trinityamps.com

I noticed yesterday when I put in new output tubes that my output plate voltages are off. I have 320vdc on pin 7 of V5 but only 299vdc on pin 7 of V4. I have 305vdc on pin 9 of both V4 and V5. B+ is 327vdc.

Is there something wrong with my OT?

_________________
Les

http://www.soundclick.com/unimind

Any ideas? Is there a way to test the OT for shorts or something? What should the resistance reading be on the OT primaries, secondaries?

_________________
Les

http://www.soundclick.com/unimind

Well..start by bleeding off the caps for safety. measure the resistance of each half of the primaries (from the plate connection to the B+ connection). They should be about the same...afew 10's of ohms each. Also check that there is no continuity from the primary leads to the metal housing or laminations. Same for the o/p windings. The individual taps on the o/p will have even less resistance. There should be no electrical connection for any o/p winding to any primary winding.

_________________
Fantasy Noise is what my shop of dreams is called and was the only way to beat my addiction, like many here I suffer from G.A.S.


Tele's make the best noise

Are you sure both power tubes are OK?

_________________
Great tones come in small glass jars!

Stoo, Taz13, Thanks. I tested the OT and things seems to check out ok. (although I did not do any advanced testing so there still might be a problem there.)

Yes. I now have 2 sets and both sets have the problem even if I swap tubes from v4 and v5.

_________________
Les

http://www.soundclick.com/unimind

After testing the OT I set all controls to 5, powered up and checked my voltages. I got 327vdc on both V4 and V5 plates.

I set the gains at 10 and PPIMV at 8-9 and I got 305vdc on V4 and 325vdc on V5.

I set the PPIMV back to 5 and I got 325vdc on both V4 and V5.

With the PPIMV at 7 or below I get 325vdc on both V4 and V5 but with the PPIMV at 10 I get 288vdc on V4 and 325vdc on V5.

I am now sure this is what is causing my severe blocking distortion problem with the PPIMV above 7.

Question is.... what is causing the voltage to drop in V4 when I turn up the PPIMV?

_________________
Les

http://www.soundclick.com/unimind

I suspect ultrasonic oscillation, which is overloading one of the power tubes. If you check in the dark, you may even find that V5 red-plating.

_________________
Great tones come in small glass jars!

I have narrowed it down to V1a. As soon as I start to turn up VR1 (bright channel gain) the plate voltage starts to drop in V4. The normal channel is fine i.e. there is no effect on V4 plate voltage when I turn up VR2. I have tried different tubes in V1 with no improvement. Also no other controls (other than PPIMV) seem to affect the V4 voltage.

I am going to try removing the cascade and send the input straight to V1a and see if that helps.

Edit: I am going to continue this on my Plexi brown - fizzie when dimed thread (viewtopic.php?f=7&t=2978) as it is that issue that I am tracking down.

_________________
Les

http://www.soundclick.com/unimind

Is the output from both sides of the PI equal????

_________________
http://pdfelectronics.com

Possibly not, after the parasitic oscillation starts to kick in.

_________________
Great tones come in small glass jars!