Peter, got a question.

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Hey_bert_whtcha_doin_bert

Hey_bert_whtcha_doin_bert

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Can you tell me how many volts it takes to increase bias by 1 ma? I have very hot voltage in my house and most places I play don't. It pisses me off because it always sounds different.

Thanks,

-Nick
 
The bias is generated from a seperate winding of the power transformer. In Diezels thats a 60V winding. With the resitors, caps and trimmer thats adjusted to something between -40 and -50 Volts for your tubes. So a few volts change your bias dramatically . . .

So once you get a higher/lower primary voltage not just the bias voltage will go up/down, but also the so called B+ (plate voltage), which comes off a seperate winding too. In Diezels thats somethign around 480 Volts DC.

We are rehearsing with the band in an old military bunker, which is located 10 miles off the next village - with the result that the mains wires are old and have a long distance to the next mains-station. Resulting a primary of 210 Volts (instead of 230V), which goes down to 190V with our PA fired on. A pain . . .

So the only way to get out of this dilemma is to buy a voltage regulator which buffers anything above 120V and below 120V so that you have a constant amount of voltage going into the transformers primary ---> Furman.

Attached is a pic which shows the average range of a mains voltage in euro-land over 30 minutes - and as you can imagine its even worse in the early evenings when all housemen are doing their laundry, cooking, . . .
 

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Thanks sir. Would you happen to know the average in change though, or a math formula to figure it out? Money is kinda lacking at the moment to buy anything over a couple hundred dollars. Really what I want to do is just figure out were it should be if the voltage were a normal 120-117 the clubs around here average, instead of my 122 to 128 hotness, very rarely does it ever get to 120, but whatever it reads for the day at least it's consistent, I'd shoot myself if it read 128 and dropped to 120 while I was biasing. I always have to bias hotter because of this and never know if it's actually we're I want it to be but I know I have to be close because it always sounds GREAT at the clubs, especially Pop's which runs about 118-119.

Thanks again,

-Nick
 
One could install a switch (in the bias circuitry) with two resitors to toggle between the primary voltage and the correct bias for it. You'd need a tech to do that though . . . and since its a Herbert, you'd need three switches.

If I were you I'd bias at at a location where you have your preferred primary voltage (say 120V AC) and then keep it like this and live with the sound it makes at home . . .

Believe me, the easiest way is a regulator ---> ebay.
 
A voltmeter and a Variac should take care of the problem. Plug the variac into the wall, then take voltage reading, and adjust the variac to you get a reading at 120.

You may be tempted to run the voltages even lower. --I urge you NOT to do this, as this is hard on both the power supply and your tubes in your amp.
 
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