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Just finished my Plexi build (temporary until I get some extra coax from Stephen) and the Voltages seem way out of wack. My B+ is 119 and the rectifier voltages are around 303 but when I test V7 on the power tube plates my tester goes all wonky. I have an auto ranging tester that works just fine until I get to V7.

FYI...I am a newbie

Can you post some pictures? Need some more details.

Which step are you in the start-up procedure?
With tubes out except rectifier B+ should be over 400, is it? Other voltages are invalid until tubes are installed.

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

I was a little tired when I wrote that post. I had just installed the rectifier tube.

I wasn't sure how to test the filament voltages. Is that the heater wires? I assume that testing the plate voltages means to test the pins on the tube socket. pin + ground will give you the voltage?

I had 119 VAC at the main. After reviewing the docs again I realize that I did not check the B+ properly. Will have to do that again. I checked and double checked as I went and am confident that everything is where it should be. I would imagine that it is user error at this point, since I am relatively new to circuit testing.

Here are some photos of my build so far. Any feedback would be appreciated.

[img][img]http://i172.photobucket.com/albums/w37/stonge007/TubeSockets.jpg[/img]

Ooops. Apparently I didn't load my completed pics yet. Will have to do that when I get home later.[/img]

Okay here are the finished pics. As soon as I post these I'm going to go check the voltages as best as I can.

[img][img]http://i172.photobucket.com/albums/w37/stonge007/P1020429.jpg[/img]

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[img][img]http://i172.photobucket.com/albums/w37/stonge007/P1020431.jpg[/img]

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[img][img]http://i172.photobucket.com/albums/w37/stonge007/P1020433.jpg[/img]

Ciao for now[/img]

A) Build looks very neat. Nice job.
B) the filament voltages are the heater wires . 6.3 VAC
C) Testing the plate voltages means to measure between the pins on the tube socket pin (or corresponding turret on the board) and ground. this will will give you the DC voltage. True for all DC voltage tests in the amp.

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

Excellent. Thanks Stephen for the compliment and tips. Okay. Just measured the plate voltages. Some are really out of wack.

AC Mains - 117.7
B+ No tubes - 443
B+ with tubes - forgot to record it but I think it was about the same




V1

Pin 1 - 206
Pin 3 - 163
Pin 6 - 205
Pin 8 - 163

V2

Pin 1 - 195.6
Pin 3 - 163.8
Pin 6 - 208
Pin 8 - 196

V3

Pin 1 - 200
Pin 2 - 157
Pin 3 - 171.1
Pin 6 - 200.6
Pin 7 - 158
Pin 8 - 171.3

V4

Pin 3 - 30.8
Pin 7 - 232
Pin 9 - 213

V5

Pin 1 - 30.9
Pin 7 - 221.7
Pin 9 - 213

V6

Pin 1 - 280
Pin 3 - 263
Pin 7 - 280


I also notice a slight smell of burning rubber but couldn't find anything burning or melted.

All components seemed to be cool except for the Xicon 5W resistor which almost burnt me it was so hot.

With speaker plugged in I got a bit of a hum but when I plugged in my guitar I go not sound at all except for the same hum.

Does any of this make sense?

When V1 pins 3 & 8 are so high, I always check to make sure the cathode bypass caps are really grounded. Check that they are and that the copper bus bar is also grounded.

That resistor should NOT get that hot at all. Check the wiring around the Power tubes again.

Be sure to do any testing with the tubes lit up, with a load. i.e. hook up a speaker & turn the vol down of get a 10W 8 ohm load.

The voltages are not quite right but if you check the grounding, and the tube wiring, it might sort out.

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

I've just been going over the layout again and I have this question: Is the ground wire that runs from the Vol on channel 2 supposed to be soldered to the copper bus bar? And then is there supposed to be another lead that runs from the copper bus bar to the pre-amp ground???

If so, I think I know at least one thing I did wrong! I have the ground wire running directly from the Vol to the pre-amp ground.

