Easy Bias Question

[lgehrig4]

Let's assume you have an amp properly biased amp with El34s and you wanted to hear how it sounds with a matched set of NOS EL34s, would you need to be concerned about bias or would the fact the it was already biased for EL34s be good enough?

Thanks!

[TehSuperFox]

Let's assume you have an amp properly biased amp with El34s and you wanted to hear how it sounds with a matched set of NOS EL34s, would you need to be concerned about bias or would the fact the it was already biased for EL34s be good enough?

Thanks!

I'd probably rebias it to be safe. I swapped the tubes in my Super Reverb today, and the tubes different tubes were both 6L6's but had very different mA levels.

[lgehrig4]

Shoot. I would attempt it if the amp has external bias points, but I'm not going inside.

I have a Straub Cantus and I wanted to try some NOS Telsas that I purchased for another amp. I guess I can see how the preamps sound in it.

[TehSuperFox]

Yeah, it wouldn't be worth it to take the amp apart. But I wouldn't dismiss the idea so quickly - after all, I'm just basing it on my personal experience and I biased the amp with a probe and multimeter that I got from Eurotubes for $35.

[lgehrig4]

I have a multimeter, I'm just not confortable doing it the conventioal way. I've biased amps with external points.

[HCStraub]

Let's assume you have an amp properly biased amp with El34s and you wanted to hear how it sounds with a matched set of NOS EL34s, would you need to be concerned about bias or would the fact the it was already biased for EL34s be good enough?

Thanks!

Bias it......matched sets of the same tubes idle at different currents.

To give you an idea, even with new JJ's(like the ones in your amp) set at 35ma, if you buy another new set of matched JJ's they will range from 15ma to 45ma depending. That much difference between sets of the same tubes from the same factory is common.....I have matched sets in the shop that that range that much.
The last thing you want to do is buy an expensive set matched NOS tubes and put them in without biasing. Say they are idling at 10ma, you will think they sound lifeless and think you waisted your money. Or the reverse, if they are running at 45-50ma they will sound harsh. Or worse, if they are hotter than that, they can red plate and short......you don't want that.
Chances are, with the NOS matched tubes you will like them enough to keep them in the amp. Pay the $30 for the bias job....and enjoy them knowing they are setup correctly and will last a long time.

[lgehrig4]

Thanks Harry. I understand the process, but have only done it with amps equipt with external bias test points. Could you tell me what I need to do? I have enough experience and sense not to get electrocuted.

[HCStraub]

Give me a call......I will PM you my info.

[GenoBluzGtr]

TehSuperFox, glad to see you are still playing the Super... how's it holding up?

[lgehrig4]

Just a quick update. I spoke with Harry and he walked me through the process. It was pretty easy. Hardest part was getting the chassis in and out of the cab without scratching the beautiful wood.

I've read a million times about what a great guy he is and believe me it's written for a reason. Between Harry and Greg Germino I can't think of any instances where customer service was ever better.

Love this amp!