The Gretsch Pages: Discussions: Other Amps: Vintage Reverberocket Scare

Vintage Reverberocket Scare - Amp Guru Advice Solicited

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- Rated: 212 ↑
Nov 17, 2008 8:25 p.m. Proteus:

My late 60s Reverberocket (GS-12) is one of my prides and joys.

I'd been playing along tonight when suddenly it started losing power and getting that ultra-gritty farty intermodulating power-losing sound of horror. NOT musical distortion by any means...I was at low volume, and this was the sound of death.

I peers in the back, I does, and taps some tubes, some of which produce loud cracklesnap, but no improvement in the ugliness emitting out front.

Then I note the plates in one of the 7591 power tubes were glowing cherry red, whilst the other was its usual lovely blue self.

And it smelled hot.

I turned it off. Then, pretending it was a digital device and just needed rebooted, less than a minute later I turned it back on.

Lovely Ampeggian clarity returned, the tube was no longer redhot and looked like the other. Half an hour later, as I continue to play it, no change - it still sounds and looks right.

I don't really believe in spontaneous amplifier remission, though, so I'm sure I'm headed for trouble here.

What just happened? Is it "just" a tube, or something else driving the tube mad?

Don't tell me this lovely piece of gear is going to require major surgery.
- Rated: 9 ↑
Nov 17, 2008 8:29 p.m. twangmeisternyc:

God, grant me the serenity to accept the things I cannot change...the courage to change the things I can...and, the wisdom to know the difference.
- Rated: 212 ↑
Nov 17, 2008 8:31 p.m. Proteus:

...and the wisdsom to know the difference...

between what they cost, of course. Which is what I'm wondering.
- Rated: 10 ↑
Nov 17, 2008 8:34 p.m. Thilton59:

Well, we're gonna need some candles, incense, a quigi board, and a Necronomicon. Obtain these items along with some kind of animal sacrifice, a simple house cat will suffice, and we may just be able to banish the demons that lurk within that which is most holy to you.
- Rated: 9 ↑
Nov 17, 2008 8:35 p.m. twangmeisternyc:

Sleep on it...but as Thilton59 says, "Kill the cat!"
- Rated: 212 ↑
Nov 17, 2008 8:36 p.m. Proteus:

(Of course I deserve all this.

But be it noted that, even when I'm a smartass, I try to deliver useful information.)

(I just happen to have a housecat about ready for sacrifice, though, just in case.)

(And I'm hoping we'll hear from Billy Z, or JBGretschGuy, or one of the tube-guts-knowledgable guys eVENtually.)
- Rated: 9 ↑
Nov 17, 2008 8:39 p.m. twangmeisternyc:

Now, that we have that understood...

Did you have the trem/reverb oscillating to any noticeable amount?
- Rated: 56 ↑
Nov 17, 2008 8:40 p.m. otterbean:

Gremlins
- Rated: 212 ↑
Nov 17, 2008 8:43 p.m. Proteus:

Hot tube cooked the gremlins, I've emptied their crispy dessicated carcasses from the back of the amp.

Dying flatulence was experienced with reverb/trem either on or off, and at various settings.
- Rated: 7 ↑
Nov 17, 2008 8:45 p.m. googoobaby:

That's the thing I dislike most about tube amps. They sound great, but there's more magic than I like in terms of consistency and problems. My SS amps are nowhere near as good, but they're always precisely the same.
- Rated: 10 ↑
Nov 17, 2008 8:46 p.m. Thilton59:

Well, all smartassedness aside, when something of this magnitude happens to me I usually let it go. Especially in older vintagey stuff(I learned mechanics on old Volkswagons, where things fix them selves...) But if it begins to repeat, then I start going through and seeing what, if any components look "different" etc... That's the layman way, but it usually works for me. I'm sure one of the masters will chime in soon. But in the mean time, it never hurts to sacrifice a cat or two. I think that's what got my deluxe working again, that or the the new rectifier. Science...bah.
- Rated: 9 ↑
Nov 17, 2008 8:46 p.m. twangmeisternyc:

