Old Traynor Low Output and Red Plating

Peter Zhong

Member
Messages
5
The amp is a traynor YBA-3, old one no master volume.

The amp has really low output (maybe 5 watt, supposed to be 120), and on top of that the output tubes actually glow red hot when I crank the thing; they technically all go red plate eventually, but one pair goes red quicker. It doesn't red plate while idling, just when I play it at full volume (once again, full volume being pretty quiet). I've checked bias by putting in a 1 ohm resistor between cathode and ground, bias all checked out good, I set them to around 27mA, which is really low for any amp. And I replaced all the filtering caps.

Has anyone else ever seen similar issues where both low output and red plate happen at the same time?
 

eolon

Gold Supporting Member
Messages
507
It is odd that the bias is ok, that is what I would suspect. Check the bias voltage - is it within reasonable range? Make sure you do not have excess ripple on the bias voltage, and test the bias capacitor(s) for failure. Check the 20W screen resistor R30 for a 15V drop across the resistor; you adjust this voltage drop with pot R8A. Be careful - there is very high voltage on R30 (530 V + !) Just my first thoughts.

Best Regards,

Don
 

pdf64

Member
Messages
8,929

pdf64

Member
Messages
8,929
That's got a master volume, so can't be exactly right for this amp, so to avoid confusion it's probably best not to used component references.
 

eolon

Gold Supporting Member
Messages
507
That's got a master volume, so can't be exactly right for this amp, so to avoid confusion it's probably best not to used component references.

The only No Master Volume YBA-3 I can find uses 7027s. This:
I can't find a No Master with EL34s, but I'll keep looking.

Could someone have changed the 7027s to EL34s at some point?

Regardless of the correct schematic, I would want to know what the plate voltage is on each of the output tubes when they are red-plating. When you checked the bias was the amp red-plating? Was the amp making funny noises when red-plating? Distortion?

Best Regards,

Don
 

Tone_Terrific

Silver Supporting Member
Messages
37,172
Regardless of the correct schematic, I would want to know what the plate voltage is on each of the output tubes when they are red-plating. When you checked the bias was the amp red-plating? Was the amp making funny noises when red-plating? Distortion?
If tubes are good, HV is right, bias is right and signal is right.....the problem has to be downstream.
 

JJman

Member
Messages
994
Ultrasonic parasitic oscillation? I would add small caps to ground on each el34 grid as a test. ~2000pf or so.
 




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