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(@hyperborea)
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Joined: 15 years ago
Posts: 833
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Ho ho, I'm almost there. Last night I replaced the coupling cap from the reverb, the plate load resistor on the reverb recovery tube half (it was on the same eyelet as the coupling cap so why not), and the two B+ dropping resistors (both with 2W flameproof). The crackling has gone away and has now revealed a distortion. The clicking from the standby switch is gone and it just took some contact cleaner and flipping the switch to remove the gunk.

When you play a note there is a slight fuzziness to it and if you hold it becomes worse and then unacceptable after maybe a second. This fuzziness occurs at all volume levels. Any ideas of what to check? Any tests to narrow it down? I have ruled out the reverb and vibrato as these can be pretty much fully disconnected using a footswitch and when done the problem remains.

Thanks again for any help.

Edit: I think I found the answer to the distortion. It seems to be the speaker. If I strike a chord and then reach in and grab the yoke for the voice coil and give a bit of a squeeze the distortion stops and as I stop squeezing it comes back. Looks to be the answer.

Coincidentally, I'm picking up an Eminence Red Fang tomorrow that I found on the local Craig's list. I had planned to wait on swapping the speaker but I got it for $90 and these regularly go for $160 from Musician's Friend, etc. That's a pretty good deal especially since it's only got about 8 hours on it - being changed because the owner doesn't like the sound. I'll swap that in and verify that the problem goes away. Pretty lucky timing on that.

It may turn out that I don't like the sound of the Red Fang (supposed to be like a Celestion Blue - one of the speakers that people like in these Traynor combos) but at this low price I should be able to get my cash back and maybe try a Greenback (another speaker that people like in these Traynor combos).

Pop music is about stealing pocket money from children. - Ian Anderson


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(@ricochet)
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Joined: 19 years ago
Posts: 7850
 

The spider in the original speaker may have dirt in it, or may be misaligned and rubbing on the side. Either way, basically you'd be looking at reconing to fix it if you didn't replace it.

"A cheerful heart is good medicine."


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(@hyperborea)
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Joined: 15 years ago
Posts: 833
Topic starter  

That's the Red Fang in and I like it. It took a little to grow on me. It was a big change from the Marsland in there. Depending on the tone settings (a pretty cool Baxandall tone stack - wide variation out of two knobs) I can get a big round jazzy tone to something more Voxy (my Jumpin' Jack Flash has a very old school Stone's sound) to some Tweedy blues sounds. I'll have to decide what to do with the Marsland speaker. There's some info on the Weber pages (in their FAQ) about removing dirt from a speaker - if it doesn't work it will kill the speaker and it will need reconed but then it's already dead so no loss.

I still have two unwanted noises. With the reverb on (not shut off by the footswitch) I get a hum/hiss/pop combo that is somewhat low volume, at least in comparison to the other noises I've gotten rid of, but still loud enough to be unacceptable. I've tracked it down to the input wire running from the amp to the reverb tank. The ground on the tank end is disconnected. I'll have to reattach that. On this amp the wires to and from the reverb tank are coax but in searching the net on reverb tank cable they all seem to be some sort of two strand wire. Is that the case? Why the difference? I'm wondering because there isn't a lot of extra wire and putting on the old RCA connector or perhaps a new one may mean taking off some wire and there may not be enough. That would mean new wire.

The second noise is much lower but still annoying. It's a hum that occurs all the time. I know that tube amps will almost all always hum but this is more than that. It's affected somewhat by the volume but only goes up slightly until the volume is set to 8 or more and then the volume of the noise jumps considerably. When the volume is up at 8 or more then the tone controls seem to change the sound of that noise but below 8 there isn't much (maybe any) appreciable change with the tone controls. I'm going to start poking through the grounds particularly in the early pre-amp stages to see if the issue lies there. Perhaps it's the volume control itself? Any other suggestions? I'll see about getting an MP3 of the noise if that would help.

