2A3 Monoblocks
- Cressy Snr
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#377
Cheers Ed, those diagrams are food for thought.
I'd like my next project to be a British amplifier
maybe using these:
March 2010 was the last time I thought about these RAF transmitter valves.
10K OPT and I might have a go.
6.5W at 800V HT in class A1
Could be run in A2 for a lot more power.
I'd like my next project to be a British amplifier
maybe using these:
March 2010 was the last time I thought about these RAF transmitter valves.
10K OPT and I might have a go.
6.5W at 800V HT in class A1
Could be run in A2 for a lot more power.
Last edited by Cressy Snr on Sun Mar 11, 2012 10:31 am, edited 1 time in total.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
#378
I have some 10k transformers around somewhere you can press into service if you like?
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
- Cressy Snr
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#379
Now how can I refuse an offer like that.Nick wrote:I have some 10k transformers around somewhere you can press into service if you like?
I'll pm you next week to arrange something.
Cheers Nick!
Steve
Sgt. Baker started talkin’ with a Bullhorn in his hand.
#380
that top photo provokes thought....
you know how dog owners are supposed to take on the facial appearance of their dogs....well, it looks like Steve has taken this on board
you know how dog owners are supposed to take on the facial appearance of their dogs....well, it looks like Steve has taken this on board
There's nowhere you can be that isn't where you're meant to be
- Cressy Snr
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#381
In the end I did the next best thing to fixed bias by using a currently out-of-fashion method.
I wired the output stage cathode for Ultrapath with a nice pair of 30uF oilers, removing the 100uF Silmic electrolytic cathode bypass altogether.
Ahhhhh.........that's better.
I've always had a soft spot for DHTs using the Western Electric connection.
It might be currently out of favour with the cognescenti but good is still good in my book.
I wired the output stage cathode for Ultrapath with a nice pair of 30uF oilers, removing the 100uF Silmic electrolytic cathode bypass altogether.
Ahhhhh.........that's better.
I've always had a soft spot for DHTs using the Western Electric connection.
It might be currently out of favour with the cognescenti but good is still good in my book.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
#382
Just goes to show, I should keep up with fashion, I still thought ultrapath was a great thingSteveTheShadow wrote: It might be currently out of favour with the cognescenti but good is still good in my book.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
- Cressy Snr
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#383
Anyway here is what the original amps have finally evolved into.
From this:
To this
Peace at last.
All the advantages of PSU welly, Series regulation, Shunt regulation and the WE connection.
A long and highly educational evolution of a pretty basic 2A3 amp,
but it's lovely, it really is.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
- Cressy Snr
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#384
It is interesting (to me anyway) to note that over the amp's evolution, the audio circuit has been simplified, whilst the power supply has become more complex.
It was also interesting to have heard the sound steadily improve as the influence of capacitors has been gradually purged from the amp system.
I honestly did not think the results of all this cap neutralisation would have
produced these gains.
That Mr Barker might be onto something after all.
It was also interesting to have heard the sound steadily improve as the influence of capacitors has been gradually purged from the amp system.
I honestly did not think the results of all this cap neutralisation would have
produced these gains.
That Mr Barker might be onto something after all.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
- Paul Barker
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#385
You do still have the 100 cap on the cathode don't you (it's not in the drawing)? Then 20 is optimal ultrapath.
I find it interesting that the ultrapath helps when you have a shunt regulated power supply. But at the same time as correcting errors on the HT through the cathode it is correcting errors in the filament supply through the anode, so I suppose it still has that job to do.
I find it interesting that the ultrapath helps when you have a shunt regulated power supply. But at the same time as correcting errors on the HT through the cathode it is correcting errors in the filament supply through the anode, so I suppose it still has that job to do.
- Cressy Snr
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#386
Nope there is no cap bypassing the cathode of the 6B4G.Paul Barker wrote:You do still have the 100 cap on the cathode don't you (it's not in the drawing)?
Now here is an interesting thing.
I have always had a degree of mechanical hum from the mains transformers on both the monoblocks right from the start. I have just accepted it as part and parcel of the amplifiers.
However on firing up the first monoblock after fitting the Ultrapaths, the transformer noise disappeared completely.
After competing the mods to the other amp, exactly the same thing happened, the mechanical hum just zeroed out.
In fact both amp chassis are almost completely silent, the noise floor at the output is stygian in its blackness. I think it is this more tha anything that has helped out.
The Ultrapath connection looks as if it has had an indirect effect on the amplifier's sound, by nulling out vibration, hence microphony, leading to a cleaner overall presentation.
Soundstaging the best I've heard from any amp I have built. The bass depth goes waaay down and resolution and tone is first rate.
This thing now represents everything I want from a valve amplifier.
What I would ideally like is the same sound but with a bit more power.
Achieving that would be incredibly difficult but another higher powered project with the same degree of attention to the PSUs would tell me one way or the other...hopefully it won't be the other.
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- Paul Barker
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#387
Yes sorry I was confusing what has become known as ultrapath, with something which came out previous, which was to put a cap from B+ to cathode that was (cathode bypass capacitor value)/(mu of valve +1).
I no longer remember what this connection was named. I thought it was ultrapath, but seemingly my memory is poor.
The mecahnism by which it works is to in ac terms negate any noise in both directions.
Obviously something similar is also happening in what has become known as ultrapath where the cathode is not bypassed, but I wonder if it is as complete in cancellation.
How do you decide the ultrapath cap value?
I no longer remember what this connection was named. I thought it was ultrapath, but seemingly my memory is poor.
The mecahnism by which it works is to in ac terms negate any noise in both directions.
Obviously something similar is also happening in what has become known as ultrapath where the cathode is not bypassed, but I wonder if it is as complete in cancellation.
How do you decide the ultrapath cap value?
- Paul Barker
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#388
Isn't it odd how the web evovles and you lose track of previous stuff. All searches nowadays leed only to the method you have used Steve, so that must be the presently approved method.
The circuit I am recalling was seminal at a time when people were just trying things out. I didn't realize it hadn't passed the test of time, and I cannot find a single example of it.
The circuit I am recalling was seminal at a time when people were just trying things out. I didn't realize it hadn't passed the test of time, and I cannot find a single example of it.
- Cressy Snr
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#389
I didn't really work anything out. I just used something I had usedPaul Barker wrote: How do you decide the ultrapath cap value?
on a 2A3 DRD amp I had done once before, that I knew had worked.
I had got the original 30uF value from a Jack Elliano DRD 2A3 amp on the electra-print website. That schematic has however been changed since then
He is now using a 1000uF electrolytic as his ultrapath cap in his recent designs., with both 300B and 2A3 Go figure
Sgt. Baker started talkin’ with a Bullhorn in his hand.
#390
I think thats the Western Electric circuit. At least that what folk were calling it at the time.Paul Barker wrote:Yes sorry I was confusing what has become known as ultrapath, with something which came out previous, which was to put a cap from B+ to cathode that was (cathode bypass capacitor value)/(mu of valve +1).
I no longer remember what this connection was named. I thought it was ultrapath, but seemingly my memory is poor.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.