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Old 14th January 2011, 10:36 PM   #21
rmyauck is offline rmyauck  Canada
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I second Jim for tubes. He may have an crooked or slightly tilted one to sell too as he lists those for less $ @ $13.50 if he has any near top of listings. EH EL34 is way down and sells singles too. EH 6CA7 might be considered too. Some like sonics better.

If you have $ Gold Lion reissues are really liked for sonics etc. if you google about the KT-66, KT-77, & KT-88 . They are said to sound as good or better than the best NOS tubes.

He also sells those Russian 6N3C-E or 6P3S-E which might be worth trying, @ $29.50 a pair. They are a military grade tube and should last! Well liked by many for sonics. I bought some and they are really heavy compared to others.

Good to have spares if you can afford it and you get to try different tubes.

Last edited by rmyauck; 14th January 2011 at 10:48 PM.
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Old 14th January 2011, 11:26 PM   #22
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Lots of good suggestions here. I've tried the EH EL34, and had bad luck with a dud pair. They had issues with bad screens - glowing wires and nasty stuff. Similar problems were seen with some Sovtek EL34G - they look an awful lot like the EH EL34. I have a couple sets of EH 6CA7. I like their sound, but they have a weird mechanical jingling thing going on. Others have noticed it too, and I worry about their long term reliability. I've used the Russian 6P3S-E tubes, and was very pleased with them. If you get a set that is well tested (not gassy), you won't likely find a nicer tube for the price. I'd highly recommend them. I also like my New Sensor Gold Lion KT88. They were pricey, but I don't regret the money I spent on them as they are excellent tubes. I'd imagine their other KT tubes are nice, and hope to try them someday.

Make sure you swap the EL34 between channels. Be absolutely certain you've got a bad tube, and not a dud solder joint at the tube socket.
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Old 15th January 2011, 02:08 PM   #23
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Hi,
Can I really swap all those tube (KT66, KT77, KT88, 6N3C-E, 6P3S-E, 6CA7) without any modification to the amp? My Rx7 are 560 ohm.

In short, I want to know what type of tube that I can put, and maybe the characteristics of each, so that I can maybe buy two pairs to experience different sound.

Best regards,

Last edited by spacemen12; 15th January 2011 at 02:21 PM.
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Old 15th January 2011, 11:00 PM   #24
rmyauck is offline rmyauck  Canada
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George has a chart on the Tubelab site for different values for all the tubes you can use.

The bigger tubes should just be swappable as if that R of 560 ohms is for the EL34's it will give a lower voltage than what say KT-88's could take leading to an easier life for them. It might be a trade off for sonics though.
The 6P3S-E is like a 6L6 and 6CA7 probably would run the same as the EL34's. They all look close on the chart.

What is your B+ , PS transformer specs or make and model #, and do you have a choke?
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Old 16th January 2011, 02:21 AM   #25
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Originally Posted by rmyauck View Post
What is your B+ , PS transformer specs or make and model #, and do you have a choke?
Hi,
I consider myself a kit builder, so sometime, I don't totally understand the technical stuff, but I will try to give you all the info I can. I don't understand how to read the chart on the tubelab web site

My power transfo is the Edcor XPWR035 "This transformer has multiple voltage windings, 740V (370-0-370) at 200mA center tapped, 6.3V (3.15-0-3.15) at 5A center tapped and 5V at 2A." from EDCOR Electronics Corporation. XPWR035-120

My output transfo are the gsxe from edcor again.

I also have a little hammond choke 156R (1.5H @ 200mA DC).

No motor cap.

Tube rectifier (no solid state option installed).

I usually run it on triode mode and without cathode feedback. I honestly don't know what this all mean, but I like the sound better that way.

Thanks,
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Old 16th January 2011, 05:03 AM   #26
rknize is offline rknize  United States
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You have the amp setup for EL34s. They are more or less the "least common denominator" of the various types in terms of plate current. Similar tubes, like the 6L6GC and 6P3S-E, will work just fine. Bigger tubes will also work fine and as rmyauck said, will probably last forever. They won't be operating at their optimal point sonically, though. They'll "want" more plate current and for that will need smaller value cathode resistors.

The nitty gritty is here:

Tubes & Transformers
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Old 16th January 2011, 07:16 AM   #27
rmyauck is offline rmyauck  Canada
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So the B+ is about 450V?

What is the primary impedence of OPT transformer. Like say 3000K or 5000K ohms?

All shown on charts.

How about adding Dave Gillespie's bias mod which would maybe allow adjustment with a screw driver? Maybe Voltages are too high for the up to -37V regulator.
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Last edited by rmyauck; 16th January 2011 at 07:21 AM.
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Old 16th January 2011, 11:54 AM   #28
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Quote:
Originally Posted by spacemen12 View Post
Can I really swap all those tube (KT66, KT77, KT88, 6N3C-E, 6P3S-E, 6CA7) without any modification to the amp? My Rx7 are 560 ohm.

My power transfo is the Edcor XPWR035 "This transformer has multiple voltage windings, 740V (370-0-370) at 200mA...
I started with 560 ohm cathode resistors in mine, but thought that many of the "smaller" tubes (EL34, 6L6, etc.) were running just a little too hot. The larger tubes (KT88, 6550) are fine with 560 ohm.

Yes, you can put any of those tubes in your amp. You might not need to change anything, but I would keep a very close eye on the color of the plates in a dark room. If you start to see hints of red color on the plates, consider increasing the 560 ohm resistors. I settled on 810 ohms for mine.
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Old 16th January 2011, 01:15 PM   #29
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Originally Posted by rmyauck View Post
So the B+ is about 450V?

What is the primary impedence of OPT transformer. Like say 3000K or 5000K ohms?
15W, single ended tube output transformer for 5K Ohms to 8 Ohms.
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Old 16th January 2011, 06:19 PM   #30
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I'll second Ty's suggestion of 810 r when using the 6P3S-E. Sound is excellent. And nothing seems to be stressed.
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