Tubes Asylum Questions about tubes and gear that glows. FAQ

---

[ Follow Ups ] Thread: [ Display  All  Email ] [ Tubes Asylum ]

---

[ Alert Moderator ] [ Edit ] [ Delete ]

---

Re: Weak XF1s, with lots of flashing

Posted by steven oda on March 14, 2002 at 14:19:26

In Reply to: Weak XF1s, with lots of flashing posted by Bob S on March 14, 2002 at 13:02:30:

Bob,

The idle bias and plate voltage on your unit could have been too "hot." With EL34's is not that difficult to burn off a good percentage of their life in a few months of constant use, at underbiased or high idle current settings.

When the first dealer said that they were good, what were the mmHos measured? What are the values now? And the hours of use on those tubes, in between? What were they biased to? And at what plate voltage?

As an tidbit:

A dealer just sold a new "matched" quad of JJ E34L to a friend. I was fixing his guitar amp---as it sounded thin, even with the new JJ's.

Marked on each box were "7000" or more. But, when I tested the tubes two were below 6000, one---which was unused (his amp uses two EL34 and he wanted two spares)---tested 5500 on my B&K.

So, out of the four, two came close to being matched and were strong.

Now, I don't know how these tubes were "matched"---but I usually let them idle a bit before reading. Then, allow the meter to settle to a steady-state. I know a fairly well-known guitar amp tech that just puts the tube in, presses the button, and reads whatever the number is, after a second or two.

Sometimes, this is a false reading, as the tube heats a bit, it may change enough to make the final stable reading more than 5-10% off the original reading.

Best to get your own tester. I changed all the electrolytic caps. New tubes, & recalibrated it. Then, you can double check orders and buy bulk stuff. Ferret out the good tubes and save some money.

I've found that amps with original tubes (over 30 years old) sound great. Some amps have tube with no getter rings---I've seen more than a few TS 6550 with none of the getter rings left and the amp sounds good.

But, gotta remember---the rest of the amp is original, too. Once, you replace the filter caps or even some of the gain stage tubes--the new parts can stress the old tubes. And now the thing might not sound too good, anymore.

This post is made possible by the generous support of people like you and our sponsors:

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2025, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---