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I started the final testing of the Triwatt. The PT seems to be fine, (6.2 Volts to the Heater Wires & 700 volts for the high voltage, but the voltages @ Pin 3 on both Power Tubes are pushing 1000 volts. Tubes are not yet installed.

OT Transformer Problem?

Thanks for any help!

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ROB

Desolder all the wires from the OT

Primaries:
Red to Blue - 39.5 Ohms

Reb to Brown - 33 Ohms

Secondaries:
All seem Shorted

Am I missing something?

Thanks:

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ROB

Dont know how you can get more voltage on the tubes than the power supply is providing??

It's normal to have a higher voltage than the final B+ with out tubes in place.

You should be measuring AC off the transformer and DC off the board.

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

Should the Secondaries of the OT seem like they are shorted, and should that effect the B+ voltage.

Should I try the amp with the power tubes, or will there be a good chance they will be fried by the high voltage?

Thanks:

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ROB

It's almost like you have a full wave bridge instead of a full wave with centertap...Hmm are you sure you have the centertap grounded?
Stew

Good point Stoo. Check the power supply wiring.
You can post a pic if you want. Your B+ w/o tubes should not be 1000V!

OT
---
There should be low resistance on those OT windings as they are strictly a 'long' piece of wire, wrapped around a core.

If you want I can measure here & confirm?

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

I'm having trouble posting a picture from my system. I will email Stephen a Zip File with them.

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ROB

Stew Wrote:


You are talking about the Red w/Yellow stripe Wire on the PT?

It's attached to ground

The volt readings between Red Transformer Wires seems normal - about 700 volts.

At the power tube #3 pins is were I am getting about 1000 volts

Thanks.

Thanks:

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ROB

Rob.
Please don't be offended by these next questions...I have no idea of your skill level or elec. background ect. OK?
The 700volts you measure is AC ..right?
The 1000v you are seeing ...Is that with the meter on D.C.??
Is it possible you are reading mV ..(millivolts?) Some autoscale meters are a pain that way.
just need to get that strait...No offense!
Stew

700 volts AC - Red Wire to Red Wire

It's not the best digital meter, So the scale could be adjusting - and at seeing 1000 Volts AC, I am not keeping the power to try to get a better reading.

As for my knowledge, I have dealt with mainly DC Control Circuits, and AC Prewired Underflood Distrbution Systems, but only minimally with AC Circuits.

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ROB

Ok..you should only have DC on the plates(anodes) of the tubes. The power supply should take care of that for you. Be carefull but measure for DC on pins 3 of the output tube sockets. Any AC on them should just be ripple riding on the DC. I still think it's a range issue with your meter.
BTW check at the + side of those big can caps too.
Stew

Yes, It was a range issue with the meter. Voltages seem fine! Installed tube, and voltages are still fine.

Now the problem is the amp is silent with the speaker & guitar plugged in. Not even hum!

Thanks:

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ROB

Well, good job you guys. I was going to check my fluke, I dont think it will do 1000V.

On to step #2.

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

Are all the tubes in or just the 6v6s? Check the bias voltage on pin 5 of the 6v6s and while your at it see if you don't hear some noise in the speakers as your meter leads touch the pins. If not check the secondary wiring. BTW these speakers were OK previously?
Stew

What did you bias the tubes at??

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

1) Still no sound thru speakers.

2) All tubes are in.

3) Pin 5 Voltage for the 6V6's were a negative voltage pretty close to the 39 Volts (recommended value)

4) Tubes were biased to 20 ma for one & 18 ma for the other. (So much for Matched Power Tube Sets, well that's what I get for not having the Matched Triode PI - Yes I know Phil thinks the Power Tube Matching is B.S.)

5) Speakers (2X12 with Celestion Vintage 30s) & Speaker Cable were tested & worked today with a Tech21 Trademark 30. The most noise I heard through the Speakers, while hooked to the Triwatt, was a click while cheaking the speaker jacks for continuity with the Ohm Meter.

BTW - Transformers seem to be running at a relativing cool temperature, Which is a good thing.

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ROB

2mA is close enough to call a matched pair. Most tube stores call a matched pair anything that has a bias cathode current that doesn't differ by more than 5mA.

Yes, that's normal. They have very little resistance.

And no, it doesn't.

Definitely - a sheer waste of money. Unmatched tubes will generally give better tone.

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Great tones come in small glass jars!

I would think that my problem of having no sound thru the speaker would be either in the PI or Power Section of the amp. If they was a problem in the Preamp Section, you would at least hear humming in the speaker?

Should I see if using another PI Tube makes a difference?

Thanks:

PS: Phil, at least I didn't pay more for the match power tubes where I got them, and I wasn't going to pay more for the Matched Triode 12AT7

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ROB

How about checking the output impedance switch and o/p jack by measuring the resistance at the end of your speaker cable after you remove it from the speaker. You should see just a few ohms of the secondary winding. this is AFTER you turn off all power ect!!!
But certainly you can change tubes too!
Stew