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Sazafras said.... If yes disconect the first 8.2k dropping resistor (Decouples pre amp from power amp power supply)

1) the 8k2 2watt resistor?
2) and once disconnected... then what?

If you take the tube that worked in V5, and put it in V4 ( nothing in V5 position), does it fail? All this sure looks like a bad power tube, if the voltages are all OK.

If you want to test the OT you can measure the resistances. I believe they are posted in the resource forum.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

After some more thorough experimentation...

Rectifier in, plugged in through trouble light.... powered on.... soon as I flip from standby..

Tube in V5.... things stay on... for about 10 seconds, then the trouble light slowly gains and the power light drops...

Move the tube to V4.... same thing....

Once the light trips, cycling the power will produce instant failure... wait a minute and it seems to work again as above... its almost as if a cap needs to discharge

If I let it reset, and put tubes in both V5 and V4, the light trips as soon as I take it off standby

Thoughts?

Could be happening as the tube heats up and starts conducting. Is this a known good tube?
Pretty strange behaviour? You have cause to be confused!

Temporarily disconnect the bypass cap on the EL84 150R 5 W and retry.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I've tried this was 4 different tubes... two of which were in the amp originally and two of which were purchased in case the first two were blown....

Alright.. so, in reading



I somehow translated that into.. bypass the 150R 5W resistor and retry... so, I pulled the resistor and retried... and it seemed to work. One tube, two tubes... didn't trip the trouble light... thought you were brilliant....

So, when I went to type this response, I realized that I was an idiot

I put the resistor back in and pulled the 50 uF cap...

and the problems came right back. Whether the tube was in V4 or V5.

pull ome end again, and measure the resistance. see if it is really low.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Not sure what you meant... ome end.....

I did check the resistor while it was out and it was to spec.

1) yes

2) With the 8.2k 2 watt resistor disconected you retest the power supply rectifier tube and power tubes like you have been to see if the problem still exists .
There was like a 5% chance something funky happening in the preamp section with the 8.2k disconnected the preamp is no longer involved.

OK! this eliminates a bad cathode resistor And also a bad cathode bypass cap.

So, to recap, when you put the rectifier tube and V4 in (no other tubes), after a short period, the fuse will blow. When you move it to V5, same thing.

If you havent tried a rectifier tube, it could be that as it heats up, under load it fails.

Pull everything out except the rectifier , turn ot on and let the amp sit for a minute to see.

At least you're getting good use out of your light bulb limiter!

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I don't have time tonight to fire up the iron... but...

Just running the rectifier tube is no problem... up to 10 minutes right now.

Stupid question though... why did it work when the resistor was pulled? The implication would be that it was the current running through the resistor that was creating the problem is it not?



Yep...gonna need to buy a back up bulb soon

Alright... restored everything back to plan...

Disconnected the 8K2 2w resistor

Symptoms remain... fizzle out after 8-10 seconds in either v4 or v5....

That was the idea. I really believe it is power amp side related. It is still possible that the rectifier is overloading under load.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I know it is so easy to think that. The very first thing I did when this started was swap out the rectifier. I just put a brand new tube in (Tesla) and are still getting the same issue, so I'm pretty certain that the tube is OK (for the record... we're testing this with 3 different rectifier tubes and 4 different power tubes... )

Testing 18 OT

Hmm, well If you suspect your OT for some reason, you can do a resistance check to get an idea of it's health.

Disconnect all the wires from the circuit, then use a digital ohm meter to measure the following resistances.

Primary
Brown - Red: 275 ohms
Brown/White - Red: 160 ohms
Blue - Red: 331 ohms
Blue/White - Red: 166 ohms
Brown - Blue: 606 ohms
Brown/White - Blue/White: 326 ohms

Secondary
Black - Orange: 1.0 ohms
Black - Green: 0.7 ohms
Black - Yellow: 0.6 ohms

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I really don't know what to think anymore; I've gone through this a hundred times and can't see what I'm missing...everything seems to test out normal.

FTW, didn't test out the /white wires as they're nicely capped and tucked under the board (although I have pulled them out to make sure they weren't grounding out etc)... all the OT resistances are within normal range...

I also checked all the flying leads and the connections on the underside of the board (hadn't remembered to check those before).. they're all good too.

If its not tubes, or OT, it really has to be the wiring but only wiring that is in circuit when the power tubes are in. At this point, I would probably re wire the output stage.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

OK, I'm still stumped. I rewired everything thru the OT and still no changes....

I still can't figure out why things appear to work when R20 (150R 5W) is out of the circuit...

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

with 150r not in the circuit three no path to ground for the tubes i.e. current does not flow and you light bulb won't dim and fuses don't blow

Doh.. .of course.... really missed seeing the forest for the trees on that one....