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stereo SE kt88 build ... abdellah diyaudioprojects design
stereo SE kt88 build ... abdellah diyaudioprojects design
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Old 13th September 2009, 12:55 AM   #21
Tube-Head is offline Tube-Head  Netherlands
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Quote:
Originally Posted by 88man View Post
I am wondering what brand of NOS 61NP tubes will work well with an EH KT88?...
I use russian 6N1P tubes that i bought on ebay.
They have a red print on the tubes. Can't find them on ebay anymore.
Use them for the 6N1P Headphone Amp from Bruce Bender. And they sound nice !

When you look at ebay you find many Voskhod tubes ( with the rocket symbol ).
I have some 6N2P's from voskhod and tryed them in my Phono preamp and i wasn't satisfied about these tubes. Maybe the 6N1P are good. i dont know.

You can always try Svetlana 6N1P
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Old 13th September 2009, 01:59 AM   #22
jmillerdoc is offline jmillerdoc  United States
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I found a pair of these James OPTs on eBay for $274.00 a pair. Is that a fair price for these or should I look to find them cheaper. They will be shipped from USA so S?H is about 20 bucks, not too bad. This gu has about 10 or more pairs up for sale on eBay at the moment but his listing is over in a day or two.
My previous question about the cathode resistor adjustment via switching a parallel resistor on next to it never was answered. Can somebody tell me which value is intended for the KT88 and which is for the EL34. Also, what about KT77 and 6L6 use in this circuit, could they use about the same cathode load resistor value as the EL34???
Thanks,
Jeff
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Old 13th September 2009, 02:01 AM   #23
jmillerdoc is offline jmillerdoc  United States
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Tim,
AES sells that tube relay for around 4 or 5 bucks as I recall. It may be a couple of dollars more now. They are physically about the same size as a 12SL7 or similar tube.
Jeff
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Old 13th September 2009, 12:41 PM   #24
porkchop61 is offline porkchop61  United States
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Quote:
Originally Posted by jmillerdoc View Post
My previous question about the cathode resistor adjustment via switching a parallel resistor on next to it never was answered. Can somebody tell me which value is intended for the KT88 and which is for the EL34. Also, what about KT77 and 6L6 use in this circuit, could they use about the same cathode load resistor value as the EL34???
Thanks,
Jeff
Jeff-
With the switch open as shown, it's for operation with EL34/6CA7/KT66/6G6 tubes. With the switch closed, the resistance is back to the original value of 470R (471.91R actually) for use with KT88's. The 470R is a little too close to the max plate dissipation for my taste. The 560R gives me around 19W plate dissipation. You can tailor this scheme to suit your needs for whatever bias point you choose to run your tubes at. I've seen implementations of this design using multiple position rotary switches to choose a bias resistor for each different type of tube used.

Take a look at my page to see my bias measurements for some different types of tubes that I use. You can also see my layout of this amp. The Shuguang KT66's sound really nice to me, as well as the EH 6CA7's.

http://webpages.charter.net/porkchop...8_SET_amp.html

Good luck!
Glenn

[EDIT]
The three star grounds can be a common point, I built mine on an aluminum plate and just decided to keep the sections separated preamp/poweramp/power supply. They are all tied to the aluminum plate anyway. I've had no issues doing this in all my guitar amps I've built, and this amp is DEAD quiet.
You should read Aiken's grounding advice, it's very helpful:
http://www.aikenamps.com/StarGround.html

All his Tech Info is worth reading:
http://www.aikenamps.com/
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Last edited by porkchop61; 13th September 2009 at 12:54 PM.
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Old 13th September 2009, 07:55 PM   #25
jmillerdoc is offline jmillerdoc  United States
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Porkchop,
You say this amp is dead quiet and I believe you. I did run a simulation of the PSU of this amp on PSUD2 and I found quite a bit of ripple on the simulation. Maybe I ran the sim wrong. Anyway, I have seen this amp built with added chokes on the B+ for the preamp stage. Did you build this amp exactly as the schematic shown at the beginning of this thread?

Do you think $274 for a pair of these James OPTs is a good price? I can get a pair of Edcors for about 50-60 bucks less. I guess what I am asking is are the James OPTs really that good that I might spend the extra few bucks on them?

Thanks for all you great input!
Jeff
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Old 13th September 2009, 09:33 PM   #26
porkchop61 is offline porkchop61  United States
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I think I did the same thing with the power supply (running the PSUD2 sim), but I don't recall what the ripple was. The thing that I feel contributed to the ripple being very low on the power supply was the use of the motor run capacitors ( I used ASC brand). I did build the amp just as the schematic is drawn (I drew that version of the schematic). I have seen other schematics using additional chokes, but I don't feel these are necessary as the amp is very quiet, at least in my case.

I've never heard the James OPT's, so I can't comment on the sound. I'm happy with the Hammonds, especially after they fixed their frequency response for this series of transformers. I did look at the Edcor's initially, but at the time no one had much of a chance to try them and report back on the sound.

Good luck!
Post some pictures as you build.

Glenn
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Old 13th September 2009, 11:32 PM   #27
Zekk is offline Zekk  Singapore
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Default Joy from Mikael Abdullah's SE KT88 built.

James 6123HS OPT sounds fantastic to me, with the dynamics needed for my pop music listenning. Paid US$210 here in Singapore.
Built mine exactly as schematic except using 390R for the cathode for my Amperex or Mullard EL34. IMO, they're much better than the re-issue Gold Lion KT88 with 470R biasing which I've tried out
For preamp, I uses Gary Kaufman's single 2C22 design.

Have A Nice Weekend!

Zekk
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Old 14th September 2009, 02:18 AM   #28
jmillerdoc is offline jmillerdoc  United States
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I think I will go with Edcors for two reasons. First is it appears it has not been done by anybody here so I will have something new to report. Second, the price is lower.

Porkchop, can you tell me where to find these motor run capacitors?

I happen to have enough capacitance in Solen caps to build the project. I was thinking of using these. I picked up x2 82uF Solens for $10 once on ebay and I have been waiting to use them somewhere. I have enough smaller values to make the proper values give or take a couple of uF's. Any thoughts on using these Solen caps?

Also, how big of a chassis would be considered optimal? I am building mine from scratch from wood with a thick aluminum plate for the top. I was thinking about 10x16.

Thanks,
Jeff
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Old 14th September 2009, 04:41 AM   #29
jmillerdoc is offline jmillerdoc  United States
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Tim,
I misspelled the relay tube I was telling you about earlier. It is the 6N030 - DELAY-RELAY, AMPERITE found here:
http://www.tubesandmore.com/
Jeff
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Old 14th September 2009, 11:23 AM   #30
porkchop61 is offline porkchop61  United States
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Jeff-
I bought my ASC caps on Ebay. Be sure you get motor RUN caps, not motor START caps.
I have CAD drawings for my top plate in pdf format somewhere, so I'm not sure how large my plate was (I'm not at home right now). Let me look around to see if I can find it.

I've heard that Solen caps are very nice sounding, but have no first hand experience with them.

As stated previously, the tube rectifier gives you a "soft start", so you really don't need a B+ relay delay

Glenn
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