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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

SimpleSE / Edcor CXSE OPT

I have a Tubelab SimpleSE board in hand and I've been looking into what parts I should buy for it.

I'm wondering if anyone at all has tried the Edcor CXSE transformers yet? I know the cheaper XSE ones are decent, but would anyone be able to provide a comparison between the better Edcor and say, James? I was thinking about using James for another project before I decided on this one (and before I knew of Edcor). From what I can see, the approximate pair cost is $160 Edcor and $215 for James (rated 20W instead of the 25W of the Edcor). Besides, the open leads aren't an option due to the cat, and I figure I can keep the chassis a bit smaller without having to mount them underneath.

I'm thinking about running EH KT88 or TS 6550 as the final tube set. I was considering a set of the cheap 6L6GC for testing, at the price of $18 for 4 that can't be beat! Any suggestions for the first stage tube would also be appreciated.

Finally, I was curious how grounding should work. I am thinking about designing my own enclosure wooden sides / Al top. I would still like the jacks to be on the back, is there a grounding method that will work? I presume Anodized Aluminum is out of the question since it isn't a good conductor?

The twist of fate in this is that I now am the proud owner of a better set of speakers - Telefunken RB46 AlNiCo speakers, in Teak cabinets (~1964). They sound incredible compared to what I had before. Sadly, I have not been able to find an exact sensitivity rating but they have got to be considerably more efficient and should prove a better match for the new tube gear! :D

Thanks!
 
I'm wondering if anyone at all has tried the Edcor CXSE transformers yet?

I bought a set of these when I was developing the SimpleSE design. I tested them electrically against the big Hammonds and other transformers. The Hammonds showed lower distortion, so I installed them in an amp that I was building for use with big speakers to make big bass. The big Edcors sat on the shelf. I didn't have time to do any critical listening tests between the Edcors and the Hammonds. Recently the big Edcors came off the shelf for testing on a TubelabSE with 300B's. This setup sounded so good that I am building it into a permanent amplifier as soon as I have the time. I would think that they would do fine in a SimpleSE.

I have heard good things about James transformers, but I have not heard them myself. I am working on a new amplifier project that requires 600 ohm SE OPT's. I am currently using some Eastern Audio transformers that I got from another forum member, but I plan on getting a pair of James once everything is working.

I have a large selection of used 12AT7's and I have tried a bunch of them. A small percentage seem to sound congested when playing complex music. This does not seem to be brand specific. Several customers have recommended JJ 12AT7's, so I ordered some. I have not had time to listen to them yet.

All of the hard audio grounding stuff is handled by the PC board. If you wire the input jacks to the PC board using shielded cable the input jacks will be grounded through the shield in the cable regardless of how they are mounted. You MUST have a safety ground from the third pin on the power connector to all exposed metal on the amp. Run a piece of wire (Green with a yellow stripe if you want to follow code) from the third pin to the ground connection of one input connector. Run another wire from the third power pin (ground) to any convenient point on the metal top plate (I use a transformer mounting screw). Check continuity from the third power pin to all exposed metal on the amp before powering it up.

I have put SimpleSE's and TubelabSE's into wood, plastic, and metal boxes using the same method. Anodozed aluminum works fine, you just have to scratch through the anodizing (on the inside surface) to make contact. A star washer on the underside of the chassis is usually all that is needed.
 
Thanks for the information! I'm curious if any of the Edcor power transformers would be suitable to use with the SimpleSE? I'm gathering all the parts (most are on order) and I want to make sure I've got transformers once the board gets built for testing :)

Would any component values need to be changed to make the bias the same as in the original design (I believe with a Hammond transformer?)

Thanks!
 
I have a pair of James 6123HS OPTs in a pair of KT88 SE monoblocks and everyone that has heard them think they sound great. The amps aren't SimpleSE amps however.

The James definitely have the aesthetic edge over the Edcors (IMHO anyway, though the Edcor blue is a nice color). Another possible advantage of the James is the multiple secondary taps available. Mine have 5K, 3.5K and 2.5K plus screen tap IIRC. That would allow some experimentation.
 
Sherman - Thanks for the input. I really wish I could audition the various transformers without having to buy all of them (since I can't as a student!)

When I first started thinking about building an amp, I was considering the James transformers since their frequency response was superior to the Hammond. The Edcors are considerably cheaper than the James, but show good performance, possibly a decent compromise for my first amplifier.

What impedance are you running on your OPTs? I am planning on using KT88's or 6550's as my final set of tubes one I make sure the amp is operating properly.
 
Zap said:
The Edcors are considerably cheaper than the James, but show good performance, possibly a decent compromise for my first amplifier.
What impedance are you running on your OPTs? I am planning on using KT88's or 6550's as my final set of tubes one I make sure the amp is operating properly.

