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New SE 6P15P project

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just completed this 6P15P amp. It is a variation of this amp http://www.geocities.com/dmitrynizh/6p14p-twzsh-pio.htm

Changes are that I am running 6P15P (EL83) instead of 6P14P. Gain was a little low, so I added a 1500uF cathode bypass cap on the 6P15P cathode resistor. Also wired switcheable cathode feedback and since the output transformer has an ultralinear tap, I made that selectable on/off as well. Power supply is 5U4G, 47uF-5H choke - 47uF - 22R - 68uF - 22R - 80uF motor run cap.

Chassis is something I picked up in Singapore last week for $40 Singapore dollars, about $28 US dollars. Back panel was pre cut for IEC power socket, fuse holder and two sets of input sockets.

This is my third valve amp project. First was a SimpleSE from TubeLab. Second project was a push pull 6BM8 point-to-point wired project that did not work out very well. It did kind of work, but the hum was awful. Forced me to get in to the books and look a little more closely to how I was doing things. I have dis-mantled it and will now attempt a re-build. This project is a little simpler, and I gave myself a little more room with the chassis. Hum is almost non-existent (have to put ear inside of speaker cone to hear any hum).

Overall it sounds pretty good. Not quite as good as my SimpleSE, but as a "learner" project, I feel pretty that I have met my goal of a hum free amp. This project will be used to power a set of mini-fonken speakers using Fostex FE 127E drivers. Speakers are just about finished, just waiting for the paint to dry. The whole package will be a Christmas gift for my girlfriend to be used as computer sound system in her office to accompany her new iMac computer.

Now if only I could get the internal wiring looking as neat as some of the people posting here!

Cheers,

Chris
 

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Here she is next to my TubeLab SimpleSE...

Think I forgot to mention before that output transformers are Edcor XSE 15-8-5K. Input valve is 6N1P. All valves (5U4G, 6N1P, 6P15P) are Soviet sourced cheap on Ebay. Motor run cap is $12 Ebay. Power transformer was $40 Singapore 150 mA 270-0-270, 5H 150 mA Hammond open frame choke. No other fancy components inside, just stock resistors from the local electronics shop. Figured it was not worth spending mega-dollars on a learning project that was going to be playing MP3s from a computer.

Cheers,

Chris
 

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Thanks for the compliment Sal.

Both the amps use the Edcor transformers. For the SimpleSE I used spade connectors to attach to the solder lugs, then covered with heat shrink. For the new amp, I simply soldered to the tags and covered with heat shrink. The 6BM8 failed project (not a real failure, it taught me a lot) used the slightly smaller 10 watt push pull transformers. I will re-use them for the re-build on a chassis the same size as this project. The amp is playing at the moment, so cannot connect to the scope to see the total output power. As the topology (in triode mode) is very similar to the Decware Zen, and it uses the same valves, I am guessing around 2 watts per channel.

Chris
 
Chassis was purchased from Well Audio Labs,

Ground floor, Burlington Square (behind Fatty's Restaurant). Burlington Square is next to Sim Lim Square.

This is the smaller chassis. 11" x 8" x 2.25". Top, bottom, front , back, sides are all screwed to each other and you can remove all individually - very convenient when building. Steel construction with aluminium front plate. The recesses part of the front plate detaches for easy drilling of switch/knob holes. Not bad for the price. Picked up two of these, one for this project and one to re-build 6BM8 that I will use to go in my office to play iTunes from Mac.

Larger version available for $60 Singapore dollars, 14" x 10.25" x 2.25". I got one of these too to build a push pull EL84 ("Baby Huey").

Chris
 
Here she is next to my TubeLab SimpleSE...

Two pretty amps in a row. If you are not careful, you may come down with a full blown case of Single Ended Fever. The only cure is to build a push pull amp. The recovery process is not foolproof though. I have started down the path twice only to have a relapse. My P-P amp has been pushed aside and there are two unfinished SE amps on my workbench.

Just kidding, your second amp looks better than the first, whats next?
 
Thanks George,

I must admit, since my SimpleSE was so quiet, I "borrowed" a few features. The power supply is almost a direct copy, the 22R resistors were used to bring the voltage to the required level (just modelled in PSII). The cathode bias is a direct copy also...

Next project? I plan to re-build the 6BM8 push-pull project that did not quite work out. I don't really consider it as a failure, it was just a little ambitious as a first point to point project. What I learned from that build allowed me to build this quiet amp ;-) When that is finished, I plan to build a push pull EL84 (6P14P actually) using this http://www.diyaudio.com/forums/showthread.php?postid=826626#post826626

Have sourced many of the parts, just power transformer, resistors and power supply electrolytics to go. Could not see any suitable (275-0-275 volt 200 mA) power transformers available in Singapore when I was there, and Antique electronic supply don't have the 300 series Hammond in stock at the moment. Suggestions?

