Allen Accomplice Motor Boating

[Platefire]

It's ever so slight, low of volume and at pretty quick pace. I turned off the reverb and it continued. I pulled V1 and it continued. I pulled V4 PI and it stopped. So am I right in assuming it is either a leaking coupling cap into the PI, or after the PI, or a Filter Cap going bad? I did check the power tubes to see if they were flickering in sink with the motor boating but I didn't see any of that. 

 Judging from what I've checked so far, my guess is it's a leaking coupling cap in the power amp section.  This amp is about 20 years old now even though it seems like I just put it together yesterday. I've never had motor boat problems before, so let me know if my reasoning is off. I know it's time for new filter caps, check coupling caps and resistor values

[bmccowan]

I've never had motor boat problems before

Platefire, you are blessed. Man have I had motor boat problems: failed prop seals, seized lower unit, cracked rings, them points (Slingblade), fouled carbs, broken shear pins, etc...
Ok, enough of that. At 20 years I would put filter caps at the front of the line. At 20 years its a good time to replace them anyway (of course I have been negligent with my own 20 year old builds) so nothing is really lost if you have to keep fishing.

[sluckey]

I would suspect filter caps first because they are easy to check. Just get a 20 or 40µF axial cap. Use a gator clip test lead to connect the negative lead to chassis. Slip a piece of wire insulation onto the positive lead but leave about a 1/4" exposed. This will be your probe tip. Now hold the body of the cap in your hand same as you would hold a meter probe. Touch and hold the "probe tip" to one of the filter caps positive lead. Repeat for all four filter caps. If you find that touching one of the filter caps stops the motor boating then you have found the rotten egg.

BTW, back in the '60s most service shops had such a test cap already built with a permanently attached negative clip lead and hanging above the bench. Very handy test gadget that got used quite a bit back in the days of tube tv sets.

[Latole]

Is there any mods on the amps.
Did you ear the amp working well ? Before motorboating ?

[Platefire]

OK sluckey! Thanks for the info. I have a bunch of old Electrolytics, so doing that shouldn't be any problem. I dug out the old file folder on this one and it's actually younger than a thought. Completed 11 July 2007, only 16 years old.

bmccowan, I've had my share of motor boat adventures, like the time in the 70's I went fishing with Dad in his aluminum boat with 6HP Evenrude fishing in Toledo Bend Lake. I was getting a strike fishing with top water Tiny Torpedo. The bate hung on a limb. Wanting to cast again to get another chance at the hard hitting bass, I jerked the line to free it from the limb. It broke loose and came flying back to me like a bullet and hit me on the left side of my face close to my eye. Both treble hooks stuck in. Dad got so excited when he saw what happened be flooded the motor trying to crank the boat no matter how he tried, wouldn't start. We both ended up paddling about a mile back to the landing. He took me to the closest ER in Many La but once they looked at it, they wouldn't attempt to take it out because it was too close to my left eye. So Dad took me to P & S hospital in Shreveport La where they performed emergency surgery and took it out. My eye was fine. Had a little scar but not too bad. So yeah, I've have had some motor boat experience

Latole. Got it new as a kit and put it together, a 1-12 Combo. Only problem I ever had with it is a power tube shorted out and blew a fuse. Later a GZ34 Rectifier went out and blew a fuse. Other than that, until now,  its worked perfect.

[bmccowan]

Good story. Despite being a Mainer, I have kayaked the bayous of La quite a bit. We go for the music, the people and the Etouffee. We usually rent a cabin near Breaux Bridge.

I like Sluckey's approach on testing the filter caps. 16 years is not bad IMO, so if its not the caps you won't waste the time and money.

[AlNewman]

I've never had motor boat problems before

Platefire, you are blessed. Man have I had motor boat problems: failed prop seals, seized lower unit, cracked rings, them points (Slingblade), fouled carbs, broken shear pins, etc...

True story, if amp woes are getting you down you've never owned a boat.

[sluckey]

Boat is just an acronym for "break out another thousand".

[Latole]

Good story. Despite being a Mainer, I have kayaked the bayous of La quite a bit. We go for the music, the people and the Etouffee. We usually rent a cabin near Breaux Bridge.

I like Sluckey's approach on testing the filter caps. 16 years is not bad IMO, so if its not the caps you won't waste the time and money.

It's not impossible, depending on the quality of the capacitors.

On the other hand, 16 years is still new in my opinion. The year 2000 was yesterday.
I have so much electronic equipment that is over (and much over) 20 years old and working very well, and having worked in the electronics field, devices that were 40 years old were the norm.

[Platefire]

sluckey---went through my old saved caps and ended up picking an 82uf/500 because it had the longest leads and large body size make it easier to hold. I don't think the higher uf would make any difference but I'm just wondering?? you recommended 20-40 uf

[sluckey]

82 is fine for a test cap.

[Platefire]

OK, Good Deal.  Thanks!

[Platefire]

Well I finally got around to checking this motorboat issue. So I removed the chassis, set it up on a stand, hooked the reverb, speaker to the speaker cab and fired it up getting ready to use my cap-checker-tool to check my electrolytes. Guess what?? No motorboating!!! I changed the volume around, tone controls and reverb controls trying to get it to motor boat and nothing.

So I checked the bias and voltages trying to give it time to act up. I run it for an hour or more at  pretty high volume and I just can't get it to do it again. Only thing I can figure at this point is I moved it to another room to work on it and the problem must have been with the voltage in that room which is my computer/wash room. I'm not going to put it back together just yet. I will fire it up several more times to see if I can get it to do it anymore first. Platefire 

[dude]

Well I finally got around to checking this motorboat issue. So I removed the chassis, set it up on a stand, hooked the reverb, speaker to the speaker cab and fired it up getting ready to use my cap-checker-tool to check my electrolytes. Guess what?? No motorboating!!! I changed the volume around, tone controls and reverb controls trying to get it to motor boat and nothing.

So I checked the bias and voltages trying to give it time to act up. I run it for an hour or more at  pretty high volume and I just can't get it to do it again. Only thing I can figure at this point is I moved it to another room to work on it and the problem must have been with the voltage in that room which is my computer/wash room. I'm not going to put it back together just yet. I will fire it up several more times to see if I can get it to do it anymore first. Platefire 

Ha, doesn't that piss you off you . I run across this kind of problem occasionally, intermittent issues are frustrating. But usually it's a simple cause, just a pain in the *ss to find it, could just be a lose tube, like the PI tube..? Good luck 

[Platefire]

Yeah, that's the way it goes sometimes. I'm just glad it running perfect now, perfectly quiet. It's a fine amp and want to keep it running top notch