Alrighty then! I corrected the ground wire issue and got the following plate voltages:

AC Mains - 117.7
B+ No tubes - 443
B+ with tubes - 328.7


V1

Pin 1 - 138
Pin 3 - .79
Pin 6 - 140.5
Pin 8 - .79

V2

Pin 1 - 145.3
Pin 3 - 1.073
Pin 6 - 238.1
Pin 8 - 145.6

V3

Pin 1 - 185.5
Pin 2 - 44.3
Pin 3 - 65.8
Pin 6 - 191.8
Pin 7 - 46.3
Pin 8 - 66

V4

Pin 3 - 10.7
Pin 7 - 317.6
Pin 9 - 300.6

V5

Pin 1 - 10.7
Pin 7 - 314
Pin 9 - 300.5

V6

Pin 1 - 294.8
Pin 3 - 328.3
Pin 7 - 294.7

Now the voltages seem kinda low. However, I did plug the old guitar into it and got some pretty raunchy tones out of it. It wasn't as loud as I expected it to be. I have a DRRI that is waaaayyy louder. I don't know if that is symptomatic of the low voltages or not. Any ideas?? How are the voltages now??

Yes , the voltages are low but all in the approx ranges.

B+ No tubes - 443 is good under no load
B+ with tubes - 328.7 is very low. Something might be drawing too much current?

What tubes did you use. Were they all new?

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

Tubes are all brand new. Got them from the tubestore:

RFT 6CA4 / EZ81 x 1
Electro-Harmonix EL84 x 2(matched pair)
Tung-Sol 12AX7 x 3

I'm going to try and crank it later on today if no one is home to see what it sounds like. I also noted that the Plexi channel is kinda lacking in gain. I was hoping to be able to crank either the gain or MV to get a nice crunch then control the overall volume with the volume.

I noticed in the manual that there are some tweaks I can do to increase gain on the Plexii channel. I may consider doing this when everything is sorta out and in the normal range.

I wonder what could be drawing too much current?

If you are VERY careful, you can measure the current drain by inserting your meter in series with the stand-by to filter cap. It should not draw more than 150 MA DC full and about 100ma DC idle.

You'd need to disconnect the lead from the standby switch to 32/32 cap and insert your meter in there.

Bad tubes can draw a lot of current. But these are new.

Measure the voltage drop across the 5W 120 ohm cathode resistor for the power tubes. You can do a rough calculation on the current flowing there using ohms law. V=IR i.e. I = V drop/120 ohms

Not enough gain when you crank that channel gain up??

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

Okay. Just did a short plugged in test with a Strat and LP and I have a couple of corrections to make.

Loud - oh yeah baby.
Gain - for sure when it's turned up a notch but not at lower volume with gain on 10.

I will have to measure current drain etc later on. Don't have time right now. I'll get back to you though.

Please note: What this amp does it does very well and sounds fantastic. I can definitely get those Marshall crunch tones I love (except the super high gain Gary Moore type stuff - but he likely uses a pedal) As for the gain issue, I was hoping to be able to play it at basement level night time volumes with a good crunch - at this point I don't think there is enough gain for that. That's one of the reasons I really like the dirty channel on a Classic 30. Unless I did something wrong, I'll probably need a pedal with this amp.

Anyways, I'll get back to you once I've done those current tests.

As a bit of an update to the whole gain issue. I just listened to the sIII clips on main page and my amp doesn't have anywhere near that much gain or crunch. I'm not sure if that helps in the diagnosis department but I thought I would mention it.

More to come.

Progress is being made. If what you want is to play it at basement level night time volumes with a good crunch, you'll be wanting a VRM. Coming soon!!

Also, whart guitar/pick-ups are you using? and did you flip the boost switch on?

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

Oh, also jump the two channels, that'll add some kick too!

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

I think I'll be wanting the VRM for sure. Did another test run while a had a few minutes. I used a few guitars: Strat with Area 58/61 pups, LP with 498t in bridge and a Yamaha AES620 with SD JB in the bridge.

The tones are to die for. ACDC for days, lots of good crunch with and without the boost switch.

Won't be able to do much in the form of curcuit testing tonight. Too much on the go.

Now, that's more like it!!

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

Sounds to me like you are where most of us want to be.

I love these forums. I learn something new every day.