That was helpful googoobaby...
- Rated: 40 ↑
Nov 17, 2008 8:47 p.m. roadjunkie:

Tim I don't know if that's a fixed bias or an adjustable bias. You told me once you just put in a match set with no adjustments. Find a good amp tech and find out how to adjust the bias. The set you have in there have probably drifted so far off that you would never know they were once a matched set! I just bought a set of small bottle TADS for the Tophat. The tads tested out at 28. I'm not to sure what that means but I can give that number to the Tubes Store with my next order. According to them I wouldn't have to bias it again. I'll still check them out with the Bias-Rite nonetheless!
- Rated: 9 ↑
Nov 17, 2008 8:51 p.m. twangmeisternyc:

I say its the rectifier tube...just a guess, but solid state is the future.

I need a schematic...
- Rated: 212 ↑
Nov 17, 2008 8:53 p.m. Proteus:

Is this gallows humour?
- Rated: 40 ↑
Nov 17, 2008 8:54 p.m. roadjunkie:

Nothing drastic! Just get her to a doctor!
- Rated: 41 ↑
Nov 17, 2008 9:21 p.m. dubkitty:

"solid state is the future"

or at least that's what they said in 1975...
- Rated: 13 ↑
Nov 17, 2008 9:25 p.m. Rex:

http://www.torresengineering.com/repredhottub.html
- Rated: 57 ↑
Nov 17, 2008 9:26 p.m. Curt:

If I remember that's how my old Deluxe acted when it needed new capacitors. It would do the 60 cycle dance when it warmed up and got progressively worse. Not sure that you have the same problem but if it is it's a good bad thing to happen.
- Rated: 37 ↑
Nov 17, 2008 9:32 p.m. Nobody:

Yeah, where's JB when you need him?
- Rated: 212 ↑
Nov 17, 2008 9:33 p.m. Proteus:

Now - that Torres info is what I'm counting on! Clean the sockets, yeah.

Turning it off and back on sent a sudden leetle arc of voltage across the sockets to the pins and cleared a path for the eeelectricity.

Sounds plausible till something woise happens.
- Rated: 42 ↑
Nov 17, 2008 11:24 p.m. JBGretschguy:

The Torres solution sounds plausible for sure. Somehow one tube lost a connection somewhere - internally or externally, and probably to the negative voltage bias supply. I have seen bias wiggle tremolo circuits that would cause the tubes to red plate. Also, if the tubes aren't matched closely, one will red plate much brighter at first. I would change the power tubes, re-bias, and keep a close eye on it for a short while.

Billy Zoom has FAR greater knowledge and experience than I do, so I hope he will see this thread and chime in.
- Rated: 8 ↑
Nov 17, 2008 11:28 p.m. Ripley1046:

Being new to tube amps, I have no idea what any of you are talking about, but I have to comment. I love the wealth of knowledge on this page! Any musical questions anyone has, there is an expert in our midst. Whether it be some crazy instrument made at "Bob's house of git-fiddles" in Podunk Illinois, or a mass production model. I love it.
- Rated: 19 ↑
Nov 18, 2008 9:45 p.m. CnW:

Hi Proteus, I'm hardly an amp guru, but I do own an Ampeg Gemini I. Not so well-versed on Reverborockets, but I think your amp is cathode-biased. No need to rebias when changing tubes---it's a self-adjusting circuit. So this wouldn't be a bias adjustment situation in the usual sense. It would be more like bias gone out of whack. As JB said, something not making contact. Hence Torres' suggestion to re-tension the tube sockets.

Switching the two 7591's around , like Torres' article suggests, would be worth trying. If you get the same action in the same position, I'd turn your amp off and take it to your tech. We're talking about your baby here.......
- Rated: 22 ↑
Nov 18, 2008 10:15 p.m. MrAstroJet:

When you do, check for leaking capacitors in the signal path from the phase inverter to the grids of the 7591's and check that the grid resistors haven't drifted too far out of spec. There's not much to go wrong in a tube circuit, it's either a bad cap, tube or resistor and the parts are easier to get than, say, the mainboard for a Behringer.