Author Topic: Retube time  (Read 2614 times)

Offline Syntho

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Retube time
« on: October 29, 2019, 09:20:55 AM »
Have to retube my amp, mainly the power section with four EL34Bs. I notice a little noise and popping coming from my amp, and after tapping on all the tubes with the amp on, two power tubes are creating a bit of noise when tapped. The other two power tubes don't make a sound, and neither do any of the 12ax7s.

This started when a while back I smelled something burning near my amp and I realized that there is plastic mesh fabric near the top vents on the amp that started to melt. I don't know if the power tubes got so hot that it started to melt the plastic or if it was something else that was generating that heat. I'm praying it was just the tubes.

Long ago I remember having my amp turned on without my cab being connected. Once for like 45 minutes, the other time for about 15 minutes. I don't know if this caused any damage, but I also had the volume very low. I think I need to have a tech look at everything and have a checkup but I also don't have the $$$ for both a retube and to get a tech to look it over. I live in the middle of nowhere so I'd have to ship it. It's got to be done at some point though.

You guys have any ideas? Maybe there is an amp tech here among us.

Offline ssp3

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Re: Retube time
« Reply #1 on: October 29, 2019, 01:16:47 PM »
Syntho, wrong forum! ;)


two power tubes are creating a bit of noise when tapped. The other two power tubes don't make a sound, and neither do any of the 12ax7s.
This is normal. Tubes differ in their internal construction. Some are more microphonic than the others. (The old Mullards in my Marantz 8b ring a lot).
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..plastic mesh fabric near the top vents on the amp that started to melt.
This is indication that output tubes got too hot and, most probably, their operating point was/is wrongly set.
Without schematics, without knowing what amp, what brand of tubes, what plate voltage, what operating conditions, I can't say anything more. If it's one of the chinese creations - good luck with it, it could be anything. From wrong resistor values to leaking coupling caps to incorrect operating voltages..
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Long ago I remember having my amp turned on without my cab being connected.
Bad idea. You were risking output transformer damage.
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I also don't have the $$$ for both a retube and to get a tech to look it over.
Well, if you dont have the funds to keep your tube amp in shape, stay away from tubed units. Or, stop buying all other junk and invest the money in your amp, if it is important to you. Bring it to the qualified tech and pay him. (Techs have to feed their families too, btw.)
Or, if you have the measuring equipment (scope, oscillator, voltmeter etc.) and are prepared to deal with high (and potentially lethal) voltages, then do it yourself. The Tube Amp Book by Aspen Pittman is a good starting point.

Offline Syntho

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Re: Retube time
« Reply #2 on: October 29, 2019, 04:56:54 PM »
The noise I'm hearing isn't normal. Perhaps when tapping on it, ok, maybe that's normal, though I've read differently. There's definitely this weird sound coming from it at times so it's worth getting a new set of them.

I don't have around, say, $450 for a new set of tubes, shipping back and forth as well as the fee for a tech at the moment. I'm not poor or anything. I'll stick with my tube amp since it sounds the way I want and hopefully come up with some $$$ soon.

Just wanted to get some threads going in this section...

Offline FdB

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Re: Retube time?
« Reply #3 on: October 31, 2019, 06:44:07 PM »
Like to think that this is all because I have more patience than money,
                                                        but it’s probably just more like OCD.


Years of dust & nicotine?

Just for giggles, I’d try carefully cleaning all the tube sockets and legs of all the tubes and (very) closely inspect connections to all tube sockets. Got a powerful opti-visor or a really good magnifying glass?

Have one of the first-made Fender Blues Juniors here and it started acting up last year and eventually wouldn’t output at all (other than just hellish noise). When I attempted to remove the tubes for closer inspection, it was very difficult to pull them from their sockets. Afterwards I assumed that this was the result of oxidation, or even possibly mild corrosion that had occurred over time. (Metal to metal contact and repeated heat-up / cool-down cycles.) Poor connections also tend to generate additional heat.

Eventually ended up re-soldering all of the tube sockets and I did replace two tubes after cleaning everything. The new tubes went in and out easily and even the original tubes did the same after the cleaning. I used a tiny piece of Scotch-brite™ pad clamped in hemostats on each of the tubes’ legs and a paper clip back & forth (in/out) in the sockets themselves… and all with a bit of electronics cleaner present. Turns out that I didn’t need the new tubes after all. Worked great again! (and since)

This approach may not work for you, but if it does… saves that packaging, shipping, waiting and tech cost. And of course, I let the amp sit for a week unplugged before delving into the realm of possible shock. ::)

*I wouldn't doubt that this Blues Jr. amp did its' fair share of smoky bar gigs long before I owned it. It came with its' own little burned roach present inside... of who-knows-what plant origin.
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Offline mrhappy

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Re: Retube time
« Reply #4 on: October 31, 2019, 07:59:14 PM »

This started when a while back I smelled something burning near my amp and I realized that there is plastic mesh fabric near the top vents on the amp that started to melt. I don't know if the power tubes got so hot that it started to melt the plastic or if it was something else that was generating that heat. I'm praying it was just the tubes.


This is concerning. Does the amp still work and sound normal? If you fire it up (bad choice of words! ;D) keep an eye on those tubes to see if something starts glowing red hot. Maybe a tube was starting to short out and drawing way too much current or similar?

Offline FdB

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Re: Retube time
« Reply #5 on: January 22, 2020, 09:20:05 PM »
Hey Syntho, how'd the situation turn out?
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Offline Syntho

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Re: Retube time
« Reply #6 on: January 23, 2020, 02:45:47 PM »
I retubed and it seems to have fixed the problem. Only switched out the power tubes. Admittedly I haven't had enough time in the last while to play since I've been busy, but I'm pretty sure it did the trick. Was only about $100 for a set of 4 matching power tubes.

Offline Syntho

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Re: Retube time
« Reply #7 on: February 03, 2020, 12:17:05 AM »
Been so busy lately that I haven't had time to play much, but I've been running my rig for a few hours now and I haven't heard one single fart coming from the amp. Those power tubes were the culprit, I'm sure. I left the preamp tubes alone since they seem fine. I'll keep running them until they die.

Offline mrhappy

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Re: Retube time
« Reply #8 on: February 03, 2020, 06:43:11 AM »
Excellent Syntho...Rock out!!!! ;D