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Old 31st October 2006, 11:21 AM   #1
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Default Ecological recycling amplifier (6CU6)

Hi guys

I have recovered these beautiful valves from an old television destined to scrap. From this I have saved the 6CU6 (h.deflection) and a double triode without name. And in an old radio I have pulled out also a 6K7G
Click the image to open in full size.
Click the image to open in full size.

My intention is to build a single ended guitar-amplifier with these tubes
6CU6 plate max = 600V & 11W

The schematics that I would like to use is very similar to Fender Princeton but "tuned" for my 6CU6
Click the image to open in full size.

Every suggestion is welcome !
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Old 31st October 2006, 11:50 AM   #2
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The Achilles Heel of high perveance sweep tubes is a very low maximum screen voltage rating. You could potentially use a separate screen supply at 150-200V.
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Old 31st October 2006, 02:06 PM   #3
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The 6K7 is a remote cutoff pentode intended for gain controlled amplifier use. These tend to distort a lot when used for audio. It still may be useful as the input stage in a guitar amp. Look for the old Fender Champ schematic that used a 6SJ7 for the input tube.

Your dual triode is probably a 6BL7 or 6BX7. These have a relatively low gain for guitar amp use. It may be a 6SN7 which has similar gain.

The 6CU6 is a sweep tube that has a 200 volt maximum screen voltage rating. I have built a few guitar amps with sweep tubes. They usually sound awesome. Some sweep tubes don't seem to mind having their screen grid voltage violated, while others glow red in anger. Only testing will tell how the 6CU6 responds. The technically correct thing to do would be to regulate the screen voltage to about 200 volts. What I would try would be a resistor in series with the screen. Adjust the value until there is no glow on the screen grid wires, and then increase it slightly. This is not optimum from a distortion stand point, but it may work for a guitar amp.

When I was young (and tube TV sets were in trash dumps for free) I made guitar amps entirely from old TV parts. If the TV is still around, grab the power transformer, and the vertical output transformer. Also get any other tubes that are available. The power transformer can power up a 50 watt guitar amp without breaking a sweat. The vertical output transformer can be used as an OPT in your SE guitar amp. I recycled the caps and resistors, but this was in the 1960's. The parts were not that old then. Don't bother with them today, they are at least 50 years old.
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Old 31st October 2006, 03:33 PM   #4
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Quote:
Originally posted by tubelab.com
The 6K7 is a remote cutoff pentode intended for gain controlled amplifier use. These tend to distort a lot when used for audio. It still may be useful as the input stage in a guitar amp. Look for the old Fender Champ schematic that used a 6SJ7 for the input tube.

Your dual triode is probably a 6BL7 or 6BX7. These have a relatively low gain for guitar amp use. It may be a 6SN7 which has similar gain.

The 6CU6 is a sweep tube that has a 200 volt maximum screen voltage rating. I have built a few guitar amps with sweep tubes. They usually sound awesome. Some sweep tubes don't seem to mind having their screen grid voltage violated, while others glow red in anger. Only testing will tell how the 6CU6 responds. The technically correct thing to do would be to regulate the screen voltage to about 200 volts. What I would try would be a resistor in series with the screen. Adjust the value until there is no glow on the screen grid wires, and then increase it slightly. This is not optimum from a distortion stand point, but it may work for a guitar amp.

When I was young (and tube TV sets were in trash dumps for free) I made guitar amps entirely from old TV parts. If the TV is still around, grab the power transformer, and the vertical output transformer. Also get any other tubes that are available. The power transformer can power up a 50 watt guitar amp without breaking a sweat. The vertical output transformer can be used as an OPT in your SE guitar amp. I recycled the caps and resistors, but this was in the 1960's. The parts were not that old then. Don't bother with them today, they are at least 50 years old.
unfortunately I have saved only the tubes
I would like above all to make to relive even these old valves using some conservative tensions
I think to supply anodic with 310V and limit the screen around 150V


I now look me the schematics of Fender Champ
http://www.drtube.com/schematics/fen...-5c1-schem.gif

Tnx !
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Old 31st October 2006, 06:48 PM   #5
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Perhaps to use one 6K7G as audio driver is a bad idea.
even however for an guitar-amp it can plays well
Then I can use as audio driver a 6BH6 sharp-cutoff pentode.

mumble mumble... the schematics of fender champ is without
global NFB. How can I add this ?
I need to place a cathod resistor on audio driver...
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Old 31st October 2006, 09:07 PM   #6
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Off Topic.

I have found this online Tube-museum http://www.r-type.org/static/museum.htm
http://www.r-type.org/inx/ages.htm

I am constantly to the search of information on the tubes
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Old 1st November 2006, 11:25 AM   #7
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Some question around the Fender Champ schematics...
does it seem me that the first valve works in A2 calss ?
I have added the nfb and polarization to the first pentode.

now "my" schematics is like this :

Click the image to open in full size.

and i do adjust the value of circuit
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Old 1st November 2006, 11:46 AM   #8
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Quote:
Originally posted by Gold_xyz
Some question around the Fender Champ schematics...
does it seem me that the first valve works in A2 calss ?
I have added the nfb and polarization to the first pentode.
Hi Gold

The first valve works in grid bias mode.

If you use feedback ( a good idea ) change the 1 MOhm pot for a 1 M resistor and put a 100k pot at the input of the first valve.

A feedback amplifier will try to maintain constant the voltage gain and the inclusion of a pot inside the loop will completely defeat the situation.

Ci vediamo
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Old 1st November 2006, 12:17 PM   #9
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Quote:
Originally posted by Tube_Dude


Hi Gold

The first valve works in grid bias mode.

If you use feedback ( a good idea ) change the 1 MOhm pot for a 1 M resistor and put a 100k pot at the input of the first valve.

A feedback amplifier will try to maintain constant the voltage gain and the inclusion of a pot inside the loop will completely defeat the situation.

Ci vediamo
Hi Tube_Dude
Thanks for the answer !

Now i have modified the circuit with Your suggestions

Click the image to open in full size.

Ciao
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Old 1st November 2006, 12:34 PM   #10
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For the lower arm feedback resistor , from the input tube decoupling capacitor to ground , i will use 100 Ohms.

The other feedback resistor, to the output transformer secondary depends of the overall voltage gain you want.

V (gain) =( R (fed) / 100 ) +1

The cathode decoupled resistor depends of the operating point you choose .

Discard the 5 MOhms grid resistor, because you are note using grid bias anymore and use 470 Kohms or 220 k instead...

The 0,02 uF input capacitor is not needed anymore...

Arrivederce
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