Edcor OPT in S5 Electronics K-16LS kit?

[damilkman81]

Still waiting for My Edcor Opts

As raved about above, I called Edcor and ordered a set of opts. Has anyone used molex connectors for quick disconnect of circuit boards. I am tempted but am cautious. I also wondered what type of a beating these tubes can take. I have already removed them from the board a couple of times for retro fitting in a cabinet. I assume that they are more fragile when hot so I don't move the unit shortly after operating. It also gives the Caps a chance to discharge due to the lack of resistors.

I am great full for all of the comments out there from new and old. Thank you for sharing your experience with the rest of us.

Take care,

 

[Fran604g]

Hey guys, thanks for all the effort and advice I've found here on this amp!

I gave one to my son for Christmas, and he's got the board finished, nice simple project, a great way for him to learn how to solder!

We're going to complete the kit as stock and after a listen, I'm going to suggest that he make some of the mods that everyone's come up with (PS caps & bleeder resistors, signal caps, snubbers, diodes, etc.)

I have an old pair of Bose 501's that he can use (4ohm) so we can get an idea of the sound. But, ultimately, we're doing a speaker build with AR4x's that need rebuilding/modding, so likely we'll be wanting 8 ohm taps.

The OPT's are obviously the highest cost, so we'll have to evaluate whether or not they are "neccessary," can someone tell me how much they are?

Also, I have never ordered tranformers before, is there a part # at Edcor, or should I just ask about the OPT's for a, "S-5 K16LS"?

Thanks in advance for your help!

 

[123rmp]

The transformer part numbers I used are in the first entry of this thread......Edcor CXPP25-8-5K.

I selected these based on suggestions from others in this forum. They were about $50 each I think. The Edcor website has lots of info and you can order on-line from them.

I am not 100% sure that these transformers have both 4 and 8 ohm taps. They may, I just can't recall. Edcor website has the data.

 

[Fran604g]

Thanks, 123rmp!

 

[Rukahs]

Just a quick question, for new OPT's on the K-16LS. Do the stock (and new EDCOR replacements) have a 5k primary impedance or 2.5k because of parallel push pull?

 

[Rukahs]

or as the 2nd post said, is it ok to get 5k primary impedance and load the secondry with 4 ohms instead of the 8 the OPT is spec'd for ?

 

[highfieldrebel]

K-16LS stock OPT turns ratio

This thread looks long cold, but in case someone wanders across it again....

I measured the voltage stepdown in the included output transformers, got a turns ratio of 35.4, square that equals 1252 and so a 4 ohm load reflects as 5 kOhm.

 

[paulwd]

problem

Hi All,

I've just purchased the CXPP25-8-5K OT's for my K16LS, but am having trouble installing them.

After reading through the advice on this thread, I connected up both Edcor OT's with the red, brown and blue wires connecting to the corresponding RD (red), BN (brown) and BL (blue) on the board. Then I connected up the OT's yellow and white wires to the corrosponding GN (green) and BL (black). The white/blue and white/brown screen wires have been taped off.

My problem is when I turn on the amp, I immediately get a fairly loud hum, and can just faintly hear the music. I double checked all the connections, but couldn't get it to work.

When I swapped back to the original OT's, it worked fine. This is my first adventure into DIY tube amps, and I am probably just missing something basic here, but for the life of me, I can't work it out!

If anyone can help me, that would be fantastic!

Cheers,
Paul

 

[alexcp]

Most likely you wired Edcors wrong; wire colors may or may not be the same for them as for the original trafos. Pls see a working example of K-8LS with Edcors:

 

[paulwd]

Thanks for the reply!

Ok, so you have the yellow and white wires from the Edcor going to your speaker posts first and then to the board?

That looks to be the only difference to the way I had mine wired in.

 

[alexcp]

Wiring yellow and white to speaker posts first and then to the board is not essential. Important is that whites are grounded, the feedback is taken from yellows, that reds connects to B+, and that blue and brown are not swapped.

 

[paulwd]

I've attached a photo showing how I have wired them in, which as far as I can tell is correct. I also tested the connections with a meter to make sure the solder joints are ok.

I still have the problem that I get a reasonably loud hum as soon as the amp is switched on.

Another weird thing is that if the ground lug on the right channel touches the red speaker plug, the hum disappears and I get sound out of the right channel only. The most worrying thing is that the power transformer starts to smell like its overheating after a few moments, so I switch it off after a few seconds.

Again, if I switch back to original OT's, everything is fine.

 

[Jpeg]

I have heard that Edcor does not always use the same colors for it's wires. Can you post what the sticker says on the bottom?

 

[paulwd]

Yep,

Here is the sticker info:

CXPP25-8-5K
25 WATTS
SCREEN VOLTAGE 40%
SECONDARY: 8 OHMS


BLUE - PLATE

WHITE/BLUE - SCREEN || 8 OHMS - YELLOW

RED - B+

WHITE/BROWN - SCREEN || COMMON - WHITE

BROWN - PLATE

 

[Jpeg]

After looking at the schematic, it looks like you have wired them correctly. Let me scratch my head for a bit...hmmm

 

[BlindAgent]

Sorry to dig up an old thread. I'm completely new to tube amplifiers and was wanting to do this Edcor Output Transformer mod listed. I notice the output is rated for 8ohms, however, I would like to power 4ohm speakers. Can this be done with the following transformer as a straight drop in without additional modifications: CXPP25-8-2.5K?

 

[Jpeg]

I think it is the other way around. I think that would give you a 1.25K load on a 4 ohm speaker. (The ratio between them stays the same) There is this guy CXPP25-6-7.6K with a 7.6k load at 6 ohms. That should give you about 5K on the plate with a 4 ohm speaker. There is also it's little brother GXPP15-4-5K which has a 5K load on a 4 ohm speaker. I ordered a pair of the 10 watt GXPPs for my S5 K-12, but they have not come yet, so I don't know if they are a substantial improvement over the stock ones. I will post my findings when I know.

 

[BlindAgent]

I think it is the other way around. I think that would give you a 1.25K load on a 4 ohm speaker. (The ratio between them stays the same) There is this guy CXPP25-6-7.6K with a 7.6k load at 6 ohms. That should give you about 5K on the plate with a 4 ohm speaker. There is also it's little brother GXPP15-4-5K which has a 5K load on a 4 ohm speaker. I ordered a pair of the 10 watt GXPPs for my S5 K-12, but they have not come yet, so I don't know if they are a substantial improvement over the stock ones. I will post my findings when I know.

Thanks Jpeg! I get how it works now and I'm assuming I can just swap these in without any further mods elsewhere in the schematic? I was looking at the GXPP15-4-5K but I noticed that it's only rated for 15W but the K16 is 16W...does the 1W make a whole lot of difference?

 

[Jpeg]

You should be able just hook it up as is. The Edcore will have a ultra-linear tap that you won't use, make sure you insulate this well, it will have somthing like 250 volts on it. I wouldn't worry about using a 15 what transformer on this particular amp. In a review of the K12 http://diyaudioprojects.com/Tubes/K-12M/audioXpress-review-of-S5-Electronics-K-12M-Tube-Amp-Kit.pdf they say that it actually only puts out about 4.5 watts and in order to get 8 watts out of it, you have to push it to the point of 28% distortion. I have not seen measurements on the K-16ls but I would expect them to be similar. I would expect better bass performance from the larger ones though.

 

[BlindAgent]

Thanks Jpeg. I'm looking forward to your findings on the GXPP's!