Anyway, here is what I have collected so far for "Baby Huey".

So when can we expect to see the TubeLab SimplePP? :D
 

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So when can we expect to see the TubeLab SimplePP?

I have been working on it off and on for several months. A familly emergency has unfortunately sidelined most Tubelab activities for the past several months. The situation should improve in January.

The TubelabPP breadboard was on my workbench when a dead TubelabSE came in for repair. It had the large Edcor OPT's and 300B tubes. It was a combination that I never tried before, and it sounded so good, that I kept it around for a week just to listen to it. Now that it is gone, I got the fever again, and I just have to make one since I already have the Edcors and all of the other parts. The parts are all on the bench, but I don't have the time to assemble them. I have to leave town for two weeks, so.... next year!

I have not defined the TubelabPP yet. I have looked at a SimplePP style project using EL84's or maybe 6V6's, and I have been looking at making a new PCB for the driver board used in my 300Beast (a P-P amp) which could be used to drive just about anything. If I get a break next year, I'll do both.

I haven't spent much time looking for 240 volt transformers since we don't need them here, let me look around.
 
I have only found three 275-0-275 volt transformers that operate off of 240 volts.

The Hammond 370 HX, which is hard to find, but can be special ordered through most suppliers.

The ugly Hammond 260G which is even harder to find.

The ANTEK AN-3T275 is a reasonably priced toroid that has enough current capability. It does not have a 5 volt winding so you must use SS rectifiers or something like a 6BY5. I have used other Antek toriods with good results. http://toroid-transformer.com/ They are often found on Ebay. Search for user ID johnango.

The One Electron BFT-1B is a posibility, but it is quite expensive so I have never tried one.

I am just using my old standby the Allied 6K56VG cheap and effective, but only 120 volt primary. It is also operating slightly over its ratings, but doesn't seem to get too excited about it.
 
Thanks for that George,

I might see how long the Hammond 370HX is on backorder for. Other possibility might be to get the Hammond 302AX, 300-0-300 200mA, about $7 more and tweak the power supply. Should still be able to get two of these and a choke in to the USPS flat rate box (20lb limit).

Cheers,

Chris
 
Antique Electronics Supply was willing to order me "anything from the Hammond catalog" when I wanted some transformers last year. There were no extra charges, but the transformers had to be paid for at the time of order.

Radio Daze claims the same thing on their web site, but I have not dealt with them.

Another possibility is to use a 240 to 120 volt step down transformer like the Triad N6U (I think the U stands for ugly) to make 120 volts. Then run a 120 volt 50Hz transformer. Keep in mind that many 120 volt transformers are not usable on 50Hz. The Allieds (6K56VG and 6K7VG) are but you must stick to the published ratings. I can get away with overloading them a bit on 60Hz. The N6U is $28 USD from Allied or Mouser. The 6K56VG is $41 from Allied. www.alliedelec.com

I have a stereo P-P test amp using 4 X 6V6's that runs fine on the Allied transformer. It gets about as warm as the 6K56VG in my TubelabSE. It might get too hot on 50 Hz though. If you don't find any other path you could use two, one for each channel.

Some have suggested wiring two 120 volt transformers in series across a 240 volt line. I wouldn't suggest doing that since there is a strong possibility that one channel could draw more current than the other causing unequal voltages between the two transformers. This is a quick way to make toasted parts!
 
tubelab.com said:


Some have suggested wiring two 120 volt transformers in series across a 240 volt line. I wouldn't suggest doing that since there is a strong possibility that one channel could draw more current than the other causing unequal voltages between the two transformers. This is a quick way to make toasted parts!


If they are identical connect secondaries in parallel and call it "SimplePT" :clown:
 
Thanks for the help guys. Will be away with work for the next three weeks, so not in any real rush to get these. I will be in Singapore over Christmas, so will search a round a little more up there during a break. Anyway, this is just a hobby to keep the brain active when I am not at work. I have plenty of amps to power my speakers, so waiting a little is no problem.

Cheers,

Chris
 
Hi Chris,

Great looking amp - it must be the time of year for finished projects. Looks really neat, I love the chassis. I noticed that tubelab mentioned radiodaze. I can vouch for those guys and have bought quite a bit of stuff from them. They are really easy to deal with, honest and super quick - like really quick. I always check to see if they have what I want before I buy anywhere else. The ordering system is clunky and antiquated but once you get over that they are fantastic to deal with.

Looking forward to seeing you next project.

Cheers,

Rob
 
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