Plexi kit 50W, Plates voltage issue

iFrancisG · Post by **iFrancisG** » Fri Jul 10, 2015 10:42 pm

Hi there
I just finished a plexi 50 W kit after preliminary test I found the plate voltage are way higher than those written in the Metro 50 watt plexi kit voltage chart.
I got:

v1 1)160V 6)212V
v2 1)170V 6)305V
v3 1)350V 6)352V
Im using Classic Tone transfo, B+ is 450V, NOS Mustard caps, brand new 12ax7s
Most parts come from ValveStorm.

Any hints would be helpful

Thanks

http://i1029.photobucket.com/albums/y35 ... 7pootv.jpg

RockinRocket · Post by **RockinRocket** » Tue Jul 14, 2015 10:00 am

Well the metro kit volts chart if im not mistaken are based off of a 420 b+. 30 extra volts is most likely why you are seeing Valve 1 and 2 higher. V3 check the resistors to make sure they are correct. What are the plate Volts of the 34s?

guitarist1977 · Post by **guitarist1977** » Wed Jul 15, 2015 5:48 pm

I recently built 50 watt with Classic Tone transformers as well. As far as I remember B+ in mine is also 450V but the voltages are about the same as in manual. I will double check that later.

BTW have you measured the voltages with power tubes installed? If not that will explain the difference.

iFrancisG · Post by **iFrancisG** » Wed Jul 15, 2015 10:59 pm

I'll check power tubes voltage.
I've taken the voltage without power tubes in, that may explain why I don't have voltage value near what in the chart, ill check voltage back with power tubes in.
I just have a single 30W Celestion speaker 16 Ohms as load, not much to evaluate how it sound but on channel I/volume I got a loud hum/hiss, channel II/volume II is silent. No clean sound just slight distortion on every channel even at low volume.

It doesnt sound loud at all, my computer plastic loudspeakers sound louder than that, maybe cause I just got one 30w speaker.
I dont hear much difference when playing with tone controls. All tube run quite hot, bias is about 37mV.
JJ 12ax7 and NOS Telefunken el34s

Thanks

iFrancisG · Post by **iFrancisG** » Fri Jul 17, 2015 5:50 am

I re checked voltage on v1 to v3 with power tubes in this time, voltage are now way closer to those in the chart but yeah V3 is an issue, ill check resistor value.
Its my first built so im quite nervous about it.

vh junkie · Post by **vh junkie** » Fri Jul 17, 2015 9:21 am

Sounds like you have a 470k (between the (2) 1megs) in the PI (v3)... that should be a 470 ohm instead...

iFrancisG · Post by **iFrancisG** » Fri Jul 17, 2015 9:58 am

Exactly !!

thank you !

iFrancisG · Post by **iFrancisG** » Fri Jul 17, 2015 11:17 pm

I changed the resistor and now it sound as it should.

Voltages are now back to normal, now i have to figure out why there is still sound when vol I is closed.

Thanks again

iFrancisG · Post by **iFrancisG** » Mon Jul 20, 2015 1:38 pm

Here is a pic

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Plexi kit 50W, Plates voltage issue

Plexi kit 50W, Plates voltage issue

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Re: Plexi kit 50W, Plates voltage issue

Re: Plexi kit 50W, Plates voltage issue

Re: Plexi kit 50W, Plates voltage issue

Re: Plexi kit 50W, Plates voltage issue

Re: Plexi kit 50W, Plates voltage issue

Re: Plexi kit 50W, Plates voltage issue