4P1L Series or parallel filament:
Series:
- Greater Vf means higher bias-slew along the length of the filament;
- needs higher value of bias resistor (filament bias designs): this may lower distortion but ra is raised, so load must be considered
Parallel mode should be better, generally, but it can be worth trying both and measuring distortion at the important signal levels.
The filament regulators can have resistors for series and parallel modes included in the kits, so you can try both.
Series:
- Greater Vf means higher bias-slew along the length of the filament;
- needs higher value of bias resistor (filament bias designs): this may lower distortion but ra is raised, so load must be considered
Parallel mode should be better, generally, but it can be worth trying both and measuring distortion at the important signal levels.
The filament regulators can have resistors for series and parallel modes included in the kits, so you can try both.
Excellent thanks!!
So what about fixed bias?
Can I ground the center tap of the four 4P1L filaments, and run the regulator at 2.6A? 650mA each
+ output of regulator to both filament ends (pins 1 and 7) and the - to the center tap (pin 8) and ground.
It would give me 2v across each filament within the envelope. Then I can make the control grid of the 4P1L -16v or so (I plan to run the 4P1L at ~225v). I am going to put 1% precision 1R current sense resistors at the anodes of the tubes. This is for a power amp not a line preamp, two of the 4P1L's in parallel each channel.
Thanks again.
So what about fixed bias?
Can I ground the center tap of the four 4P1L filaments, and run the regulator at 2.6A? 650mA each
+ output of regulator to both filament ends (pins 1 and 7) and the - to the center tap (pin 8) and ground.
It would give me 2v across each filament within the envelope. Then I can make the control grid of the 4P1L -16v or so (I plan to run the 4P1L at ~225v). I am going to put 1% precision 1R current sense resistors at the anodes of the tubes. This is for a power amp not a line preamp, two of the 4P1L's in parallel each channel.
Thanks again.
This is how I'd rebuild my previous 4P1L PSE with fixed bias and A2 drive:
The driver is the 6e5p (or better 6e6p-dr) which is very linear and works well with a bit of degeneration in the cathode. As the stage is a hybrid mu-follower (i.e. gyrator load) the reflected cathode resistor in the anode isn't impacting the output impedance. The follower is a classic MOSFET (high GM, low Crss) follower using a symmetric +/-80V to provide enough headroom. The HT is a bit marginal for the driver but provides good headroom for the 4P1L.
The rest of the circuit is self explanatory
As I don't need the A2 power, I end up with the 4P1L PSE with filament bias I have now. Probably will rebuild this version as the follower drives well the PSE pair. I'd go for 3 valves next time.
Hope this helps.
Cheers
Ale
The driver is the 6e5p (or better 6e6p-dr) which is very linear and works well with a bit of degeneration in the cathode. As the stage is a hybrid mu-follower (i.e. gyrator load) the reflected cathode resistor in the anode isn't impacting the output impedance. The follower is a classic MOSFET (high GM, low Crss) follower using a symmetric +/-80V to provide enough headroom. The HT is a bit marginal for the driver but provides good headroom for the 4P1L.
The rest of the circuit is self explanatory
As I don't need the A2 power, I end up with the 4P1L PSE with filament bias I have now. Probably will rebuild this version as the follower drives well the PSE pair. I'd go for 3 valves next time.
Hope this helps.
Cheers
Ale
I've really been itching to do one of these guys at some point. Definitely thinking A2 with source followers, maybe parallel output tubes. Probably go for the loktal 7F7 as a driver, for some headroom for cathode degeneration/global feedback. Black industrial style wrinkle paint is a must 
Where are you guys finding affordable tubes? EBay is getting pricy, and I've been burned twice by the affordably priced Russian sellers I've tried to order from.
Where are you guys finding affordable tubes? EBay is getting pricy, and I've been burned twice by the affordably priced Russian sellers I've tried to order from.
Well, 7F7 isn't good for a 4P1L. Way too much gain. Reserve it for a 2A3 or 300B amp. The beauty of 4P1L is that it doesn't need the same drive as the other DHTs.
Global feedback? No way, not even think about it. The low RA of the 4P1L is great. Local feedback in a pentode is nice, global feedback, arghhhh!
Global feedback? No way, not even think about it. The low RA of the 4P1L is great. Local feedback in a pentode is nice, global feedback, arghhhh!
Fixed bias will work very well. Connect the filaments exactly as you state for parallel operation. Operating multiple tubes in parallel-filament arrangement is OK, but only if they are in the same L or R channel (parallel across L and R will give crosstalk of anode-current).
EDIT: I should say that the POSITIVE output of the regulator should be connected to the system ground, for best sound.
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Hi Ale
After I finish my phono stage, I would like to plan for a new 4P1L based amp.
I have both 6E6P's, left from an unsuccessful 6E6P/6C4C monkey amp, and a number of 01A's that I collected to build your Gen2 linestage down the road.
So, your suggested 4P1L rebuild using 6E6P's is intriguing, but I would like to ask if you've ever been tempted to build the Pt.4 version of the East vs West amp you published on your website?
01A into parallel(or triple?) 4P1L's, gyrators, source follower, grid bias etc. How could that not sound fantastic ?
Thanks, Peter
After I finish my phono stage, I would like to plan for a new 4P1L based amp.
