Traynor YGM-3 Restoration

[misterc57]

I picked up a neglected YGM-3. Came without tubes and all jacks in back disconnected, missing panels, etc.

I have verified the PT and OT are good. I am starting with the power supply which has SS rectification.

I have good V at the heaters and negative bias. The HV is weird as there is a long delay in coming up to high voltage at the first filter cap (fisrt time I have seen this). I would expect it to be almost instantaneous.

The rectification uses two in series diodes (schematic shows only one) on each side of the HV from the PT.

I plan to replace the filter caps and diodes (using 1N4007) and think I should only use one diode on each leg as shown in the schematic. Thoughts?

What would cause the delay in HV at the first filter cap?

Thank you, MarkO

[misterc57]

Also wanted to mention the 150K R2 to the negative bias diode looks cooked but is reading 190K. Is a 1/2 W resistor okay to use here?

[g1]

Those diodes are stock, so you have the wrong version of schematic. I'll see if I have a better match. What are the first 3 digits of serial # ?

[g1]

pg.1 of attached schematics looks like a match. The 150K is spec'd as a 2W so that is what I would use there.
The HV will not come up properly til standby switch grounds the CT, so check that the standby switch is ok.

[misterc57]

Stupid me... I have the back of the amp facing me and did not see the standby switch on the front panel. HV reads fine now.

Thank you for the correct schematic. Someone put a 1/2W instead of 2W R in the bias, that would explain why it is cooked.

I think the serial numbers are on the upper back panel which is missing. :-(

Thanks so far. I am sure more questions will arise.

MarkO

[misterc57]

I installed tubes and replaced all the rectifier diodes with 1N4007

Amp sounds good but I think my output tubes are running too hot. R and VD measurements taken from plates to OT center tap.




I still have the 1/2W grid bias R which measures 195K, schematic states 150K / 2W

I am seeing -22V at the output of the bias diode, the plates are reading -12V

R36 in the bias circuit is a 15K but the schematic states 1M

Other resistors in bias circuit measure good, 1500, 100K, etc

Wondering about the bias cap needing replacement

[g1]

Are you sure that is R36 and not R38 that is 15K?
Bias caps always good to replace if old, for reliability sake.
The 195K may be worse with voltage applied, in any case it is reducing bias voltage so replace it with proper 150K and check bias voltage at C29 again.

[misterc57]

Amplifier	Output Tube	Voltage Drop (VD)	Resistance R	Plate Current (PC) = V/R	Plate Voltage (PV)	Plate Dissipation Watts (PV)(PC)	Grid V
Traynor YGM-3	EL84 - V5	4	152	0.0263	385	10.13	-15.60
Traynor YGM-3	EL84 - V6	2.8	115	0.0243	386	9.40	-15.60

150K 2W is installed and all seems well now. Thank you G1 for the help. MarkO