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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 21st September 2019, 12:24 PM   #11
Neville is offline Neville  United States
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I was planning on going with Edcors - power - XPWR035 and OPT - CXSE25-8-5K.

Maybe I am going about this the wrong way. I want to use El34 tubes and dont want to drive them hard and only need 2 watts. If I can get the same setup to also use 6550/KT88 then that will be a bonus (probably needing adjustments on KR). This "flea watt" will only be used to drive 12ohm speakers but also bonus if it could handle other sensitive load speakers.
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Old 21st September 2019, 12:42 PM   #12
zman01 is offline zman01  Bangladesh
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Neville,

No worries. There are ways to have your cake and eat it too when it comes to using EL34 and KT88 in the same setup.

If your power transformer is around 720-750 VCT, my estimation is it will support both the EL34 and KT88/6550. If 750 VCT is high for the EL34, then you can drop the B+ voltage by using a 5U4G rectifier instead of a 5AR4 rectifier. With the 2 rectifiers you can experiment with the sound at different B+ voltages.

Your choice of power transformer (XPWR035) is rated for 2 amps on the 5V tap - you should get one with 3 amps on 5V. This is one option:

EDCOR - XPWR002

Don't worry, I think you're on your way to building yourself a rocking amp.

George's simulations will tell you that both the EL34 and KT88 can work with 3K or 5K transformers and anything in between.

Last edited by zman01; 21st September 2019 at 12:45 PM.
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Old 21st September 2019, 01:12 PM   #13
Neville is offline Neville  United States
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This thread talks about 3-5K OPT as well. Post 15, guy says he had to max his volume out with 5K and suggested 3.5k OPT.

As you said as long as I have the right transformer and 3-5K OPT I should be good.

Thx for sticking with me on this. Appreciate your help.
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Old 21st September 2019, 01:53 PM   #14
zman01 is offline zman01  Bangladesh
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Neville,

Will look up that thread.

Yes, ouput transformers within 3k-5k should be fine with the right power transformer (again can be through a range of voltages to choose from).

Last edited by zman01; 21st September 2019 at 01:58 PM.
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Old 22nd September 2019, 03:14 PM   #15
Neville is offline Neville  United States
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Is anybody applying thermal paste or thermal pads between diode and heatsink? I think I saw George mention somewhere he used Artic Silver cpu paste which I have on hand but prefer to use the thermal pads, just because it less messy and I have a lot of them from my Pass diy build.
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Old 22nd September 2019, 07:56 PM   #16
Neville is offline Neville  United States
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And just for kicks I was trying to calculate the B+ on my future build but it does not tie up with others with the same setup. Edcor XPRW035+ CXSE25-5K 8ohms x 2:

370 x 1.414 = 523V peak AC which then flows into tube rectifier (GZ34/5AR4)
523V - 30V voltage drop from rectifier - 500V DC out

I have seen others post B+ of around 460V. Where am I going wrong ?

I also have Hammond 193H choke in mind.

Thx
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Old 24th September 2019, 01:25 PM   #17
Tubelab_com is offline Tubelab_com  United States
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Quote:
370 x 1.414 = 523V peak AC which then flows into tube rectifier (GZ34/5AR4) 523V - 30V voltage drop from rectifier - 500V DC out....I have seen others post B+ of around 460V. Where am I going wrong ?
The 1.414 number is a theoretical number that will be achieved with a perfect sine wave into your transformer at exactly it's rated input voltage and zero or a very light load current. None of these are true in a real world amp. The real world number is somewhere around 1.3.

My SSE runs about 460 to 465 volts with solid state rectification and 425 to 435 with a 5AR4.

Quote:
thermal paste or thermal pads between diode and heatsink?
The large diodes are only needed if the solid state rectifier is used. If you plan to use only tube rectification, leave them out. No heat sink is needed if they are used.

The 10M45's are current source chips which are required in all builds. They need small heat sinks, but no compound is needed. I usually just screw the heat sink to the chip, but this will put 300+ volts on the heat sinks. Insulating thermal pads could be used if desired.


I looked up your speakers but the manufacturer does not have any impedance VS frequency data posted for the MKII version. If they are like the MKI's, the impedance drops into the 8-10 ohm range in the midrange frequencies where distortion is most audible, so an 8 OHM OPT would be the right choice.


If the speakers do actually have a 12 to 16 ohm impedance over the whole audio frequency range, then the output tubes will see a true load in the 8 to 10 K ohm range. Most tubes produce less output power, LOWER distortion, and a higher damping factor when operated class A into a higher than recommended load. This may be exactly what you want.

You could always try putting a resistor in parallel with your speakers to lower the load impedance on the tube. Yes, it will waste power, but you have plenty, and it may improve the sound, but it's just a guess. I have done this when connecting 32 ohm and higher headphones to a TSE amp and it sometimes helps.
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Old 24th September 2019, 05:27 PM   #18
Neville is offline Neville  United States
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Thx George, exactly what I was looking for. btw Zu Audio also sells 25ohm load resistors to reduce impedance of their speakers down to around 8ohmd. I could try that out on 8ohm tap but let me get my SSE built and listen to it first.
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Old 12th October 2019, 12:39 PM   #19
Neville is offline Neville  United States
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Does anybody know if its easy to convert this to only a preamp?
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