Question about VOX Amplification Vox Valvetronix VT50 Modeling Combo Amp

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Why is the valve ingoing voltage too high ?

Hi, the transfo delivers 7.4V to the valve, whichs quickly blows out ... What can I do ? Thanx

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2 Answers

Amp keeps blowing fuses


Blowing fuses, was caused by many thing.
Short of rectifier,resistor,elco,tube heater,tube pin, and also trafo itself (primary or secondary winding). It must check step by step.
CAUTION :
THIS IS HIGH VOLTAGE AREA.
RISK OF ELECTRIC SHOCK THAT CAN KILL.
DON'T DO THIS IF YOU ARE NOT TECHNICIAN OR NOT FAMILIAR WITH VACUM TUBE CIRCUIT. THE CIRCUIT MAY STILL CONTAINS ELECTRIC SHOCK EVEN IF IF THE AMP IS NOT POWER PLUGGED.


The simple steps (see picture) are:
  1. Disconnect all connection from secondary of power trafo (PLV,PDCH,PACH and PHV).
    Power ON the amp. If fuse is not blowing,trafo is good.
  2. Power OFF the amp. Unplug the cord.
    Connect PLV1-PLV2-PLV3 (this are Bias voltage,+/-15VDC and Backlight PCB voltage) to power trafo.Power ON the amp. If fuse is not blowing,PLV circuit is good.If fuse blowing,there are parts is damage (dioda,elco,7815/7915,resistor) in this PLV circuit.
  3. If step 2 is good,go to next step.
    Power OFF the amp. Unplug the cord.
    With PLV circuit stay connected,connect PDCH 1-2 and PACH 1-2 to power trafo. Power ON the amp.
    If fuse is not blowing,PDCH and PACH circuit is good and all tubes heater/filaments are lights after a few seconds.
    If fuse blowing,there are parts is damage (dioda,elco,tube heater pins) in this PDCH/PACH circuit.
  4. If step 3 is good,go to next step.
    Power OFF the amp. Unplug the cord.
    With PLV,PDCH,PACH circuit stay connected,connect PHV 1-2 to power trafo.
    Power ON the amp. CAUTION: HIGH VOLTAGE AREA is ON.
    If fuse is not blowing,PHV circuit is good.
    If fuse blowing,there are parts is damage (dioda,elco,tube pins) in this PHV circuit.
.amp-keeps-blowing-fuses-01sk4vtrndbaaguwe2brflsj-5-0.jpg
Notes:
  • Steps had to be done sequentially from 1 to 4, not upside down.
  • If tube/heater pin is short,it can't be repair. The tube must be replacing.
  • PDCH circuit is voltage for V1-2-3-4 heater/filaments.
  • PACH circuit is voltage for V5-6-7 heater/filaments.
  • Always replace fuse with same type.

amp-keeps-blowing-fuses-01sk4vtrndbaaguwe2brflsj-5-1.jpg

Oct 02, 2015 | Peavey 6505 Plus 120W Guitar Amp Head

1 Answer

Is it possible to lower the VOX VT50 transfo outgoing voltage?


bulbs have tolerance, that means it can work with + or - 6.3v just use the 7.6v which a diffrence of 1.is ok for it to work.

Jun 27, 2014 | VOX Amplification Vox Valvetronix VT50...

1 Answer

What kind of adapter do i use for my keyboard Casio ca-110


if you don't want to wait, you can go to radio shack and get a universal adapter for a bit more, but it should work no problem.
http://www.amazon.com/HQRP-Adapter-compatible-Keyboards-Replacement/dp/B004TXDL3C

May 26, 2012 | Casio Music

1 Answer

Soundcraft GIGRAC 600 pre-amp power supply keep blowing the low valve resistor 1ohm. they are the resistor just before the bridge rectifier, for the low voltage feed. Once resistors replaced the unit...


The resistor is acting as a fuse and will continue to blow until you fix the REAL problem. LIKELY the filter capacitor(s) beyond the bridge rectifier are failing. One needs to use test equipment to measure the current through the resistor and see if it is reasonable. The capacitors can heal briefly and then start to short. One should also check the rectifier in operation with an oscilloscope as one diode could intermittently short.

May 04, 2011 | Soundcraft Gigrac 600 Powered Mixer

2 Answers

MY ALESIS DM5 WAS PLUGGED TO 220V AND AFTER A WHILE STOP WORKING ( IT IS FOR 110 V ) IS ANY FUSE I CAN REPLACE?


Hi pcruzx,
Sometimes replacing the fuse alone with exact voltage and ampere ratings will cure the problem(you're lucky) but not all. Sometimes further damaged gone to other parts most especially the voltage regulator transistor/IC (mounted in heat sink) and the opened the fusible resistor in line with the supply(B+).
First check the fuse, for sure it was already blown. If you've replaced the fuse and immediately blew again after powering on the unit, this was an indication of shorted parts near the AC line. Click this LINK for more info.
Hope I helped you.
Have a nice day!
Thanks for using Fixya.

May 01, 2011 | Alesis Dm5 Drum Module 18 Bit

1 Answer

I was playing my guitar on my marshal until i noticed the volume started to quit down until the sound totally died out. and now the amp is turned on and all the valves are on but theres no sound whats so...


Just because the voves are lit doesn't mean there is the high voltage power to the valves.

ALSO the smaller valves have TWO heaters in them and if one half has burned out that would cause the symptom. Check if the smaller 12AX7/12AT7 types all have two heaters burning. Verify that the standby switch has not gotten bumped off.

Jan 19, 2011 | Marshall JVM410C 100 Watts Valve Guitar...

1 Answer

My Marshall JVM Has no power to the Valves


The schematics I found show SEVERAL fuses on the secondary side of the power transformer. I suspect one or more of those are blown. The fuses include the filament power.

As an electrical engineer I will have to caution you on leaving the amp in standby for extended periods. The high voltage rectifier circuit has NO bleeders in this unit and IF a power line transient occurs while in standby, the filter caps CAN be pumped up over their ratings causing them to fail.

Since you had no heaters lit in the tubes, you better pray that the heater fuses have opened as the only other thing is a failure of the power transformer since the neon pilot light is right across the 120 volt primary connections.

Dec 02, 2009 | Marshall JVM410C 100 Watts Valve Guitar...

1 Answer

I need a power transformer for roland sde -3000


I need a transformer part 32 no:11-32-000 class 2 ac power transformer mod:mw48-090200a Input:120 ac 60hz output:9vac 2000ma.
(UL) US Ite powuer supply made in japan

Dec 11, 2008 | Music

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