I would go with the Edcors. It's your first amp, they are affordable and they are very good transformers. The output impedance depends on the output tube you choose and the voltage you are running it at. Reviewing the manufacturers tube data sheet should give you an idea. A comprehensive data sheet will have a chart for distortion vs. max power vs. output impedance. As for the earlier post about the new Tung Sol 6550s, I have a set of these from Cryoset (cryo treated) and I have zero complaints. I have been extremely pleased with the sound quality of these tubes. I have not used the EHs so I can't comment on those. Happy building!
 
Zap said:
... I really wish I could audition the various transformers without having to buy all of them (since I can't as a student!)

...

What impedance are you running on your OPTs? I am planning on using KT88's or 6550's as my final set of tubes one I make sure the amp is operating properly.


That's one of the problems with tubes. The OPTs can cost a fortune and there is often no way to hear before you buy. I took a chance on the James OPTs and it worked out. (When I bought them they were only $198/pair.)

I have two pairs of the open frame Edcors, 5K SE and 8K PP. I'm still building the PP amp so I haven't heard those yet. I swapped the SE into an EL84 SE amp I have and they sound very good. I don't think you would go wrong with Edcor.

As for impedance in my KT88 amps- I am running them on the 5K tap. With the B+ at 424 and idle current at 82mA I get about 7 to 7.5 watts per channel. I'd get a bit more power running them on the 3.5K tap with a bit more distortion. (That's the trade-off with OPTs. Higher impedance gives lower distortion and lower power, lower impedance gives higher distortion and higher power.)

KT88s would be happy with 3.5K to 5K primary Z in the OPTs. 6550s should like the same.
 
Thanks again for all the input - just to clarify, I'm actually considering buying the CXSE transformers (the higher end Edcor) since I want something without open frames for safety reasons and I want a bit better frequency response. I realized I never mentioned which ones I was considering.

I'm still interested in input regarding the power transformer as well.
 
The sockets in question are the following (from AES):

3 Octal Sockets P-ST8-193
Ceramic stand-off PC mount socket has 13/16" tail diameter.

1 Noval Socket P-ST9-214
Ceramic stand-off PC mount socket with 1" tail diameter.


I've noticed they stock the Octal socket in gold and those are in stock. My question becomes whether that is a good idea. I remember reading somewhere about not mixing and matching gold with non-gold sockets/pins. I can't remember which combinations were OK and which were not recommended.

Thanks!
 
I have not tried the Edcor power transformers, but most (if not all) do not have the 5 volt winding so you are stuck using the solid state rectifiers only. I am always looking for bargains so I have been using the Allied 6K7VG power transformers wherever I can. They work great in the SimpleSE and are the lowest cost power transformer of its size. Been using them for over 10 years without issue even in some heavilly abused guitar amps. Since they are really Hammonds (for less money, $46) they do get rather warm. The 150 mA rating applies to 50Hz use, no problem at 175 mA on 60Hz. Compare to Hammond 274BX.

I also use the 6K56VG for smaller projects like a SimpleSE with 6V6's or a TubelabSE with 45's ($41).

http://www.alliedelec.com
 
Okay, I got a chance to talk to Edcor today about the power transformers.

They charge a one time fee to custom design of $20, but if someone else has already paid that, they charge just the mfg cost for the actual transformer. The biggest question becomes if a higher HV tap or no CT on the 6.3V makes a difference. That way I could use a pre-existing design that doesn't cost much more than the Allied part.

As compared to the Allied 750VCT @ 150mA HV, 6.3VCT @ 5A, 5V @ 3A ~$46

XPWR006 - 820VCT @ 200mA, 6.3VCT @ 5A, 5V @ 3A ~$63

XPWR033 - 760VCT @ 200mA, 6.3V (No CT) @ 5A, 5V @ 3A ~$60

My reasoning is that paying another shipping cost to Allied for a heavy transformer would probably add $10 to the cost, vs considerably less for the Edcor shipment with two OPTs already in it. Additionally, this way the transformers would match which would be nice as well, since I will be using the CXSE series which has better frequency response. The better Edcors are still less costly than springing for a set of James, and they seem like they would be more in the ballpark than the cheaper ones.

So, my question now is whether I need to adjust a few components to use the other transformer or if I'm looking at making things more complicated.
 
I knew it was out there somewhere... here's the link to the schematic for the SimpleSE. I see that the C/T on the 6.3V portion of the transformer isn't used, so that might make the closer HV tap value more appealing.

http://www.tubelab.com/SimpleSE_schematic.htm

I'm also curious what value of choke & motor run cap people have used in the design before - I'm not as well versed on power supply design as I'd like to be!
 

Geek

Member
2004-09-08 7:17 am
Hi,

Zap said:
The sockets in question are the following (from AES):

3 Octal Sockets P-ST8-193
Ceramic stand-off PC mount socket has 13/16" tail diameter.

1 Noval Socket P-ST9-214
Ceramic stand-off PC mount socket with 1" tail diameter.


I have them in stock. Not in gold though.

My 9-pin is the better type (non sealed) for reliability.

I will price match AES.

Cheers!