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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 29th November 2012, 08:38 AM   #31
victorm is offline victorm  Australia
diyAudio Member
Join Date: Apr 2012
Hello all, could use a recommendation/advice here,

My 300B based TSE is humming a little and I'd like to get rid of the hum, so started looking at the heater voltages and their shapes. First I noticed that 5842 heaters are getting about 4V, with 100 Hz ripple, so I shorted the R3 and added 10000 uF cap in parallel with C1. That helped a little, but not enough. The 5842 heaters are now getting DC with ripple (Vmin=4.64V, Vmax=5.44V). Obviously, these voltages above are also found at the input of the regulator.
The output of the regulator shows (Vmin=4.48V, Vmax=4.96V, 100Hz ripple), AC voltage at the 6.3V transformer winding under load is 5.5V RMS. Looks like NOT enough to get a stable 5V DC out of the regulator ;-(
So here is the question - I am planning to add another 2x15000uF in parallel with C1 and implement the trick George suggested for Davide, i.e. replace R1 with a trimmer and decrease the regulator output voltage a little to get rid of the ripple. Since my Vmin at the regulator input is 4.64V, I will probably end up with around 4V DC on the 300B filaments.

Will this affect anything in a negative way? Any other suggestions (before I start looking at the transformer replacement)?

Really appreciate your help here guys,

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