Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Alistar on October 17, 2016, 12:25:34 pm

Title: Traynor YBA-1 Low-Output Questions: SOLVED
Post by: Alistar on October 17, 2016, 12:25:34 pm

This is a continuation on a previous post, but more specific problems/questions

Got this thing, switched filter caps to 32/32/16/16 due to bad hum; resolved.
Did not get to 'test drive' beforehand
Back together - low output with distorted tones through the entire range of low volume.
I have not replaced any resistors.

Please see the voltages at the PI:
     Cathode is quite low: 6.4v -vs- 32v 
     Plates on the PI are high: 368v -vs - 248v, 382v -vs- 260v
          Could this be my problem?

Also, almost 40v low in the CF:
     Plate-Grid connection: 181v -vs- 218v
     Follower cathode/signal output: 190v -vs- 215v.

Title: Re: Traynor YBA-1 Low-Output Questions
Post by: sluckey on October 17, 2016, 12:53:19 pm

Quote

Please see the voltages at the PI:
     Cathode is quite low: 6.4v -vs- 32v 
     Plates on the PI are high: 368v -vs - 248v, 382v -vs- 260v
          Could this be my problem?

Yes. That low cathode voltage indicates the tube is barely conducting. Turn the amp off and measure resistance directly from pins 3/8 to chassis. It should be approx. 12K. I'm thinking it's probably a lot higher. If it's not approx. 12K, check that 470Ω, 6800Ω, and 4700Ω.

Title: Re: Traynor YBA-1 Low-Output Questions
Post by: eleventeen on October 17, 2016, 01:06:43 pm

100% agree with Sluckey. The PI triodes are not conducting.


As for the CF....yeah, your voltages are off, but they are right on the hairy edge of acceptable in +/-20% tube-world. They do not scream "bad" like the PI does, so attack the PI first.


You'll get it.

Title: Re: Traynor YBA-1 Low-Output Questions: SOLVED
Post by: Alistar on October 18, 2016, 10:04:59 am

Thank You!

The 470 Ohm resistor at the PI was the culprit!  Upon desoldering it, I couldn't get a measurement.
Replacing it - now I have volume!
The sound is much more clean, and many times more volume on hand.

Thanks again everyone!

Title: Re: Traynor YBA-1 Low-Output Questions: SOLVED
Post by: eleventeen on October 18, 2016, 10:54:01 am

Happy to help. THANK YOU for reporting back "what fixed it". (some/many don't)


By the way, this is a great lesson. Most folks who are learning to troubleshoot put a voltmeter probe on the plate of a given tube and while that is an important measurement and thus a clue as to what might be going on, more often the volts on the CATHODE tell the bigger story.