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6N2P/6CW5 design with toroidal outputs
6N2P/6CW5 design with toroidal outputs
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Old 16th October 2018, 04:51 PM   #11
kodabmx is offline kodabmx  Canada
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FWIW I ran triode connected 6P43P at 300V B+ using CCS cathode biasing (about 30V) as my television amp for at least a year for 24H/day with no issues. It was working until I removed the OPTs for another build using 6DQ6B.
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Old 16th October 2018, 06:16 PM   #12
Lingwendil is offline Lingwendil  United States
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6N2P/6CW5 design with toroidal outputs
I'm not a huge fan of triode-connected pentodes unless they're really special, so my tendancy is to go pentode mode and leave things a bit lean for longevity. If going triode mode I think simply using the screen regulator for the plate supply with a big heatsink would be a nice way to go, if a bit hot and wasteful.


That reminds me I need to play with the (twenty-one!) 6P43P-E that I have on hand. When I first tried them in this amplifier (as built) They redplated quickly, so I think that some experimenting needs to be done. They pulled enough current to put over 25 volts across each 500R cathode resistor for 50mA each plate current (280 volts across each tube), and blew up one of the 50 volt bypass capacitors. Redplated at 14 watts?! This was even with the screen voltage set low so I could adjust it up as needed. I have a feeling they will need a much higher value cathode resistance, or a much lower plate voltage to be happy. They seem to be a pretty close equivalent at lower voltages, but more fooling around is needed to see what their happy place is up high. I could just use a CCS on each one, but, well, I don't want to

I haven't tried them triode connected, so I can't comment on them there.



Ideally, i would like to draw up a dual mono PCB design for this amplifier setup using EasyEDA, as it could easily be made up on a pair of 100mmX100mm boards, and there sure are enough suitable tubes to make it worthwhile to have on hand. I'll have to play more with the layout I have sketched up to get something symmetrical and easy to use. Should be useful for all those builds all my friends and family keep asking for
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Last edited by Lingwendil; 16th October 2018 at 06:30 PM.
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Old 17th October 2018, 02:17 AM   #13
Tubelab_com is offline Tubelab_com  United States
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Quote:
I'm not a huge fan of triode-connected pentodes unless they're really special
Some of them can sound pretty good. The 6V6 sounds pretty good in triode if you want a low $ alternative to the 45. The 5V6 and 12V6 are still pretty cheap. The DHP 307A triode wired makes a good stand in for the 300B. Squeezing 50 to 70 watts from a pair of triode wired KT88's is cool too, and sounds pretty good as well, but as you say, most are just OK.

Quote:
triode connected 6P43P
I have never seen these, so I can't say what they will eat.

I have maybe 20 GE 6CW5's that I pulled out of a bunch of HP audio oscillators that were headed to the metal scrappers. I also have about 12 French made rebranded UL84's that I bought for the Hundred Buck Amp Challenge, and a few 16CW5's. All behave in a similar manner, you can feed the plate anything up to 400 volts as long as G2 is around 150 volts. The screen, and maybe the plate will glow if you go over 250 volts on the screen. I never tried triode or UL with any of these.
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Old 17th October 2018, 10:49 AM   #14
emk2 is offline emk2
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Quote:
I haven't tried them triode connected
I did, they sound pretty good at 200V 35-40mA with mixed bias (100 ohms cathode resistor not bypassed and about 220K g1 to ground through negative fixed bias supply) and seem to be stable. No harshness with a high load: 10K toroidy OPT. A nice low power PP amplifier, even open loop.

Some curves here:

Roehrenkennlinien

6P43P-E triode connected looks quite nice, now take a look at pentode mode
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Old 17th October 2018, 02:01 PM   #15
Lingwendil is offline Lingwendil  United States
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6N2P/6CW5 design with toroidal outputs
Those are some weird curves in pentode! I need to dig out the curves I came across a while back, they looked way, way better than those ones!

EDIT-

artasolo posted them here, in post #918-
Vacuum Tube SPICE Models

Low current definitely looks pretty funky. Perhaps triode mode is the best use for these guys? Otherwise deep into class A to keep everything straight?
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Last edited by Lingwendil; 17th October 2018 at 02:16 PM.
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Old 17th October 2018, 11:19 PM   #16
kodabmx is offline kodabmx  Canada
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Indeed, but the 6P43P triode curves are very nice, indeed
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Old 19th October 2018, 11:21 PM   #17
Sodacose is offline Sodacose  United States
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Awesome project! Have you tried the RC step-network front end with a MOSFET concertina?

