• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Anthem Integrated 1 burned resistor

Hi all.. My amp burned out a screen grid resistor and two of 8 - EL84 power tubes or the power tubes burned out taking the resistor with them. In any event I can not find a replacement for the resistor a GS-3, 2.2K ohm 3 watt IRC brand rated at 1000 volts. It appears that the GS line if these resistors regardless of brand is obsolete and there appears to be none to be had @ 2.2k ohm. There is one resistor on the screen of each of the power tubes and each pair of resistors appears to be in series screen to screen to each pair of tubes.



Other series are available with similar specs but only to a maximum of 750 volts.


My intention is to find a suitable replacement and install 8 new resistors... question is with what?



Anyone else run into this problem? if so please share your solution... Much thanks, Bill
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
I was wondering that myself. A 6BQ5 wouldn't live long running at 400 volts, never mind 500 VDC. So the voltage rating is over specified.

Those resistors are spec'd out at 350 VDC, 600 VDC surge and 750 VDC as the OP stated. So not exceeding the original spec. He just doesn't need a 1,000 VDC spec. If he did, these would probably flash over.

-Chris
 
Thanks Chris - Jon, resistors in series very doable. As to the 1000 volts it is the rating of that series of resistor..no idea of the volts on that tube as I do not have a schematic nor can I measure because of the burn out. Must have been a heck of a surge to take out that resistor though. Off the top of my head I think the voltage on the screen of an el84 is 350? I'll check out that site Jon...much thanks to all for the quick response...Bill
 
very hi plate voltages Anthem Intigrated 1

Ok so installed new resistors and one other that I found under the board that was literally fried, replace all electro caps. Brought the amp up to 120 volts with variac then installed complete set of good tubes. Amp sounded ok but within a minute they were smoking hot.... Removed the tubes and did some measuring and found 513 vdc plate voltage. Now not having a schematic to work with I am at a loss as to what to look for as I have no idea what all the correct voltages should be or what if any parts are in need of replacing to get volts down to a level where the tubes will not be destroyed in minutes. Any help would be appreciated including a copy of the schematics that I will gladly pay for... much thanks, Bill..
 
513 Volt is way too much for EL84 tubes in PP. You measured this with the tubes heated? What is the voltage without the tubes? Do you have a circuit diagram for this particular amplifier?

Regards, Gerrit

integrated-1-5-anthem
 
Hi Gerrit.. 513 volts is measured with tubes not installed. I do not have a circuit diagram hence the problem. Installing the tubes will probably bring the volts down somewhat but as I said the tubes were extremely hot in less than a minute so I shut the amp down and here we are...much thanks, Bill..
 
Hi Gerrit.. 513 volts is measured with tubes not installed. I do not have a circuit diagram hence the problem. Installing the tubes will probably bring the volts down somewhat but as I said the tubes were extremely hot in less than a minute so I shut the amp down and here we are...much thanks, Bill..
Then get the schematics before continuing.