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Hey everyone just finished my first build last night and I'm having some trouble with the tmb channel. I'm not getting any sound from the low or hi inputs and for some reason when the volume and gain are on 0 I can hear it picking up a radio station haha.

Any ideas where I can start troubleshooting? The normal channel seems to be working fine.

The only thing im not sure about is the shielded wire going to the middle pin on the gain control. Do both the core and braided wire have to be connected?

Thanks
Jordan

I would start with your input and work out from there. I had a similar problem with my Plexi. You have to be careful with the braided component of your shielded wires. The braided part of the wire should be grounded at the appropriate points in the circuit (check layout diagram). Make sure there are no loose whiskers that can come into contact with your signal wire. If this happens it will ground the signal resulting in no sound.

As far as the gain control is concerned, check the layout diagram. The core of the wire should go to the middle pin and the braided part should be connected to ground. On my plexi this is done by connecting it to ground at the gain pot. From what I can see, the MkII layout shows the braided wire connected directly to the ground bus on the board. I don't think it really matters which end you do it at, although connecting at the board will result in a shorter path to ground.

Your normal channel appears to be o.k so no worries with V1b, V3 and the power section. I would also check voltages on V1A and V2 to make sure there is nothing abnormal there.

I tested out the input jacks and they all work on the normal channel, but I noticed I'm not getting any distortion even when the volume is at 10; just loud and clean.
When I turn all the controls to 10 on the TMB channel I realized I can hear the guitar but just barely.

I double checked the layout and everything seems to be right.
I also redid the connections on the shielded wire to the gain control but it didn't seem to make any difference.
The voltages on the preamps were:

V1
P1:166
P3:0.87
P6:161
P8:0.841

V2
P1:133
P3:0.98
P6:279
P8:134

V3
P1:202
P2:58
P3:87
P6:205
P7:57
P8:87

Did you get this figured out?

Your voltages look reasonable .... anode at V2 looks a bit low but not likely to be the cause of this problem.

With no guitar cable plugged in and the TMB gain and MV turned up, do you get a decent response (pop/hum) at the speaker when you touch the grids (V1 pin2 and V2 pin2) with the probe from your meter?

Hey, yeah I did finally get it working! I went back and double checked the shielded wires and the braided parts were indeed touching the core wires. I trimmed them back some more and now everything works normally!
Thanks for your help!

O.K. Glad it worked out!

Thanks for your help DaveC

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

I'm having a similar problem with my newly built plexi mark II. In my case, the overdrive channel works great, but the normal channel (volume / tone only) gives me just a ghost of a sound. No hum or static. Can just barely hear the guitar with the vol on 10. Stephen noted that I've probably got problems with the shielded cable as well. looked things over this AM - resoldered one joint - with no improvement. Nothing else looks particularly sketchy.

My voltage numbers:

N and L at IEC socket: 117.5VAC
Indicator terminals: 117 VAC
B+ 423VDC

V1 Pin No pre-amp/power tubes all tubes in place
1 421 VDC 344.8 VDC
6 420 VDC 344.1VDC
4/5 to 9: 6.91 VAC 6.3 VAC

V2 Pin No pre-amp / power tubes all tubes in place
1 421 VDC 344.4VDC
6 424 VDC 347.8 VDC
4/5 to 9: 6.75VAC 6.3 VAC

V3 Pin No pre-amp / power tubes all tubes in place
1 419 VDC 220.4 VDC
6 420 VDC 214.0 VDC
4/5 to 9 6.86 VAC 6.42 VAC

V4 Pin No pre-amp / power tubes all tubes in place
7 424 VDC 351.4 VDC
4 to 5 6.8 VAC 6.5 VAC

V5 Pin No pre-amp / power tubes all tubes in place
7 423 VDC 349.4 VDC
4 to 5 6.83 VAC 6.53 VAC

V6 Pin no pre-amp / power tubes all tubes in place
1 to 7 615 VAC 611 VAC
4 TO 5 6.86 VAC 6.67 VAC

Any help would be appreciated. No time today, but I'll likely just rewire the input jacks shielded cables tomorrow if I have time.

Thanks! Mike Keefe

the nice spacing I had in the message got compressed. the first number in each row is with rectifier tube only and the second is after all tubes were in place.
Mike

The voltages at V1 and V2 are very high. Looks like those tubes are not drawing very much current. I'm surprised that the Plexi channel is working since it uses V2 and half of V1.

Check all the connections around V1 and V2 and all their resistors and capacitors very carefully. Make sure all the grounds are good, too.

Can you post voltages with all tubes in place. Often when voltages on the plates are very high, it is because as mitchm stated, the tubes are not drawing current. So in those cases, check your ground for the cathode resistors.

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

yes the channel is not working properly

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