Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Ghetto_Soundwave on March 28, 2013, 01:18:50 am
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Contemplating to build a push-pull 6LY8 http://tubedata.milbert.com/sheets/135/6/6LY8.pdf (http://tubedata.milbert.com/sheets/135/6/6LY8.pdf) Plate voltage will be 275, OT is Hammond 125C multi-tap
Choice of speaker cabs are 4 and 8 ohms.
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very high slope pentode. similar to 8417 gm. at what screen voltage?
in class A or AB1? for class A, around 30K plate-to-plate. for AB1 i'd start with 10-15K plate-to-plate & keep plate dissipation around 4W per tube.
maybe start 2 & 4 for 4ohm and 4 & 6 for 8ohm
--pete
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Thanks for replying Pete. Screen voltage approximately 260 -265. Will operate in class AB1. Majority of use will be with the 4 ohm cab so I'll try the 2 & 4 first. Did you use a formula or past experience with the 6LY8 or similar tube to arrive at your recommendation? Would you please post the formula if you used or know one.
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The way to establish the Output Impedance is to use the curves in the datasheet of the tube, but I've lot of trouble trying to do that and that is still too difficult to me
But there is something that can help you
having under hand the datasheet of the tube you can find the max plate dissipation and knowing your B+ ......
Quote From PRR
A good guess for load impedance is V/I of the tube. For 320V supply, 12W dissipation, about 300V across the tube, 12W/300V= 0.040A max current, and 300V/0.040A= 7,500 ohms. +/-30% is all the same.
K
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Appears that the discussion regarding the 6ly8, is based on the 8417. Are these both the same pentode type?
If so, then this means I should be looking at some RF tubes as possible sources of power tubes.
my apologies for any confusion. they are two entirely different animals. 6LY8 is a 5W power pentode the the 8417 is a 35W beam-power pentode. the only similarity is the slope characteristic.
respectfully,
--pete