This has been a lot more work than anticipated with this amp. It was a closet queen for much of it's life so I was hoping that it would only need the electrolytics replaced but there has been much more than that. Once all is right with the amp I want to go back through the old tubes and look for good ones (these are 70's made in Japan tubes).

Thanks again for any help.

Pop music is about stealing pocket money from children. - Ian Anderson


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(@ricochet)
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Joined: 19 years ago
Posts: 7850
 

I can't think why it would make a big difference whether you use coax or paired wire cable for a reverb.

Noises and hums can be very frustrating to track down. An underappreciated source of hum is in the tubes themselves, where the AC heater voltage interacts capacitively with the cathode, and also the ends of the heater wires often protrude from the ends of the cathodes, emitting electrons that bypass the control grid, make an end run around the tube structures and get to the plate. The alternating current causes the wires to heat and cool a bit at 60 Hz, modulating the stream of electrons. The first 12AX7s had heater wire that was folded back and forth longitudinally and stuffed into the cathode sleeves, and hummed terribly in this high gain tube. They were quickly replaced with the 12AX7A, which had coiled heater wires that reduced the hum greatly. Many later 12AX7 tubes have been made with folded heater wires and will hum like the originals. And if the alumina powder insulation on the heater wires gets leaky, there can be a direct leakage current of 60 Hz AC to the cathode; that'll hum like crazy. All these things happen in other tube types as well, but they're especially noticeable in higher gain tubes and in earlier stages of the amp. Tube swapping will tell you quickly if a tube's the source of the problem. And you want to make sure that no shields are missing from preamp tubes that are supposed to be shielded.

"A cheerful heart is good medicine."


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(@hyperborea)
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Joined: 15 years ago
Posts: 833
Topic starter  

I haven't had much time this week (pretty busy at work) to hunt for the noise source but I did find that the wire from the tone stack to pin 2 of preamp tube 1 is microphonic - if you tap it you can hear it through the speaker. Pin 2 of preamp tube 1 is the grid of the second half of the 12AX7 used as the second preamp stage. As I followed that back it seems as if that pin is loose - it wiggles as you tap the wire. Is there any way to stop that or do I need a new socket?

Somewhat related question too. Is there any reason that some of the wire is cloth covered and some of it is plastic coated? It seems as if the signal wire is generally cloth covered and the power section wire is plastic coated.

Pop music is about stealing pocket money from children. - Ian Anderson


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(@ricochet)
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Joined: 19 years ago
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Sometimes you can take a sharp tipped knife or small probe and gently bend the contacts in the socket toward contact with the tube pins (which have to be out to do that) to retension them.

Whether the wires are covered with cloth or plastic is immaterial. May reflect reworking of the amp.

"A cheerful heart is good medicine."


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(@hyperborea)
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Joined: 15 years ago
Posts: 833
Topic starter  

No, it wasn't a retensioning issue. The retensioning tightens the little "arms" inside the metal tube that receives each of the vacuum tube pins. I was talking about the metal tube for the pins moving more that I thought it should. I talked, over lunch yesterday, with a couple of older engineers who have worked with tube stuff in the past. They said that those metal tubes in the tube socket are supposed to be a little loose to account for variation in the pin placement on the vacuum tubes. (that's a bit of confusing double usage of tubes - maybe I should replace one of those with valves? :) )

The solution turned out to be reflowing the joint on the other end of the wire at the eyelet card. Once that was done there was no more microphonics in the wire. The noise floor is a lot lower now - maybe as low as it should be.

As for the wire differences, I'm not sure that the amp was reworked. All the components in there looked original and old style. I've found a Traynor amp Yahoo group. I'll probably end up asking about the wire issue over there.

Pop music is about stealing pocket money from children. - Ian Anderson


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(@ricochet)
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Joined: 19 years ago
Posts: 7850
 

Cool! Glad you got that fixed.

"A cheerful heart is good medicine."


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