I have both 6E6P's, left from an unsuccessful 6E6P/6C4C monkey amp, and a number of 01A's that I collected to build your Gen2 linestage down the road.
So, your suggested 4P1L rebuild using 6E6P's is intriguing, but I would like to ask if you've ever been tempted to build the Pt.4 version of the East vs West amp you published on your website?
01A into parallel(or triple?) 4P1L's, gyrators, source follower, grid bias etc. How could that not sound fantastic ?
Thanks, Peter
Hi Peter
The 6e5p/6e6p-dr can drive the 4P1L stage at full power with just 1Vrms. It will mean that you will play at 50% of the volume pot to get maximum signal. I have currently an EML20A http://www.bartola.co.uk/valves/2018/03/25/eml-20a-dht-preamp/ mesh which has a gain of 20 driving the pair of 4P1L output valves.
I think it may be on the high side in terms of gain if you go for the 6e5p/6e6p-dr, I haven't tried it yet but worth looking into it. It will depend on your source line level and your system.
Here is a review of various drivers. Probably more suitable for a 300B or GM70/211/845 SE build thread but worth sharing:
http://www.bartola.co.uk/valves/2018/04/01/driving-hard-part-i/
Cheers
Ale
The 6e5p/6e6p-dr can drive the 4P1L stage at full power with just 1Vrms. It will mean that you will play at 50% of the volume pot to get maximum signal. I have currently an EML20A http://www.bartola.co.uk/valves/2018/03/25/eml-20a-dht-preamp/ mesh which has a gain of 20 driving the pair of 4P1L output valves.
I think it may be on the high side in terms of gain if you go for the 6e5p/6e6p-dr, I haven't tried it yet but worth looking into it. It will depend on your source line level and your system.
Here is a review of various drivers. Probably more suitable for a 300B or GM70/211/845 SE build thread but worth sharing:
http://www.bartola.co.uk/valves/2018/04/01/driving-hard-part-i/
Cheers
Ale
Hey Peter,
You pushed me this morning to go and build the 6Э6П-ДР (6e6p-dr) preamp / driver!
See below for my implementation and comments:
http://www.bartola.co.uk/valves/2018/04/02/6э6п-др-6e6p-dr-preamp-driver/
Worth implementing in my view
cheers
Ale
You pushed me this morning to go and build the 6Э6П-ДР (6e6p-dr) preamp / driver!
See below for my implementation and comments:
http://www.bartola.co.uk/valves/2018/04/02/6э6п-др-6e6p-dr-preamp-driver/
Worth implementing in my view
cheers
Ale
What kind of loctal sockets are you guys using? I am having a hard time finding them.
I see some current production ones made in China that are relatively inexpensive but I am worried they are of poor quality.
I see some NOS ones on Epray but they are all outside of the US and almost quadruple the price of the tubes I am going to put in them lmao
I see some current production ones made in China that are relatively inexpensive but I am worried they are of poor quality.
I see some NOS ones on Epray but they are all outside of the US and almost quadruple the price of the tubes I am going to put in them lmao
Does anyone sell Rod's regulators in the USA?
Are the gerber files available? I enjoy etching my own PCB's and wonder if this is an option. I will pay for the files as I understand it takes time to design them.
Another option is I don't see any kits for a 4P1L amp. Would anyone be interested in helping me make a large PCB which would include the power supply for both the B+, C- supply, filament regulators, and driver circuitry? I usually use KiCad for making boards. I will do the work but the community can help me with layout and keep me from making mistakes. Two eyes are better than one. Once the board is completed we can put them on Ebay for cost, or even put them in the diyaudio store. I am thinking of triode wiring a 6AU6A for the voltage amp stage --------> source follower --------> two 4P1L's in parallel. I am open to other drivers too.
Thoughts?
Are the gerber files available? I enjoy etching my own PCB's and wonder if this is an option. I will pay for the files as I understand it takes time to design them.
Another option is I don't see any kits for a 4P1L amp. Would anyone be interested in helping me make a large PCB which would include the power supply for both the B+, C- supply, filament regulators, and driver circuitry? I usually use KiCad for making boards. I will do the work but the community can help me with layout and keep me from making mistakes. Two eyes are better than one. Once the board is completed we can put them on Ebay for cost, or even put them in the diyaudio store. I am thinking of triode wiring a 6AU6A for the voltage amp stage --------> source follower --------> two 4P1L's in parallel. I am open to other drivers too.
Thoughts?
Radu (abszero in this site) was making his own preamp version:
Products | simplepleasuretubeamps
IMHO each diyer has different ideas, "ready" PCB is the last solution for us.
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Rod and Ale are the designers and as such sell their own kits - I don't see that changing. Shipping across the pond is one of the realities we have to live with - like us Europeans having to buy 01As from the USA and you Americans having to buy 4P1Ls from Europe. I'm using 2P29L right now so all European. We have Lundahl over here but we import Hammond from Canada and OPTs from Asia. It's a global village.
Bear in mind also that if you use a lot of filament/HT/plate chokes or interstages you don't have much need for a PCB. I use hex nylon spacers with solder tags on top for all my interiors and that's frankly all that's needed.
Bear in mind also that if you use a lot of filament/HT/plate chokes or interstages you don't have much need for a PCB. I use hex nylon spacers with solder tags on top for all my interiors and that's frankly all that's needed.