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Biasing my own amp...


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well i biased my Marshall TSL122 after replacing the power tubes...

 

i had help from this link and with some good advice from fellow members here:

http://www.eurotubes.com/euro-video.htm

 

Only problem is the video clips only show the following and not your model...

 

#1. Fender Hot Rod Deville / Deluxe Bias.

#2. Marshall DSL-TSL Bias.

#3. Fender Deluxe Bias.

#4. Carvin V3, MTS, Legacy Bias.

#5. Generic Bias video using an 800 Marshall.

 

But if you got one of the above models, this worked for me... :thu: Didn't have to go internal on my amp to bias it :thu:

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I need to change the tubes in my peavey heritage vtx and was wondering if it could be possible to bias it on my own... Im a do it yourselfer and have an ok working knowledge of electronics... but still a noob

 

 

This amp uses a fixed voltage control grid on the output tubes.

The outputs are connected ultralinear with the output transformer having screen grid taps.

The output tubes are cathode driven by transistors.

You will seek R 155 and R 159 which are each grounded on one side and each are connected to each cathode drive transistor's emitter.

They are 3 ohm 5 watt - ceramic resistors.

 

Use a meter that will read millivolts accurately.

Peavey states to establish that the voltage across each of these resistors is a min of 20 mv and max of 40 mv.

Also output cathode voltage at idle shall be 75 volts min and 90 volts max.

The control grids, again, are fixed with a 15 volt source thru 1.5 k resistors to each tube.

 

There is no stock provision to actually adjust the bias.

If outside the ranges of millivolts - then establish there is good tubes in place and may need to check for problems in the drive circuit.

It is all very different than grounded cathode, with negative bias on control grid style output circuits.

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