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AUDIO FORUMS >> Replacement Tubes >> EL38
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Message started by __Jon__ on 12/11/21 at 20:30:52

Title: EL38
Post by __Jon__ on 12/11/21 at 20:30:52

Was wondering if any of the smarter folks on the forum could tell me if the EL38 is a compatible tube for the ZMA? A friend has an unused quad and it got me thinking. The recommended bias is pretty low from what I can see.

Best,
Jon

Title: Re: EL38
Post by CAJames on 12/11/21 at 21:23:16

Based on my quick perusal of the datasheet it seems like it isn't too far from an EL34 so it ought to work, with the appropriate adapter of course. And by work I mean it shouldn't blow up when you power on the amp. How it will sound is anyone's guess. Of course its your amp so take this FWIW.

Title: Re: EL38
Post by __Jon__ on 12/11/21 at 22:03:26

Thank you. That was my feeling. Now I just need to figure out how to calculate the bias for this amp. I seem to remember someone posting a calculator before. Cheers. [smiley=thumbup.gif]

Title: Re: EL38
Post by Archie on 12/11/21 at 22:48:16

Here is the bias calculator link: https://www.tedweber.com/bias-calc/

I use 480 volts for the ZMA plate voltage. I think that's what a member measured on his ZMA. If the EL38 is similar to the EL34 than the bias numbers should be the same. Or look for a tube on the list with the same plate dissipation. I think the EL34 is 25 watts.

Title: Re: EL38
Post by __Jon__ on 01/11/22 at 20:32:20

Just in case others might try, El38s will not bias in the ZMA. The meters stay at 0 no matter the bias settings. I let them warm up for 5 mins but didn’t want to try longer. When I shut off the amp, as the captors were draining and the VR tubes flickered, the meters jumped up to 50 or so and stayed there briefly. I believe this indicates they were getting too much current. Although similar to an el34, I have learned that the el38 has much higher gain and needs to be biased even lower. Makes sense.

In the tube buffer of the Lampizator, the el38 has a nice midrange for vocals but was somewhat thin on the top end and weaker in bass compared with my preferred tubes. This is of course with unused 60+ year old tubes and presumably might improve with some break in.