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Mullard 12AX7 I61 and I63 differences
Posted: Thu Oct 11, 2012 2:22 pm
by Cheech
I have two tubes I have bought in various lots that I am positive they are mullards. However one is lacking date and the "I" code. The other just has a date code.
The one with just date code says B4H4. This has copper control rods. However it has a different color top mica. One is near white and the other is shiney. It also looks like it has a extra hole on the top mica.
Are there ways to tell the difference? I believe both to be I63 but I wanted to make sure ones not a I61.
Will
Re: Mullard 12AX7 I61 and I63 differences
Posted: Wed Oct 17, 2012 12:08 pm
by Cheech
Here is a picture of one in question. Can you guys identify its time frame. The I61 from 1959 I have has a different top mica. The I63 I have from 64 and 65 have different top mica than the earlier I61. I have another that has a top mica similar to this one but its a tad thinner. Could this mullard be one of the 10M series? Sounds compressed but its very alive and I seem to like it a lot.
Re: Mullard 12AX7 I61 and I63 differences
Posted: Thu Oct 18, 2012 6:07 am
by Cheech
Actually not sure this is a mullard anymore. I am leaning more twards a Philips Heerlen Holland made. What you guys think
Re: Mullard 12AX7 I61 and I63 differences
Posted: Sat Oct 20, 2012 4:06 pm
by Cheech
Ya T confirmed that this is a Philips. Sounds very harmonic to me. However it could just have microphonics. I have another philips thats same structure that I found after I posted this. However it rates less in micromhos than this one. Maybe 200 less on each triode.
Good tubes none the less.
Re: Mullard 12AX7 I61 and I63 differences
Posted: Wed Jul 17, 2013 1:22 pm
by Melodyman
I have 3 NOS Mullard 12ax7's that say Daystrom on them but have no i61 or i63 etched in the galss. How do I tell which they are? Is there any other identifier that tells us which they are?
Thanx!