Brimar EL506 NOS vs. EH 7868 (New)

[Ziradog]

A while back in this post http://audiokarma.org/forums/index.php?threads/7868-tubes-whats-everyone-using.771802/page-2, there was reference to some matched sets of NOS EL506's for sale on the auction site. Since my Fisher 400 already had a matched set of modern Electro Harmonix 7868's from Jim McShane, with over-sized pins, I decided to give them a try. This week I had the Fisher open to fix the dial lights so I decided to give them a try.

This is by no means a scientific test, nor a serious listening test. I have this receiver hooked up to my bench speakers in my garage.

The receiver does not have IBAM or similar. I did put a pot in to adjust the bias voltage going to all four output tubes. I set the bias for the EH's. I did not go back & adjust it for the Brimar's.

Here is the mA to ground for the both sets of tubes.

Tube # EH Brimar
1 37.6 27.9
2 37.5 23.8
3 37.8 27.7
4 39.7 31.1

As you can see, much more variation than the McShane sourced tubes. I'm not sure you could hear the difference, but at least on this one measurement, the new tubes look better (after sorting & matching).

 

[gadget73]

I really wanted to give mine a listen. Unfortunately one was a dud and now I can't find any to make myself a quad with. I've half considered building a single ended 7868 type amp just to make use of them, but honestly going to the effort of making an amp for tubes that I probably can't replace seems a little silly to me.

 

[Ziradog]

You could replace it with the modern 7868 that also have the oversized pins.

 

[gadget73]

yeah I know but really at the end of the day I have no special need of the amp to start with. Spending money and building something I don't need just to use some parts up seems like effort for no good reason to me. If I had the transformers laying around already it would be a different story.

 

[Dave451]

I also bought a quad of the Brimar EL506's for my Sherwood S8000 IV. Since installed, they have played in well so far and the sound is excellent. They appeared to be carefully matched and, indeed, biased well and are quite even in their current draw in the Sherwood. As Gadget reported they are, alas, no longer apparently available anywhere I can find. From your data, it appears the EH tubes are hotter, since you are getting less cathode current on the Brimars with the same bias setting. I will be trying the EH 7868's one day soon.
Dave

 

[gadget73]

I did notice that when installing a pair of the EL506 alongside a pair of EH 7868. The EH want the grid more negative to maintain the same current. Since that particular amp has a single pot that I added to do all 4 I can't run them side by side to compare easily. The grid voltage required for the Brimar is actually a lot closer to what original 7868's want based on what my other amp with the old production tubes does.

 

[Ziradog]

When I bought the quad of EH from Jim McShane, he told me they were "hot" and verified I had a way to adjust the bias before sending them to me. At the time, it was the only matched quad he had. So the EH are probably not quite as different as my number indicate. I was more interested in how balanced the quad of Brimar's were in comparison, and on seeing if they sounded good (they do, at least with the dinky speakers I have on my bench). Were I to use them full time, I might look at some form of individual bias adjustment.