 236.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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Paul Barker
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#79
Oh yes.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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Paul Barker
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#80
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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Dave the bass
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#81
Shoddy!
Nice one Mr B, nice touch having an S0239 fitted to let the RF escape or link it to a pirate radio station
DTB
Nice one Mr B, nice touch having an S0239 fitted to let the RF escape or link it to a pirate radio station
DTB
"The fat bourgeois and his doppelganger"
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Paul Barker
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#82
The hole at the back is where a gland will go to sleeve the mains cable for the on board heater transformer.
I have high hopes for the likelyhood the design will sound pretty good without having to breadboard it.
If hum is an issue I'll have to make an off board heater module. Time will tell.
Haven't started to hook it up.
I have high hopes for the likelyhood the design will sound pretty good without having to breadboard it.
If hum is an issue I'll have to make an off board heater module. Time will tell.
Haven't started to hook it up.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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Paul Barker
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#83
Close, it's actually a patented rumble catcher which picks up the sound of the earth breathing and synchronises with the human heart beat. I got the idea from Peter Belt.Dave the bass wrote:Shoddy!
Nice one Mr B, nice touch having an S0239 fitted to let the RF escape or link it to a pirate radio station
DTB
Later I'll write in invisible ink on the aluminium top, I feel Great! Great Great Great!
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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Cressy Snr
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Paul Barker
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#85
I have just found a data sheet for the 801a which should be useable for the 10Y that with autobias max grid dc resistance is 500k. This is much more than the value I was playing safe with.
This might help as it gives me more flexibility in choice of coupling cap.
So that may look like 200k + 200k split in the middle where the hum cancellation is injected. with a 0.1µF coupling cap for 3.5Hz. I think I can get away with 3.5Hz here. If it was an IT it would have been higher. I might be able to make this value up with a few Mullard Mustard caps, those should tune up right for girl and guitar.
Further acolades from Thomas (to add to the many already received) that Andrews filament modules are the mutt's nuts have destabilised me.
The hum cancellation circuit looks a little scary against that backdrop. But it is minimal in space requirements, and the transformer isn't asked to produce more power than the valve consumes. I am using a 50 watt transformer at 35.5 watts with AC heating to all the valves. If I DC heated them I would need at least the maximum of 50 watts. This would leave no margin, and I would have to find space for four dc modules.
I am going to gamble on the px4 50 hz component. I have wound the 4v centre tapped. The 50hz component of the 10Y has a hum pot, it should be possible to null any residual 50hz at the PX4 by this adjustment. In the same way as the 100hz component in the px4 should null by use of the 5k pot on the 10Y. In both cases less than complete cancellation of the 10Y should sort out the PX4. The method is, ear in the speaker, twiddle the pots. Should AC heating with null circuitry sound better than sublime dc power supply? It might or it might not. there again it may be a total failure. I found that it worked to my satisfaction with the 6b4g when adjusting the outpout valve alone. Everything else was indirect.
So there are a lot of chances being taken in this design.
If it wasn't for the need to inject the hum I would be using grid chokes. It is quite likely that the combination of grid choke and Andrews filament supply would sound better than what you see here. But what you see here is more simple and fits the box without cramming iron next to iron and creating pathways for inductive coupling.
On that subject I am confident that the two IT's are seperated sufficiently from each other, but they are directly on top of the output transformers. To mitigate this the output transformers are R core so should contain their magnetic field quite well. The top is isolated from the bottom by a Faraday Shield. Ever hopeful this will suffice.
Perhaps it would be expedient to leave long leeds on the IT's so they could go on stilts or perhaps be mounted higher inside a metal box (can't justify the cost of mumetal) should coupling be detected (evidenced perhaps by "not sounding as good as I expected")
So where is the achilles heal. I think it is this, the interstage transformer positioning. It is all due to me trying to make something I like the idea of fit a box which only evolved because of a piece of aluminium I had to use up. But a fair amount of money is invested in the box and some time punching the sheet of aluminium. So pig headedly I thrust forward with the project.
This might help as it gives me more flexibility in choice of coupling cap.
So that may look like 200k + 200k split in the middle where the hum cancellation is injected. with a 0.1µF coupling cap for 3.5Hz. I think I can get away with 3.5Hz here. If it was an IT it would have been higher. I might be able to make this value up with a few Mullard Mustard caps, those should tune up right for girl and guitar.
Further acolades from Thomas (to add to the many already received) that Andrews filament modules are the mutt's nuts have destabilised me.
The hum cancellation circuit looks a little scary against that backdrop. But it is minimal in space requirements, and the transformer isn't asked to produce more power than the valve consumes. I am using a 50 watt transformer at 35.5 watts with AC heating to all the valves. If I DC heated them I would need at least the maximum of 50 watts. This would leave no margin, and I would have to find space for four dc modules.
I am going to gamble on the px4 50 hz component. I have wound the 4v centre tapped. The 50hz component of the 10Y has a hum pot, it should be possible to null any residual 50hz at the PX4 by this adjustment. In the same way as the 100hz component in the px4 should null by use of the 5k pot on the 10Y. In both cases less than complete cancellation of the 10Y should sort out the PX4. The method is, ear in the speaker, twiddle the pots. Should AC heating with null circuitry sound better than sublime dc power supply? It might or it might not. there again it may be a total failure. I found that it worked to my satisfaction with the 6b4g when adjusting the outpout valve alone. Everything else was indirect.
So there are a lot of chances being taken in this design.
If it wasn't for the need to inject the hum I would be using grid chokes. It is quite likely that the combination of grid choke and Andrews filament supply would sound better than what you see here. But what you see here is more simple and fits the box without cramming iron next to iron and creating pathways for inductive coupling.
On that subject I am confident that the two IT's are seperated sufficiently from each other, but they are directly on top of the output transformers. To mitigate this the output transformers are R core so should contain their magnetic field quite well. The top is isolated from the bottom by a Faraday Shield. Ever hopeful this will suffice.
Perhaps it would be expedient to leave long leeds on the IT's so they could go on stilts or perhaps be mounted higher inside a metal box (can't justify the cost of mumetal) should coupling be detected (evidenced perhaps by "not sounding as good as I expected")
So where is the achilles heal. I think it is this, the interstage transformer positioning. It is all due to me trying to make something I like the idea of fit a box which only evolved because of a piece of aluminium I had to use up. But a fair amount of money is invested in the box and some time punching the sheet of aluminium. So pig headedly I thrust forward with the project.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein