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Those Magnificent Television Tubes
Those Magnificent Television Tubes
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Old 16th January 2016, 04:43 AM   #521
smoking-amp is offline smoking-amp  United States
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Hi Anatolyi,

Your message buffer space is filled up, need to clear some space so I can send a message.

Thanks for the offer. Might cost as much to send as to get one on Ebay, but send any other tubes you want traced too.

Don
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Old 16th January 2016, 06:20 AM   #522
Mickeystan is offline Mickeystan  United States
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Quote:
Do you know if the Spice model is showing (non linear) current draw from g1?
Hello Smoking-amp, I looked at the current feeding G2 via 68 ohm series resistor from source follower as compared to the current in the resistor from G2 to G1 and there appears that there is no compression. The current is simply lower and still nice an sinusoidal in shape. Mickeystan
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Old 16th January 2016, 06:50 AM   #523
jazbo8 is offline jazbo8
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Those Magnificent Television Tubes
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Originally Posted by Wavebourn View Post
AFAIR, 1.2 kV on anode
Ok, thanks. That's a lot of power from just a pair of GU-50!
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Old 16th January 2016, 06:51 AM   #524
Wavebourn is online now Wavebourn  United States
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Those Magnificent Television Tubes
Quote:
Originally Posted by smoking-amp View Post
Hi Anatolyi,

Your message buffer space is filled up, need to clear some space so I can send a message.

Thanks for the offer. Might cost as much to send as to get one on Ebay, but send any other tubes you want traced too.

Don
Hi Don;

I will empty a bit my message box right now, probably I lost your address...
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Old 16th January 2016, 07:06 AM   #525
Wavebourn is online now Wavebourn  United States
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Those Magnificent Television Tubes
Quote:
Originally Posted by jazbo8 View Post
Ok, thanks. That's a lot of power from just a pair of GU-50!
But don't expect a clean sound in such a regime! :-)
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Old 16th January 2016, 07:14 AM   #526
jazbo8 is offline jazbo8
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Originally Posted by Wavebourn View Post
But don't expect a clean sound in such a regime! :-)
Understood, most likely it's for class B PA application, but still damn impressive!
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Old 16th January 2016, 07:52 AM   #527
TonyTecson is offline TonyTecson  Philippines
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Those Magnificent Television Tubes
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Originally Posted by Wavebourn View Post
But don't expect a clean sound in such a regime! :-)
is that at any level or just low level where cross-over distortion is present?
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Old 16th January 2016, 01:09 PM   #528
Tubelab_com is offline Tubelab_com  United States
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I can ship you one 6P41S, just give me your address......13GB5 and EL509 I don't currently have I'm afraid. But I will put them on my acquire list.
PM me the address.....I have plenty of 13GB5's...NIB Mullard / Sylvania 13GB5/XL500.

Quote:
is that at any level or just low level where cross-over distortion is present?
I have found that there is a limited range of plate voltages that can be applied to a given set of tubes when trying to extract maximum power output if we are to stay within the published maximum ratings, and provide low distortion.

At the lowish plate voltages, the plate load impedance must be reduced to make big power. There is a limit in how far this can go to stay within the peak cathode current ratings. My experiences with violating this rating has shown that you shouldn't do this.

At higher plate voltages, you will eventually run into plate dissipation limits at higher output power levels. Maximum plate dissipation does not occur at maximum power output. It is usually around half power. This is the limiting factor if the amplifier is designed to remain in dissipation spec when tested with continuous sine waves.

If we accept that most music has a peak to average ratio (crest factor) of at least 10 db, and therefore the amp will be operated below an average power output of 10% of max when pushed to clipping on peaks, we can willfully violate the dissipation spec for continuous sine wave testing. Keep such testing to brief periods. Bob Carver made his career on this fact.

As the plate voltage is increased, the idle current through each tube must be reduced to avoid excessive dissipation at idle. As the plate voltage is increased the idle current must be reduced to keep the tube's dissipation at a level where tube life is acceptable. There will be a point where the crossover distortion at low volumes can't be tolerated. This is the limiting plate voltage factor on most conventional G1 driven sweep tube amps.....hence dual drive, crazy drive, or warp drive! Screen drive can inherently operate at lower idle currents without excessive crossover. This is very tube dependent.

Using Pete's Engineer's Amp as a test board, I found that for 6HJ5's/ 6HD5's 600 volts and 30 to 35 mA of idle current with a 3300 ohm load will result in about 130 watts of power output with a faint red plate at about 75 watts continuous for 5 minutes, and no visible or audible crossover. The amp will play for hours at the edge of clipping with loud music into a speaker. 650 volts gets into trouble at both ends of the power spectrum.

The same amp with bigger tubes (I used 35LR6's) hits 250 watts with 650 volts and 2500 ohms. These are the limits of my testing ability. My biggest power supply goes to 650 volts and 1.7 amps. My biggest OPT is 1250, 2500 or 5000 ohms. No single tube works on 1250 ohms. 650 volts is about as far as it was intended to go too. Pete's board was not laid out to eat 650+ volts either.
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Old 16th January 2016, 03:02 PM   #529
smoking-amp is offline smoking-amp  United States
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Address messages sent. Thanks for the tube offers guys!

----------------
"hence dual drive, crazy drive, or warp drive!"

Warp Drive!

Hmmm, started me thinking. (dangerous) Seeing as how the current fed grid 1 is largely able to compensate the grid 2 distortion for "Crazy Drive", I wonder if one could do the current fed grid 1 operation in a previous tube, and then use that output to drive the final tubes via normal -g1 voltage.

Two problems though, the pre-distorter has the desired compressive distortion inverted at its plate. (pre-distorting cathode follower instead?) The other might be that the Crazy Drive is more than just a simple sum of g1 and g2 effects, since the currents induced by each grid affects the gm of the other as well (something like Space Charge tubes, which might be a product rather than a sum). Also, pre-distorting would be giving a product rather than a sum, so maybe OK. Well something to think about anyway.

Some dark Winter night, the evil experimenting begins.... Tubes turned to the dark side.

Last edited by smoking-amp; 16th January 2016 at 03:22 PM.
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Old 16th January 2016, 03:19 PM   #530
Tubelab_com is offline Tubelab_com  United States
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Quote:
Warp Drive!
Where tubes enter the black hole.....forever.
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