Ibanez TSA5TVR (cute little 5w TV looking amp) with no filament voltage

[christarak]

It's not to shut off the supply. It's for ripple reduction. There will be a lot of ripple on the Collector but the ripple on the Base is smoothed by C50 and as Enzo said the Emitter (output) follows the Base.

Thanks Dave. I think I need to do a transistor refresher course. I understand the concept that the Emitter is a 0.6v diode junction away from the Base, and in an amplifier configuration, the Collector provides the current to follow (amplify) the Base signal.
Here's where I'm a bit foggy. In a switch configuration I thought the Base "facilitated" (actuated) the conduction of what was on the Collector to pass through to the Emitter (less two N-P junctions)...including the ripple. After I first read your and Enzo's comment, I thought it may have something to do with phase cancellation, but if this transistor is acting similar to an Emitter follower then there's no phase inversion.

[christarak]

Oh, I forgot. For this circuit to work down under, you must turn it upside down.


(Yes, I never get tired of that joke)
.

I hear you Enzo. I am fascinated with our weather. In this very same day that we warm up for another summer, you are cooling down from your summer, winter-bound. I love the States and have been there 27 times, and this continual act of magic of our planet never fails to be amaze me. And yes, sometimes I need to hold a schematic upside down to understand it.

[Jazz P Bass]

Thanks Dave. I think I need to do a transistor refresher course. I understand the concept that the Emitter is a 0.6v diode junction away from the Base, and in an amplifier configuration, the Collector provides the current to follow (amplify) the Base signal.
Here's where I'm a bit foggy. In a switch configuration I thought the Base "facilitated" (actuated) the conduction of what was on the Collector to pass through to the Emitter (less two N-P junctions)...including the ripple. After I first read your and Enzo's comment, I thought it may have something to do with phase cancellation, but if this transistor is acting similar to an Emitter follower then there's no phase inversion.

Look up "Common Base Transistor".
That may help.

[christarak]

Look up "Common Base Transistor".
That may help.

Thanks JP. I definitely will

[Dave H]

Is it working now?

[christarak]

Hi Dave. I had a short break to go to the Harley Days Festival this weekend to celebrate my (late) mid-life cliche crisis. I rushed back determined to conquer the little Ibanez amp.
I had checked the rectifier diodes D17-20 as all OK, but I replaced them anyway. I also replaced C50 on the base of Q8. I upgraded C49 from 1000uF to 2200uF...and up she goes!! The filament is on steady 6.2V (despite the schematic showing 5V). It all works again.
What was the final cause? I'm putting my money on C50.
Can I please thank you Dave, and Enzo for your invaluable experience and willingness to help again? And thanks Jazz P Bass for the advice regarding transistor theory. Now that the Ibanez is out of my hair, its' time for a coffee and some light reading.
Chris

[Dave H]

What was the final cause? I'm putting my money on C50.

You said the 1000u (C49) measured open circuit. That would do it.

[christarak]

You said the 1000u (C49) measured open circuit. That would do it.

You're right, Dave. Thanks mate

[ahseng]

Hey Mr Christarak,.I'm currently working on one.I don't have the schematics only the block diagram to go by.since you have the schematic.Does the schematic matches the block diagram in term of signal path?Thank you in advance.

[christarak]

I am sorry I can't post the schematic. I have promised the Australian Ibanez distributor that I would keep it confidential. I hope you understand. I made a comparison with the block diagram and the schematic and the block diagram appears to be correct.

[ahseng]

I am sorry I can't post the schematic. I have promised the Australian Ibanez distributor that I would keep it confidential. I hope you understand. I made a comparison with the block diagram and the schematic and the block diagram appears to be correct.

Christarak,

My apology if my inquiry seen as asking for schematis. No no I totally understood your circumstances. Thank for confirming the block diagram. I think that's plenty helpful before I poke around. Thanks again.

[amplitech]

Hi Christarak,
I just came across this post and thought I would belatedly add my 2 cents. I am pretty certain it was the rectifier diodes. I have come across this same problem 3-4 times and each time the diodes tested ok with a meter, but replacing them solved the problem. I always used RL201 diodes (2 amp).

[christarak]

Hi Christarak,
I just came across this post and thought I would belatedly add my 2 cents. I am pretty certain it was the rectifier diodes. I have come across this same problem 3-4 times and each time the diodes tested ok with a meter, but replacing them solved the problem. I always used RL201 diodes (2 amp).

Thanks for that diode recommendation. As far as the final cause, I replaced both the diodes and C50 at the same time so I'm not sure which was the root of the problem. Even though my gut feeling is the cap, I would be unwise to not go with your greater experience in this amp. Thank you for taking the time to share your knowledge.

[drewl]

Hey, you have the rest of the schematic for this?

Got an intermittent somewhere between halves of the preamp tube on the other board.
Thanks.

[John G]

Hi,
Replace the LT diodes with the 2A ones, the originals will fail sooner or later.
Schemo attached.
John
TSA5_200.pdf