I've been thinking about putting together something similar with oddball heater tubes and Edcor XPP10s I have collecting dust:

Click the image to open in full size.

Toroid OPTs would be even cooler (though no UL).
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Old 20th October 2018, 12:21 AM   #18
Lingwendil is offline Lingwendil  United States
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6N2P/6CW5 design with toroidal outputs
I haven't, and I've been meaning to try it. Next time I order parts I plan to grab a few more types of mosfets to play with. It'll save a whole tube per channel, so worth a shot!
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Old 14th November 2018, 06:49 PM   #19
Lingwendil is offline Lingwendil  United States
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6N2P/6CW5 design with toroidal outputs
Well, I have some downtime at work, so started to draw up a PCB for this rig. Goal is to have it be semi-universal, one channel per PCB, and be 100mmX100mm. The idea is to use a separate PSU board, or traditional chokes and caps with a vacuum rectifier. Going for a modular, load it out as you like type of setup.

The connections for the plate and screen can be easily jumpered on board, or brought out to a screen supply and UL taps if desired, allowing for triode, pentode, or UL mode connections. Since the original build used garter bias successfully, I've allowed for that on the board as well, with ventilation holes under the resistors. Again, it can easily be jumpered out if standard cathode bias is desired. I may add the choice for cathode CCS loads if anybody has some good ideas for them, I'm just not sure what to choose, as everyone has their favorite CCS.

I'm considering modifying the cathode setup on the front end to allow LED or resistor/cap bias for situations that may want higher gain, with a resistor underneath to still allow for NFB to be used. Could be handy when using medium-mu tubes up front like the 6N1P, and still being able to run some NFB. It's easy enough to add the pads to the existing layout. The cathodyne setup can be biased with the step network as in the original schematic, or self-biased in the more traditional manner, too.

The front end is otherwise the same as the Flea amplifier and the posted schematic at the beginning of this thread, otherwise. should be a neat little board, and especially handy for a garter-bias, triode mode build with the 6P43P-E, 6P14P/EL84 types


Keep in mind this is very preliminary, nothing is labelled correctly yet, and I'll be modifying things as I go a bit more. Yes, I know there a few missing components, and no ground/power connections yet

Any suggestions, just let me know!
Attached Images
File Type: png PCB_NOVAL-MONO_20181114102940.png (84.4 KB, 31 views)
File Type: png t0RF3LVfWFX.png (80.1 KB, 34 views)
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Old 14th November 2018, 10:07 PM   #20
Lingwendil is offline Lingwendil  United States
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6N2P/6CW5 design with toroidal outputs
Alright, I'm in a groove, so to speak. Some more work on the PCB. I incorporated the options I listed for the cathodyne and input stage, and started labeling things. I figured having it in the documentation that you populate either the cathode LED or a cathode resistor/capacitor would mean a single LED footprint would work for both the resistor/cap and LED option, or one could simply use a wire link to run the standard cathode resistor/feedback resistor combination.

I decided to keep the same numbering scheme for things as used on the Flea amplifier, just to make it easy for refferring to the existing schematics I have drawn up on hand, and the options will be labelled differently as needed to show function a bit. Spots where wire links are intended to be placed for standard configurations are labeled "LINK" with a resistor outline on the silkscreen to make it easy to figure out at build time. As before, the intent is for you to wire up the heaters with twisted pairs of wire and jump them from socket to socket off board, but a few extra pads will be provided to make DC heaters easier to implement without jumping wire to existing components. Caps are intended to be mounted underneath the board, but will work on top if desired, everything else can go whichever way you want, although the silkscreening is on the top of the board. I'm assuming that most of the warmer resistors will end up on the top of the board so they can breathe a bit.

Yes, there are holes under the sockets for those of you that can't help themselves and feel the need to shove an LED under each tube, but wiring them up is on you
Attached Images
File Type: png PCB_NOVAL-MONO_20181114135211.png (156.7 KB, 28 views)
File Type: png dLWtbSx16St.png (84.1 KB, 22 views)
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