Help for biasing Jolida AMP

franco_rome

Hi all,
I have to change the 6550 tubes of my Jolida 502B with a KT88 or 6550 quad and I'm in trouble.
First. I haven't the user manual, but searching in this forum I found something that could help me: using a Voltmeter I should stich the negative probe in the central hole, of five ones, which are positioned between the valves and the transormer, than the red (positive) probe in the hole numbered according to the tube I want to bias.
Turn the relative screw until the correct value is on the display of the voltmeter. Is this procedure correct?

Second. Which value af tension must I obtain? Do I have to use the value present on the Valve sheet or a default value suggested for the amp?

Third. Could someone suggest a fine (open and detailed sounding) brand of KT88 or 6550 tubes to look for?

Thanks in advance.
Franco

BaggedLancer

How old is your Jolida? Do you know if it has the EZ bias?(i assume no because you are doing it the hard way, but figured I'd ask)

franco_rome

Thanks, it hasn't the EZ bias...

BaggedLancer

Here are the instructions from my 502B manual. Hope that helps.

franco_rome

this REALLY helps.
Thanks
Franco

madmax

With new tubes I normally plug them in, turn on the amp and bias after about a minute just in case the new tube bias is way off from the old. Then I let it play for an hour or so and re-bias. After a few days I check it again to be sure it is right.
madmax