About a year and a half ago, while rehearsing with my band, I noticed some intermittent feedback problems while playing my harp. This had never happened before, unless I pointed my mic directly in front of the speaker cone.
Shortly thereafter my EQ pedal went squirrelly for a while and then died. I attributed the feedback to that, but after removing the pedal from my board, the feedback got worse (I used the EQ to tweeze out any frequencies annoying to harp mics).

It was time for new tubes, so I ordered some...after installation, I had intermittent feedback on both my harp and guitar.

I removed all the gain-ier overdrive and distortion pedals from the loop, I put the old tubes back in, put new tubes back in, replaced all the patch cables, tried a new noise gate, I played straight into the amp--no pedals (it was okay until I got it loud enough to hear and then the squeal monster came back), I tried five different microphones & all my gutars...and it still had feedback issues that had never been there before.

I even took my pedalboard and plugged in to somebody else's amp, thinking it might be the problem...no dice.

Now I'm getting the same problem more frequently. It's almost to the point where I can't play harp through this amp...and guitar is getting worse.

What would cause a gently used but well-taken-care-of amp start feeding back after almost 20 years?

Thanks in advance for any advice!

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Good Vibes To Y'all!



Screamin' Armadillos
Texas Roadhouse Music
Guitar/Slide Guitar/Harp/Vocals

Without poking around inside the amp, could it be a loose valve base?
Other than circuit components I'm thinking it could be a shielding problem.

If you could ascertain which valve or valves are going bad (try them in another amp) that would probably help narrow down the suspect list.

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Do you have any High frequency Electronics near by that have not been there long or that may be going on the fritz Radio, Microwave, TV, Evan an electric motor in a fan or air conditioner can sometimes create a ghost like that. Start eliminating things and see if that helps. how about a garage door remote? Dose it occure just at home or when your out as well?
----Danny,

If by valve base you mean the socket the valve/tube/whatever (we are truly separated by a common language ), I thought of that, but all the valves/tubes are tighter than a fat man wearing skinny pants. When replacing the tubes the first time, I pulled the chassis and checked all the solder joints and saw nothing amiss.

How would I track down a shielding problem specifically?

I have no other amp to test the tubes in and no tube tester, either, so I might have to make the trip down to D/FW to get a good amp tech to check it out. In my new Locale Della rednecks there's no decent repair shop I trust.

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Good Vibes To Y'all!



Screamin' Armadillos
Texas Roadhouse Music
Guitar/Slide Guitar/Harp/Vocals

If you have one preamp tube (see I made the effort) that you know to be good. Then you can at least check the preamp section with that. Change V1, listen to the amp. Any better we can start with the problem along there. And so forth for the rest of the preamp tubes.
There's a reason valves are going bad, it could just be the luck of the draw (particularly bad luck to get bad valves twice in a row. But I've had it happen over three sets from the same manufacturer). It's more likely to be component failure.

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Other than the implant the little grey men put in my head five years ago...

I have had the same problem in a myriad of locations, both cluttered and clear of electronic gadgets.

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Good Vibes To Y'all!



Screamin' Armadillos
Texas Roadhouse Music
Guitar/Slide Guitar/Harp/Vocals

At the risk of sounding flippant, it's broken.

And that's just typical of today's modern throw away society isn't it? You have a guitar amp for just 20 years, and then suddenly it's knackered.. Just as the faded guarantee certificate has finally succumbed to rot.. Outrageous..

(Sorry, hope it's soon restored to it's former glory..)

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Fender Highway & Classic 60s Strats, Fender Toronado, Telecaster, Gretsch Projet, Charvel 3, PRS SE Soapbar II & Custom 24, Burns Batwing and many others!

That's something I thought of, too, because when I initially put the new valves ( ) in, the problem went away temporarily, but came back with a vengeance. I'm wondering if there's not another component drawing too much of something (voltage,etc.) that's either messing up the valve or a couple of the valves...

That was something I thought of, too, but during my layoff and subsequent move I rarely got to play through this amp (it was somewhat in a storage in my closet), so it would be failure out of the box (almost)...which happens. Hmm.

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Good Vibes To Y'all!



Screamin' Armadillos
Texas Roadhouse Music
Guitar/Slide Guitar/Harp/Vocals

I know it sounds stupid, but I really baby this amp. Apart from Changing speakers and branding it on the back, it looks brand new, and performed perfectly. For many years I had other amps to choose from, and if we were performing in a place that was possibly dangerous to the health of my rig, the other stuff came out with me.

I've had good luck with tube amps, too. I had a Bassman Ten that was twenty-five years old before I finally had to replace the tubes/valves. (It was my first tube amp and I didn't know any better. I played it until it didn't play any more and the tech who retubed, recapped and biased it was shocked that the '72 amp had factory "bottles" in 1997)...

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Good Vibes To Y'all!



Screamin' Armadillos
Texas Roadhouse Music
Guitar/Slide Guitar/Harp/Vocals

By the way, I don't mean to sound flippant or argumentative about what's going on...I really appreciate any and all suggestions you might give. I was just clarifying what I had observed and already tried. All good suggestions, thus far.

One person suggested a microphonic preamp tube (I think that's what Niki was suggesting, too). Is it true you can check for microphonic tubes by turning on the amp and tapping each tube lightly?

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Good Vibes To Y'all!



Screamin' Armadillos
Texas Roadhouse Music
Guitar/Slide Guitar/Harp/Vocals

Yes, that's very true. I use a chopstick to tap em with.
I also believe it could be component failure causing a tube to go bad.
I did have a schematic but lost it after a computer crash. I'll take another look round the web, see if I can find it. If you can find out which tube is making the most difference alleviating the symptom we should see where to be looking.

However, if it is a component. How comfortable are you putting your fingers in the bucket of sparks to test em?

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TV and Radio tubes Can be Temperature sensitive, If you have an unusual heat source such as an overheating transformer, that might increase the ambient temperature enough to make a difference, Dust and lint will produce the same overheating affect. Never rule out a good cleaning, especially for electrical things. some times that's all it takes
----Danny,

I do it all day long, except on medical equipment...I don't like schematics, I prefer a diagram. If there is a good diagram and if the components are readily identifiable, I'm reasonably certain I could tackle it.

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Good Vibes To Y'all!



Screamin' Armadillos
Texas Roadhouse Music
Guitar/Slide Guitar/Harp/Vocals

Found it, I think. Is this the right model no', 6G16?



Or the AA763



Or the AB763



Not great quality. Found here
http://www.turretboards.com/guitar_amplifier_builders_info_schematics_library.htm

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No no and no

I haven't looked inside a RI Vibroverb amp,but those schematics are for the original Vibroverb,and I'm pretty sure the RI wouldn't be an exact replica.
Arjay would know what components are in the RI,but I'll bet there's some PCBs in there...and fixing them (the printed circuit boards) isn't easy...if they could be causing the problem.
I could be talking outta my ying/yang,but my remarks are based on the differences between the Deluxe Reverb RI amp,and an original...of which I have three vintage DRs...I've seen the innards of the DRRI...it ain't the same.