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SurfGuitar101 Forums » Gear »

Permalink 6g15 reissue rebuild questions!

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I'll pick up a 60-80 watter. Or maybe just spring for a variable temp model.

I just got one of these.

image

I see it has crap reviews at amazon so I might buy a different one if I can find it downtown.
A guy downtown has a ECG 60watt iron

Might that do the trick?

Last edited: Mar 16, 2012 13:30:39

I prefer a flat-tip for soldering onto large surfaces because it really gets a good heat transfer

image

He who dies with the most tubes... wins

Surf Daddies

Last edited: Mar 16, 2012 13:35:53

Try eBay, where you can get a vintage (Bakelite) Weller for not much money. Make sure you have a spare tip around. They always seem to fail at the worst possible time.

Guess the old Weller's are OK. I got mine in High School. ('67 Alumni of HHS) Other than dropping it and epoxying the bakelite case back together, it works pretty good.

However +1 on the flat tip. I try to keep the tip on my gun filed a flat as I can, but usage corrodes the tip over time. As with all soldering utensils, Keep the tip tight and clean at all times.

Wow. I got that ECG 60 watt iron tonight at 269 Canal Electronics.

It glows red hot! Wasn't expecting that. Worked really well. Perfect silver pool of solder on the brass connections now.

Dwell still buzzes without the pin-8 to ground connection but... yeah, at least now I can properly solder to brass/steel.

Have you got another pre-amp tube you can pop in that slot? (doesn't matter if its a 5751, 12AX7, or 12AY7)

He who dies with the most tubes... wins

Surf Daddies

I have a spare 12AX7. I'll try that.

Any luck with the tube?

He who dies with the most tubes... wins

Surf Daddies

Wow. Tubeswell shoots... and SCORES!

I just popped my extra AX7 in there and the dwell/zero buzz is gone!
So, exactly what was my issue now? This afternoon I was trying a few things out. I would clip a jumper on to one side of the 1K5 resistor and jump the other side to the other side of the resistor and that would quiet it too. I guess that was just like attaching pin-8 to ground... the path of least resistance and all that. At my dads suggestion I clipped an additional 1K5 resistor in parallel to the 1k5 and that also solved it (depending on where I held the jumped resistor).

So, I guess it is a screwy tube? But I should not run the amp with the 12AX7 in place of a 12AT7 full time, right? That will be a problem? And why exactly is that if that is the case.

Thanks again. Good suggestion.

J

I had come down to thinking it was either the pot still or the tube, and the tube is easier to change first. Sometimes you just get a dud triode in the envelope.

You can continue to run it with a 12AX7 if you want, no harm done - it'll just have more gain on the wet channel.

He who dies with the most tubes... wins

Surf Daddies

Well, I used that 12AT7 for a while with no trouble so it seems like I must have fried it or broken it at some point. I'll order a new AT7 anyway. Glad that I can use the AX7 without worrying about it. I'm happy that this issue is finally resolved.

Congratulations!

Old punkers never die... They just become surf rockers.

Great job! And, tubeswell, your assist in this thread is really commendable. You are a thorough and patient technician.

This thread has been very educational. Thanks to you both!

Okay. Interesting development. I bought a brand new ECC81 (12AT7) tube and put it in... same DWELL buzz. So it was not a bad tube... but something in the circuit that reacts badly to a 12AT7 but works well with at 12AX7.

So, any idea what is happening?

J

The only things I can think of now are either

1) loose socket pins on that socket - in which case (with the amp off and unplugged and the filter caps drained) try wiggling the socket pins with your fingers to see if any of them are loose with the tube plugged in. Sometimes you can push loose pins further on to be 'more tight', or you could re-tension them with a small screwdriver; or

2) it could be a case of 2 dud 12AT7s (not impossible)

He who dies with the most tubes... wins

Surf Daddies

I'll look into those loose pins. I doubt that I'd get two duds. Also, remember, I used this same tube before I converted the unit and it worked fine.

I guess I could have fried it at some point.

Couldn't detect any dead pins on the socket. Very strange. Whatever differences there are INSIDE a 12AT7, it's just not compatible with my circuit? Weird. I'm not going to buy another tube just to answer this question. Maybe a cheapo chinese at7 or something used from ebay.

The main electrical differences between a 12AT7 and a 12AX7 are the lower dynamic plate resistance and higher transconductance and lower amplification factor of the former (which translates into higher plate-current, lower input-sensitivity/more clean headroom, and lower gain for a 12AT7), and a typically lower h-k voltage tolerance in the AT, all other things being equal. With a plate resistor of ~100k and cathode resistor of ~1k5 on a cathode-biased stage, there shouldn't be any drastic sonic differences and there definitely shouldn't be any performance problems with swapping the two types of tubes around in that circuit. The pin-out is the same, the heater current draw and heater voltage is the same, and even the VAmax is the same. (Granted the 12AT7 is rated as a higher dissipation tube, but all that means is that you should be able to run a 12AT7 hotter than you can run a 12AX7)

Having said that, some modern production tubes are coming out with appalling heater-cathode insulation, which can cause all sorts of problems (least of which is unwanted noise). Could be you had 2 bad tubes in a row?

What about other 12AX7s, 12AY7s, 5751s, 12BZ7s? You could try all those types in that circuit and you shouldn't have any problems. (But neither should you with 12AT7s)

He who dies with the most tubes... wins

Surf Daddies

Last edited: Mar 20, 2012 20:34:19

That's what I figured. I guess stranger things have happened.
I ordered a random AT7 tonight on ebay. A cheap, old, tested tube. I'll report back on how it does when plugged in.

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