New PP Pentode Monoblocks

What people are working on at the moment
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Cressy Snr
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#1 New PP Pentode Monoblocks

Post by Cressy Snr »

And so to business with the pair of EL34, PP pentode, monoblocks that will form the heart of my system.
This lot will work with the balanced passive silver wired control unit our Ant is building for me.
The two mono chassis will also come via our Ant's BTE company.
Because the passive will incorporate phase-splitting transformers, I will, at long last, be able to connect conventional sources.

Circuit will be plate-to-grid feedback operated pentodes. Input stage will be 6BS7 small-signal pentodes, direct-coupled to cathode follower driver stages. I'll put up a couple of schematics over the next few days.
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Thermionic Idler
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#2 Re: New PP Pentode Monoblocks

Post by Thermionic Idler »

Watching with interest. Are we going with 2 pairs of EL34's per channel for a powerhouse or just the one pair?
Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
Cressy Snr
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#3 Re: New PP Pentode Monoblocks

Post by Cressy Snr »

I'm just going with the one pair. I only have a 13 x 12 room, so can't really justify the electricity :)
I prefer instead to have a look at better ways of regulating the output stage screen grids, than just a VR tube shunt.
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#4 Re: New PP Pentode Monoblocks

Post by Cressy Snr »

This is the basic audio circuit; not a lot of change from the stereo project.
The volume control has been removed and the OPT has changed to a 5K a-a impedance.
Image
If I had been going parallel push-pull, I would have beefed up the cathode follower, possibly to a triode-strapped
pair of EL84, driving the four output valves, but I'll stay with a single pair of EL34 and concentrate on the power supply.
The audio circuit sounds so good, it would be a shame to possibly spoil things by altering it.
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Mike H
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#5 Re: New PP Pentode Monoblocks

Post by Mike H »

From experience 4 x EL34 can be bluddy hot so with 8 x EL34 might be able to make toast. :D

Remkinds me the Maplin lab ran a Velleman 8000 valve amp which had 8 x EL34, made a good room heater as I recall.
 
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#6 Re: New PP Pentode Monoblocks

Post by Cressy Snr »

Indeed
I guess, if you are wanting ultimate power, then you have to double up your output pairs and put up with the heat.
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#7 Re: New PP Pentode Monoblocks

Post by IslandPink »

Or buy some GU81M from Yuriy ....
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pre65
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#8 Re: New PP Pentode Monoblocks

Post by pre65 »

IslandPink wrote:Or buy some GU81M from Yuriy ....
Are these what Paul and Andrew I have tried ? :)
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Paul Barker
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#9 Re: New PP Pentode Monoblocks

Post by Paul Barker »

i have a pair but thats as far as it goes.
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andrew Ivimey
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#10 Re: New PP Pentode Monoblocks

Post by andrew Ivimey »

If I 'member right I tried using G3 as the anode! (SE) I have three and a pair of sockets. The sockets are more expensive than the valves. They are prodigious and, surely, not the sort of thing you'd want to do PP with!
Philosophers have only interpreted the world - the point, however, is to change it. No it isn't ... maybe we should leave it alone for a while.
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#11 Re: New PP Pentode Monoblocks

Post by Cressy Snr »

andrew Ivimey wrote:If I 'member right I tried using G3 as the anode! (SE) I have three and a pair of sockets. The sockets are more expensive than the valves. They are prodigious and, surely, not the sort of thing you'd want to do PP with!
I am too chicken to want to do ANYTHING with them! :lol:
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#12 Re: New PP Pentode Monoblocks

Post by Cressy Snr »

Right,
So we have a power supply drawing.

Image

PSU is all Danbury iron, courtesy of our Mike H.
The input stage screens will, as in the existing Barbarik, be regulated by Nick's MJ statistical regulator kits.
EL34 screens will be series-regulated, to around 300V using a 6EM7 dual triode as the pass element with the hi-gain section as the error amp.
The 6EM7 will share the same heater supply as the 5687 type cathode follower driver, which is itself elevated to 140V above ground.
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andrew Ivimey
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#13 Re: New PP Pentode Monoblocks

Post by andrew Ivimey »

It's not the voltage / current per se but here's a rule (there will be exceptions but):- What's the point when the valves are the cheapest part of the circuit?!
Philosophers have only interpreted the world - the point, however, is to change it. No it isn't ... maybe we should leave it alone for a while.
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#14 Re: New PP Pentode Monoblocks

Post by Cressy Snr »

Aye, the cost of the power supply rises exponentially as the HT increases.
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#15 Re: New PP Pentode Monoblocks

Post by Cressy Snr »

All the iron is now ordered from Danbury, courtesy of Mike.
Next thing is to order the reservoir caps and their mounting hardware plus the coupling caps,
resistors, tagboards, wire and all the rest of he twiddly bits.

I've made a spreadsheet for the bill of materials.
When you do this, you really start to see the amount of stuff that you need in order to get the project built.
It's gonna be an expensive project and it represents the most I've ever spent on a single item of DIY, but I have the chance
so why not.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
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