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Old 17th March 2012, 03:50 PM   #11
fmena is offline fmena  Canada
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Default Very Nice

Looks incredible. Congrats on the build, I bet it sounds as great as it looks. Can you tell us how many watts it produces...is it about 6 watts?

Cheers
Frank M
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Old 17th March 2012, 11:04 PM   #12
tubem is offline tubem  Canada
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Yes around 6 watts, the plate voltage could go up to 450v,which would produce a bit more power, if you push it too far the plates might start to turn orange, but it sounds fantastic right where it is.
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Old 17th March 2012, 11:51 PM   #13
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I have to join the choir appraising your build! In the pictures the fit and finish looks absolutely immaculate! Wish I had such skills...

But who on earth is this 6CB5 tube? Haven't heard of such a thing... Now I'll have to go through my stash to see if I had any...
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Old 18th March 2012, 12:06 AM   #14
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Quote:
Originally Posted by tubem View Post
Yes around 6 watts, the plate voltage could go up to 450v,which would produce a bit more power, if you push it too far the plates might start to turn orange, but it sounds fantastic right where it is.
I'd be more concerned with the screens than the plates.

jeff
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Old 18th March 2012, 12:28 AM   #15
tubem is offline tubem  Canada
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Personally I don't wish to run the tubes any hotter, however when running in triode the screens can handle the higher voltage without any trouble. If you run these tubes in pentode 220v should not be exceeded on the screens according to my manuals.
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Old 18th March 2012, 12:43 AM   #16
tubem is offline tubem  Canada
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Thank you Adolf for your comments, the zebra wood surround for the amp was custom made by LARRYLDSPKR of the forum and also a long time friend of mine, he has been a master at woodcraft for a very long time. I appreciate his talent and am fortunate to have him living close to me.
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Old 18th March 2012, 02:13 AM   #17
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Hi!

Yes in triode mode the voltage limit of the screen is not relevant. That is only for pentode mode when the plate could swing below screen voltage. This can never happen in triode mode. When run hot the tube delivers 7-8W in SE. 6CB5A tubes are very robust. Tube cost is low.

Best regards

Thomas
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Old 18th March 2012, 02:20 AM   #18
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Quote:
if you push it too far the plates might start to turn orange.....I'd be more concerned with the screens than the plates
There are few if any sweep tubes that can eat 400+ volts on the screen.

Quote:
Personally I don't wish to run the tubes any hotter, however when running in triode the screens can handle the higher voltage without any trouble. If you run these tubes in pentode 220v should not be exceeded on the screens according to my manuals.
Keep in mind that idling with no input or very low volume imposes the worst case dissipation on a Class A amp. At idle the plate and screen are at nearly the same voltage.

Look carefully into your tube after it has been sitting at idle for a minute or so to see if the screen is beginning to glow. A glowing screen will mean a short tube life and cause an unexpected runaway condition usually when idling.

Most of my 6CB5 experiments were done in push pull and even screen driven push pull. The screen is pretty rugged, but all tubes were not the same. Those experiments were several years ago and I don't remember the details.

Quote:
But who on earth is this 6CB5 tube? Haven't heard of such a thing... Now I'll have to go through my stash to see if I had any...
The 6CB5 is a TV sweep tube (line output) from the first generation of color TV sets in the 1950's. I had a 1957 vintage Emerson color TV that was actually built by RCA. It used a 6CB5A. I remembered the number ad bought a bunch when this happened, they were $2 each.

Tube sale at AES
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Old 18th March 2012, 04:41 AM   #19
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Default Single Ended Bliss!

I spent a couple hours listening to Jims 6CB5 amp on my TB 1772 speakers. Holy Mother of Crap!! This combo is AMAZING!!
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Old 18th March 2012, 03:11 PM   #20
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hey-Hey!!!,
I also got a pair of 6CB5 amps running. PP and pentode with g2 at 100V to suit a 270V/90 mA idle point. It is ov course Class A with a 5k a-a load. My driver is a pentode LTP built from EL84's.
cheers,
Douglas
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