Traynor YGL-3 Problems with PI and supply voltages

[Gerhard Grass]

Hi to all,

got a Traynor YGL-3 on my workbench. The owner told me, that it began blowing fuses and died.

First I replaced the obvious defective filter caps and the fuse. Amp came up without blowing the fuse but with a bunch of problems.

1. There is some output to the speaker, but very low and very bad distorted. Plugging a sinewave showed, that the signal on the grid of the powertubes is prosent on ONE side. The other side is dead. Waveform after the master volume pot seems to be o.k. (checked with a scope) Maybe a problem in the PI ?

2. Checked the voltages and found they are way too low.
On the filtercap I have about 375V where there should be about 430V. (A and B in the schem)

3. There is still too much hum

Any hints for me where to look?

thx in advance

Gerhard

[MarkusBass]

I would start from removing the power tubes and checking the power supply voltages.

Mark

[Enzo]

certainly it is possible the PI has a problem. Are both heaters inside the tube glowing? is there B+ on both plates? Is there signal on both plates?

[Gerhard Grass]

Hi Enzo,

you were right !
One of the anode resistors in the PI was bad.

Works fine now !

thx to all
Gerhard

[Mick Bailey]

What did you do to fix the low voltage situation?

[Gerhard Grass]

To tell the truth, I did nothing !

After having found and replaced the bad resistor (82k) in the PI I started checking the voltages again and
found them all in an acceptable range (only some volts between schematic and amp)

[Mick Bailey]

Fixing the bad resistor wouldn't account for the original observed voltage drop and hum. My original though was bad rectifier operating 1/2 wave. Could be a number of possibilities and you may find there's an intermittent problem. Hopefully not, though.

[52 Bill]

The added hum could have been caused by the lack of phase cancellation in the output.

I have replaced filter caps in these, a job that no one would want to do.