Ebay Tube Blues

I have biased the original EL34 tubes of the exact same type in the same locations and the originals bias just fine. The original tubes can handle 400mA, no matter what socket they sit in. That's why I suspect these new ones have problems. If this is not a good assumption, let me know.

I suppose the connections of the EL34 replacements could be the problem, but I have cleaned them and they appear reasonaly clean. Just to be completely sure, I plan to get the pin cleaner and then try again. But, I'm not too hopeful.

Thanks for the tip about the JAN-Phillips. Its been 5 years since I bought the amp, and since they are pretty cheap, I thought I would just start with new tubes all around.

I've generally had good luck buying tubes on eBay. If they've tested the tubes and have a lot of old feedback you can read, I don't think it is any more risky than buying from a tube dealer.

Rick,
Your assumption is not good since tubes are matched to each other. The negative grid offset voltage may vary in EL34 from -35V to -55V the more negative is grid voltage the less current flows through the testing socket.
The grid supply is adjustable in all VTL-s although I'm not sure if the pot is accsessible from outside just like the bias ones. In worst case you should bring it to tech and he/she will set the bias supply correctly for your new tubes. If you're near NY area than you can bring it to me and I'll take care of it in few minutes of waiting.

Thanks for the info.

This gives me a good understanding of the issues here and will let talk intelligently with the people I bought these from.

To your more information:
Grid-bias pot can damage the circuit if not properly adjusted or turned to the extreams. In my vintage model MB100 it's accessible from the top pannel. I don't know what's in your case but I assume that this pot might be hidden on-purpose. I'm sure that with help of VTL(call or e-mail) you'll find out fast how to locate the master-bias pot and will be able to do a simple steps that(not in either VTL website or manuals) I'll share with you.

In your case(under-bias) which is quite normal, you simply set all tubes to max possible equal bias voltage and than adjust master-bias to the nominal manufacturer recommended level taking measurements from only one of tubes. Repeat measurements on the rest of tubes to ensure their equal bias voltage. Please note that under-bias cases are not distructive unless you have a largely exceeding negative grid voltage. Your bias-voltage readings will be somewhere bellow 100mV!!! You than have a few seconds to turn your amp off. Negative grid voltage is checked between pin5 of any tube socket and ground that should be in value ranges specified by manufacturer(find that out too) with amplifier on with no tubes. Readjust the bias voltage if neccessary to normal using master-bias pot.

If the case is opposite, i.e. you're having bias voltage too high at minimum pot setting you should turn off the amp immediately, remove the tubes turn the amp back on and measure between ground and pin5(grid) of one of the tube sockets. Increase the negative voltage(using master-bias pot) by 4...5V making it for instace instead of -45 to -50V and re-measure results with tubes and amp on. Turn the amp off before installing new tubes. If after number of measurements you end-up with negative grid-bias voltage too high than either the tube is probably bad or deffected or you've got added technical issues with unit that needs to be serviced.

As you might know that aging tubes tend to change their characteristics and even if you know you're setting bias pots at extreams in order to reach normal you'd better readjust the master-bias to have your local ones in the middle area for larger bias flexibility.