1968 Traynor YBA-1 Bass Master Voltage Issue

[torren61]

The title is a mouthful.  I recently rebuilt/modded a Traynor YBA-1 head.  It sounds great but my voltages are kinda high.  I'm getting 531 VDC across pin 3 with 123 VAC.  It should be 440 VDC + or - 20%.  That makes the maximum voltage 528 VDC.  I can drop the AC voltage to 95 and it gets me the correct DC voltages but what does that do to my tubes?  Is the heater getting the correct voltage?

[sluckey]

I'm getting 531 VDC across pin 3 with 123 VAC.  It should be 440 VDC + or - 20%.

Are the tubes plugged in when you get that 531v reading?

[torren61]

Yes.  Pin 3 reads 531, Pin 4 reads 499, Pin 5 reads 45 on one tube and 44 on the other. I installed a 1 Meg resistor between Pin 1 and ground and it reads .033 on one tube and .038 on the other.

[torren61]

I'm running KT77 tubes.  Rated for 800V max.

[sluckey]

I see several schematics for the YBA-1. Many of them show 537V on the plates. I would not worry. Even with your 531V and 38mA current that's only 20 watts.

[torren61]

Could I trouble you to post some of those?  Mine is a 1968 model with a choke and diodes.

[torren61]

Here's what her guts look like after my mods:

[sluckey]

Could I trouble you to post some of those?  Mine is a 1968 model with a choke and diodes.

Just follow the link for "Tube Amp Schematics library" at the bottom of this page.