el34 change, bias question

[brit84]

I know I should, but first need to ask if there is actually a big difference betweent he svetlana el34 i have and the ruby el34bstr tubes i want to put in?

where do i find the bias pots?

and before i get yelled at, I know the dangers and will not be doing anything myself save put the tubes in. I have changed tubes before and will be looking at a bias probe soon.

 

[Gearjoneser]

Re: el34 change, bias question

The bias range is probably close enough that you could just pop in the new tubes, but it's a good idea to check the bias. When you put in the new ones, dim the lights down, and observe them in the darkness. As long as the plates don't turn orange, you won't be harming anything.

I'm not sure I'd recommend Ruby.....for the same or cheaper, JJ's are always good. JJ's and Svets are my favorite current production EL-34's.
You can buy a simple bias tool for about $20. It's just a socket with cable that connects to a multimeter. I like the mA version, so I can make sure EL-34's are between 35 and 38mA. Crank the amp at 35, 36, 37, 38 mA and decide where the amp is boldest and most toneful. It's like setting the idle on a carburetor....you just want the car to be healthiest.

 

[brit84]

Re: el34 change, bias question

i know it may seem like im going bacwards b putting ruby in them, but thats what is supposd to be in there, the version of the el diablo i have has svetlanas as that is what they used for the first models. Otherwise any suggestions for high gain metal tone would be appreciated

 

[brit84]

Re: el34 change, bias question

anyone?

 

[wixedmords]

Re: el34 change, bias question

I'm pretty much inline with what GJ said. I like both of the EL34's he mentioned. If it is the VC-100 you are talking about I would change it over to 6L6's, but that is just me.
I think it is important to find plate voltage and do the math to find out the range of bias, 50-70% and then set it by ear in that range.
The bias pot can be hard to find on some amps, it can look like this:

http://www.jaredcoberly.com/egnater/bias_pot.htm

Or like this: The white pot on the left:

http://www.mojaveampworks.com/8Gallery/Images/Plexi45/Dscn0261Sm.jpg


EDIT: It is easier to bias if you swap out the EL34's for EL34's.

 

[brit84]

Re: el34 change, bias question

how much does biasing usually cost?

 

[ErikH]

Re: el34 change, bias question

Svetlana's are really good tubes (New Sensor made). Those are my favorites currently. There's also the Winged =C= EL34's which are also Svetlana (made in the old Svetlana plant, but not owned by New Sensor - long story, Google it....LOL).

You should be fine in the short term just swapping them out but definitely get the bias checked. It can drift over time just from the normal wear and tear on the tubes. I can't remember what I paid to get my Marshall biased last but it wasn't a lot. I can tell you this, I paid $150 for a complete retube (EH's in the pre and Svetlana's in the power), pot cleaning and a bias adjustment.