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Glowing Output Tube Trouble
By Gary |
Here’s a video I saw on YouTube that is interesting by mistertonemaster. He took the time to capture a glowing output tube on tape. These come in the shop sometimes. If you experience this in your amp, turn it off immediately and take it in for repair. Simply replacing a tube may fix the problem but you could have an open bias resistor.
What this means is the bias resistor acts as a gas pedal when the input signal hits the output tube. It’s usually biased as a negative voltage. If it opens from heat, wear and tear, pulls away from the circuit board, etc. This presents a 0 voltage to the input of the output tube. This effect causes the output tube to run wide open, putting a strain on your amp as well as the tube.
Topics: amp repair (Fender) | 6 Comments »
January 28th, 2008 at 9:54 pm
Gary,
I have a 1966 Fender Vibrolux. The vibrato is unreliable and the reverb channel has a fuzzy sound to it at higher volumes. The normal channel is fine. I switched the power tubes and it makes no difference. Perhaps there’s a foul preamp tube?
Does it harm the amp playing it loud (other than wearing out tubes faster and stressing speakers?). I play it at 5 most of the time and will turn it up to 7.
Any suggestions?
Regards,
Barrie
January 28th, 2008 at 10:02 pm
Hello,
First congrats on the amp,,don’t ever sell it, unless it’s to me :)
You can try the preamp and vibrato tubes…..just switch with the other tubes..but notice that the tube next to the reverb transformer is a 12at7..switch that with the drive tube..look at the tube chart in the cab or find one to look at
Just make note of what you’re doing before you do it…
also if you mean the vibrato is intermittent when you hit the switch..or turn the knob?
If it’s not the above you have problems
No it doesn’t hurt on those settings other than what you stated…you have to crank them to get the tone…
Gary
November 23rd, 2009 at 3:59 pm
I hope that you have some words of wisdom to share with me on this problem. I
play a bass guitar and just purchased some used gear. I tested out the
equipment in the basement of the seller and at first the speakers sounded
distorted. The seller played with the controls and mimized the distortion to a
point where it was negligible. So I bought it.
First, the gear: Peavey 1810 bass cabinet with an 18-inch and two 10-inch
speakers (200 watts, 400 ohms).
Traynor Mono Block-B (I am told it is 200 watts into 400 ohms) The amp
controls include an input volume and an output volume control.
Both items are of 1970s vintage.
Now the symptom: I have tried 2 different basses: a Fender with passive pickup
and an Ibanez with active pickup and both create an annoying distortion,
almost as though the speakers are blown. At first I suspected that the two
10-inch speakers were making the distorted sound because this is where the
distortion seemed most apparent when I put my ear to the grill of the cabinet.
However, I have been able to minimize the distortion inconsistently by working
the two volume controls and the low/middle/high controls. Seems to me that a
blown speaker might sound distorted with consistency. So I am now suspecting
that the amp is the culprit. This distortion is apparent at any frequency (all
notes).
This distortion is less apparent at the beginning of a plucked note and very
apparent as the note is sustained and diminishes.
Is there a way that I can test and confirm that the amp is where I need to
focus my attention?Should I try a pot cleaner? If so, can you give me advice
on how to use it?
Thank you for your time!
Pat
November 23rd, 2009 at 4:03 pm
Hi Pat,
First thing you gotta do is run the head to known good cabinet or another head to these pv speakers.
Tell you in a second where the problem is, let me know your findings…
Even if you have to borrow gear, don’t take anything apart till you perform these tests.
Gary
November 25th, 2009 at 2:32 am
Gary,
Re: Bass guitar amp head and speaker cabinet put out a distorted sound…
I tried another amp head and the speakers sound beautiful. So now I need to
find out how to repair the old Traynor Mono Block-B. Or does it become a boat
anchor?
I wish I knew how to describe the sound it makes. Sort of fuzzy. It’s almost
like the effects some guitarists like to create in rock music.
Now that I know the problem is in the amp head, what shall I do?
Thanks,
Pat
November 25th, 2009 at 2:34 am
Hi,
Does the amp have a line out or pre-amp in? You can possibly break it down even further. For instance if you can use your borrowed amp, (if it has a line out or power amp in) run out of the known good pre amp out to power amp in of your traynor. OR the preamp out of the traynor to power amp in of your good borrowed amp.
Will tell you where the problem is in the amp. We are talking transistor power amp right?
Might be worth getting fixed but the job is probably over your head. I think there are people looking for the amp.
Gary