Minimum gr1 resistance

[Colas LeGrippa]

Hi !

• Over a year ago I designed and built a single 5881 guitar amplifier which appeared to be very reliable. I used it day after day from one to 4 hours every day. Last night as my girlfriend was out with her friends ( that's what she told me...but  'till now she's always been as reliable as this particular amplifier hey hey hey ..). I was saying as she was out, it came to my mind to draw down the schematics of this wonderful amp since my blisters were too painful to play anymore and the 3 tv channels were annoying. I opened up the amplifier carefully on the kitchen table, looked for.my Fluke and my chinese no brand cap meter and started my work. My drawing was good and all the values were logical but one: the power tube grid leak resistor was measuring 3.5kohm. I was expecting to find 220k to 470kohm. Surprisingly this amp is my best ever. Obviously I had not measured the resistor B4 soldering it in it s place when I built this amp.
• QUESTION: Is there a min grid leak value not to exceed ad what could be a possible issue using such a low value g1 resistor ? ( i m not talking about grid stopper here don t get me wrong). The data sheet of the 5881 shows a max of 500kohm.
• THANKS.

.

[sluckey]

I don't think the 5881 cares what size grid leak you use, as long as you don't exceed the maximum value. But that 3.5K sure puts a heavy load on the plate of the preceding tube. I would replace with a more appropriate value.

[Colas LeGrippa]

Heavy load on the plate or not, I will keep this out of the blue value resistor if  a " more appropriate" one changes the amp tone. I will always regret to have modded a beautifully sounding amplifier ' cause many voltages weren't standard and 6V6' s lighjtly redplating.


But thanks for the info. I ll do the swap and see what happen. MAYBE AN EVEN BETTER TONE !


COLAS

[kagliostro]

Ciao Colas

When you measured the 3.5K, the resistor was disconnected from the circuit (at least at one side) or not ?

May be there is a resistance in parallel on the circit that altered your measure ?

Franco

[Colas LeGrippa]

Ciao Kagli,  sure it was !

[kagliostro]

Ciao Colas

sure it was !

replay to the first or second question ?? 

Franco

[Colas LeGrippa]

Sorry body it was the reply to the first question .
The resistor was disconnected. Anyway, it didn t matter, connected or not , same reading. No other resistor in the path.
Ciao fratello !

[kagliostro]

Have a nice day 


Franco